Muduo学习笔记(一) 什么都不做的EventLoop

Muduo学习笔记(一) 什么都不做的EventLoop

EventLoop

EventLoop的基本接口包括构造、析构、loop()。

One Loop Per Thread 一个线程只有一个EventLoop对象、如果当前线程创建了其他 EventLoop对象,则终止程序.

CurrentThread

CurrentThread 通过__thread 关键字和系统调用syscall() 保存获取线程的的pid(不通于线程tid，tid属于进程,进程内唯一,线程pid属于内核).

#ifndef _CURRENT_THREAD
#define _CURRENT_THREAD
#include <stdint.h>
#include <stdio.h>
#include <sys/syscall.h>
#include <pthread.h>
#include <unistd.h>
namespace CurrentThread
{
  // internal
  extern __thread int t_cachedTid;
  extern __thread char t_tidString[32];
  extern __thread int t_tidStringLength;
  extern __thread const char* t_threadName;
  inline int tid()
  {
    if (__builtin_expect(t_cachedTid == 0, 0))
    {
      if (t_cachedTid == 0)
      {
        t_cachedTid = static_cast<pid_t>(::syscall(SYS_gettid));
        t_tidStringLength = snprintf(t_tidString, sizeof t_tidString, "%5d ", t_cachedTid);
      }
    }
    return t_cachedTid;
  }
  inline const char* tidString() // for logging
  {
    return t_tidString;
  }
  inline int tidStringLength() // for logging
  {
    return t_tidStringLength;
  }
  inline const char* name()
  {
    return t_threadName;
  }
}
#endif
//CurrentThread.cpp
#include "CurrentThread.hh"
namespace CurrentThread
{
  __thread int t_cachedTid = 0;
  __thread char t_tidString[32];
  __thread int t_tidStringLength = 6;
  __thread const char* t_threadName = "unknown";
}

getEventLoopOfCurrentThread

每个线程至多有一个EventLoop对象,那么我们通过static 成员函数getEventLoopOfCurrentThread() 返回此对象.

EventLoop* EventLoop::getEventLoopOfCurrentThread()
{
  return t_loopInThisThread;
}

EventLoop 源代码

#ifndef NET_EVENTLOOP_H
#define NET_EVENTLOOP_H
#include "CurrentThread.hh"
class EventLoop
{
public:
	EventLoop();
	~EventLoop();
	void loop();
	void assertInLoopThread()
	{
		if(!isInloopThread())
		{
			abortNotInLoopThread();
		}
	}
	bool isInloopThread() const {return m_threadId == CurrentThread::tid(); }
	static EventLoop* getEventLoopOfCurrentThread();
private:
	EventLoop& operator=(const EventLoop&);
	EventLoop(const EventLoop&);
	void abortNotInLoopThread();
	bool m_looping;
	const pid_t m_threadId;
};
#endif
// EventLoop.cpp
#include "EventLoop.hh"
#include "Logger.hh"
#include <assert.h>
#include <poll.h>
__thread EventLoop* t_loopInThisThread = 0;
EventLoop::EventLoop()
	:m_looping(false),
  m_threadId(CurrentThread::tid())
{
  LOG_TRACE << "EventLoop Create " << this << " in thread " << m_threadId;
  if(t_loopInThisThread)
  {  //每个线程只有一个EventLoop对象 , 如果当前线程创建了其他 EventLoop对象,则终止程序.
    LOG_FATAL << "Anthor EventLoop " << t_loopInThisThread
              << " exists in this thread " << m_threadId;
  }
  else
  {
    t_loopInThisThread = this;
  }
}
EventLoop::~EventLoop()
{
  assert(!m_looping);
  t_loopInThisThread = NULL;
}
void EventLoop::loop()
{
  assert(!m_looping);
  assertInLoopThread();
  m_looping = true;
  LOG_TRACE << "EventLoop " << this << " start loopig";
  ::poll(NULL, 0, 3*1000);
  LOG_TRACE << "EventLoop " << this << " stop loopig";
  m_looping = false;
}
void EventLoop::abortNotInLoopThread()
{
  LOG_FATAL << "EventLoop::abortNotInLoopThread - EventLoop " << this
            << " was created in threadId_ = " << m_threadId
            << ", current thread id = " <<  CurrentThread::tid();
}
EventLoop* EventLoop::getEventLoopOfCurrentThread()
{
  return t_loopInThisThread;
}

测试程序

test1

正确的逻辑.

#include <errno.h>
#include "EventLoop.hh"
#include <thread>
int main()
{
  EventLoop testloop;
  testloop.loop();
  return 0;
}

./test.out
2018-10-25 20:01:03.287601 [TRACE] [EventLoop.cpp:12] [EventLoop] EventLoop Create 0x7FFF7B1E2780 in thread 2086
2018-10-25 20:01:03.287750 [TRACE] [EventLoop.cpp:36] [loop] EventLoop 0x7FFF7B1E2780 start loopig
2018-10-25 20:01:06.291622 [TRACE] [EventLoop.cpp:40] [loop] EventLoop 0x7FFF7B1E2780 stop loopig

test2

企图在当前线程启用其他线程创建的EventLoop对象

#include <errno.h>
#include "EventLoop.hh"
#include <thread>
EventLoop* g_loop;
void test()
{
  g_loop->loop();
}
int main()
{
  EventLoop testloop;
  //testloop.loop();
  g_loop = &testloop;
  std::thread test_thread(test);
  test_thread.join();
  return 0;
}

./test.out
2018-10-25 20:05:49.618701 [TRACE] [EventLoop.cpp:12] [EventLoop] EventLoop Create 0x7FFCA55A35F0 in thread 2114
2018-10-25 20:05:49.619057 [FATAL] [EventLoop.cpp:47] EventLoop::abortNotInLoopThread - EventLoop 0x7FFCA55A35F0 was created in threadId_ = 2114, current thread id = 2115
Aborted (core dumped)