chromium/base/threading/simple_thread.h

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// WARNING: You should probably be using Thread (thread.h) instead.  Thread is
//          Chrome's message-loop based Thread abstraction, and if you are a
//          thread running in the browser, there will likely be assumptions
//          that your thread will have an associated message loop.
//
// This is a simple thread interface that backs to a native operating system
// thread.  You should use this only when you want a thread that does not have
// an associated MessageLoop.  Unittesting is the best example of this.
//
// The simplest interface to use is DelegateSimpleThread, which will create
// a new thread, and execute the Delegate's virtual Run() in this new thread
// until it has completed, exiting the thread.
//
// NOTE: You *MUST* call Join on the thread to clean up the underlying thread
// resources.  You are also responsible for destructing the SimpleThread object.
// It is invalid to destroy a SimpleThread while it is running, or without
// Start() having been called (and a thread never created).  The Delegate
// object should live as long as a DelegateSimpleThread.
//
// Thread Safety: A SimpleThread is not completely thread safe.  It is safe to
// access it from the creating thread or from the newly created thread.  This
// implies that the creator thread should be the thread that calls Join.
//
// Example:
//   class MyThreadRunner : public DelegateSimpleThread::Delegate { ... };
//   MyThreadRunner runner;
//   DelegateSimpleThread thread(&runner, "good_name_here");
//   thread.Start();
//   // Start will return after the Thread has been successfully started and
//   // initialized.  The newly created thread will invoke runner->Run(), and
//   // run until it returns.
//   thread.Join();  // Wait until the thread has exited.  You *MUST* Join!
//   // The SimpleThread object is still valid, however you may not call Join
//   // or Start again.

#ifndef BASE_THREADING_SIMPLE_THREAD_H_
#define BASE_THREADING_SIMPLE_THREAD_H_

#include <stddef.h>

#include <memory>
#include <string>
#include <vector>

#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/containers/queue.h"
#include "base/memory/raw_ptr.h"
#include "base/synchronization/lock.h"
#include "base/synchronization/waitable_event.h"
#include "base/threading/platform_thread.h"

namespace base {

// This is the base SimpleThread.  You can derive from it and implement the
// virtual Run method, or you can use the DelegateSimpleThread interface.
// SimpleThread should not be used to run a MessagePump, `base::Thread` must be
// used for that.
class BASE_EXPORT SimpleThread : public PlatformThread::Delegate { … };

// A SimpleThread which delegates Run() to its Delegate. Non-joinable
// DelegateSimpleThread are safe to delete after Run() was invoked, their
// Delegates are also safe to delete after that point from this class' point of
// view (although implementations must of course make sure that Run() will not
// use their Delegate's member state after its deletion).
class BASE_EXPORT DelegateSimpleThread : public SimpleThread { … };

// DelegateSimpleThreadPool allows you to start up a fixed number of threads,
// and then add jobs which will be dispatched to the threads.  This is
// convenient when you have a lot of small work that you want done
// multi-threaded, but don't want to spawn a thread for each small bit of work.
//
// You just call AddWork() to add a delegate to the list of work to be done.
// JoinAll() will make sure that all outstanding work is processed, and wait
// for everything to finish.  You can reuse a pool, so you can call Start()
// again after you've called JoinAll().
class BASE_EXPORT DelegateSimpleThreadPool
    : public DelegateSimpleThread::Delegate { … };

}  // namespace base

#endif  // BASE_THREADING_SIMPLE_THREAD_H_