Optimize posting of WTF::Closure and improve scheduler test mocks

third_party/WebKit/public/platform/WebTaskRunner.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebTaskRunner_h
 #define WebTaskRunner_h
 
 #include "WebCommon.h"
 #include "public/platform/WebTraceLocation.h"
+#include "public/platform/scheduler/base/task_queue.h"
 #include <memory>
 
 #ifdef INSIDE_BLINK
 #include "wtf/Functional.h"
 #endif
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace blink {
 
 using SingleThreadTaskRunner = base::SingleThreadTaskRunner;
 
 // The blink representation of a chromium SingleThreadTaskRunner.
+// TODO(alexclarke): Rename to PlatformTaskRunner and move onto the oilpan heap.
+// TODO(alexclarke): Consider using base::TimeDelta for the delays. (crbug.com/402027)
 class BLINK_PLATFORM_EXPORT WebTaskRunner {
 public:
     virtual ~WebTaskRunner() {}
 
+    using TaskHandle = scheduler::TaskQueue::TaskHandle;
+
     class BLINK_PLATFORM_EXPORT Task {
     public:
         virtual ~Task() { }
         virtual void run() = 0;
     };
 
     // Schedule a task to be run on the the associated WebThread.
     // Takes ownership of |Task|. Can be called from any thread.
     virtual void postTask(const WebTraceLocation&, Task*) = 0;
 
     // Schedule a task to be run after |delayMs| on the the associated WebThread.
     // Takes ownership of |Task|. Can be called from any thread.
     virtual void postDelayedTask(const WebTraceLocation&, Task*, double delayMs) = 0;
 
+    // Posts the given task to be run after |delay| has passed. Returns a handle
+    // which can be passed to cancelTask to cancel the task before it has run.
+    // Note this must be called from the thread the tasks are run on (i.e the
+    // thread where runsTasksOnCurrentThread returns true).
+    virtual TaskHandle postCancellableDelayedTask(const tracked_objects::Location&, const base::Closure&, double delayMs) = 0;

[alex clarke (OOO till 29th), 2016/08/22 17:43:01]

Daniel on the other patch you expressed some API concerns. Are you OK with us
adding this? If further discussion is needed, I could split this off onto a
separate patch. 

+
+    // Attempts to cancel a task posted by PostCancellableDelayedTask. Returns
+    // true on success or false otherwise. Note this will fail unless called on
+    // the same WebTaskRunner that was used to post the task. Note this must be
+    // called from the thread the tasks are run on (i.e the thread where
+    // runsTasksOnCurrentThread returns true).
+    virtual bool cancelTask(const TaskHandle&) = 0;
+
     // Returns a clone of the WebTaskRunner.
     virtual std::unique_ptr<WebTaskRunner> clone() = 0;
 
     // Returns true if the current thread is a thread on which a task may be run.
     // Can be called from any thread.
     virtual bool runsTasksOnCurrentThread() = 0;
 
     // ---
 
     // Headless Chrome virtualises time for determinism and performance (fast forwarding
     // of timers). To make this work some parts of blink (e.g. Timers) need to use virtual
     // time, however by default new code should use the normal non-virtual time APIs.
 
     // Returns a double which is the number of seconds since epoch (Jan 1, 1970).
     // This may represent either the real time, or a virtual time depending on
     // whether or not the WebTaskRunner is associated with a virtual time domain or a
     // real time domain.
     virtual double virtualTimeSeconds() const = 0;
 
     // Returns a microsecond resolution platform dependant time source.
     // This may represent either the real time, or a virtual time depending on
     // whether or not the WebTaskRunner is associated with a virtual time domain or a
     // real time domain.
     virtual double monotonicallyIncreasingVirtualTimeSeconds() const = 0;
 
     // Returns the underlying task runner object.
-    virtual SingleThreadTaskRunner* taskRunner() = 0;
+    virtual SingleThreadTaskRunner* toSingleThreadTaskRunner() = 0;
 
 #ifdef INSIDE_BLINK
     // Helpers for posting bound functions as tasks.
 
     // For cross-thread posting. Can be called from any thread.
     void postTask(const WebTraceLocation&, std::unique_ptr<CrossThreadClosure>);
     void postDelayedTask(const WebTraceLocation&, std::unique_ptr<CrossThreadClosure>, long long delayMs);
 
     // For same-thread posting. Must be called from the associated WebThread.
     void postTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>);
     void postDelayedTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>, long long delayMs);
+
+    // Posts the given same-thread closure to be run after |delay| has passed.
+    // Returns a handle which can be passed to cancelTask to cancel the task
+    // before it has run. Note this must be called from the thread the tasks are
+    // run on (i.e the thread where runsTasksOnCurrentThread returns true).
+    TaskHandle postCancellableDelayedTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>, double delayMs);
 #endif
 };
 
 } // namespace blink
 
 #endif // WebTaskRunner_h