From f94d959e84cdcc552f6f5a39ee08a85c1e52d858 Mon Sep 17 00:00:00 2001 From: brad kittenbrink Date: Wed, 1 Jul 2009 19:02:42 -0400 Subject: Fixups for windows llcommon dll linkage errors that got dropped in the merge up to viewer-2.0.0-3 --- indra/llcommon/llevents.h | 1850 ++++++++++++++++++++++----------------------- 1 file changed, 925 insertions(+), 925 deletions(-) (limited to 'indra/llcommon/llevents.h') diff --git a/indra/llcommon/llevents.h b/indra/llcommon/llevents.h index c5a27ab68e..8ebffc008f 100644 --- a/indra/llcommon/llevents.h +++ b/indra/llcommon/llevents.h @@ -1,925 +1,925 @@ -/** - * @file llevents.h - * @author Kent Quirk, Nat Goodspeed - * @date 2008-09-11 - * @brief This is an implementation of the event system described at - * https://wiki.lindenlab.com/wiki/Viewer:Messaging/Event_System, - * originally introduced in llnotifications.h. It has nothing - * whatsoever to do with the older system in llevent.h. - * - * $LicenseInfo:firstyear=2008&license=viewergpl$ - * Copyright (c) 2008, Linden Research, Inc. - * $/LicenseInfo$ - */ - -#if ! defined(LL_LLEVENTS_H) -#define LL_LLEVENTS_H - -#include -#include -#include -#include -#include -#include -#include -#include -#include -#include -#include // noncopyable -#include -#include -#include // reference_wrapper -#include -#include -#include -#include "llsd.h" -#include "llsingleton.h" -#include "lldependencies.h" - -// override this to allow binding free functions with more parameters -#ifndef LLEVENTS_LISTENER_ARITY -#define LLEVENTS_LISTENER_ARITY 10 -#endif - -// hack for testing -#ifndef testable -#define testable private -#endif - -/***************************************************************************** -* Signal and handler declarations -* Using a single handler signature means that we can have a common handler -* type, rather than needing a distinct one for each different handler. -*****************************************************************************/ - -/** - * A boost::signals Combiner that stops the first time a handler returns true - * We need this because we want to have our handlers return bool, so that - * we have the option to cause a handler to stop further processing. The - * default handler fails when the signal returns a value but has no slots. - */ -struct LLStopWhenHandled -{ - typedef bool result_type; - - template - result_type operator()(InputIterator first, InputIterator last) const - { - for (InputIterator si = first; si != last; ++si) - { - if (*si) - { - return true; - } - } - return false; - } -}; - -/** - * We want to have a standard signature for all signals; this way, - * we can easily document a protocol for communicating across - * dlls and into scripting languages someday. - * - * We want to return a bool to indicate whether the signal has been - * handled and should NOT be passed on to other listeners. - * Return true to stop further handling of the signal, and false - * to continue. - * - * We take an LLSD because this way the contents of the signal - * are independent of the API used to communicate it. - * It is const ref because then there's low cost to pass it; - * if you only need to inspect it, it's very cheap. - * - * @internal - * The @c float template parameter indicates that we will internally use @c - * float to indicate relative listener order on a given LLStandardSignal. - * Don't worry, the @c float values are strictly internal! They are not part - * of the interface, for the excellent reason that requiring the caller to - * specify a numeric key to establish order means that the caller must know - * the universe of possible values. We use LLDependencies for that instead. - */ -typedef boost::signals2::signal LLStandardSignal; -/// Methods that forward listeners (e.g. constructed with -/// boost::bind()) should accept (const LLEventListener&) -typedef LLStandardSignal::slot_type LLEventListener; -/// Result of registering a listener, supports connected(), -/// disconnect() and blocked() -typedef boost::signals2::connection LLBoundListener; -/// Storing an LLBoundListener in LLTempBoundListener will disconnect the -/// referenced listener when the LLTempBoundListener instance is destroyed. -typedef boost::signals2::scoped_connection LLTempBoundListener; - -/** - * A common idiom for event-based code is to accept either a callable -- - * directly called on completion -- or the string name of an LLEventPump on - * which to post the completion event. Specifying a parameter as const - * LLListenerOrPumpName& allows either. - * - * Calling a validly-constructed LLListenerOrPumpName, passing the LLSD - * 'event' object, either calls the callable or posts the event to the named - * LLEventPump. - * - * A default-constructed LLListenerOrPumpName is 'empty'. (This is useful as - * the default value of an optional method parameter.) Calling it throws - * LLListenerOrPumpName::Empty. Test for this condition beforehand using - * either if (param) or if (! param). - */ -class LL_COMMON_API LLListenerOrPumpName -{ -public: - /// passing string name of LLEventPump - LLListenerOrPumpName(const std::string& pumpname); - /// passing string literal (overload so compiler isn't forced to infer - /// double conversion) - LLListenerOrPumpName(const char* pumpname); - /// passing listener -- the "anything else" catch-all case. The type of an - /// object constructed by boost::bind() isn't intended to be written out. - /// Normally we'd just accept 'const LLEventListener&', but that would - /// require double implicit conversion: boost::bind() object to - /// LLEventListener, LLEventListener to LLListenerOrPumpName. So use a - /// template to forward anything. - template - LLListenerOrPumpName(const T& listener): mListener(listener) {} - - /// for omitted method parameter: uninitialized mListener - LLListenerOrPumpName() {} - - /// test for validity - operator bool() const { return bool(mListener); } - bool operator! () const { return ! mListener; } - - /// explicit accessor - const LLEventListener& getListener() const { return *mListener; } - - /// implicit conversion to LLEventListener - operator LLEventListener() const { return *mListener; } - - /// allow calling directly - bool operator()(const LLSD& event) const; - - /// exception if you try to call when empty - struct Empty: public std::runtime_error - { - Empty(const std::string& what): - std::runtime_error(std::string("LLListenerOrPumpName::Empty: ") + what) {} - }; - -private: - boost::optional mListener; -}; - -/***************************************************************************** -* LLEventPumps -*****************************************************************************/ -class LL_COMMON_API LLEventPump; - -/** - * LLEventPumps is a Singleton manager through which one typically accesses - * this subsystem. - */ -class LL_COMMON_API LLEventPumps: public LLSingleton -{ - friend class LLSingleton; -public: - /** - * Find or create an LLEventPump instance with a specific name. We return - * a reference so there's no question about ownership. obtain() @em finds - * an instance without conferring @em ownership. - */ - LLEventPump& obtain(const std::string& name); - /** - * Flush all known LLEventPump instances - */ - void flush(); - -private: - friend class LLEventPump; - /** - * Register a new LLEventPump instance (internal) - */ - std::string registerNew(const LLEventPump&, const std::string& name, bool tweak); - /** - * Unregister a doomed LLEventPump instance (internal) - */ - void unregister(const LLEventPump&); - -private: - LLEventPumps(); - ~LLEventPumps(); - -testable: - // Map of all known LLEventPump instances, whether or not we instantiated - // them. We store a plain old LLEventPump* because this map doesn't claim - // ownership of the instances. Though the common usage pattern is to - // request an instance using obtain(), it's fair to instantiate an - // LLEventPump subclass statically, as a class member, on the stack or on - // the heap. In such cases, the instantiating party is responsible for its - // lifespan. - typedef std::map PumpMap; - PumpMap mPumpMap; - // Set of all LLEventPumps we instantiated. Membership in this set means - // we claim ownership, and will delete them when this LLEventPumps is - // destroyed. - typedef std::set PumpSet; - PumpSet mOurPumps; - // LLEventPump names that should be instantiated as LLEventQueue rather - // than as LLEventStream - typedef std::set PumpNames; - PumpNames mQueueNames; -}; - -/***************************************************************************** -* details -*****************************************************************************/ -namespace LLEventDetail -{ - /// Any callable capable of connecting an LLEventListener to an - /// LLStandardSignal to produce an LLBoundListener can be mapped to this - /// signature. - typedef boost::function ConnectFunc; - - /** - * Utility template function to use Visitor appropriately - * - * @param listener Callable to connect, typically a boost::bind() - * expression. This will be visited by Visitor using boost::visit_each(). - * @param connect_func Callable that will connect() @a listener to an - * LLStandardSignal, returning LLBoundListener. - */ - template - LLBoundListener visit_and_connect(const LISTENER& listener, - const ConnectFunc& connect_func); -} // namespace LLEventDetail - -/***************************************************************************** -* LLEventTrackable -*****************************************************************************/ -/** - * LLEventTrackable wraps boost::signals2::trackable, which resembles - * boost::trackable. Derive your listener class from LLEventTrackable instead, - * and use something like - * LLEventPump::listen(boost::bind(&YourTrackableSubclass::method, - * instance, _1)). This will implicitly disconnect when the object - * referenced by @c instance is destroyed. - * - * @note - * LLEventTrackable doesn't address a couple of cases: - * * Object destroyed during call - * - You enter a slot call in thread A. - * - Thread B destroys the object, which of course disconnects it from any - * future slot calls. - * - Thread A's call uses 'this', which now refers to a defunct object. - * Undefined behavior results. - * * Call during destruction - * - @c MySubclass is derived from LLEventTrackable. - * - @c MySubclass registers one of its own methods using - * LLEventPump::listen(). - * - The @c MySubclass object begins destruction. ~MySubclass() - * runs, destroying state specific to the subclass. (For instance, a - * Foo* data member is deleted but not zeroed.) - * - The listening method will not be disconnected until - * ~LLEventTrackable() runs. - * - Before we get there, another thread posts data to the @c LLEventPump - * instance, calling the @c MySubclass method. - * - The method in question relies on valid @c MySubclass state. (For - * instance, it attempts to dereference the Foo* pointer that was - * deleted but not zeroed.) - * - Undefined behavior results. - * If you suspect you may encounter any such scenario, you're better off - * managing the lifespan of your object with boost::shared_ptr. - * Passing LLEventPump::listen() a boost::bind() expression - * involving a boost::weak_ptr is recognized specially, engaging - * thread-safe Boost.Signals2 machinery. - */ -typedef boost::signals2::trackable LLEventTrackable; - -/***************************************************************************** -* LLEventPump -*****************************************************************************/ -/** - * LLEventPump is the base class interface through which we access the - * concrete subclasses LLEventStream and LLEventQueue. - * - * @NOTE - * LLEventPump derives from LLEventTrackable so that when you "chain" - * LLEventPump instances together, they will automatically disconnect on - * destruction. Please see LLEventTrackable documentation for situations in - * which this may be perilous across threads. - */ -class LL_COMMON_API LLEventPump: public LLEventTrackable -{ -public: - /** - * Exception thrown by LLEventPump(). You are trying to instantiate an - * LLEventPump (subclass) using the same name as some other instance, and - * you didn't pass tweak=true to permit it to generate a unique - * variant. - */ - struct DupPumpName: public std::runtime_error - { - DupPumpName(const std::string& what): - std::runtime_error(std::string("DupPumpName: ") + what) {} - }; - - /** - * Instantiate an LLEventPump (subclass) with the string name by which it - * can be found using LLEventPumps::obtain(). - * - * If you pass (or default) @a tweak to @c false, then a duplicate name - * will throw DupPumpName. This won't happen if LLEventPumps::obtain() - * instantiates the LLEventPump, because obtain() uses find-or-create - * logic. It can only happen if you instantiate an LLEventPump in your own - * code -- and a collision with the name of some other LLEventPump is - * likely to cause much more subtle problems! - * - * When you hand-instantiate an LLEventPump, consider passing @a tweak as - * @c true. This directs LLEventPump() to append a suffix to the passed @a - * name to make it unique. You can retrieve the adjusted name by calling - * getName() on your new instance. - */ - LLEventPump(const std::string& name, bool tweak=false); - virtual ~LLEventPump(); - - /// group exceptions thrown by listen(). We use exceptions because these - /// particular errors are likely to be coding errors, found and fixed by - /// the developer even before preliminary checkin. - struct ListenError: public std::runtime_error - { - ListenError(const std::string& what): std::runtime_error(what) {} - }; - /** - * exception thrown by listen(). You are attempting to register a - * listener on this LLEventPump using the same listener name as an - * already-registered listener. - */ - struct DupListenerName: public ListenError - { - DupListenerName(const std::string& what): - ListenError(std::string("DupListenerName: ") + what) - {} - }; - /** - * exception thrown by listen(). The order dependencies specified for your - * listener are incompatible with existing listeners. - * - * Consider listener "a" which specifies before "b" and "b" which - * specifies before "c". You are now attempting to register "c" before - * "a". There is no order that can satisfy all constraints. - */ - struct Cycle: public ListenError - { - Cycle(const std::string& what): ListenError(std::string("Cycle: ") + what) {} - }; - /** - * exception thrown by listen(). This one means that your new listener - * would force a change to the order of previously-registered listeners, - * and we don't have a good way to implement that. - * - * Consider listeners "some", "other" and "third". "some" and "other" are - * registered earlier without specifying relative order, so "other" - * happens to be first. Now you attempt to register "third" after "some" - * and before "other". Whoops, that would require swapping "some" and - * "other", which we can't do. Instead we throw this exception. - * - * It may not be possible to change the registration order so we already - * know "third"s order requirement by the time we register the second of - * "some" and "other". A solution would be to specify that "some" must - * come before "other", or equivalently that "other" must come after - * "some". - */ - struct OrderChange: public ListenError - { - OrderChange(const std::string& what): ListenError(std::string("OrderChange: ") + what) {} - }; - - /// used by listen() - typedef std::vector NameList; - /// convenience placeholder for when you explicitly want to pass an empty - /// NameList - const static NameList empty; - - /// Get this LLEventPump's name - std::string getName() const { return mName; } - - /** - * Register a new listener with a unique name. Specify an optional list - * of other listener names after which this one must be called, likewise - * an optional list of other listener names before which this one must be - * called. The other listeners mentioned need not yet be registered - * themselves. listen() can throw any ListenError; see ListenError - * subclasses. - * - * The listener name must be unique among active listeners for this - * LLEventPump, else you get DupListenerName. If you don't care to invent - * a name yourself, use inventName(). (I was tempted to recognize e.g. "" - * and internally generate a distinct name for that case. But that would - * handle badly the scenario in which you want to add, remove, re-add, - * etc. the same listener: each new listen() call would necessarily - * perform a new dependency sort. Assuming you specify the same - * after/before lists each time, using inventName() when you first - * instantiate your listener, then passing the same name on each listen() - * call, allows us to optimize away the second and subsequent dependency - * sorts. - * - * If (as is typical) you pass a boost::bind() expression as @a - * listener, listen() will inspect the components of that expression. If a - * bound object matches any of several cases, the connection will - * automatically be disconnected when that object is destroyed. - * - * * You bind a boost::weak_ptr. - * * Binding a boost::shared_ptr that way would ensure that the - * referenced object would @em never be destroyed, since the @c - * shared_ptr stored in the LLEventPump would remain an outstanding - * reference. Use the weaken() function to convert your @c shared_ptr to - * @c weak_ptr. Because this is easy to forget, binding a @c shared_ptr - * will produce a compile error (@c BOOST_STATIC_ASSERT failure). - * * You bind a simple pointer or reference to an object derived from - * boost::enable_shared_from_this. (UNDER CONSTRUCTION) - * * You bind a simple pointer or reference to an object derived from - * LLEventTrackable. Unlike the cases described above, though, this is - * vulnerable to a couple of cross-thread race conditions, as described - * in the LLEventTrackable documentation. - */ - template - LLBoundListener listen(const std::string& name, const LISTENER& listener, - const NameList& after=NameList(), - const NameList& before=NameList()) - { - // Examine listener, using our listen_impl() method to make the - // actual connection. - // This is why listen() is a template. Conversion from boost::bind() - // to LLEventListener performs type erasure, so it's important to look - // at the boost::bind object itself before that happens. - return LLEventDetail::visit_and_connect(listener, - boost::bind(&LLEventPump::listen_impl, - this, - name, - _1, - after, - before)); - } - - /// Get the LLBoundListener associated with the passed name (dummy - /// LLBoundListener if not found) - virtual LLBoundListener getListener(const std::string& name) const; - /** - * Instantiate one of these to block an existing connection: - * @code - * { // in some local scope - * LLEventPump::Blocker block(someLLBoundListener); - * // code that needs the connection blocked - * } // unblock the connection again - * @endcode - */ - typedef boost::signals2::shared_connection_block Blocker; - /// Unregister a listener by name. Prefer this to - /// getListener(name).disconnect() because stopListening() also - /// forgets this name. - virtual void stopListening(const std::string& name); - /// Post an event to all listeners. The @c bool return is only meaningful - /// if the underlying leaf class is LLEventStream -- beware of relying on - /// it too much! Truthfully, we return @c bool mostly to permit chaining - /// one LLEventPump as a listener on another. - virtual bool post(const LLSD&) = 0; - /// Enable/disable: while disabled, silently ignore all post() calls - virtual void enable(bool enabled=true) { mEnabled = enabled; } - /// query - virtual bool enabled() const { return mEnabled; } - - /// Generate a distinct name for a listener -- see listen() - static std::string inventName(const std::string& pfx="listener"); - -private: - friend class LLEventPumps; - /// flush queued events - virtual void flush() {} - -private: - virtual LLBoundListener listen_impl(const std::string& name, const LLEventListener&, - const NameList& after, - const NameList& before); - std::string mName; - -protected: - /// implement the dispatching - LLStandardSignal mSignal; - /// valve open? - bool mEnabled; - /// Map of named listeners. This tracks the listeners that actually exist - /// at this moment. When we stopListening(), we discard the entry from - /// this map. - typedef std::map ConnectionMap; - ConnectionMap mConnections; - typedef LLDependencies DependencyMap; - /// Dependencies between listeners. For each listener, track the float - /// used to establish its place in mSignal's order. This caches all the - /// listeners that have ever registered; stopListening() does not discard - /// the entry from this map. This is to avoid a new dependency sort if the - /// same listener with the same dependencies keeps hopping on and off this - /// LLEventPump. - DependencyMap mDeps; -}; - -/***************************************************************************** -* LLEventStream -*****************************************************************************/ -/** - * LLEventStream is a thin wrapper around LLStandardSignal. Posting an - * event immediately calls all registered listeners. - */ -class LL_COMMON_API LLEventStream: public LLEventPump -{ -public: - LLEventStream(const std::string& name, bool tweak=false): LLEventPump(name, tweak) {} - virtual ~LLEventStream() {} - - /// Post an event to all listeners - virtual bool post(const LLSD& event); -}; - -/***************************************************************************** -* LLEventQueue -*****************************************************************************/ -/** - * LLEventQueue isa LLEventPump whose post() method defers calling registered - * listeners until flush() is called. - */ -class LL_COMMON_API LLEventQueue: public LLEventPump -{ -public: - LLEventQueue(const std::string& name, bool tweak=false): LLEventPump(name, tweak) {} - virtual ~LLEventQueue() {} - - /// Post an event to all listeners - virtual bool post(const LLSD& event); - -private: - /// flush queued events - virtual void flush(); - -private: - typedef std::deque EventQueue; - EventQueue mEventQueue; -}; - -/***************************************************************************** -* LLReqID -*****************************************************************************/ -/** - * This class helps the implementer of a given event API to honor the - * ["reqid"] convention. By this convention, each event API stamps into its - * response LLSD a ["reqid"] key whose value echoes the ["reqid"] value, if - * any, from the corresponding request. - * - * This supports an (atypical, but occasionally necessary) use case in which - * two or more asynchronous requests are multiplexed onto the same ["reply"] - * LLEventPump. Since the response events could arrive in arbitrary order, the - * caller must be able to demux them. It does so by matching the ["reqid"] - * value in each response with the ["reqid"] value in the corresponding - * request. - * - * It is the caller's responsibility to ensure distinct ["reqid"] values for - * that case. Though LLSD::UUID is guaranteed to work, it might be overkill: - * the "namespace" of unique ["reqid"] values is simply the set of requests - * specifying the same ["reply"] LLEventPump name. - * - * Making a given event API echo the request's ["reqid"] into the response is - * nearly trivial. This helper is mostly for mnemonic purposes, to serve as a - * place to put these comments. We hope that each time a coder implements a - * new event API based on some existing one, s/he will say, "Huh, what's an - * LLReqID?" and look up this material. - * - * The hardest part about the convention is deciding where to store the - * ["reqid"] value. Ironically, LLReqID can't help with that: you must store - * an LLReqID instance in whatever storage will persist until the reply is - * sent. For example, if the request ultimately ends up using a Responder - * subclass, storing an LLReqID instance in the Responder works. - * - * @note - * The @em implementer of an event API must honor the ["reqid"] convention. - * However, the @em caller of an event API need only use it if s/he is sharing - * the same ["reply"] LLEventPump for two or more asynchronous event API - * requests. - * - * In most cases, it's far easier for the caller to instantiate a local - * LLEventStream and pass its name to the event API in question. Then it's - * perfectly reasonable not to set a ["reqid"] key in the request, ignoring - * the @c isUndefined() ["reqid"] value in the response. - */ -class LLReqID -{ -public: - /** - * If you have the request in hand at the time you instantiate the - * LLReqID, pass that request to extract its ["reqid"]. - */ - LLReqID(const LLSD& request): - mReqid(request["reqid"]) - {} - /// If you don't yet have the request, use setFrom() later. - LLReqID() {} - - /// Extract and store the ["reqid"] value from an incoming request. - void setFrom(const LLSD& request) - { - mReqid = request["reqid"]; - } - - /// Set ["reqid"] key into a pending response LLSD object. - void stamp(LLSD& response) const; - - /// Make a whole new response LLSD object with our ["reqid"]. - LLSD makeResponse() const - { - LLSD response; - stamp(response); - return response; - } - - /// Not really sure of a use case for this accessor... - LLSD getReqID() const { return mReqid; } - -private: - LLSD mReqid; -}; - -/***************************************************************************** -* Underpinnings -*****************************************************************************/ -/** - * We originally provided a suite of overloaded - * LLEventTrackable::listenTo(LLEventPump&, ...) methods that would call - * LLEventPump::listen(...) and then pass the returned LLBoundListener to - * LLEventTrackable::track(). This was workable but error-prone: the coder - * must remember to call listenTo() rather than the more straightforward - * listen() method. - * - * Now we publish only the single canonical listen() method, so there's a - * uniform mechanism. Having a single way to do this is good, in that there's - * no question in the coder's mind which of several alternatives to choose. - * - * To support automatic connection management, we use boost::visit_each - * (http://www.boost.org/doc/libs/1_37_0/doc/html/boost/visit_each.html) to - * inspect each argument of a boost::bind expression. (Although the visit_each - * mechanism was first introduced with the original Boost.Signals library, it - * was only later documented.) - * - * Cases: - * * At least one of the function's arguments is a boost::weak_ptr. Pass - * the corresponding shared_ptr to slot_type::track(). Ideally that would be - * the object whose method we want to call, but in fact we do the same for - * any weak_ptr we might find among the bound arguments. If we're passing - * our bound method a weak_ptr to some object, wouldn't the destruction of - * that object invalidate the call? So we disconnect automatically when any - * such object is destroyed. This is the mechanism preferred by boost:: - * signals2. - * * One of the functions's arguments is a boost::shared_ptr. This produces - * a compile error: the bound copy of the shared_ptr stored in the - * boost_bind object stored in the signal object would make the referenced - * T object immortal. We provide a weaken() function. Pass - * weaken(your_shared_ptr) instead. (We can inspect, but not modify, the - * boost::bind object. Otherwise we'd replace the shared_ptr with weak_ptr - * implicitly and just proceed.) - * * One of the function's arguments is a plain pointer/reference to an object - * derived from boost::enable_shared_from_this. We assume that this object - * is managed using boost::shared_ptr, so we implicitly extract a shared_ptr - * and track that. (UNDER CONSTRUCTION) - * * One of the function's arguments is derived from LLEventTrackable. Pass - * the LLBoundListener to its LLEventTrackable::track(). This is vulnerable - * to a couple different race conditions, as described in LLEventTrackable - * documentation. (NOTE: Now that LLEventTrackable is a typedef for - * boost::signals2::trackable, the Signals2 library handles this itself, so - * our visitor needs no special logic for this case.) - * * Any other argument type is irrelevant to automatic connection management. - */ - -namespace LLEventDetail -{ - template - const F& unwrap(const F& f) { return f; } - - template - const F& unwrap(const boost::reference_wrapper& f) { return f.get(); } - - // Most of the following is lifted from the Boost.Signals use of - // visit_each. - template struct truth {}; - - /** - * boost::visit_each() Visitor, used on a template argument const F& - * f as follows (see visit_and_connect()): - * @code - * LLEventListener listener(f); - * Visitor visitor(listener); // bind listener so it can track() shared_ptrs - * using boost::visit_each; // allow unqualified visit_each() call for ADL - * visit_each(visitor, unwrap(f)); - * @endcode - */ - class Visitor - { - public: - /** - * Visitor binds a reference to LLEventListener so we can track() any - * shared_ptrs we find in the argument list. - */ - Visitor(LLEventListener& listener): - mListener(listener) - { - } - - /** - * boost::visit_each() calls this method for each component of a - * boost::bind() expression. - */ - template - void operator()(const T& t) const - { - decode(t, 0); - } - - private: - // decode() decides between a reference wrapper and anything else - // boost::ref() variant - template - void decode(const boost::reference_wrapper& t, int) const - { -// add_if_trackable(t.get_pointer()); - } - - // decode() anything else - template - void decode(const T& t, long) const - { - typedef truth<(boost::is_pointer::value)> is_a_pointer; - maybe_get_pointer(t, is_a_pointer()); - } - - // maybe_get_pointer() decides between a pointer and a non-pointer - // plain pointer variant - template - void maybe_get_pointer(const T& t, truth) const - { -// add_if_trackable(t); - } - - // shared_ptr variant - template - void maybe_get_pointer(const boost::shared_ptr& t, truth) const - { - // If we have a shared_ptr to this object, it doesn't matter - // whether the object is derived from LLEventTrackable, so no - // further analysis of T is needed. -// mListener.track(t); - - // Make this case illegal. Passing a bound shared_ptr to - // slot_type::track() is useless, since the bound shared_ptr will - // keep the object alive anyway! Force the coder to cast to weak_ptr. - - // Trivial as it is, make the BOOST_STATIC_ASSERT() condition - // dependent on template param so the macro is only evaluated if - // this method is in fact instantiated, as described here: - // http://www.boost.org/doc/libs/1_34_1/doc/html/boost_staticassert.html - - // ATTENTION: Don't bind a shared_ptr using - // LLEventPump::listen(boost::bind()). Doing so captures a copy of - // the shared_ptr, making the referenced object effectively - // immortal. Use the weaken() function, e.g.: - // somepump.listen(boost::bind(...weaken(my_shared_ptr)...)); - // This lets us automatically disconnect when the referenced - // object is destroyed. - BOOST_STATIC_ASSERT(sizeof(T) == 0); - } - - // weak_ptr variant - template - void maybe_get_pointer(const boost::weak_ptr& t, truth) const - { - // If we have a weak_ptr to this object, it doesn't matter - // whether the object is derived from LLEventTrackable, so no - // further analysis of T is needed. - mListener.track(t); -// std::cout << "Found weak_ptr<" << typeid(T).name() << ">!\n"; - } - -#if 0 - // reference to anything derived from boost::enable_shared_from_this - template - inline void maybe_get_pointer(const boost::enable_shared_from_this& ct, - truth) const - { - // Use the slot_type::track(shared_ptr) mechanism. Cast away - // const-ness because (in our code base anyway) it's unusual - // to find shared_ptr. - boost::enable_shared_from_this& - t(const_cast&>(ct)); - std::cout << "Capturing shared_from_this()" << std::endl; - boost::shared_ptr sp(t.shared_from_this()); -/*==========================================================================*| - std::cout << "Capturing weak_ptr" << std::endl; - boost::weak_ptr wp(sp); -|*==========================================================================*/ - std::cout << "Tracking shared__ptr" << std::endl; - mListener.track(sp); - } -#endif - - // non-pointer variant - template - void maybe_get_pointer(const T& t, truth) const - { - // Take the address of this object, because the object itself may be - // trackable -// add_if_trackable(boost::addressof(t)); - } - -/*==========================================================================*| - // add_if_trackable() adds LLEventTrackable objects to mTrackables - inline void add_if_trackable(const LLEventTrackable* t) const - { - if (t) - { - } - } - - // pointer to anything not an LLEventTrackable subclass - inline void add_if_trackable(const void*) const - { - } - - // pointer to free function - // The following construct uses the preprocessor to generate - // add_if_trackable() overloads accepting pointer-to-function taking - // 0, 1, ..., LLEVENTS_LISTENER_ARITY parameters of arbitrary type. -#define BOOST_PP_LOCAL_MACRO(n) \ - template \ - inline void \ - add_if_trackable(R (*)(BOOST_PP_ENUM_PARAMS(n, T))) const \ - { \ - } -#define BOOST_PP_LOCAL_LIMITS (0, LLEVENTS_LISTENER_ARITY) -#include BOOST_PP_LOCAL_ITERATE() -#undef BOOST_PP_LOCAL_MACRO -#undef BOOST_PP_LOCAL_LIMITS -|*==========================================================================*/ - - /// Bind a reference to the LLEventListener to call its track() method. - LLEventListener& mListener; - }; - - /** - * Utility template function to use Visitor appropriately - * - * @param raw_listener Callable to connect, typically a boost::bind() - * expression. This will be visited by Visitor using boost::visit_each(). - * @param connect_funct Callable that will connect() @a raw_listener to an - * LLStandardSignal, returning LLBoundListener. - */ - template - LLBoundListener visit_and_connect(const LISTENER& raw_listener, - const ConnectFunc& connect_func) - { - // Capture the listener - LLEventListener listener(raw_listener); - // Define our Visitor, binding the listener so we can call - // listener.track() if we discover any shared_ptr. - LLEventDetail::Visitor visitor(listener); - // Allow unqualified visit_each() call for ADL - using boost::visit_each; - // Visit each component of a boost::bind() expression. Pass - // 'raw_listener', our template argument, rather than 'listener' from - // which type details have been erased. unwrap() comes from - // Boost.Signals, in case we were passed a boost::ref(). - visit_each(visitor, LLEventDetail::unwrap(raw_listener)); - // Make the connection using passed function. At present, wrapping - // this functionality into this function is a bit silly: we don't - // really need a visit_and_connect() function any more, just a visit() - // function. The definition of this function dates from when, after - // visit_each(), after establishing the connection, we had to - // postprocess the new connection with the visitor object. That's no - // longer necessary. - return connect_func(listener); - } -} // namespace LLEventDetail - -// Somewhat to my surprise, passing boost::bind(...boost::weak_ptr...) to -// listen() fails in Boost code trying to instantiate LLEventListener (i.e. -// LLStandardSignal::slot_type) because the boost::get_pointer() utility function isn't -// specialized for boost::weak_ptr. This remedies that omission. -namespace boost -{ - template - T* get_pointer(const weak_ptr& ptr) { return shared_ptr(ptr).get(); } -} - -/// Since we forbid use of listen(boost::bind(...shared_ptr...)), provide an -/// easy way to cast to the corresponding weak_ptr. -template -boost::weak_ptr weaken(const boost::shared_ptr& ptr) -{ - return boost::weak_ptr(ptr); -} - -#endif /* ! defined(LL_LLEVENTS_H) */ +/** + * @file llevents.h + * @author Kent Quirk, Nat Goodspeed + * @date 2008-09-11 + * @brief This is an implementation of the event system described at + * https://wiki.lindenlab.com/wiki/Viewer:Messaging/Event_System, + * originally introduced in llnotifications.h. It has nothing + * whatsoever to do with the older system in llevent.h. + * + * $LicenseInfo:firstyear=2008&license=viewergpl$ + * Copyright (c) 2008, Linden Research, Inc. + * $/LicenseInfo$ + */ + +#if ! defined(LL_LLEVENTS_H) +#define LL_LLEVENTS_H + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include // noncopyable +#include +#include +#include // reference_wrapper +#include +#include +#include +#include "llsd.h" +#include "llsingleton.h" +#include "lldependencies.h" + +// override this to allow binding free functions with more parameters +#ifndef LLEVENTS_LISTENER_ARITY +#define LLEVENTS_LISTENER_ARITY 10 +#endif + +// hack for testing +#ifndef testable +#define testable private +#endif + +/***************************************************************************** +* Signal and handler declarations +* Using a single handler signature means that we can have a common handler +* type, rather than needing a distinct one for each different handler. +*****************************************************************************/ + +/** + * A boost::signals Combiner that stops the first time a handler returns true + * We need this because we want to have our handlers return bool, so that + * we have the option to cause a handler to stop further processing. The + * default handler fails when the signal returns a value but has no slots. + */ +struct LLStopWhenHandled +{ + typedef bool result_type; + + template + result_type operator()(InputIterator first, InputIterator last) const + { + for (InputIterator si = first; si != last; ++si) + { + if (*si) + { + return true; + } + } + return false; + } +}; + +/** + * We want to have a standard signature for all signals; this way, + * we can easily document a protocol for communicating across + * dlls and into scripting languages someday. + * + * We want to return a bool to indicate whether the signal has been + * handled and should NOT be passed on to other listeners. + * Return true to stop further handling of the signal, and false + * to continue. + * + * We take an LLSD because this way the contents of the signal + * are independent of the API used to communicate it. + * It is const ref because then there's low cost to pass it; + * if you only need to inspect it, it's very cheap. + * + * @internal + * The @c float template parameter indicates that we will internally use @c + * float to indicate relative listener order on a given LLStandardSignal. + * Don't worry, the @c float values are strictly internal! They are not part + * of the interface, for the excellent reason that requiring the caller to + * specify a numeric key to establish order means that the caller must know + * the universe of possible values. We use LLDependencies for that instead. + */ +typedef boost::signals2::signal LLStandardSignal; +/// Methods that forward listeners (e.g. constructed with +/// boost::bind()) should accept (const LLEventListener&) +typedef LLStandardSignal::slot_type LLEventListener; +/// Result of registering a listener, supports connected(), +/// disconnect() and blocked() +typedef boost::signals2::connection LLBoundListener; +/// Storing an LLBoundListener in LLTempBoundListener will disconnect the +/// referenced listener when the LLTempBoundListener instance is destroyed. +typedef boost::signals2::scoped_connection LLTempBoundListener; + +/** + * A common idiom for event-based code is to accept either a callable -- + * directly called on completion -- or the string name of an LLEventPump on + * which to post the completion event. Specifying a parameter as const + * LLListenerOrPumpName& allows either. + * + * Calling a validly-constructed LLListenerOrPumpName, passing the LLSD + * 'event' object, either calls the callable or posts the event to the named + * LLEventPump. + * + * A default-constructed LLListenerOrPumpName is 'empty'. (This is useful as + * the default value of an optional method parameter.) Calling it throws + * LLListenerOrPumpName::Empty. Test for this condition beforehand using + * either if (param) or if (! param). + */ +class LL_COMMON_API LLListenerOrPumpName +{ +public: + /// passing string name of LLEventPump + LLListenerOrPumpName(const std::string& pumpname); + /// passing string literal (overload so compiler isn't forced to infer + /// double conversion) + LLListenerOrPumpName(const char* pumpname); + /// passing listener -- the "anything else" catch-all case. The type of an + /// object constructed by boost::bind() isn't intended to be written out. + /// Normally we'd just accept 'const LLEventListener&', but that would + /// require double implicit conversion: boost::bind() object to + /// LLEventListener, LLEventListener to LLListenerOrPumpName. So use a + /// template to forward anything. + template + LLListenerOrPumpName(const T& listener): mListener(listener) {} + + /// for omitted method parameter: uninitialized mListener + LLListenerOrPumpName() {} + + /// test for validity + operator bool() const { return bool(mListener); } + bool operator! () const { return ! mListener; } + + /// explicit accessor + const LLEventListener& getListener() const { return *mListener; } + + /// implicit conversion to LLEventListener + operator LLEventListener() const { return *mListener; } + + /// allow calling directly + bool operator()(const LLSD& event) const; + + /// exception if you try to call when empty + struct Empty: public std::runtime_error + { + Empty(const std::string& what): + std::runtime_error(std::string("LLListenerOrPumpName::Empty: ") + what) {} + }; + +private: + boost::optional mListener; +}; + +/***************************************************************************** +* LLEventPumps +*****************************************************************************/ +class LL_COMMON_API LLEventPump; + +/** + * LLEventPumps is a Singleton manager through which one typically accesses + * this subsystem. + */ +class LL_COMMON_API LLEventPumps: public LLSingleton +{ + friend class LLSingleton; +public: + /** + * Find or create an LLEventPump instance with a specific name. We return + * a reference so there's no question about ownership. obtain() @em finds + * an instance without conferring @em ownership. + */ + LLEventPump& obtain(const std::string& name); + /** + * Flush all known LLEventPump instances + */ + void flush(); + +private: + friend class LLEventPump; + /** + * Register a new LLEventPump instance (internal) + */ + std::string registerNew(const LLEventPump&, const std::string& name, bool tweak); + /** + * Unregister a doomed LLEventPump instance (internal) + */ + void unregister(const LLEventPump&); + +private: + LLEventPumps(); + ~LLEventPumps(); + +testable: + // Map of all known LLEventPump instances, whether or not we instantiated + // them. We store a plain old LLEventPump* because this map doesn't claim + // ownership of the instances. Though the common usage pattern is to + // request an instance using obtain(), it's fair to instantiate an + // LLEventPump subclass statically, as a class member, on the stack or on + // the heap. In such cases, the instantiating party is responsible for its + // lifespan. + typedef std::map PumpMap; + PumpMap mPumpMap; + // Set of all LLEventPumps we instantiated. Membership in this set means + // we claim ownership, and will delete them when this LLEventPumps is + // destroyed. + typedef std::set PumpSet; + PumpSet mOurPumps; + // LLEventPump names that should be instantiated as LLEventQueue rather + // than as LLEventStream + typedef std::set PumpNames; + PumpNames mQueueNames; +}; + +/***************************************************************************** +* details +*****************************************************************************/ +namespace LLEventDetail +{ + /// Any callable capable of connecting an LLEventListener to an + /// LLStandardSignal to produce an LLBoundListener can be mapped to this + /// signature. + typedef boost::function ConnectFunc; + + /** + * Utility template function to use Visitor appropriately + * + * @param listener Callable to connect, typically a boost::bind() + * expression. This will be visited by Visitor using boost::visit_each(). + * @param connect_func Callable that will connect() @a listener to an + * LLStandardSignal, returning LLBoundListener. + */ + template + LLBoundListener visit_and_connect(const LISTENER& listener, + const ConnectFunc& connect_func); +} // namespace LLEventDetail + +/***************************************************************************** +* LLEventTrackable +*****************************************************************************/ +/** + * LLEventTrackable wraps boost::signals2::trackable, which resembles + * boost::trackable. Derive your listener class from LLEventTrackable instead, + * and use something like + * LLEventPump::listen(boost::bind(&YourTrackableSubclass::method, + * instance, _1)). This will implicitly disconnect when the object + * referenced by @c instance is destroyed. + * + * @note + * LLEventTrackable doesn't address a couple of cases: + * * Object destroyed during call + * - You enter a slot call in thread A. + * - Thread B destroys the object, which of course disconnects it from any + * future slot calls. + * - Thread A's call uses 'this', which now refers to a defunct object. + * Undefined behavior results. + * * Call during destruction + * - @c MySubclass is derived from LLEventTrackable. + * - @c MySubclass registers one of its own methods using + * LLEventPump::listen(). + * - The @c MySubclass object begins destruction. ~MySubclass() + * runs, destroying state specific to the subclass. (For instance, a + * Foo* data member is deleted but not zeroed.) + * - The listening method will not be disconnected until + * ~LLEventTrackable() runs. + * - Before we get there, another thread posts data to the @c LLEventPump + * instance, calling the @c MySubclass method. + * - The method in question relies on valid @c MySubclass state. (For + * instance, it attempts to dereference the Foo* pointer that was + * deleted but not zeroed.) + * - Undefined behavior results. + * If you suspect you may encounter any such scenario, you're better off + * managing the lifespan of your object with boost::shared_ptr. + * Passing LLEventPump::listen() a boost::bind() expression + * involving a boost::weak_ptr is recognized specially, engaging + * thread-safe Boost.Signals2 machinery. + */ +typedef boost::signals2::trackable LLEventTrackable; + +/***************************************************************************** +* LLEventPump +*****************************************************************************/ +/** + * LLEventPump is the base class interface through which we access the + * concrete subclasses LLEventStream and LLEventQueue. + * + * @NOTE + * LLEventPump derives from LLEventTrackable so that when you "chain" + * LLEventPump instances together, they will automatically disconnect on + * destruction. Please see LLEventTrackable documentation for situations in + * which this may be perilous across threads. + */ +class LL_COMMON_API LLEventPump: public LLEventTrackable +{ +public: + /** + * Exception thrown by LLEventPump(). You are trying to instantiate an + * LLEventPump (subclass) using the same name as some other instance, and + * you didn't pass tweak=true to permit it to generate a unique + * variant. + */ + struct DupPumpName: public std::runtime_error + { + DupPumpName(const std::string& what): + std::runtime_error(std::string("DupPumpName: ") + what) {} + }; + + /** + * Instantiate an LLEventPump (subclass) with the string name by which it + * can be found using LLEventPumps::obtain(). + * + * If you pass (or default) @a tweak to @c false, then a duplicate name + * will throw DupPumpName. This won't happen if LLEventPumps::obtain() + * instantiates the LLEventPump, because obtain() uses find-or-create + * logic. It can only happen if you instantiate an LLEventPump in your own + * code -- and a collision with the name of some other LLEventPump is + * likely to cause much more subtle problems! + * + * When you hand-instantiate an LLEventPump, consider passing @a tweak as + * @c true. This directs LLEventPump() to append a suffix to the passed @a + * name to make it unique. You can retrieve the adjusted name by calling + * getName() on your new instance. + */ + LLEventPump(const std::string& name, bool tweak=false); + virtual ~LLEventPump(); + + /// group exceptions thrown by listen(). We use exceptions because these + /// particular errors are likely to be coding errors, found and fixed by + /// the developer even before preliminary checkin. + struct ListenError: public std::runtime_error + { + ListenError(const std::string& what): std::runtime_error(what) {} + }; + /** + * exception thrown by listen(). You are attempting to register a + * listener on this LLEventPump using the same listener name as an + * already-registered listener. + */ + struct DupListenerName: public ListenError + { + DupListenerName(const std::string& what): + ListenError(std::string("DupListenerName: ") + what) + {} + }; + /** + * exception thrown by listen(). The order dependencies specified for your + * listener are incompatible with existing listeners. + * + * Consider listener "a" which specifies before "b" and "b" which + * specifies before "c". You are now attempting to register "c" before + * "a". There is no order that can satisfy all constraints. + */ + struct Cycle: public ListenError + { + Cycle(const std::string& what): ListenError(std::string("Cycle: ") + what) {} + }; + /** + * exception thrown by listen(). This one means that your new listener + * would force a change to the order of previously-registered listeners, + * and we don't have a good way to implement that. + * + * Consider listeners "some", "other" and "third". "some" and "other" are + * registered earlier without specifying relative order, so "other" + * happens to be first. Now you attempt to register "third" after "some" + * and before "other". Whoops, that would require swapping "some" and + * "other", which we can't do. Instead we throw this exception. + * + * It may not be possible to change the registration order so we already + * know "third"s order requirement by the time we register the second of + * "some" and "other". A solution would be to specify that "some" must + * come before "other", or equivalently that "other" must come after + * "some". + */ + struct OrderChange: public ListenError + { + OrderChange(const std::string& what): ListenError(std::string("OrderChange: ") + what) {} + }; + + /// used by listen() + typedef std::vector NameList; + /// convenience placeholder for when you explicitly want to pass an empty + /// NameList + const static NameList empty; + + /// Get this LLEventPump's name + std::string getName() const { return mName; } + + /** + * Register a new listener with a unique name. Specify an optional list + * of other listener names after which this one must be called, likewise + * an optional list of other listener names before which this one must be + * called. The other listeners mentioned need not yet be registered + * themselves. listen() can throw any ListenError; see ListenError + * subclasses. + * + * The listener name must be unique among active listeners for this + * LLEventPump, else you get DupListenerName. If you don't care to invent + * a name yourself, use inventName(). (I was tempted to recognize e.g. "" + * and internally generate a distinct name for that case. But that would + * handle badly the scenario in which you want to add, remove, re-add, + * etc. the same listener: each new listen() call would necessarily + * perform a new dependency sort. Assuming you specify the same + * after/before lists each time, using inventName() when you first + * instantiate your listener, then passing the same name on each listen() + * call, allows us to optimize away the second and subsequent dependency + * sorts. + * + * If (as is typical) you pass a boost::bind() expression as @a + * listener, listen() will inspect the components of that expression. If a + * bound object matches any of several cases, the connection will + * automatically be disconnected when that object is destroyed. + * + * * You bind a boost::weak_ptr. + * * Binding a boost::shared_ptr that way would ensure that the + * referenced object would @em never be destroyed, since the @c + * shared_ptr stored in the LLEventPump would remain an outstanding + * reference. Use the weaken() function to convert your @c shared_ptr to + * @c weak_ptr. Because this is easy to forget, binding a @c shared_ptr + * will produce a compile error (@c BOOST_STATIC_ASSERT failure). + * * You bind a simple pointer or reference to an object derived from + * boost::enable_shared_from_this. (UNDER CONSTRUCTION) + * * You bind a simple pointer or reference to an object derived from + * LLEventTrackable. Unlike the cases described above, though, this is + * vulnerable to a couple of cross-thread race conditions, as described + * in the LLEventTrackable documentation. + */ + template + LLBoundListener listen(const std::string& name, const LISTENER& listener, + const NameList& after=NameList(), + const NameList& before=NameList()) + { + // Examine listener, using our listen_impl() method to make the + // actual connection. + // This is why listen() is a template. Conversion from boost::bind() + // to LLEventListener performs type erasure, so it's important to look + // at the boost::bind object itself before that happens. + return LLEventDetail::visit_and_connect(listener, + boost::bind(&LLEventPump::listen_impl, + this, + name, + _1, + after, + before)); + } + + /// Get the LLBoundListener associated with the passed name (dummy + /// LLBoundListener if not found) + virtual LLBoundListener getListener(const std::string& name) const; + /** + * Instantiate one of these to block an existing connection: + * @code + * { // in some local scope + * LLEventPump::Blocker block(someLLBoundListener); + * // code that needs the connection blocked + * } // unblock the connection again + * @endcode + */ + typedef boost::signals2::shared_connection_block Blocker; + /// Unregister a listener by name. Prefer this to + /// getListener(name).disconnect() because stopListening() also + /// forgets this name. + virtual void stopListening(const std::string& name); + /// Post an event to all listeners. The @c bool return is only meaningful + /// if the underlying leaf class is LLEventStream -- beware of relying on + /// it too much! Truthfully, we return @c bool mostly to permit chaining + /// one LLEventPump as a listener on another. + virtual bool post(const LLSD&) = 0; + /// Enable/disable: while disabled, silently ignore all post() calls + virtual void enable(bool enabled=true) { mEnabled = enabled; } + /// query + virtual bool enabled() const { return mEnabled; } + + /// Generate a distinct name for a listener -- see listen() + static std::string inventName(const std::string& pfx="listener"); + +private: + friend class LLEventPumps; + /// flush queued events + virtual void flush() {} + +private: + virtual LLBoundListener listen_impl(const std::string& name, const LLEventListener&, + const NameList& after, + const NameList& before); + std::string mName; + +protected: + /// implement the dispatching + LLStandardSignal mSignal; + /// valve open? + bool mEnabled; + /// Map of named listeners. This tracks the listeners that actually exist + /// at this moment. When we stopListening(), we discard the entry from + /// this map. + typedef std::map ConnectionMap; + ConnectionMap mConnections; + typedef LLDependencies DependencyMap; + /// Dependencies between listeners. For each listener, track the float + /// used to establish its place in mSignal's order. This caches all the + /// listeners that have ever registered; stopListening() does not discard + /// the entry from this map. This is to avoid a new dependency sort if the + /// same listener with the same dependencies keeps hopping on and off this + /// LLEventPump. + DependencyMap mDeps; +}; + +/***************************************************************************** +* LLEventStream +*****************************************************************************/ +/** + * LLEventStream is a thin wrapper around LLStandardSignal. Posting an + * event immediately calls all registered listeners. + */ +class LL_COMMON_API LLEventStream: public LLEventPump +{ +public: + LLEventStream(const std::string& name, bool tweak=false): LLEventPump(name, tweak) {} + virtual ~LLEventStream() {} + + /// Post an event to all listeners + virtual bool post(const LLSD& event); +}; + +/***************************************************************************** +* LLEventQueue +*****************************************************************************/ +/** + * LLEventQueue isa LLEventPump whose post() method defers calling registered + * listeners until flush() is called. + */ +class LL_COMMON_API LLEventQueue: public LLEventPump +{ +public: + LLEventQueue(const std::string& name, bool tweak=false): LLEventPump(name, tweak) {} + virtual ~LLEventQueue() {} + + /// Post an event to all listeners + virtual bool post(const LLSD& event); + +private: + /// flush queued events + virtual void flush(); + +private: + typedef std::deque EventQueue; + EventQueue mEventQueue; +}; + +/***************************************************************************** +* LLReqID +*****************************************************************************/ +/** + * This class helps the implementer of a given event API to honor the + * ["reqid"] convention. By this convention, each event API stamps into its + * response LLSD a ["reqid"] key whose value echoes the ["reqid"] value, if + * any, from the corresponding request. + * + * This supports an (atypical, but occasionally necessary) use case in which + * two or more asynchronous requests are multiplexed onto the same ["reply"] + * LLEventPump. Since the response events could arrive in arbitrary order, the + * caller must be able to demux them. It does so by matching the ["reqid"] + * value in each response with the ["reqid"] value in the corresponding + * request. + * + * It is the caller's responsibility to ensure distinct ["reqid"] values for + * that case. Though LLSD::UUID is guaranteed to work, it might be overkill: + * the "namespace" of unique ["reqid"] values is simply the set of requests + * specifying the same ["reply"] LLEventPump name. + * + * Making a given event API echo the request's ["reqid"] into the response is + * nearly trivial. This helper is mostly for mnemonic purposes, to serve as a + * place to put these comments. We hope that each time a coder implements a + * new event API based on some existing one, s/he will say, "Huh, what's an + * LLReqID?" and look up this material. + * + * The hardest part about the convention is deciding where to store the + * ["reqid"] value. Ironically, LLReqID can't help with that: you must store + * an LLReqID instance in whatever storage will persist until the reply is + * sent. For example, if the request ultimately ends up using a Responder + * subclass, storing an LLReqID instance in the Responder works. + * + * @note + * The @em implementer of an event API must honor the ["reqid"] convention. + * However, the @em caller of an event API need only use it if s/he is sharing + * the same ["reply"] LLEventPump for two or more asynchronous event API + * requests. + * + * In most cases, it's far easier for the caller to instantiate a local + * LLEventStream and pass its name to the event API in question. Then it's + * perfectly reasonable not to set a ["reqid"] key in the request, ignoring + * the @c isUndefined() ["reqid"] value in the response. + */ +class LL_COMMON_API LLReqID +{ +public: + /** + * If you have the request in hand at the time you instantiate the + * LLReqID, pass that request to extract its ["reqid"]. + */ + LLReqID(const LLSD& request): + mReqid(request["reqid"]) + {} + /// If you don't yet have the request, use setFrom() later. + LLReqID() {} + + /// Extract and store the ["reqid"] value from an incoming request. + void setFrom(const LLSD& request) + { + mReqid = request["reqid"]; + } + + /// Set ["reqid"] key into a pending response LLSD object. + void stamp(LLSD& response) const; + + /// Make a whole new response LLSD object with our ["reqid"]. + LLSD makeResponse() const + { + LLSD response; + stamp(response); + return response; + } + + /// Not really sure of a use case for this accessor... + LLSD getReqID() const { return mReqid; } + +private: + LLSD mReqid; +}; + +/***************************************************************************** +* Underpinnings +*****************************************************************************/ +/** + * We originally provided a suite of overloaded + * LLEventTrackable::listenTo(LLEventPump&, ...) methods that would call + * LLEventPump::listen(...) and then pass the returned LLBoundListener to + * LLEventTrackable::track(). This was workable but error-prone: the coder + * must remember to call listenTo() rather than the more straightforward + * listen() method. + * + * Now we publish only the single canonical listen() method, so there's a + * uniform mechanism. Having a single way to do this is good, in that there's + * no question in the coder's mind which of several alternatives to choose. + * + * To support automatic connection management, we use boost::visit_each + * (http://www.boost.org/doc/libs/1_37_0/doc/html/boost/visit_each.html) to + * inspect each argument of a boost::bind expression. (Although the visit_each + * mechanism was first introduced with the original Boost.Signals library, it + * was only later documented.) + * + * Cases: + * * At least one of the function's arguments is a boost::weak_ptr. Pass + * the corresponding shared_ptr to slot_type::track(). Ideally that would be + * the object whose method we want to call, but in fact we do the same for + * any weak_ptr we might find among the bound arguments. If we're passing + * our bound method a weak_ptr to some object, wouldn't the destruction of + * that object invalidate the call? So we disconnect automatically when any + * such object is destroyed. This is the mechanism preferred by boost:: + * signals2. + * * One of the functions's arguments is a boost::shared_ptr. This produces + * a compile error: the bound copy of the shared_ptr stored in the + * boost_bind object stored in the signal object would make the referenced + * T object immortal. We provide a weaken() function. Pass + * weaken(your_shared_ptr) instead. (We can inspect, but not modify, the + * boost::bind object. Otherwise we'd replace the shared_ptr with weak_ptr + * implicitly and just proceed.) + * * One of the function's arguments is a plain pointer/reference to an object + * derived from boost::enable_shared_from_this. We assume that this object + * is managed using boost::shared_ptr, so we implicitly extract a shared_ptr + * and track that. (UNDER CONSTRUCTION) + * * One of the function's arguments is derived from LLEventTrackable. Pass + * the LLBoundListener to its LLEventTrackable::track(). This is vulnerable + * to a couple different race conditions, as described in LLEventTrackable + * documentation. (NOTE: Now that LLEventTrackable is a typedef for + * boost::signals2::trackable, the Signals2 library handles this itself, so + * our visitor needs no special logic for this case.) + * * Any other argument type is irrelevant to automatic connection management. + */ + +namespace LLEventDetail +{ + template + const F& unwrap(const F& f) { return f; } + + template + const F& unwrap(const boost::reference_wrapper& f) { return f.get(); } + + // Most of the following is lifted from the Boost.Signals use of + // visit_each. + template struct truth {}; + + /** + * boost::visit_each() Visitor, used on a template argument const F& + * f as follows (see visit_and_connect()): + * @code + * LLEventListener listener(f); + * Visitor visitor(listener); // bind listener so it can track() shared_ptrs + * using boost::visit_each; // allow unqualified visit_each() call for ADL + * visit_each(visitor, unwrap(f)); + * @endcode + */ + class Visitor + { + public: + /** + * Visitor binds a reference to LLEventListener so we can track() any + * shared_ptrs we find in the argument list. + */ + Visitor(LLEventListener& listener): + mListener(listener) + { + } + + /** + * boost::visit_each() calls this method for each component of a + * boost::bind() expression. + */ + template + void operator()(const T& t) const + { + decode(t, 0); + } + + private: + // decode() decides between a reference wrapper and anything else + // boost::ref() variant + template + void decode(const boost::reference_wrapper& t, int) const + { +// add_if_trackable(t.get_pointer()); + } + + // decode() anything else + template + void decode(const T& t, long) const + { + typedef truth<(boost::is_pointer::value)> is_a_pointer; + maybe_get_pointer(t, is_a_pointer()); + } + + // maybe_get_pointer() decides between a pointer and a non-pointer + // plain pointer variant + template + void maybe_get_pointer(const T& t, truth) const + { +// add_if_trackable(t); + } + + // shared_ptr variant + template + void maybe_get_pointer(const boost::shared_ptr& t, truth) const + { + // If we have a shared_ptr to this object, it doesn't matter + // whether the object is derived from LLEventTrackable, so no + // further analysis of T is needed. +// mListener.track(t); + + // Make this case illegal. Passing a bound shared_ptr to + // slot_type::track() is useless, since the bound shared_ptr will + // keep the object alive anyway! Force the coder to cast to weak_ptr. + + // Trivial as it is, make the BOOST_STATIC_ASSERT() condition + // dependent on template param so the macro is only evaluated if + // this method is in fact instantiated, as described here: + // http://www.boost.org/doc/libs/1_34_1/doc/html/boost_staticassert.html + + // ATTENTION: Don't bind a shared_ptr using + // LLEventPump::listen(boost::bind()). Doing so captures a copy of + // the shared_ptr, making the referenced object effectively + // immortal. Use the weaken() function, e.g.: + // somepump.listen(boost::bind(...weaken(my_shared_ptr)...)); + // This lets us automatically disconnect when the referenced + // object is destroyed. + BOOST_STATIC_ASSERT(sizeof(T) == 0); + } + + // weak_ptr variant + template + void maybe_get_pointer(const boost::weak_ptr& t, truth) const + { + // If we have a weak_ptr to this object, it doesn't matter + // whether the object is derived from LLEventTrackable, so no + // further analysis of T is needed. + mListener.track(t); +// std::cout << "Found weak_ptr<" << typeid(T).name() << ">!\n"; + } + +#if 0 + // reference to anything derived from boost::enable_shared_from_this + template + inline void maybe_get_pointer(const boost::enable_shared_from_this& ct, + truth) const + { + // Use the slot_type::track(shared_ptr) mechanism. Cast away + // const-ness because (in our code base anyway) it's unusual + // to find shared_ptr. + boost::enable_shared_from_this& + t(const_cast&>(ct)); + std::cout << "Capturing shared_from_this()" << std::endl; + boost::shared_ptr sp(t.shared_from_this()); +/*==========================================================================*| + std::cout << "Capturing weak_ptr" << std::endl; + boost::weak_ptr wp(sp); +|*==========================================================================*/ + std::cout << "Tracking shared__ptr" << std::endl; + mListener.track(sp); + } +#endif + + // non-pointer variant + template + void maybe_get_pointer(const T& t, truth) const + { + // Take the address of this object, because the object itself may be + // trackable +// add_if_trackable(boost::addressof(t)); + } + +/*==========================================================================*| + // add_if_trackable() adds LLEventTrackable objects to mTrackables + inline void add_if_trackable(const LLEventTrackable* t) const + { + if (t) + { + } + } + + // pointer to anything not an LLEventTrackable subclass + inline void add_if_trackable(const void*) const + { + } + + // pointer to free function + // The following construct uses the preprocessor to generate + // add_if_trackable() overloads accepting pointer-to-function taking + // 0, 1, ..., LLEVENTS_LISTENER_ARITY parameters of arbitrary type. +#define BOOST_PP_LOCAL_MACRO(n) \ + template \ + inline void \ + add_if_trackable(R (*)(BOOST_PP_ENUM_PARAMS(n, T))) const \ + { \ + } +#define BOOST_PP_LOCAL_LIMITS (0, LLEVENTS_LISTENER_ARITY) +#include BOOST_PP_LOCAL_ITERATE() +#undef BOOST_PP_LOCAL_MACRO +#undef BOOST_PP_LOCAL_LIMITS +|*==========================================================================*/ + + /// Bind a reference to the LLEventListener to call its track() method. + LLEventListener& mListener; + }; + + /** + * Utility template function to use Visitor appropriately + * + * @param raw_listener Callable to connect, typically a boost::bind() + * expression. This will be visited by Visitor using boost::visit_each(). + * @param connect_funct Callable that will connect() @a raw_listener to an + * LLStandardSignal, returning LLBoundListener. + */ + template + LLBoundListener visit_and_connect(const LISTENER& raw_listener, + const ConnectFunc& connect_func) + { + // Capture the listener + LLEventListener listener(raw_listener); + // Define our Visitor, binding the listener so we can call + // listener.track() if we discover any shared_ptr. + LLEventDetail::Visitor visitor(listener); + // Allow unqualified visit_each() call for ADL + using boost::visit_each; + // Visit each component of a boost::bind() expression. Pass + // 'raw_listener', our template argument, rather than 'listener' from + // which type details have been erased. unwrap() comes from + // Boost.Signals, in case we were passed a boost::ref(). + visit_each(visitor, LLEventDetail::unwrap(raw_listener)); + // Make the connection using passed function. At present, wrapping + // this functionality into this function is a bit silly: we don't + // really need a visit_and_connect() function any more, just a visit() + // function. The definition of this function dates from when, after + // visit_each(), after establishing the connection, we had to + // postprocess the new connection with the visitor object. That's no + // longer necessary. + return connect_func(listener); + } +} // namespace LLEventDetail + +// Somewhat to my surprise, passing boost::bind(...boost::weak_ptr...) to +// listen() fails in Boost code trying to instantiate LLEventListener (i.e. +// LLStandardSignal::slot_type) because the boost::get_pointer() utility function isn't +// specialized for boost::weak_ptr. This remedies that omission. +namespace boost +{ + template + T* get_pointer(const weak_ptr& ptr) { return shared_ptr(ptr).get(); } +} + +/// Since we forbid use of listen(boost::bind(...shared_ptr...)), provide an +/// easy way to cast to the corresponding weak_ptr. +template +boost::weak_ptr weaken(const boost::shared_ptr& ptr) +{ + return boost::weak_ptr(ptr); +} + +#endif /* ! defined(LL_LLEVENTS_H) */ -- cgit v1.2.3