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107 lines
4.1 KiB
C++
107 lines
4.1 KiB
C++
// Copyright 2016 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/thread_task_runner_handle.h"
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#include <utility>
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#include "base/bind.h"
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#include "base/lazy_instance.h"
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#include "base/logging.h"
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#include "base/memory/ptr_util.h"
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#include "base/run_loop.h"
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#include "base/threading/sequenced_task_runner_handle.h"
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#include "base/threading/thread_local.h"
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namespace base {
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namespace {
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base::LazyInstance<base::ThreadLocalPointer<ThreadTaskRunnerHandle>>::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<SingleThreadTaskRunner> ThreadTaskRunnerHandle::Get() {
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ThreadTaskRunnerHandle* current = lazy_tls_ptr.Pointer()->Get();
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CHECK(current) << "Error: This caller requires a single-threaded context "
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"(i.e. the current task needs to run from a "
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"SingleThreadTaskRunner).";
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return current->task_runner_;
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}
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// static
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bool ThreadTaskRunnerHandle::IsSet() {
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return !!lazy_tls_ptr.Pointer()->Get();
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}
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// static
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ScopedClosureRunner ThreadTaskRunnerHandle::OverrideForTesting(
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scoped_refptr<SingleThreadTaskRunner> overriding_task_runner) {
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// OverrideForTesting() is not compatible with a SequencedTaskRunnerHandle
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// being set (but SequencedTaskRunnerHandle::IsSet() includes
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// ThreadTaskRunnerHandle::IsSet() so that's discounted as the only valid
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// excuse for it to be true). Sadly this means that tests that merely need a
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// SequencedTaskRunnerHandle on their main thread can be forced to use a
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// ThreadTaskRunnerHandle if they're also using test task runners (that
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// OverrideForTesting() when running their tasks from said main thread). To
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// solve this: sequence_task_runner_handle.cc and thread_task_runner_handle.cc
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// would have to be merged into a single impl file and share TLS state. This
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// was deemed unecessary for now as most tests should use higher level
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// constructs and not have to instantiate task runner handles on their own.
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DCHECK(!SequencedTaskRunnerHandle::IsSet() || IsSet());
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if (!IsSet()) {
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auto top_level_ttrh = std::make_unique<ThreadTaskRunnerHandle>(
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std::move(overriding_task_runner));
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return ScopedClosureRunner(base::Bind(
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[](std::unique_ptr<ThreadTaskRunnerHandle> ttrh_to_release) {},
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base::Passed(&top_level_ttrh)));
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}
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ThreadTaskRunnerHandle* ttrh = lazy_tls_ptr.Pointer()->Get();
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// Swap the two (and below bind |overriding_task_runner|, which is now the
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// previous one, as the |task_runner_to_restore|).
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ttrh->task_runner_.swap(overriding_task_runner);
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auto no_running_during_override =
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std::make_unique<RunLoop::ScopedDisallowRunningForTesting>();
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return ScopedClosureRunner(base::Bind(
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[](scoped_refptr<SingleThreadTaskRunner> task_runner_to_restore,
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SingleThreadTaskRunner* expected_task_runner_before_restore,
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std::unique_ptr<RunLoop::ScopedDisallowRunningForTesting>
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no_running_during_override) {
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ThreadTaskRunnerHandle* ttrh = lazy_tls_ptr.Pointer()->Get();
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DCHECK_EQ(expected_task_runner_before_restore, ttrh->task_runner_.get())
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<< "Nested overrides must expire their ScopedClosureRunners "
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"in LIFO order.";
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ttrh->task_runner_.swap(task_runner_to_restore);
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},
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base::Passed(&overriding_task_runner),
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base::Unretained(ttrh->task_runner_.get()),
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base::Passed(&no_running_during_override)));
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}
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ThreadTaskRunnerHandle::ThreadTaskRunnerHandle(
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scoped_refptr<SingleThreadTaskRunner> task_runner)
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: task_runner_(std::move(task_runner)) {
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DCHECK(task_runner_->BelongsToCurrentThread());
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// No SequencedTaskRunnerHandle (which includes ThreadTaskRunnerHandles)
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// should already be set for this thread.
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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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ThreadTaskRunnerHandle::~ThreadTaskRunnerHandle() {
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DCHECK(task_runner_->BelongsToCurrentThread());
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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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