blob: f820fb756b5bcfe06d8fb5f0e59c6841cbec18d9 [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 <string>
#include "base/callback_forward.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/message_loop/message_loop_proxy.h"
#include "base/task_runner_util.h"
namespace base {
class MessageLoop;
class SequencedWorkerPool;
namespace tracked_objects {
class Location;
namespace web {
// Use DCHECK_CURRENTLY_ON_WEB_THREAD(WebThread::ID) to assert that a function
// can only be called on the named WebThread.
// TODO(ios): rename to DCHECK_CURRENTLY_ON once iOS is independent from
// content/ so it won't collide with the macro DCHECK_CURRENTLY_ON in content/.
#define DCHECK_CURRENTLY_ON_WEB_THREAD(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.
// Invoke a task by thread ID:
// WebThread::PostTask(WebThread::IO, FROM_HERE, task);
// The return value is false if the task couldn't be posted because the target
// thread doesn't exist. If this could lead to data loss, you need to check the
// result and restructure the code to ensure it doesn't occur.
// This class automatically handles the lifetime of different threads.
// It's always safe to call PostTask on any thread. If it's not yet created,
// the task is deleted. There are no race conditions. If the thread that the
// task is posted to is guaranteed to outlive the current thread, then no locks
// are used. 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 interacts with the database.
// This is the thread that interacts with the file system.
// Used for file system operations that block user interactions.
// Responsiveness of this thread affect users.
// This is the thread to handle slow HTTP cache operations.
// This is the thread that processes non-blocking IO, i.e. IPC and network.
// Blocking IO should happen on other threads like DB, FILE,
// FILE_USER_BLOCKING and CACHE depending on the usage.
// NOTE: do not add new threads here that are only used by a small number of
// files. Instead you should just use a Thread class and pass its
// MessageLoopProxy around. Named threads there are only for threads that
// are used in many places.
// This identifier does not represent a thread. Instead it counts the
// number of well-known threads. Insert new well-known threads before this
// identifier.
// These are the same methods as in message_loop.h, but are guaranteed to
// either get posted to the MessageLoop if it's still alive, or be deleted
// otherwise.
// They return true iff the thread existed and the task was posted.
static bool PostTask(ID identifier,
const tracked_objects::Location& from_here,
const base::Closure& task);
static bool PostDelayedTask(ID identifier,
const tracked_objects::Location& from_here,
const base::Closure& task,
base::TimeDelta delay);
static bool PostTaskAndReply(ID identifier,
const tracked_objects::Location& from_here,
const base::Closure& task,
const base::Closure& reply);
template <typename ReturnType, typename ReplyArgType>
static bool PostTaskAndReplyWithResult(
ID identifier,
const tracked_objects::Location& from_here,
const base::Callback<ReturnType(void)>& task,
const base::Callback<void(ReplyArgType)>& reply) {
scoped_refptr<base::MessageLoopProxy> message_loop_proxy =
return base::PostTaskAndReplyWithResult(message_loop_proxy.get(), from_here,
task, reply);
template <class T>
static bool DeleteSoon(ID identifier,
const tracked_objects::Location& from_here,
const T* object) {
return GetMessageLoopProxyForThread(identifier)
->DeleteSoon(from_here, object);
// Simplified wrappers for posting to the blocking thread pool. Use this
// for doing things like blocking I/O.
// The first variant will run the task in the pool with no sequencing
// semantics, so may get run in parallel with other posted tasks. The second
// variant will all post a task with no sequencing semantics, and will post a
// reply task to the origin TaskRunner upon completion. The third variant
// provides sequencing between tasks with the same sequence token name.
// These tasks are guaranteed to run before shutdown.
// If you need to provide different shutdown semantics (like you have
// something slow and noncritical that doesn't need to block shutdown),
// or you want to manually provide a sequence token (which saves a map
// lookup and is guaranteed unique without you having to come up with a
// unique string), you can access the sequenced worker pool directly via
// GetBlockingPool().
// If you need to PostTaskAndReplyWithResult, use
// base::PostTaskAndReplyWithResult() with GetBlockingPool() as the task
// runner.
static bool PostBlockingPoolTask(const tracked_objects::Location& from_here,
const base::Closure& task);
static bool PostBlockingPoolSequencedTask(
const std::string& sequence_token_name,
const tracked_objects::Location& from_here,
const base::Closure& task);
// Returns the thread pool used for blocking file I/O. Use this object to
// perform random blocking operations such as file writes.
static base::SequencedWorkerPool* GetBlockingPool() WARN_UNUSED_RESULT;
// Returns a pointer to the thread's message loop, which will become
// invalid during shutdown, so you probably shouldn't hold onto it.
// This must not be called before the thread is started, or after
// the thread is stopped, or it will DCHECK.
// Ownership remains with the WebThread implementation, so you must not
// delete the pointer.
static base::MessageLoop* UnsafeGetMessageLoopForThread(ID identifier);
// Callable on any thread. Returns whether execution is currently on the
// given thread. To DCHECK this, use the DCHECK_CURRENTLY_ON_WEB_THREAD()
// macro above.
static bool CurrentlyOn(ID identifier) WARN_UNUSED_RESULT;
// Callers can hold on to a refcounted MessageLoopProxy beyond the lifetime
// of the thread.
static scoped_refptr<base::MessageLoopProxy> GetMessageLoopProxyForThread(
ID identifier);
// Returns an appropriate error message for when
static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
WebThread() {}
} // namespace web