1 // Copyright 2015 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 #include "base/threading/sequenced_task_runner_handle.h" 6 7 #include <utility> 8 9 #include "base/lazy_instance.h" 10 #include "base/logging.h" 11 #include "base/threading/sequenced_worker_pool.h" 12 #include "base/threading/thread_local.h" 13 #include "base/threading/thread_task_runner_handle.h" 14 15 namespace base { 16 17 namespace { 18 19 base::LazyInstance<base::ThreadLocalPointer<SequencedTaskRunnerHandle>>::Leaky 20 lazy_tls_ptr = LAZY_INSTANCE_INITIALIZER; 21 22 } // namespace 23 24 // static 25 scoped_refptr<SequencedTaskRunner> SequencedTaskRunnerHandle::Get() { 26 // Return the registered SequencedTaskRunner, if any. 27 const SequencedTaskRunnerHandle* handle = lazy_tls_ptr.Pointer()->Get(); 28 if (handle) { 29 // Various modes of setting SequencedTaskRunnerHandle don't combine. 30 DCHECK(!base::ThreadTaskRunnerHandle::IsSet()); 31 DCHECK(!SequencedWorkerPool::GetSequencedTaskRunnerForCurrentThread()); 32 return handle->task_runner_; 33 } 34 35 // Return the SequencedTaskRunner obtained from SequencedWorkerPool, if any. 36 scoped_refptr<base::SequencedTaskRunner> task_runner = 37 SequencedWorkerPool::GetSequencedTaskRunnerForCurrentThread(); 38 if (task_runner) { 39 DCHECK(!base::ThreadTaskRunnerHandle::IsSet()); 40 return task_runner; 41 } 42 43 // Return the SingleThreadTaskRunner for the current thread otherwise. 44 return base::ThreadTaskRunnerHandle::Get(); 45 } 46 47 // static 48 bool SequencedTaskRunnerHandle::IsSet() { 49 return lazy_tls_ptr.Pointer()->Get() || 50 SequencedWorkerPool::GetWorkerPoolForCurrentThread() || 51 base::ThreadTaskRunnerHandle::IsSet(); 52 } 53 54 SequencedTaskRunnerHandle::SequencedTaskRunnerHandle( 55 scoped_refptr<SequencedTaskRunner> task_runner) 56 : task_runner_(std::move(task_runner)) { 57 DCHECK(task_runner_->RunsTasksOnCurrentThread()); 58 DCHECK(!SequencedTaskRunnerHandle::IsSet()); 59 lazy_tls_ptr.Pointer()->Set(this); 60 } 61 62 SequencedTaskRunnerHandle::~SequencedTaskRunnerHandle() { 63 DCHECK(task_runner_->RunsTasksOnCurrentThread()); 64 DCHECK_EQ(lazy_tls_ptr.Pointer()->Get(), this); 65 lazy_tls_ptr.Pointer()->Set(nullptr); 66 } 67 68 } // namespace base 69