1 files changed, 284 insertions, 0 deletions
diff --git a/gfx/layers/CanvasDrawEventRecorder.h b/gfx/layers/CanvasDrawEventRecorder.h
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+++ b/gfx/layers/CanvasDrawEventRecorder.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_CanvasDrawEventRecorder_h
+#define mozilla_layers_CanvasDrawEventRecorder_h
+
+#include "mozilla/gfx/DrawEventRecorder.h"
+#include "mozilla/ipc/CrossProcessSemaphore.h"
+#include "mozilla/ipc/SharedMemoryBasic.h"
+
+namespace mozilla {
+namespace layers {
+
+class CanvasEventRingBuffer final : public gfx::EventRingBuffer {
+ public:
+  /**
+   * WriterServices allows consumers of CanvasEventRingBuffer to provide
+   * functions required by the write side of a CanvasEventRingBuffer without
+   * introducing unnecessary dependencies on IPC code.
+   */
+  class WriterServices {
+   public:
+    virtual ~WriterServices() = default;
+
+    /**
+     * @returns true if the reader of the CanvasEventRingBuffer has permanently
+     *          stopped processing, otherwise returns false.
+     */
+    virtual bool ReaderClosed() = 0;
+
+    /**
+     * Causes the reader to resume processing when it is in a stopped state.
+     */
+    virtual void ResumeReader() = 0;
+  };
+
+  /**
+   * ReaderServices allows consumers of CanvasEventRingBuffer to provide
+   * functions required by the read side of a CanvasEventRingBuffer without
+   * introducing unnecessary dependencies on IPC code.
+   */
+  class ReaderServices {
+   public:
+    virtual ~ReaderServices() = default;
+
+    /**
+     * @returns true if the writer of the CanvasEventRingBuffer has permanently
+     *          stopped processing, otherwise returns false.
+     */
+    virtual bool WriterClosed() = 0;
+  };
+
+  CanvasEventRingBuffer() {}
+
+  /**
+   * Initialize the write side of a CanvasEventRingBuffer returning handles to
+   * the shared memory for the buffer and the two semaphores for waiting in the
+   * reader and the writer.
+   *
+   * @param aOtherPid process ID to share the handles to
+   * @param aReadHandle handle to the shared memory for the buffer
+   * @param aReaderSem reading blocked semaphore
+   * @param aWriterSem writing blocked semaphore
+   * @param aWriterServices provides functions required by the writer
+   * @returns true if initialization succeeds
+   */
+  bool InitWriter(base::ProcessId aOtherPid,
+                  ipc::SharedMemoryBasic::Handle* aReadHandle,
+                  CrossProcessSemaphoreHandle* aReaderSem,
+                  CrossProcessSemaphoreHandle* aWriterSem,
+                  UniquePtr<WriterServices> aWriterServices);
+
+  /**
+   * Initialize the read side of a CanvasEventRingBuffer.
+   *
+   * @param aReadHandle handle to the shared memory for the buffer
+   * @param aReaderSem reading blocked semaphore
+   * @param aWriterSem writing blocked semaphore
+   * @param aReaderServices provides functions required by the reader
+   * @returns true if initialization succeeds
+   */
+  bool InitReader(const ipc::SharedMemoryBasic::Handle& aReadHandle,
+                  const CrossProcessSemaphoreHandle& aReaderSem,
+                  const CrossProcessSemaphoreHandle& aWriterSem,
+                  UniquePtr<ReaderServices> aReaderServices);
+
+  bool good() const final { return mGood; }
+
+  bool WriterFailed() const { return mWrite->state == State::Failed; }
+
+  void SetIsBad() final {
+    mGood = false;
+    mRead->state = State::Failed;
+  }
+
+  void write(const char* const aData, const size_t aSize) final;
+
+  bool HasDataToRead();
+
+  /*
+   * This will put the reader into a stopped state if there is no more data to
+   * read. If this returns false the caller is responsible for continuing
+   * translation at a later point. If it returns false the writer will start the
+   * translation again when more data is written.
+   *
+   * @returns true if stopped
+   */
+  bool StopIfEmpty();
+
+  /*
+   * Waits for data to become available. This will wait for aTimeout duration
+   * aRetryCount number of times, checking to see if the other side is closed in
+   * between each one.
+   *
+   * @param aTimeout duration to wait
+   * @param aRetryCount number of times to retry
+   * @returns true if data is available to read.
+   */
+  bool WaitForDataToRead(TimeDuration aTimeout, int32_t aRetryCount);
+
+  int32_t ReadNextEvent();
+
+  void read(char* const aOut, const size_t aSize) final;
+
+  /**
+   * Writes a checkpoint event to the buffer.
+   *
+   * @returns the write count after the checkpoint has been written
+   */
+  uint32_t CreateCheckpoint();
+
+  /**
+   * Waits until the given checkpoint has been read from the buffer.
+   *
+   * @params aCheckpoint the checkpoint to wait for
+   * @params aTimeout duration to wait while reader is not active
+   * @returns true if the checkpoint was reached, false if the reader is closed
+   *          or we timeout.
+   */
+  bool WaitForCheckpoint(uint32_t aCheckpoint);
+
+  /**
+   * Used to send data back to the writer. This is done through the same shared
+   * memory so the writer must wait and read the response after it has submitted
+   * the event that uses this.
+   *
+   * @param aData the data to be written back to the writer
+   * @param aSize the number of chars to write
+   */
+  void ReturnWrite(const char* aData, size_t aSize);
+
+  /**
+   * Used to read data sent back from the reader via ReturnWrite. This is done
+   * through the same shared memory so the writer must wait until all expected
+   * data is read before writing new events to the buffer.
+   *
+   * @param aOut the pointer to read into
+   * @param aSize the number of chars to read
+   */
+  void ReturnRead(char* aOut, size_t aSize);
+
+ protected:
+  bool WaitForAndRecalculateAvailableSpace() final;
+  void UpdateWriteTotalsBy(uint32_t aCount) final;
+
+ private:
+  enum class State : uint32_t {
+    Processing,
+
+    /**
+     * This is the important state to make sure the other side signals or starts
+     * us as soon as data or space is available. We set AboutToWait first and
+     * then re-check the condition. If we went straight to Waiting or Stopped
+     * then in between the last check and setting the state, the other side
+     * could have used all available data or space and never have signaled us
+     * because it didn't know we were about to wait, causing a deadlock.
+     * While we are in this state, the other side must wait until we resolve the
+     * AboutToWait state to one of the other states and then signal or start us
+     * if it needs to.
+     */
+    AboutToWait,
+    Waiting,
+    Stopped,
+    Failed,
+  };
+
+  struct ReadFooter {
+    Atomic<uint32_t> count;
+    Atomic<uint32_t> returnCount;
+    Atomic<State> state;
+  };
+
+  struct WriteFooter {
+    Atomic<uint32_t> count;
+    Atomic<uint32_t> returnCount;
+    Atomic<uint32_t> requiredDifference;
+    Atomic<State> state;
+  };
+
+  CanvasEventRingBuffer(const CanvasEventRingBuffer&) = delete;
+  void operator=(const CanvasEventRingBuffer&) = delete;
+
+  void IncrementWriteCountBy(uint32_t aCount);
+
+  bool WaitForReadCount(uint32_t aReadCount, TimeDuration aTimeout);
+
+  bool WaitForAndRecalculateAvailableData();
+
+  void UpdateReadTotalsBy(uint32_t aCount);
+  void IncrementReadCountBy(uint32_t aCount);
+
+  void CheckAndSignalReader();
+
+  void CheckAndSignalWriter();
+
+  uint32_t WaitForBytesToWrite();
+
+  uint32_t WaitForBytesToRead();
+
+  RefPtr<ipc::SharedMemoryBasic> mSharedMemory;
+  UniquePtr<CrossProcessSemaphore> mReaderSemaphore;
+  UniquePtr<CrossProcessSemaphore> mWriterSemaphore;
+  UniquePtr<WriterServices> mWriterServices;
+  UniquePtr<ReaderServices> mReaderServices;
+  char* mBuf = nullptr;
+  uint32_t mOurCount = 0;
+  WriteFooter* mWrite = nullptr;
+  ReadFooter* mRead = nullptr;
+  bool mGood = false;
+};
+
+class CanvasDrawEventRecorder final : public gfx::DrawEventRecorderPrivate {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(CanvasDrawEventRecorder, final)
+  explicit CanvasDrawEventRecorder(){};
+
+  bool Init(base::ProcessId aOtherPid, ipc::SharedMemoryBasic::Handle* aHandle,
+            CrossProcessSemaphoreHandle* aReaderSem,
+            CrossProcessSemaphoreHandle* aWriterSem,
+            UniquePtr<CanvasEventRingBuffer::WriterServices> aWriterServices) {
+    return mOutputStream.InitWriter(aOtherPid, aHandle, aReaderSem, aWriterSem,
+                                    std::move(aWriterServices));
+  }
+
+  void RecordEvent(const gfx::RecordedEvent& aEvent) final {
+    if (!mOutputStream.good()) {
+      return;
+    }
+
+    aEvent.RecordToStream(mOutputStream);
+  }
+
+  void RecordSourceSurfaceDestruction(void* aSurface) final;
+
+  void Flush() final {}
+
+  void ReturnRead(char* aOut, size_t aSize) {
+    mOutputStream.ReturnRead(aOut, aSize);
+  }
+
+  uint32_t CreateCheckpoint() { return mOutputStream.CreateCheckpoint(); }
+
+  /**
+   * Waits until the given checkpoint has been read by the translator.
+   *
+   * @params aCheckpoint the checkpoint to wait for
+   * @returns true if the checkpoint was reached, false if the reader is closed
+   *          or we timeout.
+   */
+  bool WaitForCheckpoint(uint32_t aCheckpoint) {
+    return mOutputStream.WaitForCheckpoint(aCheckpoint);
+  }
+
+ private:
+  CanvasEventRingBuffer mOutputStream;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_CanvasDrawEventRecorder_h