libgui: Change BufferQueue to use free lists
BufferQueue used to choose free buffers by scanning through its array
of slots and picking one based on timestamp. This changes that
mechanism to use a pair of free lists: one with buffers attached and
one without. This makes it easier to choose either type of free slot
depending on the needs of the current operation.
Fixes an issue with the first version of this change, found in bugs
20482952, 20443314, and 20464549.
Bug: 13175420
Change-Id: I9b6e83cfe8f9b4329a976025cb8e291d51fb6d4a
diff --git a/libs/gui/BufferQueueConsumer.cpp b/libs/gui/BufferQueueConsumer.cpp
index 526c3b7..c7d5e00 100644
--- a/libs/gui/BufferQueueConsumer.cpp
+++ b/libs/gui/BufferQueueConsumer.cpp
@@ -120,6 +120,7 @@
if (mCore->stillTracking(front)) {
// Front buffer is still in mSlots, so mark the slot as free
mSlots[front->mSlot].mBufferState = BufferSlot::FREE;
+ mCore->mFreeBuffers.push_back(front->mSlot);
}
mCore->mQueue.erase(front);
front = mCore->mQueue.begin();
@@ -173,6 +174,8 @@
ATRACE_INT(mCore->mConsumerName.string(), mCore->mQueue.size());
+ mCore->validateConsistencyLocked();
+
return NO_ERROR;
}
@@ -199,6 +202,7 @@
mCore->freeBufferLocked(slot);
mCore->mDequeueCondition.broadcast();
+ mCore->validateConsistencyLocked();
return NO_ERROR;
}
@@ -217,18 +221,11 @@
Mutex::Autolock lock(mCore->mMutex);
- // Make sure we don't have too many acquired buffers and find a free slot
- // to put the buffer into (the oldest if there are multiple).
+ // Make sure we don't have too many acquired buffers
int numAcquiredBuffers = 0;
- int found = BufferQueueCore::INVALID_BUFFER_SLOT;
for (int s = 0; s < BufferQueueDefs::NUM_BUFFER_SLOTS; ++s) {
if (mSlots[s].mBufferState == BufferSlot::ACQUIRED) {
++numAcquiredBuffers;
- } else if (mSlots[s].mBufferState == BufferSlot::FREE) {
- if (found == BufferQueueCore::INVALID_BUFFER_SLOT ||
- mSlots[s].mFrameNumber < mSlots[found].mFrameNumber) {
- found = s;
- }
}
}
@@ -238,6 +235,17 @@
mCore->mMaxAcquiredBufferCount);
return INVALID_OPERATION;
}
+
+ // Find a free slot to put the buffer into
+ int found = BufferQueueCore::INVALID_BUFFER_SLOT;
+ if (!mCore->mFreeSlots.empty()) {
+ auto slot = mCore->mFreeSlots.begin();
+ found = *slot;
+ mCore->mFreeSlots.erase(slot);
+ } else if (!mCore->mFreeBuffers.empty()) {
+ found = mCore->mFreeBuffers.front();
+ mCore->mFreeBuffers.remove(found);
+ }
if (found == BufferQueueCore::INVALID_BUFFER_SLOT) {
BQ_LOGE("attachBuffer(P): could not find free buffer slot");
return NO_MEMORY;
@@ -271,6 +279,8 @@
// for attached buffers.
mSlots[*outSlot].mAcquireCalled = false;
+ mCore->validateConsistencyLocked();
+
return NO_ERROR;
}
@@ -311,6 +321,7 @@
mSlots[slot].mEglFence = eglFence;
mSlots[slot].mFence = releaseFence;
mSlots[slot].mBufferState = BufferSlot::FREE;
+ mCore->mFreeBuffers.push_back(slot);
listener = mCore->mConnectedProducerListener;
BQ_LOGV("releaseBuffer: releasing slot %d", slot);
} else if (mSlots[slot].mNeedsCleanupOnRelease) {
@@ -325,6 +336,7 @@
}
mCore->mDequeueCondition.broadcast();
+ mCore->validateConsistencyLocked();
} // Autolock scope
// Call back without lock held
diff --git a/libs/gui/BufferQueueCore.cpp b/libs/gui/BufferQueueCore.cpp
index edebc45..29415c9 100644
--- a/libs/gui/BufferQueueCore.cpp
+++ b/libs/gui/BufferQueueCore.cpp
@@ -53,6 +53,8 @@
mConnectedProducerListener(),
mSlots(),
mQueue(),
+ mFreeSlots(),
+ mFreeBuffers(),
mOverrideMaxBufferCount(0),
mDequeueCondition(),
mUseAsyncBuffer(true),
@@ -76,6 +78,9 @@
BQ_LOGE("createGraphicBufferAlloc failed");
}
}
+ for (int slot = 0; slot < BufferQueueDefs::NUM_BUFFER_SLOTS; ++slot) {
+ mFreeSlots.insert(slot);
+ }
}
BufferQueueCore::~BufferQueueCore() {}
@@ -190,12 +195,20 @@
void BufferQueueCore::freeBufferLocked(int slot) {
BQ_LOGV("freeBufferLocked: slot %d", slot);
+ bool hadBuffer = mSlots[slot].mGraphicBuffer != NULL;
mSlots[slot].mGraphicBuffer.clear();
if (mSlots[slot].mBufferState == BufferSlot::ACQUIRED) {
mSlots[slot].mNeedsCleanupOnRelease = true;
}
+ if (mSlots[slot].mBufferState != BufferSlot::FREE) {
+ mFreeSlots.insert(slot);
+ } else if (hadBuffer) {
+ // If the slot was FREE, but we had a buffer, we need to move this slot
+ // from the free buffers list to the the free slots list
+ mFreeBuffers.remove(slot);
+ mFreeSlots.insert(slot);
+ }
mSlots[slot].mBufferState = BufferSlot::FREE;
- mSlots[slot].mFrameNumber = UINT32_MAX;
mSlots[slot].mAcquireCalled = false;
// Destroy fence as BufferQueue now takes ownership
@@ -204,6 +217,7 @@
mSlots[slot].mEglFence = EGL_NO_SYNC_KHR;
}
mSlots[slot].mFence = Fence::NO_FENCE;
+ validateConsistencyLocked();
}
void BufferQueueCore::freeAllBuffersLocked() {
@@ -236,4 +250,48 @@
}
}
+void BufferQueueCore::validateConsistencyLocked() const {
+ static const useconds_t PAUSE_TIME = 0;
+ for (int slot = 0; slot < BufferQueueDefs::NUM_BUFFER_SLOTS; ++slot) {
+ bool isInFreeSlots = mFreeSlots.count(slot) != 0;
+ bool isInFreeBuffers =
+ std::find(mFreeBuffers.cbegin(), mFreeBuffers.cend(), slot) !=
+ mFreeBuffers.cend();
+ if (mSlots[slot].mBufferState == BufferSlot::FREE) {
+ if (mSlots[slot].mGraphicBuffer == NULL) {
+ if (!isInFreeSlots) {
+ BQ_LOGE("Slot %d is FREE but is not in mFreeSlots", slot);
+ usleep(PAUSE_TIME);
+ }
+ if (isInFreeBuffers) {
+ BQ_LOGE("Slot %d is in mFreeSlots "
+ "but is also in mFreeBuffers", slot);
+ usleep(PAUSE_TIME);
+ }
+ } else {
+ if (!isInFreeBuffers) {
+ BQ_LOGE("Slot %d is FREE but is not in mFreeBuffers", slot);
+ usleep(PAUSE_TIME);
+ }
+ if (isInFreeSlots) {
+ BQ_LOGE("Slot %d is in mFreeBuffers "
+ "but is also in mFreeSlots", slot);
+ usleep(PAUSE_TIME);
+ }
+ }
+ } else {
+ if (isInFreeSlots) {
+ BQ_LOGE("Slot %d is in mFreeSlots but is not FREE (%d)",
+ slot, mSlots[slot].mBufferState);
+ usleep(PAUSE_TIME);
+ }
+ if (isInFreeBuffers) {
+ BQ_LOGE("Slot %d is in mFreeBuffers but is not FREE (%d)",
+ slot, mSlots[slot].mBufferState);
+ usleep(PAUSE_TIME);
+ }
+ }
+ }
+}
+
} // namespace android
diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index 6452cdd..a27d5f0 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -161,8 +161,6 @@
}
}
- // Look for a free buffer to give to the client
- *found = BufferQueueCore::INVALID_BUFFER_SLOT;
int dequeuedCount = 0;
int acquiredCount = 0;
for (int s = 0; s < maxBufferCount; ++s) {
@@ -173,15 +171,6 @@
case BufferSlot::ACQUIRED:
++acquiredCount;
break;
- case BufferSlot::FREE:
- // We return the oldest of the free buffers to avoid
- // stalling the producer if possible, since the consumer
- // may still have pending reads of in-flight buffers
- if (*found == BufferQueueCore::INVALID_BUFFER_SLOT ||
- mSlots[s].mFrameNumber < mSlots[*found].mFrameNumber) {
- *found = s;
- }
- break;
default:
break;
}
@@ -214,6 +203,8 @@
}
}
+ *found = BufferQueueCore::INVALID_BUFFER_SLOT;
+
// If we disconnect and reconnect quickly, we can be in a state where
// our slots are empty but we have many buffers in the queue. This can
// cause us to run out of memory if we outrun the consumer. Wait here if
@@ -223,6 +214,19 @@
if (tooManyBuffers) {
BQ_LOGV("%s: queue size is %zu, waiting", caller,
mCore->mQueue.size());
+ } else {
+ if (!mCore->mFreeBuffers.empty()) {
+ auto slot = mCore->mFreeBuffers.begin();
+ *found = *slot;
+ mCore->mFreeBuffers.erase(slot);
+ } else if (!mCore->mFreeSlots.empty()) {
+ auto slot = mCore->mFreeSlots.begin();
+ // Only return free slots up to the max buffer count
+ if (*slot < maxBufferCount) {
+ *found = *slot;
+ mCore->mFreeSlots.erase(slot);
+ }
+ }
}
// If no buffer is found, or if the queue has too many buffers
@@ -335,6 +339,8 @@
*outFence = mSlots[found].mFence;
mSlots[found].mEglFence = EGL_NO_SYNC_KHR;
mSlots[found].mFence = Fence::NO_FENCE;
+
+ mCore->validateConsistencyLocked();
} // Autolock scope
if (returnFlags & BUFFER_NEEDS_REALLOCATION) {
@@ -355,7 +361,6 @@
return NO_INIT;
}
- mSlots[*outSlot].mFrameNumber = UINT32_MAX;
mSlots[*outSlot].mGraphicBuffer = graphicBuffer;
} // Autolock scope
}
@@ -414,6 +419,7 @@
mCore->freeBufferLocked(slot);
mCore->mDequeueCondition.broadcast();
+ mCore->validateConsistencyLocked();
return NO_ERROR;
}
@@ -438,27 +444,19 @@
return NO_INIT;
}
- // Find the oldest valid slot
- int found = BufferQueueCore::INVALID_BUFFER_SLOT;
- for (int s = 0; s < BufferQueueDefs::NUM_BUFFER_SLOTS; ++s) {
- if (mSlots[s].mBufferState == BufferSlot::FREE &&
- mSlots[s].mGraphicBuffer != NULL) {
- if (found == BufferQueueCore::INVALID_BUFFER_SLOT ||
- mSlots[s].mFrameNumber < mSlots[found].mFrameNumber) {
- found = s;
- }
- }
- }
-
- if (found == BufferQueueCore::INVALID_BUFFER_SLOT) {
+ if (mCore->mFreeBuffers.empty()) {
return NO_MEMORY;
}
+ int found = mCore->mFreeBuffers.front();
+ mCore->mFreeBuffers.remove(found);
+
BQ_LOGV("detachNextBuffer detached slot %d", found);
*outBuffer = mSlots[found].mGraphicBuffer;
*outFence = mSlots[found].mFence;
mCore->freeBufferLocked(found);
+ mCore->validateConsistencyLocked();
return NO_ERROR;
}
@@ -506,6 +504,8 @@
mSlots[*outSlot].mFence = Fence::NO_FENCE;
mSlots[*outSlot].mRequestBufferCalled = true;
+ mCore->validateConsistencyLocked();
+
return returnFlags;
}
@@ -640,9 +640,7 @@
// mark it as freed
if (mCore->stillTracking(front)) {
mSlots[front->mSlot].mBufferState = BufferSlot::FREE;
- // Reset the frame number of the freed buffer so that it is
- // the first in line to be dequeued again
- mSlots[front->mSlot].mFrameNumber = 0;
+ mCore->mFreeBuffers.push_front(front->mSlot);
}
// Overwrite the droppable buffer with the incoming one
*front = item;
@@ -664,6 +662,8 @@
// Take a ticket for the callback functions
callbackTicket = mNextCallbackTicket++;
+
+ mCore->validateConsistencyLocked();
} // Autolock scope
// Wait without lock held
@@ -724,10 +724,11 @@
return;
}
+ mCore->mFreeBuffers.push_front(slot);
mSlots[slot].mBufferState = BufferSlot::FREE;
- mSlots[slot].mFrameNumber = 0;
mSlots[slot].mFence = fence;
mCore->mDequeueCondition.broadcast();
+ mCore->validateConsistencyLocked();
}
int BufferQueueProducer::query(int what, int *outValue) {
@@ -1009,13 +1010,19 @@
}
mCore->freeBufferLocked(slot); // Clean up the slot first
mSlots[slot].mGraphicBuffer = buffers[i];
- mSlots[slot].mFrameNumber = 0;
mSlots[slot].mFence = Fence::NO_FENCE;
+
+ // freeBufferLocked puts this slot on the free slots list. Since
+ // we then attached a buffer, move the slot to free buffer list.
+ mCore->mFreeSlots.erase(slot);
+ mCore->mFreeBuffers.push_front(slot);
+
BQ_LOGV("allocateBuffers: allocated a new buffer in slot %d", slot);
}
mCore->mIsAllocating = false;
mCore->mIsAllocatingCondition.broadcast();
+ mCore->validateConsistencyLocked();
} // Autolock scope
}
}