muduo网络库源码学习————线程类

muduo库里面的线程类是使用基于对象的编程思想，源码目录为muduo/base，如下所示：

线程类头文件：

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)
//线程类
#ifndef MUDUO_BASE_THREAD_H
#define MUDUO_BASE_THREAD_H

#include <muduo/base/Atomic.h>
#include <muduo/base/Types.h>

#include <boost/function.hpp>
#include <boost/noncopyable.hpp>
#include <pthread.h>
//线程类头文件
namespace muduo
{

class Thread : boost::noncopyable
{
 public:
  typedef boost::function<void ()> ThreadFunc;//函数适配接收的函数
//线程构造函数，参数为回调函数和线程名称
  explicit Thread(const ThreadFunc&, const string& name = string());//名称默认值为空的字符串类
//线程析构函数
  ~Thread();
  void start();//启动线程
  int join(); // return pthread_join()
  bool started() const { return started_; }//线程是否已经启动
  // pthread_t pthreadId() const { return pthreadId_; }
  pid_t tid() const { return tid_; }//线程的真实pid
  const string& name() const { return name_; }//线程的名称
  static int numCreated() { return numCreated_.get(); }//已经启动的线程个数

 private:
  static void* startThread(void* thread);//现成的入口函数，调用runInThread函数
  void runInThread();//调用回调函数func_
  bool       started_;//线程是否已经启动
  pthread_t  pthreadId_;//线程的pthread_t
  pid_t      tid_;//线程真实的 pid
  ThreadFunc func_;//线程的回调函数
  string     name_;//线程的名称
  static AtomicInt32 numCreated_;//已经创建的线程的个数，每当创建一个线程，该值就加一(原子整数类)
};

}
#endif

线程类的实现文件：

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)
//线程类实现文件
#include <muduo/base/Thread.h>
#include <muduo/base/CurrentThread.h>
#include <muduo/base/Exception.h>
//#include <muduo/base/Logging.h>
//暂时不用日志文件，先注释掉
#include <boost/static_assert.hpp>
#include <boost/type_traits/is_same.hpp>

#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <linux/unistd.h>

namespace muduo
{
namespace CurrentThread
{//__thread两个下划线是gcc 内置的线程局部存储设施
//每个线程各有一个，并不会去共享他
//缓存获取tid是为了提高获取tid的效率
  __thread int t_cachedTid = 0;//线程真实pid的缓存，如果每次都用系统调用去获取pid,效率会低
  __thread char t_tidString[32];//tid的字符串表示形式
  __thread const char* t_threadName = "unknown";//线程的名称
  const bool sameType = boost::is_same<int, pid_t>::value;//如果是相同类型，返回true
  BOOST_STATIC_ASSERT(sameType);//编译时断言
}

namespace detail
{

pid_t gettid()//通过系统调用SYS_gettid获得tid
{
  return static_cast<pid_t>(::syscall(SYS_gettid));//类型转化为pid_t
}

void afterFork()//子进程调用的
{
  muduo::CurrentThread::t_cachedTid = 0;//当前线程pid赋值0
  muduo::CurrentThread::t_threadName = "main";//名称赋值name
  CurrentThread::tid();//进行缓存
  // no need to call pthread_atfork(NULL, NULL, &afterFork);
}

class ThreadNameInitializer
{
 public:
  ThreadNameInitializer()//构造函数
  {
    muduo::CurrentThread::t_threadName = "main";//线程名称赋为main，即为主线程名称
    CurrentThread::tid();//缓存当前线程的pid
    //#include <pthread.h>
    //int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));
      //调用fork时，内部创建子进程前在父进程中会调用prepare，
      //内部创建子进程成功后，父进程会调用parent ，子进程会调用child
    pthread_atfork(NULL, NULL, &afterFork);//如果使用fork函数，那么子进程会调用邋afterFork
  }
};

ThreadNameInitializer init;
}
}

using namespace muduo;

void CurrentThread::cacheTid()
{
  if (t_cachedTid == 0)
  {
    t_cachedTid = detail::gettid();//调用gettid函数获得tid
    int n = snprintf(t_tidString, sizeof t_tidString, "%5d ", t_cachedTid);//将tid格式化保存在t_tidString中
    assert(n == 6);//断言长度是6，5d后面还有一个空格，所以是6
    (void) n;//这一句主要是预防n没有使用从而产生警告
  }
}

bool CurrentThread::isMainThread()
{
  return tid() == ::getpid();//查看tid是否等于当前进程id
}

AtomicInt32 Thread::numCreated_;
//构造函数，初始化
Thread::Thread(const ThreadFunc& func, const string& n) : started_(false), pthreadId_(0),tid_(0),func_(func),name_(n)
{
  numCreated_.increment();//创建的线程的个数加一，为原子性操作
}

Thread::~Thread()
{
  // no join
}

void Thread::start()
{
  assert(!started_);
  started_ = true;
  //创建线程，startThread为线程的入口函数
  errno = pthread_create(&pthreadId_, NULL, &startThread, this);
  if (errno != 0)
  {//日志
   // LOG_SYSFATAL << "Failed in pthread_create";
  }
}

int Thread::join()
{
  assert(started_);
  return pthread_join(pthreadId_, NULL);
}
//线程的入口函数
void* Thread::startThread(void* obj)
{//this指针传到obj
  Thread* thread = static_cast<Thread*>(obj);//转化为线程基类的指针
  thread->runInThread();//调用线程函数runInThread
  return NULL;
}
//被线程的入口函数调用
void Thread::runInThread()
{
  tid_ = CurrentThread::tid();//获取线程的tid
  muduo::CurrentThread::t_threadName = name_.c_str();//缓存该线程的名称
  try
  {
    func_();//调用回调函数
    muduo::CurrentThread::t_threadName = "finished";
  }
  catch (const Exception& ex)//异常捕捉
  {
    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
  }
}

CurrentThread头文件

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_CURRENTTHREAD_H
#define MUDUO_BASE_CURRENTTHREAD_H

namespace muduo
{//CurrentThread的名称空间
namespace CurrentThread
{
  // internal
  extern __thread int t_cachedTid;
  extern __thread char t_tidString[32];
  extern __thread const char* t_threadName;
  void cacheTid();

  inline int tid()
  {
    if (t_cachedTid == 0)//还没有缓存过
    {//t_cachedTid初值 是0
      cacheTid();//进行缓存
    }
    return t_cachedTid;//返回缓存的tid
  }

  inline const char* tidString() // for logging
  {
    return t_tidString;//返回tid的字符串表示形式
  }

  inline const char* name()
  {
    return t_threadName;//返回线程名称
  }

  bool isMainThread();//是否是主线程
}
}

#endif

测试代码位于muduo/base/tests

//线程测试程序
#include <muduo/base/Thread.h>
#include <muduo/base/CurrentThread.h>

#include <string>
#include <boost/bind.hpp>
#include <stdio.h>

void threadFunc()
{
  printf("tid=%d\n", muduo::CurrentThread::tid());
}

void threadFunc2(int x)
{
  printf("tid=%d, x=%d\n", muduo::CurrentThread::tid(), x);
}

class Foo
{
 public:
  explicit Foo(double x) : x_(x)
  {
  }

  void memberFunc()
  {
    printf("tid=%d, Foo::x_=%f\n", muduo::CurrentThread::tid(), x_);
  }

  void memberFunc2(const std::string& text)
  {
    printf("tid=%d, Foo::x_=%f, text=%s\n", muduo::CurrentThread::tid(), x_, text.c_str());
  }

 private:
  double x_;
};

int main()
{//获取当前线程的pid(进程id 线程pid)
  printf("pid=%d, tid=%d\n", ::getpid(), muduo::CurrentThread::tid());
//创建一个线程对象，传递一个函数
  muduo::Thread t1(threadFunc);
  t1.start();//启动线程
  t1.join();
//threadFunc2带了一个参数，用boost::bind函数传递进去，最后是线程的名称，可以不传
  muduo::Thread t2(boost::bind(threadFunc2, 42), "thread for free function with argument");
  t2.start();
  t2.join();
//创建一个对象
  Foo foo(87.53);
//创建第三个线程(成员函数的话一定要用&)
  muduo::Thread t3(boost::bind(&Foo::memberFunc, &foo), "thread for member function without argument");
  t3.start();
  t3.join();
//创建第四个线程，这里传进去的函数是带参数的
  muduo::Thread t4(boost::bind(&Foo::memberFunc2, boost::ref(foo), std::string("Shuo Chen")));
  t4.start();
  t4.join();
//打印最后创建的线程总数
  printf("number of created threads %d\n", muduo::Thread::numCreated());
}

单独编译后运行结果如下：