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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/task/single_thread_task_runner.h"
#include <memory>
#include <utility>
#include "base/check.h"
#include "base/check_op.h"
#include "base/compiler_specific.h"
#include "base/dcheck_is_on.h"
#include "base/functional/bind.h"
#include "base/lazy_instance.h"
#include "base/run_loop.h"
namespace base {
namespace {
constinit thread_local SingleThreadTaskRunner::CurrentDefaultHandle*
current_default_handle = nullptr;
// This function can be removed, and the calls below replaced with direct
// variable accesses, once the MSAN workaround is not necessary.
SingleThreadTaskRunner::CurrentDefaultHandle* GetCurrentDefaultHandle() {
// Workaround false-positive MSAN use-of-uninitialized-value on
// thread_local storage for loaded libraries:
// https://github.com/google/sanitizers/issues/1265
MSAN_UNPOISON(¤t_default_handle,
sizeof(SingleThreadTaskRunner::CurrentDefaultHandle*));
return current_default_handle;
}
} // namespace
bool SingleThreadTaskRunner::BelongsToCurrentThread() const {
return RunsTasksInCurrentSequence();
}
// static
const scoped_refptr<SingleThreadTaskRunner>&
SingleThreadTaskRunner::GetCurrentDefault() {
const auto* const handle = GetCurrentDefaultHandle();
CHECK(handle && handle->task_runner_)
<< "Error: This caller requires a single-threaded context (i.e. the "
"current task needs to run from a SingleThreadTaskRunner). If you're "
"in a test refer to //docs/threading_and_tasks_testing.md."
<< (SequencedTaskRunner::HasCurrentDefault()
? " Note: base::SequencedTaskRunner::GetCurrentDefault() "
"is set; "
"consider using it if the current task can run from a "
"SequencedTaskRunner."
: "");
return handle->task_runner_;
}
// static
bool SingleThreadTaskRunner::HasCurrentDefault() {
return !!GetCurrentDefaultHandle() &&
!!GetCurrentDefaultHandle()->task_runner_;
}
SingleThreadTaskRunner::CurrentDefaultHandle::CurrentDefaultHandle(
scoped_refptr<SingleThreadTaskRunner> task_runner)
: CurrentDefaultHandle(std::move(task_runner), MayAlreadyExist{}) {
CHECK(!previous_handle_ || !previous_handle_->task_runner_);
}
SingleThreadTaskRunner::CurrentDefaultHandle::~CurrentDefaultHandle() {
DCHECK_EQ(GetCurrentDefaultHandle(), this);
current_default_handle = previous_handle_;
}
SingleThreadTaskRunner::CurrentDefaultHandle::CurrentDefaultHandle(
scoped_refptr<SingleThreadTaskRunner> task_runner,
MayAlreadyExist)
: task_runner_(std::move(task_runner)),
previous_handle_(GetCurrentDefaultHandle()),
sequenced_handle_(
task_runner_,
SequencedTaskRunner::CurrentDefaultHandle::MayAlreadyExist{}) {
// Support overriding the current default with a null task runner or a task
// runner that belongs to the current thread.
DCHECK(!task_runner_ || task_runner_->BelongsToCurrentThread());
current_default_handle = this;
}
SingleThreadTaskRunner::CurrentHandleOverrideForTesting::
CurrentHandleOverrideForTesting(
scoped_refptr<SingleThreadTaskRunner> overriding_task_runner)
: current_default_handle_(std::move(overriding_task_runner),
CurrentDefaultHandle::MayAlreadyExist{}),
no_running_during_override_(
std::make_unique<ScopedDisallowRunningRunLoop>()) {}
SingleThreadTaskRunner::CurrentHandleOverrideForTesting::
~CurrentHandleOverrideForTesting() = default;
} // namespace base
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