cef/libcef/cef_thread.h

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// Copyright (c) 2010 The Chromium Embedded Framework Authors.
// Portions copyright (c) 2010 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 _CEF_THREAD_H
#define _CEF_THREAD_H
#include "base/synchronization/lock.h"
#include "base/task.h"
#include "base/threading/thread.h"
namespace base {
class MessageLoopProxy;
}
///////////////////////////////////////////////////////////////////////////////
// CefThread
//
// This class represents a thread that is known by a browser-wide name. For
// example, there is one IO thread for the entire browser process, and various
// pieces of code find it useful to retrieve a pointer to the IO thread's
// Invoke a task by thread ID:
//
// CefThread::PostTask(CefThread::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 CefThread : public base::Thread {
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 file system.
FILE,
// This is the thread that processes network and schema messages.
IO,
// 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
};
// Construct a CefThread with the supplied identifier. It is an error
// to construct a CefThread that already exists.
explicit CefThread(ID identifier);
// Special constructor for the main (UI) thread and unittests. We use a dummy
// thread here since the main thread already exists.
CefThread(ID identifier, MessageLoop* message_loop);
virtual ~CefThread();
// These methods are the same as in message_loop.h, but are guaranteed to
// either post the Task to the MessageLoop (if it's still alive), or to
// delete the Task otherwise.
// They return true if the thread existed and the task was posted. Note that
// even if the task is posted, there's no guarantee that it will run; for
// example the target loop may already be quitting, or in the case of a
// delayed task a Quit message may preempt it in the message loop queue.
// Conversely, a return value of false is a guarantee the task will not run.
static bool PostTask(ID identifier,
const tracked_objects::Location& from_here,
Task* task);
static bool PostDelayedTask(ID identifier,
const tracked_objects::Location& from_here,
Task* task,
int64 delay_ms);
static bool PostNonNestableTask(ID identifier,
const tracked_objects::Location& from_here,
Task* task);
static bool PostNonNestableDelayedTask(
ID identifier,
const tracked_objects::Location& from_here,
Task* task,
int64 delay_ms);
// TODO(ajwong): Remove the functions above once the Task -> Closure migration
// is complete.
//
// There are 2 sets of Post*Task functions, one which takes the older Task*
// function object representation, and one that takes the newer base::Closure.
// We have this overload to allow a staged transition between the two systems.
// Once the transition is done, the functions above should be deleted.
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,
int64 delay_ms);
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,
int64 delay_ms);
template <class T>
static bool DeleteSoon(ID identifier,
const tracked_objects::Location& from_here,
T* object) {
return PostNonNestableTask(
identifier, from_here, new DeleteTask<T>(object));
}
template <class T>
static bool ReleaseSoon(ID identifier,
const tracked_objects::Location& from_here,
T* object) {
return PostNonNestableTask(
identifier, from_here, new ReleaseTask<T>(object));
}
// Callable on any thread. Returns whether the given ID corresponds to a well
// known thread.
static bool IsWellKnownThread(ID identifier);
// Callable on any thread. Returns whether you're currently on a particular
// thread.
static bool CurrentlyOn(ID identifier);
// 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);
// Callers can hold on to a refcounted MessageLoopProxy beyond the lifetime
// of the thread.
static scoped_refptr<base::MessageLoopProxy> GetMessageLoopProxyForThread(
ID identifier);
// Use these templates in conjuction with RefCountedThreadSafe 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 -> FILE -> IO), and thread
// switching delays can mean that the final IO tasks executes before the FILE
// task's stack unwinds. This would lead to the object destructing on the
// FILE 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(T* x) {
if (CurrentlyOn(thread)) {
delete x;
} else {
DeleteSoon(thread, FROM_HERE, x);
}
}
};
// Sample usage:
// class Foo
// : public base::RefCountedThreadSafe<
// Foo, CefThread::DeleteOnIOThread> {
//
// ...
// private:
// friend class CefThread;
// friend class DeleteTask<Foo>;
//
// ~Foo();
struct DeleteOnUIThread : public DeleteOnThread<UI> { };
struct DeleteOnIOThread : public DeleteOnThread<IO> { };
struct DeleteOnFileThread : public DeleteOnThread<FILE> { };
private:
// Common initialization code for the constructors.
void Initialize();
static bool PostTaskHelper(
ID identifier,
const tracked_objects::Location& from_here,
Task* task,
int64 delay_ms,
bool nestable);
static bool PostTaskHelper(
ID identifier,
const tracked_objects::Location& from_here,
const base::Closure& task,
int64 delay_ms,
bool nestable);
// The identifier of this thread. Only one thread can exist with a given
// identifier at a given time.
ID identifier_;
// This lock protects |cef_threads_|. Do not read or modify that array
// without holding this lock. Do not block while holding this lock.
static base::Lock lock_;
// An array of the CefThread objects. This array is protected by |lock_|.
// The threads are not owned by this array. Typically, the threads are owned
// on the UI thread by the g_browser_process object. CefThreads remove
// themselves from this array upon destruction.
static CefThread* cef_threads_[ID_COUNT];
};
#define REQUIRE_UIT() DCHECK(CefThread::CurrentlyOn(CefThread::UI))
#define REQUIRE_IOT() DCHECK(CefThread::CurrentlyOn(CefThread::IO))
#endif // _CEF_THREAD_H