path: root/indra/llcommon/llcoros.h

/**
 * @file   llcoros.h
 * @author Nat Goodspeed
 * @date   2009-06-02
 * @brief  Manage running boost::coroutine instances
 * 
 * $LicenseInfo:firstyear=2009&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#if ! defined(LL_LLCOROS_H)
#define LL_LLCOROS_H

#include <boost/fiber/fss.hpp>
#include <boost/fiber/future/promise.hpp>
#include <boost/fiber/future/future.hpp>
#include "llsingleton.h"
#include <boost/ptr_container/ptr_map.hpp>
#include <boost/function.hpp>
#include <string>

/**
 * Registry of named Boost.Coroutine instances
 *
 * The Boost.Coroutine library supports the general case of a coroutine
 * accepting arbitrary parameters and yielding multiple (sets of) results. For
 * such use cases, it's natural for the invoking code to retain the coroutine
 * instance: the consumer repeatedly calls into the coroutine, perhaps passing
 * new parameter values, prompting it to yield its next result.
 *
 * Our typical coroutine usage is different, though. For us, coroutines
 * provide an alternative to the @c Responder pattern. Our typical coroutine
 * has @c void return, invoked in fire-and-forget mode: the handler for some
 * user gesture launches the coroutine and promptly returns to the main loop.
 * The coroutine initiates some action that will take multiple frames (e.g. a
 * capability request), waits for its result, processes it and silently steals
 * away.
 *
 * This usage poses two (related) problems:
 *
 * # Who should own the coroutine instance? If it's simply local to the
 *   handler code that launches it, return from the handler will destroy the
 *   coroutine object, terminating the coroutine.
 * # Once the coroutine terminates, in whatever way, who's responsible for
 *   cleaning up the coroutine object?
 *
 * LLCoros is a Singleton collection of currently-active coroutine instances.
 * Each has a name. You ask LLCoros to launch a new coroutine with a suggested
 * name prefix; from your prefix it generates a distinct name, registers the
 * new coroutine and returns the actual name.
 *
 * The name
 * can provide diagnostic info: we can look up the name of the
 * currently-running coroutine.
 */
class LL_COMMON_API LLCoros: public LLSingleton<LLCoros>
{
    LLSINGLETON(LLCoros);
public:
    /// The viewer's use of the term "coroutine" became deeply embedded before
    /// the industry term "fiber" emerged to distinguish userland threads from
    /// simpler, more transient kinds of coroutines. Semantically they've
    /// always been fibers. But at this point in history, we're pretty much
    /// stuck with the term "coroutine."
    typedef boost::fibers::fiber coro;
    /// Canonical callable type
    typedef boost::function<void()> callable_t;

    /**
     * Create and start running a new coroutine with specified name. The name
     * string you pass is a suggestion; it will be tweaked for uniqueness. The
     * actual name is returned to you.
     *
     * Usage looks like this, for (e.g.) two coroutine parameters:
     * @code
     * class MyClass
     * {
     * public:
     *     ...
     *     // Do NOT NOT NOT accept reference params!
     *     // Pass by value only!
     *     void myCoroutineMethod(std::string, LLSD);
     *     ...
     * };
     * ...
     * std::string name = LLCoros::instance().launch(
     *    "mycoro", boost::bind(&MyClass::myCoroutineMethod, this,
     *                          "somestring", LLSD(17));
     * @endcode
     *
     * Your function/method can accept any parameters you want -- but ONLY BY
     * VALUE! Reference parameters are a BAD IDEA! You Have Been Warned. See
     * DEV-32777 comments for an explanation.
     *
     * Pass a nullary callable. It works to directly pass a nullary free
     * function (or static method); for other cases use a lambda expression,
     * std::bind() or boost::bind(). Of course, for a non-static class method,
     * the first parameter must be the class instance. Any other parameters
     * should be passed via the enclosing expression.
     *
     * launch() tweaks the suggested name so it won't collide with any
     * existing coroutine instance, creates the coroutine instance, registers
     * it with the tweaked name and runs it until its first wait. At that
     * point it returns the tweaked name.
     */
    std::string launch(const std::string& prefix, const callable_t& callable);

    /**
     * Abort a running coroutine by name. Normally, when a coroutine either
     * runs to completion or terminates with an exception, LLCoros quietly
     * cleans it up. This is for use only when you must explicitly interrupt
     * one prematurely. Returns @c true if the specified name was found and
     * still running at the time.
     */
//  bool kill(const std::string& name);

    /**
     * From within a coroutine, look up the (tweaked) name string by which
     * this coroutine is registered. Returns the empty string if not found
     * (e.g. if the coroutine was launched by hand rather than using
     * LLCoros::launch()).
     */
    std::string getName() const;

    /**
     * For delayed initialization. To be clear, this will only affect
     * coroutines launched @em after this point. The underlying facility
     * provides no way to alter the stack size of any running coroutine.
     */
    void setStackSize(S32 stacksize);

    /// for delayed initialization
    void printActiveCoroutines();

    /// get the current coro::id for those who really really care
    static coro::id get_self();

    /**
     * Most coroutines, most of the time, don't "consume" the events for which
     * they're suspending. This way, an arbitrary number of listeners (whether
     * coroutines or simple callbacks) can be registered on a particular
     * LLEventPump, every listener responding to each of the events on that
     * LLEventPump. But a particular coroutine can assert that it will consume
     * each event for which it suspends. (See also llcoro::postAndSuspend(),
     * llcoro::VoidListener)
     */
    static void set_consuming(bool consuming);
    static bool get_consuming();

    /**
     * RAII control of the consuming flag
     */
    class OverrideConsuming
    {
    public:
        OverrideConsuming(bool consuming):
            mPrevConsuming(get_consuming())
        {
            set_consuming(consuming);
        }
        ~OverrideConsuming()
        {
            set_consuming(mPrevConsuming);
        }

    private:
        bool mPrevConsuming;
    };

    /**
     * Aliases for promise and future. An older underlying future implementation
     * required us to wrap future; that's no longer needed. However -- if it's
     * important to restore kill() functionality, we might need to provide a
     * proxy, so continue using the aliases.
     */
    template <typename T>
    using Promise = boost::fibers::promise<T>;
    template <typename T>
    using Future = boost::fibers::future<T>;
    template <typename T>
    static Future<T> getFuture(Promise<T>& promise) { return promise.get_future(); }

    /// for data local to each running coroutine
    template <typename T>
    using local_ptr = boost::fibers::fiber_specific_ptr<T>;

private:
    std::string generateDistinctName(const std::string& prefix) const;
    void toplevel(const std::string& name, const callable_t& callable);
    struct CoroData;
#if LL_WINDOWS
    static void winlevel(const callable_t& callable);
#endif
    CoroData& get_CoroData(const std::string& caller);
    const CoroData& get_CoroData(const std::string& caller) const;

    S32 mStackSize;

    // coroutine-local storage, as it were: one per coro we track
    struct CoroData
    {
        CoroData(const std::string& name);

        // tweaked name of the current coroutine
        const std::string mName;
        // set_consuming() state
        bool mConsuming;
        F64 mCreationTime; // since epoch
    };
    typedef boost::ptr_map<std::string, CoroData> CoroMap;
    CoroMap mCoros;

    // Identify the current coroutine's CoroData. This local_ptr isn't static
    // because it's a member of an LLSingleton, and we rely on it being
    // cleaned up in proper dependency order.
    // As each coroutine terminates, use our custom cleanup function to remove
    // the corresponding entry from mCoros.
    local_ptr<CoroData> mCurrent{delete_CoroData};

    // Cleanup function for each fiber's instance of mCurrent.
    static void delete_CoroData(CoroData* cdptr);
};

#endif /* ! defined(LL_LLCOROS_H) */