rippled/modules/beast_basics/threads/beast_CallQueue.cpp

//------------------------------------------------------------------------------
/*
    This file is part of Beast: https://github.com/vinniefalco/Beast
    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

CallQueue::CallQueue (String name)
    : m_name (name)
{
}

CallQueue::~CallQueue ()
{
    // Someone forget to close the queue.
    bassert (m_closed.isSignaled ());

    // Can't destroy queue with unprocessed calls.
    bassert (m_queue.empty ());
}

bool CallQueue::isAssociatedWithCurrentThread () const
{
    return Thread::getCurrentThreadId () == m_id;
}

// Adds a call to the queue of execution.
void CallQueue::queuep (Work* c)
{
    // If this goes off it means calls are being made after the
    // queue is closed, and probably there is no one around to
    // process it.
    bassert (!m_closed.isSignaled ());

    if (m_queue.push_back (c))
        signal ();
}

// Append the Work to the queue. If this call is made from the same
// thread as the last thread that called synchronize(), then the call
// will execute synchronously.
//
void CallQueue::callp (Work* c)
{
    queuep (c);

    // If we are called on the process thread and we are not
    // recursed into doSynchronize, then process the queue. This
    // makes calls from the process thread synchronous.
    //
    // NOTE: The value of isBeingSynchronized is invalid/volatile unless
    // this thread is the last process thread.
    //
    // NOTE: There is a small window of opportunity where we
    // might get an undesired synchronization if new thread
    // calls synchronize() concurrently.
    //
    if (isAssociatedWithCurrentThread () &&
            m_isBeingSynchronized.trySignal ())
    {
        doSynchronize ();

        m_isBeingSynchronized.reset ();
    }
}

bool CallQueue::synchronize ()
{
    bool did_something;

    // Detect recursion into doSynchronize(), and
    // break ties for concurrent calls atomically.
    //
    if (m_isBeingSynchronized.trySignal ())
    {
        // Remember this thread.
        m_id = Thread::getCurrentThreadId ();

        did_something = doSynchronize ();

        m_isBeingSynchronized.reset ();
    }
    else
    {
        did_something = false;
    }

    return did_something;
}

// Can still have pending calls, just can't put new ones in.
void CallQueue::close ()
{
    m_closed.signal ();

    synchronize ();
}

// Process everything in the queue. The list of pending calls is
// acquired atomically. New calls may enter the queue while we are
// processing.
//
// Returns true if any functors were called.
//
bool CallQueue::doSynchronize ()
{
    bool did_something;

    // Reset since we are emptying the queue. Since we loop
    // until the queue is empty, it is possible for us to exit
    // this function with an empty queue and signaled state.
    //
    reset ();

    Work* call = m_queue.pop_front ();

    if (call)
    {
        did_something = true;

        // This method of processing one at a time has the desired
        // side effect of synchronizing nested calls to us from a functor.
        //
        for (;;)
        {
            call->operator () ();
            delete call;

            call = m_queue.pop_front ();

            if (call == 0)
                break;
        }
    }
    else
    {
        did_something = false;
    }

    return did_something;
}