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* Copyright 2014 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <ui/Fence.h>
#include <ui/GraphicBuffer.h>
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <utils/StrongPointer.h>
namespace android {
class Fence;
// BufferState tracks the states in which a buffer slot can be.
struct BufferState {
// All slots are initially FREE (not dequeued, queued, acquired, or shared).
: mDequeueCount(0),
mShared(false) {
uint32_t mDequeueCount;
uint32_t mQueueCount;
uint32_t mAcquireCount;
bool mShared;
// A buffer can be in one of five states, represented as below:
// | mShared | mDequeueCount | mQueueCount | mAcquireCount |
// --------|---------|---------------|-------------|---------------|
// FREE | false | 0 | 0 | 0 |
// DEQUEUED| false | 1 | 0 | 0 |
// QUEUED | false | 0 | 1 | 0 |
// ACQUIRED| false | 0 | 0 | 1 |
// SHARED | true | any | any | any |
// FREE indicates that the buffer is available to be dequeued by the
// producer. The slot is "owned" by BufferQueue. It transitions to DEQUEUED
// when dequeueBuffer is called.
// DEQUEUED indicates that the buffer has been dequeued by the producer, but
// has not yet been queued or canceled. The producer may modify the
// buffer's contents as soon as the associated release fence is signaled.
// The slot is "owned" by the producer. It can transition to QUEUED (via
// queueBuffer or attachBuffer) or back to FREE (via cancelBuffer or
// detachBuffer).
// QUEUED indicates that the buffer has been filled by the producer and
// queued for use by the consumer. The buffer contents may continue to be
// modified for a finite time, so the contents must not be accessed until
// the associated fence is signaled. The slot is "owned" by BufferQueue. It
// can transition to ACQUIRED (via acquireBuffer) or to FREE (if another
// buffer is queued in asynchronous mode).
// ACQUIRED indicates that the buffer has been acquired by the consumer. As
// with QUEUED, the contents must not be accessed by the consumer until the
// acquire fence is signaled. The slot is "owned" by the consumer. It
// transitions to FREE when releaseBuffer (or detachBuffer) is called. A
// detached buffer can also enter the ACQUIRED state via attachBuffer.
// SHARED indicates that this buffer is being used in shared buffer
// mode. It can be in any combination of the other states at the same time,
// except for FREE (since that excludes being in any other state). It can
// also be dequeued, queued, or acquired multiple times.
inline bool isFree() const {
return !isAcquired() && !isDequeued() && !isQueued();
inline bool isDequeued() const {
return mDequeueCount > 0;
inline bool isQueued() const {
return mQueueCount > 0;
inline bool isAcquired() const {
return mAcquireCount > 0;
inline bool isShared() const {
return mShared;
inline void reset() {
*this = BufferState();
const char* string() const;
inline void dequeue() {
inline void detachProducer() {
if (mDequeueCount > 0) {
inline void attachProducer() {
inline void queue() {
if (mDequeueCount > 0) {
inline void cancel() {
if (mDequeueCount > 0) {
inline void freeQueued() {
if (mQueueCount > 0) {
inline void acquire() {
if (mQueueCount > 0) {
inline void acquireNotInQueue() {
inline void release() {
if (mAcquireCount > 0) {
inline void detachConsumer() {
if (mAcquireCount > 0) {
inline void attachConsumer() {
struct BufferSlot {
: mGraphicBuffer(nullptr),
mNeedsReallocation(false) {
// mGraphicBuffer points to the buffer allocated for this slot or is NULL
// if no buffer has been allocated.
sp<GraphicBuffer> mGraphicBuffer;
// mEglDisplay is the EGLDisplay used to create EGLSyncKHR objects.
EGLDisplay mEglDisplay;
// mBufferState is the current state of this buffer slot.
BufferState mBufferState;
// mRequestBufferCalled is used for validating that the producer did
// call requestBuffer() when told to do so. Technically this is not
// needed but useful for debugging and catching producer bugs.
bool mRequestBufferCalled;
// mFrameNumber is the number of the queued frame for this slot. This
// is used to dequeue buffers in LRU order (useful because buffers
// may be released before their release fence is signaled).
uint64_t mFrameNumber;
// mEglFence is the EGL sync object that must signal before the buffer
// associated with this buffer slot may be dequeued. It is initialized
// to EGL_NO_SYNC_KHR when the buffer is created and may be set to a
// new sync object in releaseBuffer. (This is deprecated in favor of
// mFence, below.)
EGLSyncKHR mEglFence;
// mFence is a fence which will signal when work initiated by the
// previous owner of the buffer is finished. When the buffer is FREE,
// the fence indicates when the consumer has finished reading
// from the buffer, or when the producer has finished writing if it
// called cancelBuffer after queueing some writes. When the buffer is
// QUEUED, it indicates when the producer has finished filling the
// buffer. When the buffer is DEQUEUED or ACQUIRED, the fence has been
// passed to the consumer or producer along with ownership of the
// buffer, and mFence is set to NO_FENCE.
sp<Fence> mFence;
// Indicates whether this buffer has been seen by a consumer yet
bool mAcquireCalled;
// Indicates whether the buffer was re-allocated without notifying the
// producer. If so, it needs to set the BUFFER_NEEDS_REALLOCATION flag when
// dequeued to prevent the producer from using a stale cached buffer.
bool mNeedsReallocation;
} // namespace android