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// Copyright (c) 2006-2008 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 CHROME_BROWSER_CHROME_THREAD_H__
#define CHROME_BROWSER_CHROME_THREAD_H__
#include "base/lock.h"
#include "base/logging.h"
#include "base/thread.h"
///////////////////////////////////////////////////////////////////////////////
// ChromeThread
//
// 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
// MessageLoop by name:
//
// MessageLoop* io_loop = ChromeThread::GetMessageLoop(ChromeThread::IO);
//
// On the UI thread, it is often preferable to obtain a pointer to a well-known
// thread via the g_browser_process object, e.g. g_browser_process->io_thread();
//
// Code that runs on a thread other than the UI thread must take extra care in
// handling pointers to threads because many of the well-known threads are owned
// by the UI thread and can be deallocated without notice.
//
class ChromeThread : public base::Thread {
public:
// An enumeration of the well-known threads.
enum ID {
// This is the thread that processes IPC and network messages.
IO,
// This is the thread that interacts with the file system.
FILE,
// This is the thread that interacts with the database.
DB,
// This is the thread that interacts with the history database.
HISTORY,
// 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 ChromeThread with the supplied identifier. It is an error
// to construct a ChromeThread that already exists.
explicit ChromeThread(ID identifier);
virtual ~ChromeThread();
// Callable on any thread, this helper function returns a pointer to the
// thread's MessageLoop.
//
// WARNING:
// Nothing in this class prevents the MessageLoop object returned from this
// function from being destroyed on another thread. Use with care.
//
static MessageLoop* GetMessageLoop(ID identifier);
private:
// The identifier of this thread. Only one thread can exist with a given
// identifier at a given time.
ID identifier_;
// This lock protects |chrome_threads_|. Do not read or modify that array
// without holding this lock. Do not block while holding this lock.
static Lock lock_;
// An array of the ChromeThread objects. This array is protected by |lock_|.
// The threads are not owned by this array. Typically, the threads are owned
// on the IU thread by the g_browser_process object. ChromeThreads remove
// themselves from this array upon destruction.
static ChromeThread* chrome_threads_[ID_COUNT];
};
#endif // #ifndef CHROME_BROWSER_CHROME_THREAD_H__
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