content/browser/renderer_host/render_widget_resize_helper.h

   1 // Copyright 2014 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 CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_RESIZE_HELPER_H_
   6 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_RESIZE_HELPER_H_
   7
   8 #include "base/lazy_instance.h"
   9 #include "base/single_thread_task_runner.h"
  10 #include "base/synchronization/lock.h"
  11 #include "base/synchronization/waitable_event.h"
  12 #include "ipc/ipc_message.h"
  13
  14 namespace content {
  15
  16 // RenderWidgetResizeHelper is used to make resize appear smooth. That is to
  17 // say, make sure that the window size and the size of the content being drawn
  18 // in that window are resized in lock-step. This is accomplished by waiting
  19 // inside -[RenderWidgetHostViewCocoa setFrameSize:] for the renderer (and
  20 // potentially browser compositor as well) to produce a frame of same size
  21 // as the RenderWidgetHostViewCocoa.
  22 //
  23 // The function of waiting for a frame of the correct size is done inside
  24 // RenderWidgetHostImpl::WaitForSurface. That function will call
  25 // RenderWidgetResizeHelper::WaitForSingleTaskToRun until a timeout occurs,
  26 // or the corresponding RenderWidgetHostViewCocoa has a renderer frame of the
  27 // same size as its NSView.
  28 //
  29 // This is somewhat complicated because waiting for frames requires that
  30 // that the browser handle the IPCs (from the renderer and the GPU processes)
  31 // that are required to pick up a new frame. In the ordinary run of things
  32 // (ignoring RenderWidgetResizeHelper), those IPCs arrive on the IO thread
  33 // and are posted as tasks to the UI thread either by the RenderMessageFilter
  34 // (for renderer processes) or the GpuProcessHostUIShim (for the GPU process).
  35 // The IPCs that are required to create new frames for smooth resize are sent
  36 // to the RenderWidgetResizeHelper using the PostRendererProcessMsg and
  37 // PostGpuProcessMsg methods. These functions will post them as tasks to the UI
  38 // thread (as usual), and will also enqueue them into a queue which will be
  39 // read and run in RenderWidgetResizeHelper::WaitForSingleTaskToRun, potentially
  40 // before the task posted to the UI thread is run. Some care is taken (see
  41 // WrappedTask) to make sure that the messages are only executed once.
  42 //
  43 // This is further complicated because, in order for a frame to appear, it is
  44 // necessary to run tasks posted by the ui::Compositor. To accomplish this, the
  45 // RenderWidgetResizeHelper provides a base::SingleThreadTaskRunner which,
  46 // when a task is posted to it, enqueues the task in the aforementioned queue,
  47 // which may be pumped by RenderWidgetResizeHelper::WaitForSingleTaskToRun.
  48 //
  49 class RenderWidgetResizeHelper {
  50  public:
  51   static RenderWidgetResizeHelper* Get();
  52   scoped_refptr<base::SingleThreadTaskRunner> task_runner() const;
  53
  54   // UI THREAD ONLY -----------------------------------------------------------
  55
  56   // Waits at most |max_delay| for a task to run. Returns true if a task ran,
  57   // false if no task ran.
  58   bool WaitForSingleTaskToRun(const base::TimeDelta& max_delay);
  59
  60   // IO THREAD ONLY -----------------------------------------------------------
  61
  62   // This will cause |msg| to be handled by the RenderProcessHost corresponding
  63   // to |render_process_id|, on the UI thread. This will either happen when the
  64   // ordinary message loop would run it, or potentially earlier in a call to
  65   // WaitForSingleTaskToRun .
  66   void PostRendererProcessMsg(int render_process_id, const IPC::Message& msg);
  67
  68   // This is similar to PostRendererProcessMsg, but will handle the message in
  69   // the GpuProcessHostUIShim corresponding to |gpu_host_id|.
  70   void PostGpuProcessMsg(int gpu_host_id, const IPC::Message& msg);
  71
  72  private:
  73   friend struct base::DefaultLazyInstanceTraits<RenderWidgetResizeHelper>;
  74   RenderWidgetResizeHelper();
  75   ~RenderWidgetResizeHelper();
  76
  77   // This helper is needed to create a ScopedAllowWait inside the scope of a
  78   // class where it is allowed.
  79   static void EventTimedWait(
  80       base::WaitableEvent* event,
  81       base::TimeDelta delay);
  82
  83   // The task runner to which the helper will post tasks. This also maintains
  84   // the task queue and does the actual work for WaitForSingleTaskToRun.
  85   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
  86
  87   DISALLOW_COPY_AND_ASSIGN(RenderWidgetResizeHelper);
  88 };
  89
  90 }  // namespace content
  91
  92 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_RESIZE_HELPER_H_