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