cc/base/swap_promise.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CC_BASE_SWAP_PROMISE_H_
   6 #define CC_BASE_SWAP_PROMISE_H_
   7
   8 #include "cc/output/compositor_frame_metadata.h"
   9
  10 namespace cc {
  11
  12 // When a change to the compositor's state/invalidation/whatever happens, a
  13 // Swap Promise can be inserted into LayerTreeHost/LayerTreeImpl, to track
  14 // whether the compositor's reply to the new state/invaliadtion/whatever is
  15 // completed in the compositor, i.e. the compositor knows it has been sent
  16 // to its output or not.
  17 //
  18 // If the new compositor state is sent to the output, SwapPromise::DidSwap()
  19 // will be called, and if the compositor fails to send its new state to the
  20 // output, SwapPromise::DidNotSwap() will be called.
  21 //
  22 // Client wishes to use SwapPromise should have a subclass that defines
  23 // the behavior of DidSwap() and DidNotSwap(). Notice that the promise can
  24 // be broken at either main or impl thread, e.g. commit fails on main thread,
  25 // new frame data has no actual damage so LayerTreeHostImpl::SwapBuffers()
  26 // bails out early on impl thread, so don't assume that DidSwap() and
  27 // DidNotSwap() are called at a particular thread. It is better to let the
  28 // subclass carry thread-safe member data and operate on that member data in
  29 // DidSwap() and DidNotSwap().
  30 class CC_EXPORT SwapPromise {
  31  public:
  32   enum DidNotSwapReason {
  33     DID_NOT_SWAP_UNKNOWN,
  34     SWAP_FAILS,
  35     COMMIT_FAILS,
  36     COMMIT_NO_UPDATE,
  37   };
  38
  39   SwapPromise() {}
  40   virtual ~SwapPromise() {}
  41
  42   virtual void DidSwap(CompositorFrameMetadata* metadata) = 0;
  43   virtual void DidNotSwap(DidNotSwapReason reason) = 0;
  44
  45   // A non-zero trace id identifies a trace flow object that is embedded in the
  46   // swap promise. This can be used for registering additional flow steps to
  47   // visualize the object's path through the system.
  48   virtual int64 TraceId() const = 0;
  49 };
  50
  51 }  // namespace cc
  52
  53 #endif  // CC_BASE_SWAP_PROMISE_H_