diff options
Diffstat (limited to 'indra/llcommon/llsingleton.h')
| -rw-r--r-- | indra/llcommon/llsingleton.h | 586 |
1 files changed, 314 insertions, 272 deletions
diff --git a/indra/llcommon/llsingleton.h b/indra/llcommon/llsingleton.h index 7def9b019c..30a5b21cf8 100644 --- a/indra/llcommon/llsingleton.h +++ b/indra/llcommon/llsingleton.h @@ -30,18 +30,10 @@ #include <list> #include <vector> #include <typeinfo> - -#if LL_WINDOWS -#pragma warning (push) -#pragma warning (disable:4265) -#endif -// warning C4265: 'std::_Pad' : class has virtual functions, but destructor is not virtual - -#include <mutex> - -#if LL_WINDOWS -#pragma warning (pop) -#endif +#include "mutex.h" +#include "lockstatic.h" +#include "llthread.h" // on_main_thread() +#include "llmainthreadtask.h" class LLSingletonBase: private boost::noncopyable { @@ -51,15 +43,13 @@ public: private: // All existing LLSingleton instances are tracked in this master list. typedef std::list<LLSingletonBase*> list_t; - static list_t& get_master(); - // This, on the other hand, is a stack whose top indicates the LLSingleton - // currently being initialized. - static list_t& get_initializing(); + // Size of stack whose top indicates the LLSingleton currently being + // initialized. + static list_t::size_type get_initializing_size(); // Produce a vector<LLSingletonBase*> of master list, in dependency order. typedef std::vector<LLSingletonBase*> vec_t; static vec_t dep_sort(); - bool mCleaned; // cleanupSingleton() has been called // we directly depend on these other LLSingletons typedef boost::unordered_set<LLSingletonBase*> set_t; set_t mDepends; @@ -68,8 +58,8 @@ protected: typedef enum e_init_state { UNINITIALIZED = 0, // must be default-initialized state + QUEUED, // construction queued, not yet executing CONSTRUCTING, // within DERIVED_TYPE constructor - CONSTRUCTED, // finished DERIVED_TYPE constructor INITIALIZING, // within DERIVED_TYPE::initSingleton() INITIALIZED, // normal case DELETED // deleteSingleton() or deleteAll() called @@ -115,21 +105,23 @@ protected: // Remove 'this' from the init stack in case of exception in the // LLSingleton subclass constructor. static void reset_initializing(list_t::size_type size); -private: - // logging - static void log_initializing(const char* verb, const char* name); protected: // If a given call to B::getInstance() happens during either A::A() or // A::initSingleton(), record that A directly depends on B. - void capture_dependency(list_t& initializing, EInitState); + void capture_dependency(); - // delegate LL_ERRS() logging to llsingleton.cpp + // delegate logging calls to llsingleton.cpp static void logerrs(const char* p1, const char* p2="", const char* p3="", const char* p4=""); - // delegate LL_WARNS() logging to llsingleton.cpp static void logwarns(const char* p1, const char* p2="", const char* p3="", const char* p4=""); + static void loginfos(const char* p1, const char* p2="", + const char* p3="", const char* p4=""); + static void logdebugs(const char* p1, const char* p2="", + const char* p3="", const char* p4=""); static std::string demangle(const char* mangled); + // these classname() declarations restate template functions declared in + // llerror.h because we avoid #including that here template <typename T> static std::string classname() { return demangle(typeid(T).name()); } template <typename T> @@ -139,6 +131,9 @@ protected: virtual void initSingleton() {} virtual void cleanupSingleton() {} + // internal wrapper around calls to cleanupSingleton() + void cleanup_(); + // deleteSingleton() isn't -- and shouldn't be -- a virtual method. It's a // class static. However, given only Foo*, deleteAll() does need to be // able to reach Foo::deleteSingleton(). Make LLSingleton (which declares @@ -148,32 +143,15 @@ protected: public: /** - * Call this to call the cleanupSingleton() method for every LLSingleton - * constructed since the start of the last cleanupAll() call. (Any - * LLSingleton constructed DURING a cleanupAll() call won't be cleaned up - * until the next cleanupAll() call.) cleanupSingleton() neither deletes - * nor destroys its LLSingleton; therefore it's safe to include logic that - * might take significant realtime or even throw an exception. - * - * The most important property of cleanupAll() is that cleanupSingleton() - * methods are called in dependency order, leaf classes last. Thus, given - * two LLSingleton subclasses A and B, if A's dependency on B is properly - * expressed as a B::getInstance() or B::instance() call during either - * A::A() or A::initSingleton(), B will be cleaned up after A. - * - * If a cleanupSingleton() method throws an exception, the exception is - * logged, but cleanupAll() attempts to continue calling the rest of the - * cleanupSingleton() methods. - */ - static void cleanupAll(); - /** - * Call this to call the deleteSingleton() method for every LLSingleton - * constructed since the start of the last deleteAll() call. (Any - * LLSingleton constructed DURING a deleteAll() call won't be cleaned up - * until the next deleteAll() call.) deleteSingleton() deletes and - * destroys its LLSingleton. Any cleanup logic that might take significant - * realtime -- or throw an exception -- must not be placed in your - * LLSingleton's destructor, but rather in its cleanupSingleton() method. + * deleteAll() calls the cleanupSingleton() and deleteSingleton() methods + * for every LLSingleton constructed since the start of the last + * deleteAll() call. (Any LLSingleton constructed DURING a deleteAll() + * call won't be cleaned up until the next deleteAll() call.) + * deleteSingleton() deletes and destroys its LLSingleton. Any cleanup + * logic that might take significant realtime -- or throw an exception -- + * must not be placed in your LLSingleton's destructor, but rather in its + * cleanupSingleton() method, which is called implicitly by + * deleteSingleton(). * * The most important property of deleteAll() is that deleteSingleton() * methods are called in dependency order, leaf classes last. Thus, given @@ -181,9 +159,9 @@ public: * expressed as a B::getInstance() or B::instance() call during either * A::A() or A::initSingleton(), B will be cleaned up after A. * - * If a deleteSingleton() method throws an exception, the exception is - * logged, but deleteAll() attempts to continue calling the rest of the - * deleteSingleton() methods. + * If a cleanupSingleton() or deleteSingleton() method throws an + * exception, the exception is logged, but deleteAll() attempts to + * continue calling the rest of the deleteSingleton() methods. */ static void deleteAll(); }; @@ -203,9 +181,16 @@ struct LLSingleton_manage_master { LLSingletonBase::reset_initializing(size); } - // For any LLSingleton subclass except the MasterList, obtain the init - // stack from the MasterList singleton instance. - LLSingletonBase::list_t& get_initializing() { return LLSingletonBase::get_initializing(); } + // For any LLSingleton subclass except the MasterList, obtain the size of + // the init stack from the MasterList singleton instance. + LLSingletonBase::list_t::size_type get_initializing_size() + { + return LLSingletonBase::get_initializing_size(); + } + void capture_dependency(LLSingletonBase* sb) + { + sb->capture_dependency(); + } }; // But for the specific case of LLSingletonBase::MasterList, don't. @@ -218,20 +203,14 @@ struct LLSingleton_manage_master<LLSingletonBase::MasterList> void pop_initializing (LLSingletonBase*) {} // since we never pushed, no need to clean up void reset_initializing(LLSingletonBase::list_t::size_type size) {} - LLSingletonBase::list_t& get_initializing() - { - // The MasterList shouldn't depend on any other LLSingletons. We'd - // get into trouble if we tried to recursively engage that machinery. - static LLSingletonBase::list_t sDummyList; - return sDummyList; - } + LLSingletonBase::list_t::size_type get_initializing_size() { return 0; } + void capture_dependency(LLSingletonBase*) {} }; // Now we can implement LLSingletonBase's template constructor. template <typename DERIVED_TYPE> LLSingletonBase::LLSingletonBase(tag<DERIVED_TYPE>): - mCleaned(false), - mDeleteSingleton(NULL) + mDeleteSingleton(nullptr) { // This is the earliest possible point at which we can push this new // instance onto the init stack. LLSingleton::constructSingleton() can't @@ -273,10 +252,19 @@ class LLParamSingleton; * leading back to yours, move the instance reference from your constructor to * your initSingleton() method. * - * If you override LLSingleton<T>::cleanupSingleton(), your method will be - * called if someone calls LLSingletonBase::cleanupAll(). The significant part - * of this promise is that cleanupAll() will call individual - * cleanupSingleton() methods in reverse dependency order. + * If you override LLSingleton<T>::cleanupSingleton(), your method will + * implicitly be called by LLSingleton<T>::deleteSingleton() just before the + * instance is destroyed. We introduce a special cleanupSingleton() method + * because cleanupSingleton() operations can involve nontrivial realtime, or + * throw an exception. A destructor should do neither! + * + * If your cleanupSingleton() method throws an exception, we log that + * exception but carry on. + * + * If at some point you call LLSingletonBase::deleteAll(), all remaining + * LLSingleton<T> instances will be destroyed in reverse dependency order. (Or + * call MySubclass::deleteSingleton() to specifically destroy the canonical + * MySubclass instance.) * * That is, consider LLSingleton subclasses C, B and A. A depends on B, which * in turn depends on C. These dependencies are expressed as calls to @@ -284,33 +272,34 @@ class LLParamSingleton; * It shouldn't matter whether these calls appear in A::A() or * A::initSingleton(), likewise B::B() or B::initSingleton(). * - * We promise that if you later call LLSingletonBase::cleanupAll(): - * 1. A::cleanupSingleton() will be called before - * 2. B::cleanupSingleton(), which will be called before - * 3. C::cleanupSingleton(). + * We promise that if you later call LLSingletonBase::deleteAll(): + * 1. A::deleteSingleton() will be called before + * 2. B::deleteSingleton(), which will be called before + * 3. C::deleteSingleton(). * Put differently, if your LLSingleton subclass constructor or * initSingleton() method explicitly depends on some other LLSingleton * subclass, you may continue to rely on that other subclass in your * cleanupSingleton() method. - * - * We introduce a special cleanupSingleton() method because cleanupSingleton() - * operations can involve nontrivial realtime, or might throw an exception. A - * destructor should do neither! - * - * If your cleanupSingleton() method throws an exception, we log that - * exception but proceed with the remaining cleanupSingleton() calls. - * - * Similarly, if at some point you call LLSingletonBase::deleteAll(), all - * remaining LLSingleton instances will be destroyed in dependency order. (Or - * call MySubclass::deleteSingleton() to specifically destroy the canonical - * MySubclass instance.) - * - * As currently written, LLSingleton is not thread-safe. */ template <typename DERIVED_TYPE> class LLSingleton : public LLSingletonBase { private: + // LLSingleton<DERIVED_TYPE> must have a distinct instance of + // SingletonData for every distinct DERIVED_TYPE. It's tempting to + // consider hoisting SingletonData up into LLSingletonBase. Don't do it. + struct SingletonData + { + // Use a recursive_mutex in case of constructor circularity. With a + // non-recursive mutex, that would result in deadlock. + typedef std::recursive_mutex mutex_t; + mutex_t mMutex; // LockStatic looks for mMutex + + EInitState mInitState{UNINITIALIZED}; + DERIVED_TYPE* mInstance{nullptr}; + }; + typedef llthread::LockStatic<SingletonData> LockStatic; + // Allow LLParamSingleton subclass -- but NOT DERIVED_TYPE itself -- to // access our private members. friend class LLParamSingleton<DERIVED_TYPE>; @@ -319,17 +308,17 @@ private: // purpose for its subclass LLParamSingleton is to support Singletons // requiring constructor arguments. constructSingleton() supports both use // cases. + // Accepting LockStatic& requires that the caller has already locked our + // static data before calling. template <typename... Args> - static void constructSingleton(Args&&... args) + static void constructSingleton(LockStatic& lk, Args&&... args) { - auto prev_size = LLSingleton_manage_master<DERIVED_TYPE>().get_initializing().size(); - // getInstance() calls are from within constructor - sData.mInitState = CONSTRUCTING; + auto prev_size = LLSingleton_manage_master<DERIVED_TYPE>().get_initializing_size(); + // Any getInstance() calls after this point are from within constructor + lk->mInitState = CONSTRUCTING; try { - sData.mInstance = new DERIVED_TYPE(std::forward<Args>(args)...); - // we have called constructor, have not yet called initSingleton() - sData.mInitState = CONSTRUCTED; + lk->mInstance = new DERIVED_TYPE(std::forward<Args>(args)...); } catch (const std::exception& err) { @@ -343,62 +332,56 @@ private: // There isn't a separate EInitState value meaning "we attempted // to construct this LLSingleton subclass but could not," so use // DELETED. That seems slightly more appropriate than UNINITIALIZED. - sData.mInitState = DELETED; + lk->mInitState = DELETED; // propagate the exception throw; } - } - static void finishInitializing() - { - // getInstance() calls are from within initSingleton() - sData.mInitState = INITIALIZING; + // Any getInstance() calls after this point are from within initSingleton() + lk->mInitState = INITIALIZING; try { // initialize singleton after constructing it so that it can // reference other singletons which in turn depend on it, thus // breaking cyclic dependencies - sData.mInstance->initSingleton(); - sData.mInitState = INITIALIZED; + lk->mInstance->initSingleton(); + lk->mInitState = INITIALIZED; // pop this off stack of initializing singletons - pop_initializing(); + pop_initializing(lk->mInstance); } catch (const std::exception& err) { // pop this off stack of initializing singletons here, too -- // BEFORE logging, so log-machinery LLSingletons don't record a // dependency on DERIVED_TYPE! - pop_initializing(); + pop_initializing(lk->mInstance); logwarns("Error in ", classname<DERIVED_TYPE>().c_str(), "::initSingleton(): ", err.what()); - // and get rid of the instance entirely + // Get rid of the instance entirely. This call depends on our + // recursive_mutex. We could have a deleteSingleton(LockStatic&) + // overload and pass lk, but we don't strictly need it. deleteSingleton(); // propagate the exception throw; } } - static void pop_initializing() + static void pop_initializing(LLSingletonBase* sb) { // route through LLSingleton_manage_master so we Do The Right Thing // (namely, nothing) for MasterList - LLSingleton_manage_master<DERIVED_TYPE>().pop_initializing(sData.mInstance); + LLSingleton_manage_master<DERIVED_TYPE>().pop_initializing(sb); } - // Without this 'using' declaration, the static method we're declaring - // here would hide the base-class method we want it to call. - using LLSingletonBase::capture_dependency; - static void capture_dependency() + static void capture_dependency(LLSingletonBase* sb) { // By this point, if DERIVED_TYPE was pushed onto the initializing // stack, it has been popped off. So the top of that stack, if any, is // an LLSingleton that directly depends on DERIVED_TYPE. If // getInstance() was called by another LLSingleton, rather than from // vanilla application code, record the dependency. - sData.mInstance->capture_dependency( - LLSingleton_manage_master<DERIVED_TYPE>().get_initializing(), - sData.mInitState); + LLSingleton_manage_master<DERIVED_TYPE>().capture_dependency(sb); } // We know of no way to instruct the compiler that every subclass @@ -411,20 +394,6 @@ private: // subclass body. virtual void you_must_use_LLSINGLETON_macro() = 0; - // The purpose of this struct is to engage the C++11 guarantee that static - // variables declared in function scope are initialized exactly once, even - // if multiple threads concurrently reach the same declaration. - // https://en.cppreference.com/w/cpp/language/storage_duration#Static_local_variables - // Since getInstance() declares a static instance of SingletonInitializer, - // only the first call to getInstance() calls constructSingleton(). - struct SingletonInitializer - { - SingletonInitializer() - { - constructSingleton(); - } - }; - protected: // Pass DERIVED_TYPE explicitly to LLSingletonBase's constructor because, // until our subclass constructor completes, *this isn't yet a @@ -439,97 +408,176 @@ protected: LLSingleton_manage_master<DERIVED_TYPE>().add(this); } -public: +protected: virtual ~LLSingleton() { - // remove this instance from the master list + // This phase of cleanup is performed in the destructor rather than in + // deleteSingleton() to defend against manual deletion. When we moved + // cleanup to deleteSingleton(), we hit crashes due to dangling + // pointers in the MasterList. + LockStatic lk; + lk->mInstance = nullptr; + lk->mInitState = DELETED; + + // Remove this instance from the master list. LLSingleton_manage_master<DERIVED_TYPE>().remove(this); - sData.mInstance = NULL; - sData.mInitState = DELETED; } +public: /** - * @brief Immediately delete the singleton. + * @brief Cleanup and destroy the singleton instance. * - * A subsequent call to LLProxy::getInstance() will construct a new - * instance of the class. + * deleteSingleton() calls this instance's cleanupSingleton() method and + * then destroys the instance. * - * Without an explicit call to LLSingletonBase::deleteAll(), LLSingletons - * are implicitly destroyed after main() has exited and the C++ runtime is - * cleaning up statically-constructed objects. Some classes derived from - * LLSingleton have objects that are part of a runtime system that is - * terminated before main() exits. Calling the destructor of those objects - * after the termination of their respective systems can cause crashes and - * other problems during termination of the project. Using this method to - * destroy the singleton early can prevent these crashes. + * A subsequent call to LLSingleton<T>::getInstance() will construct a new + * instance of the class. * - * An example where this is needed is for a LLSingleton that has an APR - * object as a member that makes APR calls on destruction. The APR system is - * shut down explicitly before main() exits. This causes a crash on exit. - * Using this method before the call to apr_terminate() and NOT calling - * getInstance() again will prevent the crash. + * Without an explicit call to LLSingletonBase::deleteAll(), or + * LLSingleton<T>::deleteSingleton(), LLSingleton instances are simply + * leaked. (Allowing implicit destruction at shutdown caused too many + * problems.) */ static void deleteSingleton() { - delete sData.mInstance; - // SingletonData state handled by destructor, above + // Hold the lock while we call cleanupSingleton() and the destructor. + // Our destructor also instantiates LockStatic, requiring a recursive + // mutex. + LockStatic lk; + // of course, only cleanup and delete if there's something there + if (lk->mInstance) + { + lk->mInstance->cleanup_(); + delete lk->mInstance; + // destructor clears mInstance (and mInitState) + } } static DERIVED_TYPE* getInstance() { - // call constructSingleton() only the first time we get here - static SingletonInitializer sInitializer; - - switch (sData.mInitState) - { - case UNINITIALIZED: - // should never be uninitialized at this point - logerrs("Uninitialized singleton ", - classname<DERIVED_TYPE>().c_str()); - return NULL; - - case CONSTRUCTING: - // here if DERIVED_TYPE's constructor (directly or indirectly) - // calls DERIVED_TYPE::getInstance() - logerrs("Tried to access singleton ", - classname<DERIVED_TYPE>().c_str(), - " from singleton constructor!"); - return NULL; - - case CONSTRUCTED: - // first time through: set to CONSTRUCTED by - // constructSingleton(), called by sInitializer's constructor; - // still have to call initSingleton() - finishInitializing(); - break; - - case INITIALIZING: - // here if DERIVED_TYPE::initSingleton() (directly or indirectly) - // calls DERIVED_TYPE::getInstance(): go ahead and allow it - case INITIALIZED: - // normal subsequent calls - break; - - case DELETED: - // called after deleteSingleton() - logwarns("Trying to access deleted singleton ", - classname<DERIVED_TYPE>().c_str(), - " -- creating new instance"); - // This recovery sequence is NOT thread-safe! We would need a - // recursive_mutex a la LLParamSingleton. - constructSingleton(); - finishInitializing(); - break; - } - - // record the dependency, if any: check if we got here from another - // LLSingleton's constructor or initSingleton() method - capture_dependency(); - return sData.mInstance; + // We know the viewer has LLSingleton dependency circularities. If you + // feel strongly motivated to eliminate them, cheers and good luck. + // (At that point we could consider a much simpler locking mechanism.) + + // If A and B depend on each other, and thread T1 requests A at the + // same moment thread T2 requests B, you could get a sequence like this: + // - T1 locks A + // - T2 locks B + // - T1, having constructed A, calls A::initSingleton(), which calls + // B::getInstance() and blocks on B's lock + // - T2, having constructed B, calls B::initSingleton(), which calls + // A::getInstance() and blocks on A's lock + // In other words, classic deadlock. + + // Avoid that by constructing and initializing every LLSingleton on + // the main thread. In that scenario: + // - T1 locks A + // - T2 locks B + // - T1 discovers A is UNINITIALIZED, so it queues a task for the main + // thread, unlocks A and blocks on the std::future. + // - T2 discovers B is UNINITIALIZED, so it queues a task for the main + // thread, unlocks B and blocks on the std::future. + // - The main thread executes T1's request for A. It locks A and + // starts to construct it. + // - A::initSingleton() calls B::getInstance(). Fine: nobody's holding + // B's lock. + // - The main thread locks B, constructs B, calls B::initSingleton(), + // which calls A::getInstance(), which returns A. + // - B::getInstance() returns B to A::initSingleton(), unlocking B. + // - A::getInstance() returns A to the task wrapper, unlocking A. + // - The task wrapper passes A to T1 via the future. T1 resumes. + // - The main thread executes T2's request for B. Oh look, B already + // exists. The task wrapper passes B to T2 via the future. T2 + // resumes. + // This still works even if one of T1 or T2 *is* the main thread. + // This still works even if thread T3 requests B at the same moment as + // T2. Finding B still UNINITIALIZED, T3 also queues a task for the + // main thread, unlocks B and blocks on a (distinct) std::future. By + // the time the main thread executes T3's request for B, B already + // exists, and is simply delivered via the future. + + { // nested scope for 'lk' + // In case racing threads call getInstance() at the same moment, + // serialize the calls. + LockStatic lk; + + switch (lk->mInitState) + { + case CONSTRUCTING: + // here if DERIVED_TYPE's constructor (directly or indirectly) + // calls DERIVED_TYPE::getInstance() + logerrs("Tried to access singleton ", + classname<DERIVED_TYPE>().c_str(), + " from singleton constructor!"); + return nullptr; + + case INITIALIZING: + // here if DERIVED_TYPE::initSingleton() (directly or indirectly) + // calls DERIVED_TYPE::getInstance(): go ahead and allow it + case INITIALIZED: + // normal subsequent calls + // record the dependency, if any: check if we got here from another + // LLSingleton's constructor or initSingleton() method + capture_dependency(lk->mInstance); + return lk->mInstance; + + case DELETED: + // called after deleteSingleton() + logwarns("Trying to access deleted singleton ", + classname<DERIVED_TYPE>().c_str(), + " -- creating new instance"); + // fall through + case UNINITIALIZED: + case QUEUED: + // QUEUED means some secondary thread has already requested an + // instance, but for present purposes that's semantically + // identical to UNINITIALIZED: either way, we must ourselves + // request an instance. + break; + } + + // Here we need to construct a new instance. + if (on_main_thread()) + { + // On the main thread, directly construct the instance while + // holding the lock. + constructSingleton(lk); + capture_dependency(lk->mInstance); + return lk->mInstance; + } + + // Here we need to construct a new instance, but we're on a secondary + // thread. + lk->mInitState = QUEUED; + } // unlock 'lk' + + // Per the comment block above, dispatch to the main thread. + loginfos(classname<DERIVED_TYPE>().c_str(), + "::getInstance() dispatching to main thread"); + auto instance = LLMainThreadTask::dispatch( + [](){ + // VERY IMPORTANT to call getInstance() on the main thread, + // rather than going straight to constructSingleton()! + // During the time window before mInitState is INITIALIZED, + // multiple requests might be queued. It's essential that, as + // the main thread processes them, only the FIRST such request + // actually constructs the instance -- every subsequent one + // simply returns the existing instance. + loginfos(classname<DERIVED_TYPE>().c_str(), + "::getInstance() on main thread"); + return getInstance(); + }); + // record the dependency chain tracked on THIS thread, not the main + // thread (consider a getInstance() overload with a tag param that + // suppresses dep tracking when dispatched to the main thread) + capture_dependency(instance); + loginfos(classname<DERIVED_TYPE>().c_str(), + "::getInstance() returning on requesting thread"); + return instance; } // Reference version of getInstance() - // Preferred over getInstance() as it disallows checking for NULL + // Preferred over getInstance() as it disallows checking for nullptr static DERIVED_TYPE& instance() { return *getInstance(); @@ -539,7 +587,9 @@ public: // Use this to avoid accessing singletons before they can safely be constructed. static bool instanceExists() { - return sData.mInitState == INITIALIZED; + // defend any access to sData from racing threads + LockStatic lk; + return lk->mInitState == INITIALIZED; } // Has this singleton been deleted? This can be useful during shutdown @@ -547,23 +597,12 @@ public: // cleaned up. static bool wasDeleted() { - return sData.mInitState == DELETED; + // defend any access to sData from racing threads + LockStatic lk; + return lk->mInitState == DELETED; } - -private: - struct SingletonData - { - // explicitly has a default constructor so that member variables are zero initialized in BSS - // and only changed by singleton logic, not constructor running during startup - EInitState mInitState; - DERIVED_TYPE* mInstance; - }; - static SingletonData sData; }; -template<typename T> -typename LLSingleton<T>::SingletonData LLSingleton<T>::sData; - /** * LLParamSingleton<T> is like LLSingleton<T>, except in the following ways: @@ -588,47 +627,86 @@ class LLParamSingleton : public LLSingleton<DERIVED_TYPE> { private: typedef LLSingleton<DERIVED_TYPE> super; - // Use a recursive_mutex in case of constructor circularity. With a - // non-recursive mutex, that would result in deadlock rather than the - // logerrs() call in getInstance(). - typedef std::recursive_mutex mutex_t; + using typename super::LockStatic; -public: - using super::deleteSingleton; - using super::instanceExists; - using super::wasDeleted; - - // Passes arguments to DERIVED_TYPE's constructor and sets appropriate states + // Passes arguments to DERIVED_TYPE's constructor and sets appropriate + // states, returning a pointer to the new instance. template <typename... Args> - static void initParamSingleton(Args&&... args) + static DERIVED_TYPE* initParamSingleton_(Args&&... args) { // In case racing threads both call initParamSingleton() at the same // time, serialize them. One should initialize; the other should see // mInitState already set. - std::unique_lock<mutex_t> lk(getMutex()); + LockStatic lk; // For organizational purposes this function shouldn't be called twice - if (super::sData.mInitState != super::UNINITIALIZED) + if (lk->mInitState != super::UNINITIALIZED) { super::logerrs("Tried to initialize singleton ", super::template classname<DERIVED_TYPE>().c_str(), " twice!"); + return nullptr; + } + else if (on_main_thread()) + { + // on the main thread, simply construct instance while holding lock + super::logdebugs(super::template classname<DERIVED_TYPE>().c_str(), + "::initParamSingleton()"); + super::constructSingleton(lk, std::forward<Args>(args)...); + return lk->mInstance; } else { - super::constructSingleton(std::forward<Args>(args)...); - super::finishInitializing(); + // on secondary thread, dispatch to main thread -- + // set state so we catch any other calls before the main thread + // picks up the task + lk->mInitState = super::QUEUED; + // very important to unlock here so main thread can actually process + lk.unlock(); + super::loginfos(super::template classname<DERIVED_TYPE>().c_str(), + "::initParamSingleton() dispatching to main thread"); + // Normally it would be the height of folly to reference-bind + // 'args' into a lambda to be executed on some other thread! By + // the time that thread executed the lambda, the references would + // all be dangling, and Bad Things would result. But + // LLMainThreadTask::dispatch() promises to block until the passed + // task has completed. So in this case we know the references will + // remain valid until the lambda has run, so we dare to bind + // references. + auto instance = LLMainThreadTask::dispatch( + [&](){ + super::loginfos(super::template classname<DERIVED_TYPE>().c_str(), + "::initParamSingleton() on main thread"); + return initParamSingleton_(std::forward<Args>(args)...); + }); + super::loginfos(super::template classname<DERIVED_TYPE>().c_str(), + "::initParamSingleton() returning on requesting thread"); + return instance; } } +public: + using super::deleteSingleton; + using super::instanceExists; + using super::wasDeleted; + + /// initParamSingleton() constructs the instance, returning a reference. + /// Pass whatever arguments are required to construct DERIVED_TYPE. + template <typename... Args> + static DERIVED_TYPE& initParamSingleton(Args&&... args) + { + return *initParamSingleton_(std::forward<Args>(args)...); + } + static DERIVED_TYPE* getInstance() { // In case racing threads call getInstance() at the same moment as // initParamSingleton(), serialize the calls. - std::unique_lock<mutex_t> lk(getMutex()); + LockStatic lk; - switch (super::sData.mInitState) + switch (lk->mInitState) { case super::UNINITIALIZED: + case super::QUEUED: super::logerrs("Uninitialized param singleton ", super::template classname<DERIVED_TYPE>().c_str()); break; @@ -639,25 +717,13 @@ public: " from singleton constructor!"); break; - case super::CONSTRUCTED: - // Should never happen!? The CONSTRUCTED state is specifically to - // navigate through LLSingleton::SingletonInitializer getting - // constructed (once) before LLSingleton::getInstance()'s switch - // on mInitState. But our initParamSingleton() method calls - // constructSingleton() and then calls finishInitializing(), which - // immediately sets INITIALIZING. Why are we here? - super::logerrs("Param singleton ", - super::template classname<DERIVED_TYPE>().c_str(), - "::initSingleton() not yet called"); - break; - case super::INITIALIZING: // As with LLSingleton, explicitly permit circular calls from // within initSingleton() case super::INITIALIZED: // for any valid call, capture dependencies - super::capture_dependency(); - return super::sData.mInstance; + super::capture_dependency(lk->mInstance); + return lk->mInstance; case super::DELETED: super::logerrs("Trying to access deleted param singleton ", @@ -677,30 +743,6 @@ public: { return *getInstance(); } - -private: - // sMutex must be a function-local static rather than a static member. One - // of the essential features of LLSingleton and friends is that they must - // support getInstance() even when the containing module's static - // variables have not yet been runtime-initialized. A mutex requires - // construction. A static class member might not yet have been - // constructed. - // - // We could store a dumb mutex_t*, notice when it's NULL and allocate a - // heap mutex -- but that's vulnerable to race conditions. And we can't - // defend the dumb pointer with another mutex. - // - // We could store a std::atomic<mutex_t*> -- but a default-constructed - // std::atomic<T> does not contain a valid T, even a default-constructed - // T! Which means std::atomic, too, requires runtime initialization. - // - // But a function-local static is guaranteed to be initialized exactly - // once, the first time control reaches that declaration. - static mutex_t& getMutex() - { - static mutex_t sMutex; - return sMutex; - } }; /** @@ -725,9 +767,9 @@ public: using super::instanceExists; using super::wasDeleted; - static void construct() + static DT* construct() { - super::initParamSingleton(); + return super::initParamSingleton(); } }; |