blob: c51cc9806ed057f307af96afd6b48730d2d30a72 [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.
#ifndef IOS_WEB_PUBLIC_WEB_THREAD_H_
#define IOS_WEB_PUBLIC_WEB_THREAD_H_
#include <string>
#include "base/callback_forward.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/task_runner_util.h"
namespace base {
class MessageLoop;
class SequencedWorkerPool;
}
namespace tracked_objects {
class Location;
}
namespace web {
class WebThreadDelegate;
// 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/.
// http://crbug.com/438202
#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 {
public:
// 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.
UI,
// This is the thread that interacts with the database.
DB,
// This is the thread that interacts with the file system.
FILE,
// Used for file system operations that block user interactions.
// Responsiveness of this thread affect users.
FILE_USER_BLOCKING,
// This is the thread to handle slow HTTP cache operations.
CACHE,
// 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.
IO,
// 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
// SingleThreadTaskRunner 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.
ID_COUNT
};
// 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 PostNonNestableTask(ID identifier,
const tracked_objects::Location& from_here,
const base::Closure& task);
static bool PostNonNestableDelayedTask(
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::SingleThreadTaskRunner> task_runner =
GetTaskRunnerForThread(identifier);
return base::PostTaskAndReplyWithResult(task_runner.get(), from_here, task,
reply);
}
template <class T>
static bool DeleteSoon(ID identifier,
const tracked_objects::Location& from_here,
const T* object) {
return GetTaskRunnerForThread(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 PostBlockingPoolTaskAndReply(
const tracked_objects::Location& from_here,
const base::Closure& task,
const base::Closure& reply);
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 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_WEB_THREAD()
// macro above.
static bool CurrentlyOn(ID identifier) WARN_UNUSED_RESULT;
// Callable on any thread. Returns whether the threads message loop is valid.
// If this returns false it means the thread is in the process of shutting
// down.
static bool IsMessageLoopValid(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;
// Callers can hold on to a refcounted SingleThreadTaskRunner beyond the
// lifetime of the thread.
static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
ID identifier);
// Sets the delegate for the specified WebThread.
//
// Only one delegate may be registered at a time. Delegates may be
// unregistered by providing a nullptr pointer.
//
// If the caller unregisters a delegate before CleanUp has been
// called, it must perform its own locking to ensure the delegate is
// not deleted while unregistering.
static void SetDelegate(ID identifier, WebThreadDelegate* delegate);
// Returns an appropriate error message for when
// DCHECK_CURRENTLY_ON_WEB_THREAD() fails.
static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
private:
friend class WebThreadImpl;
WebThread() {}
DISALLOW_COPY_AND_ASSIGN(WebThread);
};
} // namespace web
#endif // IOS_WEB_PUBLIC_WEB_THREAD_H_