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// Copyright (c) 2012 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 <memory>
#include <string>
#include <utility>
#include "base/callback.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/scoped_refptr.h"
#include "base/single_thread_task_runner.h"
#include "base/task_runner_util.h"
#include "base/time/time.h"
#include "content/common/content_export.h"
namespace content {
// TODO(1026641): Include browser_task_traits.h directly when the migration to
// Get(UI|IO)ThreadTaskrunner() is complete and the cyclic dependency of
// browser_task_traits.h on BrowserThread::ID is broken.
class BrowserTaskTraits;
class BrowserThreadImpl;
// Use DCHECK_CURRENTLY_ON(BrowserThread::ID) to assert that a function can only
// be called on the named BrowserThread.
#define DCHECK_CURRENTLY_ON(thread_identifier) \
(DCHECK(::content::BrowserThread::CurrentlyOn(thread_identifier)) \
<< ::content::BrowserThread::GetDCheckCurrentlyOnErrorMessage( \
// The main entry point to post tasks to the UI thread. Tasks posted with the
// same |traits| will run in posting order (i.e. according to the
// SequencedTaskRunner contract). Tasks posted with different |traits| can be
// re-ordered. You may keep a reference to this task runner, it's always
// thread-safe to post to it though it may start returning false at some point
// during shutdown when it definitely is no longer accepting tasks.
// In unit tests, there must be a content::BrowserTaskEnvironment in scope for
// this API to be available.
// TODO(1026641): Make default traits |{}| the default param when it's possible
// to include browser_task_traits.h in this file (see note above on the
// BrowserTaskTraits fwd-decl).
CONTENT_EXPORT scoped_refptr<base::SingleThreadTaskRunner>
GetUIThreadTaskRunner(const BrowserTaskTraits& traits);
// The BrowserThread::IO counterpart to GetUIThreadTaskRunner().
CONTENT_EXPORT scoped_refptr<base::SingleThreadTaskRunner>
GetIOThreadTaskRunner(const BrowserTaskTraits& traits);
// BrowserThread
// Utility functions for threads that are known by a browser-wide name.
class CONTENT_EXPORT BrowserThread {
// An enumeration of the well-known threads.
enum ID {
// The main thread in the browser. It stops running tasks during shutdown
// and is never joined.
// This is the thread that processes non-blocking I/O, i.e. IPC and network.
// Blocking I/O should happen in base::ThreadPool. It is joined on shutdown
// (and thus any task posted to it may block shutdown).
// NOTE: do not add new threads here. Instead you should just use
// base::ThreadPool::Create*TaskRunner to run tasks on the base::ThreadPool.
// This identifier does not represent a thread. Instead it counts the
// number of well-known threads. Insert new well-known threads before this
// identifier.
// Delete/ReleaseSoon() helpers allow future deletion of an owned object on
// its associated thread. If you already have a task runner bound to a
// BrowserThread you should use its SequencedTaskRunner::DeleteSoon() member
// method.
// TODO(1026641): Get rid of the last few callers to these in favor of an
// explicit call to content::GetUIThreadTaskRunner({})->DeleteSoon(...).
template <class T>
static bool DeleteSoon(ID identifier,
const base::Location& from_here,
const T* object) {
return GetTaskRunnerForThread(identifier)->DeleteSoon(from_here, object);
template <class T>
static bool DeleteSoon(ID identifier,
const base::Location& from_here,
std::unique_ptr<T> object) {
return DeleteSoon(identifier, from_here, object.release());
template <class T>
static void ReleaseSoon(ID identifier,
const base::Location& from_here,
scoped_refptr<T>&& object) {
->ReleaseSoon(from_here, std::move(object));
// Posts a |task| to run at BEST_EFFORT priority using an arbitrary
// |task_runner| for which we do not control the priority.
// This is useful when a task needs to run on |task_runner| (for thread-safety
// reasons) but should be delayed until after critical phases (e.g. startup).
// TODO( Add support for sequence-funneling and remove this
// method.
static void PostBestEffortTask(const base::Location& from_here,
scoped_refptr<base::TaskRunner> task_runner,
base::OnceClosure task);
// Callable on any thread. Returns whether the given well-known thread is
// initialized.
static bool IsThreadInitialized(ID identifier) WARN_UNUSED_RESULT;
// Callable on any thread. Returns whether you're currently on a particular
// thread. To DCHECK this, use the DCHECK_CURRENTLY_ON() macro above.
static bool CurrentlyOn(ID identifier) WARN_UNUSED_RESULT;
// If the current message loop is one of the known threads, returns true and
// sets identifier to its ID. Otherwise returns false.
static bool GetCurrentThreadIdentifier(ID* identifier) WARN_UNUSED_RESULT;
// Use these templates in conjunction with RefCountedThreadSafe or scoped_ptr
// when you want to ensure that an object is deleted on a specific thread.
// This is needed when an object can hop between threads (i.e. UI -> IO ->
// UI), and thread switching delays can mean that the final UI tasks executes
// before the IO task's stack unwinds. This would lead to the object
// destructing on the IO thread, which often is not what you want (i.e. to
// unregister from NotificationService, to notify other objects on the
// creating thread etc). Note: see base::OnTaskRunnerDeleter and
// base::RefCountedDeleteOnSequence to bind to SequencedTaskRunner instead of
// specific BrowserThreads.
template <ID thread>
struct DeleteOnThread {
template <typename T>
static void Destruct(const T* x) {
if (CurrentlyOn(thread)) {
delete x;
} else {
if (!DeleteSoon(thread, FROM_HERE, x)) {
#if defined(UNIT_TEST)
// Only logged under unit testing because leaks at shutdown
// are acceptable under normal circumstances.
LOG(ERROR) << "DeleteSoon failed on thread " << thread;
#endif // UNIT_TEST
template <typename T>
inline void operator()(T* ptr) const {
enum { type_must_be_complete = sizeof(T) };
// Sample usage with RefCountedThreadSafe:
// class Foo
// : public base::RefCountedThreadSafe<
// Foo, BrowserThread::DeleteOnIOThread> {
// ...
// private:
// friend struct BrowserThread::DeleteOnThread<BrowserThread::IO>;
// friend class base::DeleteHelper<Foo>;
// ~Foo();
// Sample usage with scoped_ptr:
// std::unique_ptr<Foo, BrowserThread::DeleteOnIOThread> ptr;
// Note: see base::OnTaskRunnerDeleter and base::RefCountedDeleteOnSequence to
// bind to SequencedTaskRunner instead of specific BrowserThreads.
struct DeleteOnUIThread : public DeleteOnThread<UI> {};
struct DeleteOnIOThread : public DeleteOnThread<IO> {};
// Returns an appropriate error message for when DCHECK_CURRENTLY_ON() fails.
static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
// Runs all pending tasks for the given thread. Tasks posted after this method
// is called (in particular any task posted from within any of the pending
// tasks) will be queued but not run. Conceptually this call will disable all
// queues, run any pending tasks, and re-enable all the queues.
// If any of the pending tasks posted a task, these could be run by calling
// this method again or running a regular RunLoop. But if that were the case
// you should probably rewrite you tests to wait for a specific event instead.
// NOTE: Can only be called from the UI thread.
static void RunAllPendingTasksOnThreadForTesting(ID identifier);
// For DeleteSoon(). Requires that the BrowserThread with the provided
// |identifier| was started.
static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
ID identifier);
friend class BrowserThreadImpl;
BrowserThread() = default;
// Runs |task| on the thread specified by |thread_id| if already on that thread,
// otherwise posts a task to that thread.
// This is intended to be a temporary helper function for the IO/UI thread
// simplification effort.
CONTENT_EXPORT void RunOrPostTaskOnThread(const base::Location& location,
BrowserThread::ID thread_id,
base::OnceClosure task);
} // namespace content