From 0d09a9bec07b3bec78bd473ff0bfcf0a261f3f25 Mon Sep 17 00:00:00 2001 From: Glenn Kasten Date: Mon, 24 Jun 2013 12:06:46 -0700 Subject: Use mFutex as an event flag rather than semaphore An event flag can be more fault-tolerant in case of loss of synchronization, as it cannot overflow. It also allows more bits to be used in the future. See http://en.wikipedia.org/wiki/Event_flag Change-Id: I01ca25d951eb263124da54bb4738f0d94ec4a48b --- media/libmedia/AudioTrackShared.cpp | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'media/libmedia/AudioTrackShared.cpp') diff --git a/media/libmedia/AudioTrackShared.cpp b/media/libmedia/AudioTrackShared.cpp index f034164..4b7f368 100644 --- a/media/libmedia/AudioTrackShared.cpp +++ b/media/libmedia/AudioTrackShared.cpp @@ -207,15 +207,15 @@ status_t ClientProxy::obtainBuffer(Buffer* buffer, const struct timespec *reques ts = NULL; break; } - int32_t old = android_atomic_dec(&cblk->mFutex); - if (old <= 0) { + int32_t old = android_atomic_and(~CBLK_FUTEX_WAKE, &cblk->mFutex); + if (!(old & CBLK_FUTEX_WAKE)) { int rc; if (measure && !beforeIsValid) { clock_gettime(CLOCK_MONOTONIC, &before); beforeIsValid = true; } int ret = __futex_syscall4(&cblk->mFutex, - mClientInServer ? FUTEX_WAIT_PRIVATE : FUTEX_WAIT, old - 1, ts); + mClientInServer ? FUTEX_WAIT_PRIVATE : FUTEX_WAIT, old & ~CBLK_FUTEX_WAKE, ts); // update total elapsed time spent waiting if (measure) { struct timespec after; @@ -484,9 +484,8 @@ void ServerProxy::releaseBuffer(Buffer* buffer) } if (!mDeferWake && mAvailToClient + stepCount >= minimum) { ALOGV("mAvailToClient=%u stepCount=%u minimum=%u", mAvailToClient, stepCount, minimum); - // could client be sleeping, or not need this increment and counter overflows? - int32_t old = android_atomic_inc(&cblk->mFutex); - if (old == -1) { + int32_t old = android_atomic_or(CBLK_FUTEX_WAKE, &cblk->mFutex); + if (!(old & CBLK_FUTEX_WAKE)) { (void) __futex_syscall3(&cblk->mFutex, mClientInServer ? FUTEX_WAKE_PRIVATE : FUTEX_WAKE, 1); } -- cgit v1.1