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90 lines
3.4 KiB
C++
90 lines
3.4 KiB
C++
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/threading/sequenced_task_runner_handle.h"
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#include <utility>
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#include "base/lazy_instance.h"
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#include "base/logging.h"
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#include "base/threading/sequenced_worker_pool.h"
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#include "base/threading/thread_local.h"
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#include "base/threading/thread_task_runner_handle.h"
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namespace base {
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namespace {
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LazyInstance<ThreadLocalPointer<SequencedTaskRunnerHandle>>::Leaky
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lazy_tls_ptr = LAZY_INSTANCE_INITIALIZER;
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} // namespace
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// static
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scoped_refptr<SequencedTaskRunner> SequencedTaskRunnerHandle::Get() {
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// Return the registered SingleThreadTaskRunner, if any. This must be at the
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// top so that a SingleThreadTaskRunner has priority over a
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// SequencedTaskRunner (RLZ registers both on the same thread despite that
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// being prevented by DCHECKs).
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// TODO(fdoray): Move this to the bottom once RLZ stops registering a
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// SingleThreadTaskRunner and a SequencedTaskRunner on the same thread.
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// https://crbug.com/618530#c14
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if (ThreadTaskRunnerHandle::IsSet()) {
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// Various modes of setting SequencedTaskRunnerHandle don't combine.
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DCHECK(!lazy_tls_ptr.Pointer()->Get());
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DCHECK(!SequencedWorkerPool::GetSequenceTokenForCurrentThread().IsValid());
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return ThreadTaskRunnerHandle::Get();
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}
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// Return the registered SequencedTaskRunner, if any.
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const SequencedTaskRunnerHandle* handle = lazy_tls_ptr.Pointer()->Get();
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if (handle) {
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// Various modes of setting SequencedTaskRunnerHandle don't combine.
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DCHECK(!SequencedWorkerPool::GetSequenceTokenForCurrentThread().IsValid());
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return handle->task_runner_;
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}
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// If we are on a worker thread for a SequencedBlockingPool that is running a
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// sequenced task, return a SequencedTaskRunner for it.
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scoped_refptr<SequencedWorkerPool> pool =
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SequencedWorkerPool::GetWorkerPoolForCurrentThread();
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// Note if you hit this: the problem isn't the lack of a |pool|, it's the lack
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// of a sequenced context above. The |pool| is just the last desperate attempt
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// at finding such a context from the deprecated SequencedWorkerPool.
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CHECK(pool) << "Error: This caller requires a sequenced context (i.e. the "
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"current task needs to run from a SequencedTaskRunner).";
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SequencedWorkerPool::SequenceToken sequence_token =
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SequencedWorkerPool::GetSequenceTokenForCurrentThread();
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DCHECK(sequence_token.IsValid());
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scoped_refptr<SequencedTaskRunner> sequenced_task_runner(
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pool->GetSequencedTaskRunner(sequence_token));
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DCHECK(sequenced_task_runner->RunsTasksInCurrentSequence());
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return sequenced_task_runner;
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}
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// static
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bool SequencedTaskRunnerHandle::IsSet() {
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return lazy_tls_ptr.Pointer()->Get() ||
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SequencedWorkerPool::GetSequenceTokenForCurrentThread().IsValid() ||
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ThreadTaskRunnerHandle::IsSet();
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}
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SequencedTaskRunnerHandle::SequencedTaskRunnerHandle(
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scoped_refptr<SequencedTaskRunner> task_runner)
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: task_runner_(std::move(task_runner)) {
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DCHECK(task_runner_->RunsTasksInCurrentSequence());
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DCHECK(!SequencedTaskRunnerHandle::IsSet());
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lazy_tls_ptr.Pointer()->Set(this);
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}
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SequencedTaskRunnerHandle::~SequencedTaskRunnerHandle() {
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DCHECK(task_runner_->RunsTasksInCurrentSequence());
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DCHECK_EQ(lazy_tls_ptr.Pointer()->Get(), this);
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lazy_tls_ptr.Pointer()->Set(nullptr);
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}
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} // namespace base
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