Allow SequencedTaskRunnerHandle::Get() while running unsequenced tasks.

base/threading/sequenced_task_runner_handle_unittest.cc

 // 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.
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/sequence_checker_impl.h"
 #include "base/sequenced_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/test/sequenced_worker_pool_owner.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/simple_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 class SequencedTaskRunnerHandleTest : public ::testing::Test {
  protected:
   static void GetTaskRunner(const Closure& callback) {

[gab, 2015/11/10 19:54:18]

A "Get" method that returns void feels weird to me.

[Bernhard Bauer, 2015/11/10 20:31:47]

Done.

-    // Use SequenceCheckerImpl to make sure it's not a no-op in Release builds.
-    scoped_ptr<SequenceCheckerImpl> sequence_checker(new SequenceCheckerImpl);
     ASSERT_TRUE(SequencedTaskRunnerHandle::IsSet());
     scoped_refptr<SequencedTaskRunner> task_runner =
         SequencedTaskRunnerHandle::Get();
     ASSERT_TRUE(task_runner);
+
+    // Use SequenceCheckerImpl to make sure it's not a no-op in Release builds.
+    scoped_ptr<SequenceCheckerImpl> sequence_checker(new SequenceCheckerImpl);
     task_runner->PostTask(
         FROM_HERE, base::Bind(&SequencedTaskRunnerHandleTest::CheckValidThread,
                               base::Passed(&sequence_checker), callback));
   }
 
  private:
   static void CheckValidThread(scoped_ptr<SequenceCheckerImpl> sequence_checker,
                                const Closure& callback) {
     EXPECT_TRUE(sequence_checker->CalledOnValidSequencedThread());
     callback.Run();
   }
 
   MessageLoop message_loop_;
 };
 
 TEST_F(SequencedTaskRunnerHandleTest, FromMessageLoop) {
   RunLoop run_loop;
   GetTaskRunner(run_loop.QuitClosure());
   run_loop.Run();
 }
 
-TEST_F(SequencedTaskRunnerHandleTest, FromSequencedWorkerPool) {
+TEST_F(SequencedTaskRunnerHandleTest, FromSequencedWorkerPoolTask) {
   // Wrap the SequencedWorkerPool to avoid leaks due to its asynchronous
   // destruction.
   SequencedWorkerPoolOwner owner(3, "Test");
   WaitableEvent event(false, false);
   owner.pool()->PostSequencedWorkerTask(
       owner.pool()->GetSequenceToken(), FROM_HERE,
       base::Bind(&SequencedTaskRunnerHandleTest::GetTaskRunner,
                  base::Bind(&WaitableEvent::Signal, base::Unretained(&event))));
   event.Wait();
   owner.pool()->Shutdown();
 }
 
+TEST_F(SequencedTaskRunnerHandleTest, FromUnsequencedTask) {

[gab, 2015/11/10 19:54:18]

Did you confirm that this test failed prior to the product side changes of this
CL?

[Bernhard Bauer, 2015/11/10 20:31:47]

Yes: 

[ RUN      ] SequencedTaskRunnerHandleTest.FromUnsequencedTask
../../base/threading/sequenced_task_runner_handle_unittest.cc:27: Failure
Value of: SequencedTaskRunnerHandle::IsSet()
  Actual: false
Expected: true
(It hangs after that, because I was too lazy to add something that would call
the callback in case of failure... 😃)

+  // Wrap the SequencedWorkerPool to avoid leaks due to its asynchronous
+  // destruction.
+  SequencedWorkerPoolOwner owner(3, "Test");
+  WaitableEvent event(false, false);
+  owner.pool()->PostWorkerTask(
+      FROM_HERE,
+      base::Bind(&SequencedTaskRunnerHandleTest::GetTaskRunner,
+                 base::Bind(&WaitableEvent::Signal, base::Unretained(&event))));
+  event.Wait();
+  owner.pool()->Shutdown();
+}
+
 class ThreadRunner : public DelegateSimpleThread::Delegate {
  public:
   void Run() override {
     ASSERT_FALSE(SequencedTaskRunnerHandle::IsSet());
   }
 
  private:
   Closure callback_;
 };
 
 TEST_F(SequencedTaskRunnerHandleTest, FromSimpleThread) {
   ThreadRunner thread_runner;
   DelegateSimpleThread thread(&thread_runner, "Background thread");
   thread.Start();
   thread.Join();
 }
 
 }  // namespace
 }  // namespace base