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Commit f6bbd44a authored by Mathias Agopian's avatar Mathias Agopian
Browse files

simplify further vsync handling 

- we now clean-up "dead" connection in the main loop,
this entirely avoid the problem with the side effects of
releasing strong references. We now only hold on to strong
reference for the connection we will signal.

- also simplify how we build the list of "ready" connections, by
only adding them to the list when we did receive a vsync event

Change-Id: I2a84da431320a2af8e8a93e07622a1d258236f43
parent bc46e0ad

services/surfaceflinger/EventThread.cpp

+75 −84
Original line number Diff line number Diff line
@@ -60,14 +60,6 @@ status_t EventThread::registerDisplayEventConnection( 
    return NO_ERROR;

}



status_t EventThread::unregisterDisplayEventConnection(

        const wp<EventThread::Connection>& connection) {

    Mutex::Autolock _l(mLock);

    mDisplayEventConnections.remove(connection);

    mCondition.broadcast();

    return NO_ERROR;

}



void EventThread::removeDisplayEventConnection(

        const wp<EventThread::Connection>& connection) {

    Mutex::Autolock _l(mLock);
@@ -122,43 +114,63 @@ void EventThread::onVSyncReceived(int, nsecs_t timestamp) { 
}



bool EventThread::threadLoop() {



    nsecs_t timestamp;

    size_t vsyncCount;

    DisplayEventReceiver::Event vsync;

    Vector< sp<EventThread::Connection> > activeConnections;

    Vector< sp<EventThread::Connection> > signalConnections;

    signalConnections = waitForEvent(&vsync);



    do {

        // release our references

        signalConnections.clear();

        activeConnections.clear();

    // dispatch vsync events to listeners...

    const size_t count = signalConnections.size();

    for (size_t i=0 ; i<count ; i++) {

        const sp<Connection>& conn(signalConnections[i]);

        // now see if we still need to report this VSYNC event

        status_t err = conn->postEvent(vsync);

        if (err == -EAGAIN || err == -EWOULDBLOCK) {

            // The destination doesn't accept events anymore, it's probably

            // full. For now, we just drop the events on the floor.

            // Note that some events cannot be dropped and would have to be

            // re-sent later. Right-now we don't have the ability to do

            // this, but it doesn't matter for VSYNC.

        } else if (err < 0) {

            // handle any other error on the pipe as fatal. the only

            // reasonable thing to do is to clean-up this connection.

            // The most common error we'll get here is -EPIPE.

            removeDisplayEventConnection(signalConnections[i]);

        }

    }

    return true;

}



Vector< sp<EventThread::Connection> > EventThread::waitForEvent(

        DisplayEventReceiver::Event* event)

{

    Mutex::Autolock _l(mLock);



    size_t vsyncCount;

    nsecs_t timestamp;

    Vector< sp<EventThread::Connection> > signalConnections;



    do {

        // latch VSYNC event if any

        bool waitForVSync = false;

        vsyncCount = mVSyncCount;

        timestamp = mVSyncTimestamp;

        mVSyncTimestamp = 0;



        // find out connections waiting for VSYNC events

        // find out connections waiting for events

        size_t count = mDisplayEventConnections.size();

        for (size_t i=0 ; i<count ; i++) {

            sp<Connection> connection(mDisplayEventConnections[i].promote());

            if (connection != NULL) {

                activeConnections.add(connection);

                if (connection->count >= 0) {

                    // we need vsync events because at least

                    // one connection is waiting for it

                    waitForVSync = true;

                    if (timestamp) {

                        // we consume the event only if it's time

                        // (ie: we received a vsync event)

                        if (connection->count == 0) {

                            // fired this time around

                        if (timestamp) {

                            // only "consume" this event if we're going to

                            // report it

                            connection->count = -1;

                        }

                            signalConnections.add(connection);

                        } else if (connection->count == 1 ||

                                (vsyncCount % connection->count) == 0) {
@@ -167,29 +179,25 @@ bool EventThread::threadLoop() { 
                        }

                    }

                }

            } else {

                // we couldn't promote this reference, the connection has

                // died, so clean-up!

                mDisplayEventConnections.removeAt(i);

                --i; --count;

            }

        }



        if (timestamp) {

            // we have a vsync event we can dispatch

            if (!waitForVSync) {

        // Here we figure out if we need to enable or disable vsyncs

        if (timestamp && !waitForVSync) {

            // we received a VSYNC but we have no clients

            // don't report it, and disable VSYNC events

            disableVSyncLocked();

            } else {

                // report VSYNC event

                break;

            }

        } else {

            // never disable VSYNC events immediately, instead

            // we'll wait to receive the event and we'll

            // reevaluate whether we need to dispatch it and/or

            // disable VSYNC events then.

            if (waitForVSync) {

                // enable

        } else if (!timestamp && waitForVSync) {

            enableVSyncLocked();

        }

        }



        // note: !timestamp implies signalConnections.isEmpty()

        if (!timestamp) {

            // wait for something to happen

            if (CC_UNLIKELY(mUseSoftwareVSync && waitForVSync)) {

                // h/w vsync cannot be used (screen is off), so we use
@@ -200,39 +208,21 @@ bool EventThread::threadLoop() { 
                    mVSyncCount++;

                }

            } else {

            if (!timestamp || signalConnections.isEmpty()) {

                // This is where we spend most of our time, waiting

                // for a vsync events and registered clients

                mCondition.wait(mLock);

            }

        }

    } while (!timestamp || signalConnections.isEmpty());

    } while (signalConnections.isEmpty());



    // dispatch vsync events to listeners...

    vsync.header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;

    vsync.header.timestamp = timestamp;

    vsync.vsync.count = vsyncCount;

    // here we're guaranteed to have a timestamp and some connections to signal



    const size_t count = signalConnections.size();

    for (size_t i=0 ; i<count ; i++) {

        const sp<Connection>& conn(signalConnections[i]);

        // now see if we still need to report this VSYNC event

        status_t err = conn->postEvent(vsync);

        if (err == -EAGAIN || err == -EWOULDBLOCK) {

            // The destination doesn't accept events anymore, it's probably

            // full. For now, we just drop the events on the floor.

            // Note that some events cannot be dropped and would have to be

            // re-sent later. Right-now we don't have the ability to do

            // this, but it doesn't matter for VSYNC.

        } else if (err < 0) {

            // handle any other error on the pipe as fatal. the only

            // reasonable thing to do is to clean-up this connection.

            // The most common error we'll get here is -EPIPE.

            removeDisplayEventConnection(signalConnections[i]);

        }

    }

    // dispatch vsync events to listeners...

    event->header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;

    event->header.timestamp = timestamp;

    event->vsync.count = vsyncCount;



    return true;

    return signalConnections;

}



void EventThread::enableVSyncLocked() {
@@ -280,7 +270,8 @@ EventThread::Connection::Connection( 
}



EventThread::Connection::~Connection() {

    mEventThread->unregisterDisplayEventConnection(this);

    // do nothing here -- clean-up will happen automatically

    // when the main thread wakes up

}



void EventThread::Connection::onFirstRef() {

services/surfaceflinger/EventThread.h

+3 −1
Original line number Diff line number Diff line
@@ -65,7 +65,6 @@ public: 


    sp<Connection> createEventConnection() const;

    status_t registerDisplayEventConnection(const sp<Connection>& connection);

    status_t unregisterDisplayEventConnection(const wp<Connection>& connection);



    void setVsyncRate(uint32_t count, const sp<Connection>& connection);

    void requestNextVsync(const sp<Connection>& connection);
@@ -79,6 +78,9 @@ public: 
    // called when receiving a vsync event

    void onVSyncReceived(int display, nsecs_t timestamp);



    Vector< sp<EventThread::Connection> > waitForEvent(

            DisplayEventReceiver::Event* event);



    void dump(String8& result, char* buffer, size_t SIZE) const;



private: