muduo源码学习之Thread, EventLoopThread和 EventLoopThreadPool

---

本来没想看这一块, 但是看TCPServer class的时候里面用到了, 所以先总结一下这两个类的封装

功能

这三个类并不难理解, 没有很复杂的逻辑, 是对一些操作的简单封装
前面说了只要创建运行了EventLoop的线程就是 IO 线程, EventLoopThread是对 IO 线程的封装, EventLoopThreadPool是 IO 线程池, 负责创建和分发 IO 线程,

Thread class

介绍EventLoopThread之前, 先介绍一下Thread class, 在EventLoopThread有一个Thread类的对象

Thread.h

#ifndef MUDUO_BASE_THREAD_H
#define MUDUO_BASE_THREAD_H

#include 
#include 
#include 

#include 
#include 
#include 

namespace muduo
{

class Thread : noncopyable
{
 public:
  typedef std::function ThreadFunc;

  explicit Thread(ThreadFunc, const string& name = string()); //显示构造函数
  // FIXME: make it movable in C++11
  ~Thread();

  void start();
  int join(); // return pthread_join()

  bool started() const { return started_; }
  // pthread_t pthreadId() const { return pthreadId_; }
  pid_t tid() const { return tid_; }
  const string& name() const { return name_; }

  static int numCreated() { return numCreated_.get(); }

 private:
  void setDefaultName();

  bool       started_;
  bool       joined_;
  pthread_t  pthreadId_;
  pid_t      tid_;
  ThreadFunc func_;
  string     name_;
  CountDownLatch latch_;

  static AtomicInt32 numCreated_;
};

}  // namespace muduo
#endif  // MUDUO_BASE_THREAD_H

Thread.cc

#include 
#include 
#include 
#include 

#include 

#include 
#include 
#include 
#include 
#include 
#include 
#include 

namespace muduo
{
namespace detail
{

pid_t gettid()
{
  return static_cast(::syscall(SYS_gettid));
}

void afterFork()
{
  muduo::CurrentThread::t_cachedTid = 0;
  muduo::CurrentThread::t_threadName = "main";
  CurrentThread::tid();
  // no need to call pthread_atfork(NULL, NULL, &afterFork);
}

class ThreadNameInitializer
{
 public:
  ThreadNameInitializer()
  {
    muduo::CurrentThread::t_threadName = "main";
    CurrentThread::tid();
    pthread_atfork(NULL, NULL, &afterFork);
  }
};

ThreadNameInitializer init;

struct ThreadData
{
  typedef muduo::Thread::ThreadFunc ThreadFunc;
  ThreadFunc func_;
  string name_;
  pid_t* tid_;
  CountDownLatch* latch_;

  ThreadData(ThreadFunc func,
             const string& name,
             pid_t* tid,
             CountDownLatch* latch)
    : func_(std::move(func)),
      name_(name),
      tid_(tid),
      latch_(latch)
  { }

  void runInThread()
  {
    *tid_ = muduo::CurrentThread::tid();
    tid_ = NULL;
    latch_->countDown();
    latch_ = NULL;

    muduo::CurrentThread::t_threadName = name_.empty() ? "muduoThread" : name_.c_str();
    ::prctl(PR_SET_NAME, muduo::CurrentThread::t_threadName);
    try
    {
      func_(); //执行指定的线程函数,即 EventLoopThread::threadFunc
      muduo::CurrentThread::t_threadName = "finished";
    }
    catch (const Exception& ex)
    {
      muduo::CurrentThread::t_threadName = "crashed";
      fprintf(stderr, "exception caught in Thread %s\n", name_.c_str());
      fprintf(stderr, "reason: %s\n", ex.what());
      fprintf(stderr, "stack trace: %s\n", ex.stackTrace());
      abort();
    }
    catch (const std::exception& ex)
    {
      muduo::CurrentThread::t_threadName = "crashed";
      fprintf(stderr, "exception caught in Thread %s\n", name_.c_str());
      fprintf(stderr, "reason: %s\n", ex.what());
      abort();
    }
    catch (...)
    {
      muduo::CurrentThread::t_threadName = "crashed";
      fprintf(stderr, "unknown exception caught in Thread %s\n", name_.c_str());
      throw; // rethrow
    }
  }
};

void* startThread(void* obj)
{
  ThreadData* data = static_cast(obj);
  data->runInThread();
  delete data;
  return NULL;
}

}  // namespace detail

void CurrentThread::cacheTid()
{
  if (t_cachedTid == 0)
  {
    t_cachedTid = detail::gettid();
    t_tidStringLength = snprintf(t_tidString, sizeof t_tidString, "%5d ", t_cachedTid);
  }
}

bool CurrentThread::isMainThread()
{
  return tid() == ::getpid();
}

void CurrentThread::sleepUsec(int64_t usec)
{
  struct timespec ts = { 0, 0 };
  ts.tv_sec = static_cast(usec / Timestamp::kMicroSecondsPerSecond);
  ts.tv_nsec = static_cast(usec % Timestamp::kMicroSecondsPerSecond * 1000);
  ::nanosleep(&ts, NULL);
}

AtomicInt32 Thread::numCreated_;

Thread::Thread(ThreadFunc func, const string& n)
  : started_(false),
    joined_(false),
    pthreadId_(0),
    tid_(0),
    func_(std::move(func)),
    name_(n),
    latch_(1)
{
  setDefaultName();
}

Thread::~Thread()
{
  if (started_ && !joined_)
  {
    pthread_detach(pthreadId_);
  }
}

void Thread::setDefaultName()
{
  int num = numCreated_.incrementAndGet();
  if (name_.empty())
  {
    char buf[32];
    snprintf(buf, sizeof buf, "Thread%d", num);
    name_ = buf;
  }
}

//EventLoopThread::startLoop会调用该函数( thread_::start() )
//func_变量在EventLoopThread的构造函数中被指定为EventLoopThread::threadFunc

void Thread::start()
{
  assert(!started_);
  started_ = true;
  // FIXME: move(func_)
  //创建一个ThreadData类对象,其中保存有被指定的线程函数EventLoopThread::threadFunc
  //再将该对象传入创建的线程中
  //在该线程中执行被指定的线程函数
  detail::ThreadData* data = new detail::ThreadData(func_, name_, &tid_, &latch_);
  if (pthread_create(&pthreadId_, NULL, &detail::startThread, data))
  {
    started_ = false;
    delete data; // or no delete?
    LOG_SYSFATAL << "Failed in pthread_create";
  }
  else
  {
    latch_.wait();
    assert(tid_ > 0);
  }
}

int Thread::join()
{
  assert(started_);
  assert(!joined_);
  joined_ = true;
  return pthread_join(pthreadId_, NULL);
}

}  // namespace muduo

在EventLoopThread::startLoop中会调用Thread::start(), 并执行在EventLoopThread中指定的线程函数

EventLoopThread

IO 线程不一定是主线程, 我们可以在任意一个线程中创建并运行EventLoopThread, 一个程序也可以拥有不止一个 IO 线程, EventLoopThread会启动自己的线程, 并运行EventLoop::loop
主线程创建EventLoopThread对象, 调用EventLoopThread::startLoop()创建 IO 线程, 该函数会等待 IO 线程创建完成才返回

EventLoopThread.h

#ifndef MUDUO_NET_EVENTLOOPTHREAD_H
#define MUDUO_NET_EVENTLOOPTHREAD_H

#include 
#include 
#include 

namespace muduo
{
namespace net
{

class EventLoop;

class EventLoopThread : noncopyable
{
 public:
  typedef std::function ThreadInitCallback;

  EventLoopThread(const ThreadInitCallback& cb = ThreadInitCallback(),
                  const string& name = string());
  ~EventLoopThread();
  EventLoop* startLoop(); //启动线程,该线程成为IO线程
 
 private:
  void threadFunc();  //线程函数

  EventLoop* loop_ GUARDED_BY(mutex_);  //指向一个EventLoop对象
  bool exiting_;
  Thread thread_; //Thread是对线程的一些操作进行封装
  MutexLock mutex_;
  Condition cond_ GUARDED_BY(mutex_);
  ThreadInitCallback callback_;
};

}  // namespace net
}  // namespace muduo

#endif  // MUDUO_NET_EVENTLOOPTHREAD_H

EventLoopThread.cc

#include 

#include 

using namespace muduo;
using namespace muduo::net;
 
EventLoopThread::EventLoopThread(const ThreadInitCallback& cb,
                                 const string& name)
  : loop_(NULL),
    exiting_(false),
    //将线程函数绑定为threadFunc
    thread_(std::bind(&EventLoopThread::threadFunc, this), name), 
    mutex_(),
    cond_(mutex_),
    callback_(cb)
{
}

EventLoopThread::~EventLoopThread()
{
  exiting_ = true;
  if (loop_ != NULL) // not 100% race-free, eg. threadFunc could be running callback_.
  {
    // still a tiny chance to call destructed object, if threadFunc exits just now.
    // but when EventLoopThread destructs, usually programming is exiting anyway.
    loop_->quit();
    thread_.join();
  }
}

EventLoop* EventLoopThread::startLoop()
{
  assert(!thread_.started());
 //在Thread::start中执行指定的线程函数,即EventLoopThread::threadFunc,
  //创建EventLoop对象
  thread_.start();

  EventLoop* loop = NULL;
  {
    MutexLockGuard lock(mutex_);
    while (loop_ == NULL)
    {
      //需要等待直到指定的EventLoop对象被创建
      cond_.wait();
    }
    loop = loop_;
  }

  //返回一个指向栈上对象的EventLoop指针
  return loop;
}

void EventLoopThread::threadFunc()
{
  EventLoop loop;

  if (callback_)
  {
    //该回调函数callback_由TcpServer::setThreadInitCallback()指定
    ///需要由用户手动指定
    //没有就不执行
    callback_(&loop);
  }

  {
    MutexLockGuard lock(mutex_);
    //loop_指向一个栈上的局部变量,因为该函数退出,意味着线程结束了,那么EventLoopThread对象也就没有存在价值了
    loop_ = &loop;
    //创建好了,发送通知
    cond_.notify();
  }

  //在这里循环,知道EventLoopThread析构,然后也不会再用loop_访问EventLoop了
  loop.loop();
  //assert(exiting_);
  MutexLockGuard lock(mutex_);
  loop_ = NULL;
}

EventLoop* EventLoopThread::startLoop()返回的是创建的EventLoop对象 (位于栈上) 的指针, 这样我们在主线程调用该函数拿到的就是指向创建的 IO 线程的指针,然后就向上一片博客中介绍的那样, 可以调用EventLoop::runInLoop来执行任务

EventLoopThreadPool

IO线程池创建分发 IO 线程

EventLoopThreadPool.h

#ifndef MUDUO_NET_EVENTLOOPTHREADPOOL_H
#define MUDUO_NET_EVENTLOOPTHREADPOOL_H

#include 
#include 

#include 
#include 
#include 

namespace muduo
{

namespace net
{

class EventLoop;
class EventLoopThread;

class EventLoopThreadPool : noncopyable
{
 public:
  typedef std::function ThreadInitCallback;

  EventLoopThreadPool(EventLoop* baseLoop, const string& nameArg);
  ~EventLoopThreadPool();
  //设置线程池线程数目
  void setThreadNum(int numThreads) { numThreads_ = numThreads; }
  void start(const ThreadInitCallback& cb = ThreadInitCallback());

  // valid after calling start()
  /// round-robin
  EventLoop* getNextLoop();

  /// with the same hash code, it will always return the same EventLoop
  EventLoop* getLoopForHash(size_t hashCode);

  std::vector getAllLoops();

  bool started() const
  { return started_; }

  const string& name() const
  { return name_; }

 private:

  EventLoop* baseLoop_;
  string name_;
  bool started_;
  int numThreads_;  //线程数
  int next_;        //有新连接到来时需要选择的新的EventLoop对象的下标
  std::vector> threads_; //IO线程列表
  std::vector loops_; 
};

}  // namespace net
}  // namespace muduo

#endif  // MUDUO_NET_EVENTLOOPTHREADPOOL_H

EventLoopThreadPool.cc

主要是其start函数

#include 

#include 
#include 

#include 

using namespace muduo;
using namespace muduo::net;

EventLoopThreadPool::EventLoopThreadPool(EventLoop* baseLoop, const string& nameArg)
  : baseLoop_(baseLoop),
    name_(nameArg),
    started_(false),
    numThreads_(0),
    next_(0)
{
}

EventLoopThreadPool::~EventLoopThreadPool()
{
  // Don't delete loop, it's stack variable
}

void EventLoopThreadPool::start(const ThreadInitCallback& cb)
{
  assert(!started_);
  baseLoop_->assertInLoopThread();

  started_ = true;

  for (int i = 0; i < numThreads_; ++i)
  {
    char buf[name_.size() + 32];
    snprintf(buf, sizeof buf, "%s%d", name_.c_str(), i);
    //由TCPServer::start中调用该函数时传入cb
    //创建一个IO线程并运行
    EventLoopThread* t = new EventLoopThread(cb, buf);
    //压入IO线程列表
    threads_.push_back(std::unique_ptr(t));
    //t->startLoop函数返回一个栈上的EventLoop对象指针
    loops_.push_back(t->startLoop());
  }
  //只有一个EventLoop,在其进入循环之前,调用cb
  if (numThreads_ == 0 && cb)
  {
    cb(baseLoop_);
  }
}

EventLoop* EventLoopThreadPool::getNextLoop()
{
  baseLoop_->assertInLoopThread();
  assert(started_);
  EventLoop* loop = baseLoop_;

  if (!loops_.empty())
  {
    // round-robin
    loop = loops_[next_];
    ++next_;
    if (implicit_cast(next_) >= loops_.size())
    {
      next_ = 0;
    }
  }
  return loop;
}

EventLoop* EventLoopThreadPool::getLoopForHash(size_t hashCode)
{
  baseLoop_->assertInLoopThread();
  EventLoop* loop = baseLoop_;

  if (!loops_.empty())
  {
    loop = loops_[hashCode % loops_.size()];
  }
  return loop;
}

std::vector EventLoopThreadPool::getAllLoops()
{
  baseLoop_->assertInLoopThread();
  assert(started_);
  if (loops_.empty())
  {
    return std::vector(1, baseLoop_);
  }
  else
  {
    return loops_;
  }
}

上面介绍过了, EventLoopThread创建号 IO 线程后直接执行loop函数进入循环, EventLoopThreadPool创建 IO 线程, 保存他们的指针