blob: a2d5f4b1abcd4f5b5234e874594d9971d512360e [file] [log] [blame]
// Copyright 2014 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/check_op.h"
#include "base/compiler_specific.h"
#include "base/location.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/single_thread_task_runner.h"
#include "base/task_runner_util.h"
namespace base {
class Location;
namespace web {
class WebThreadDelegate;
// Use DCHECK_CURRENTLY_ON(WebThread::ID) to assert that a function can only be
// called on the named WebThread.
#define DCHECK_CURRENTLY_ON(thread_identifier) \
(DCHECK(::web::WebThread::CurrentlyOn(thread_identifier)) \
<< ::web::WebThread::GetDCheckCurrentlyOnErrorMessage(thread_identifier))
// WebThread
// Utility functions for threads that are known by name. For example, there is
// one IO thread for the entire process, and various pieces of code find it
// useful to retrieve a pointer to the IO thread's message loop.
// See web_task_traits.h for posting Tasks to a WebThread.
// This class automatically handles the lifetime of different threads. You
// should never need to cache pointers to MessageLoops, since they're not thread
// safe.
class WebThread {
// An enumeration of the well-known threads.
// NOTE: threads must be listed in the order of their life-time, with each
// thread outliving every other thread below it.
enum ID {
// The main thread in the browser.
// This is the thread that processes non-blocking IO, i.e. IPC and network.
// Blocking IO should happen in ThreadPool.
// NOTE: do not add new threads here. Instead you should just use
// base::Create*TaskRunner to run tasks on the 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.
// NOTE: Task posting APIs have moved to post_task.h. See web_task_traits.h.
// Delete/ReleaseSoon() helpers allow future deletion of an owned object on
// its associated thread. If you already have a task runner bound to a
// WebThread you should use its SequencedTaskRunner::DeleteSoon() member
// method. If you don't, the helpers below avoid having to do
// base::CreateSingleThreadTaskRunner({WebThread::ID})->DeleteSoon(...) which
// is equivalent.
template <class T>
static bool DeleteSoon(ID identifier,
const base::Location& from_here,
const T* object) {
return GetTaskRunnerForThread(identifier)->DeleteSoon(from_here, object);
// 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 execution is currently on the
// given 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.
static bool GetCurrentThreadIdentifier(ID* identifier) WARN_UNUSED_RESULT;
// Sets the delegate for WebThread::IO.
// This only supports the IO thread.
// Only one delegate may be registered at a time. Delegates may be
// unregistered by providing a nullptr pointer.
// The delegate can only be registered through this call before
// WebThreadImpl(WebThread::IO) is created and unregistered after
// it was destroyed and its underlying thread shutdown.
static void SetIOThreadDelegate(WebThreadDelegate* delegate);
// Returns an appropriate error message for when DCHECK_CURRENTLY_ON() fails.
static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
// Use these templates in conjunction with RefCountedThreadSafe or
// std::unique_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. IO -> UI -> IO), and thread switching delays can mean that the final
// IO tasks executes before the UI task's stack unwinds. This would lead to
// the object destructing on the UI thread, which often is not what you want
// (i.e. to unregister from NotificationService, to notify other objects on
// the creating thread etc).
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)) {
// Leaks at shutdown are acceptable under normal circumstances,
// do not report.
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, web::WebThread::DeleteOnIOThread> {
// ...
// private:
// friend struct web::WebThread::DeleteOnThread<web::WebThread::IO>;
// friend class base::DeleteHelper<Foo>;
// ~Foo();
// Sample usage with std::unique_ptr:
// std::unique_ptr<Foo, web::WebThread::DeleteOnIOThread> ptr;
struct DeleteOnUIThread : public DeleteOnThread<UI> {};
struct DeleteOnIOThread : public DeleteOnThread<IO> {};
friend class WebThreadImpl;
// For DeleteSoon() only.
static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
ID identifier);
WebThread() {}
} // namespace web