muduo网络库学习之MutexLock类、MutexLockGuard类、Condition类、CountDownLatch类封装中的知识点

一、MutexLock 类

class MutexLock : boost::noncopyable

二、MutexLockGuard类

class MutexLockGuard : boost::noncopyable

三、Condition类

class Condition : boost::noncopyable

某个线程：加锁 while (条件) wait(); //1、解锁；2、等待通知；3、得到通知返回前重新加锁解锁
另一个线程：加锁 更改条件 通知notify（可以移到锁外）解锁

四、CountDownLatch类

class CountDownLatch : boost::noncopyable

既可以用于所有子线程等待主线程发起 “起跑”
也可以用于主线程等待子线程初始化完毕才开始工作

下面写两个程序测试一下CountDownLatch 的作用：

CountDownLatch_test1: C++ Code 1
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#include <muduo/base/CountDownLatch.h>
#include <muduo/base/Thread.h>

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

using namespace muduo;

class Test
{
public:
Test(int numThreads)
: latch_(1),
threads_(numThreads)
{
for (int i = 0; i < numThreads; ++i)
{
char name[32];
snprintf(name, sizeof name, "work thread %d", i);
threads_.push_back(new muduo::Thread(
boost::bind(&Test::threadFunc, this), muduo::string(name)));
}
for_each(threads_.begin(), threads_.end(), boost::bind(&Thread::start, _1));
}

void run()
{
latch_.countDown();
}

void joinAll()
{
for_each(threads_.begin(), threads_.end(), boost::bind(&Thread::join, _1));
}

private:

void threadFunc()
{
latch_.wait();
printf("tid=%d, %s started\n",
CurrentThread::tid(),
CurrentThread::name());



printf("tid=%d, %s stopped\n",
CurrentThread::tid(),
CurrentThread::name());
}

CountDownLatch latch_;
boost::ptr_vector<Thread> threads_;
};

int main()
{
printf("pid=%d, tid=%d\n", ::getpid(), CurrentThread::tid());
Test t(3);
sleep(3);
printf("pid=%d, tid=%d %s running ...\n", ::getpid(), CurrentThread::tid(), CurrentThread::name());
t.run();
t.joinAll();

printf("number of created threads %d\n", Thread::numCreated());
}



执行结果如下：

simba@ubuntu:~/Documents/build/debug/bin$ ./countdownlatch_test1
pid=2994, tid=2994
pid=2994, tid=2994 main running ...
tid=2997, work thread 2 started
tid=2997, work thread 2 stopped
tid=2996, work thread 1 started
tid=2996, work thread 1 stopped
tid=2995, work thread 0 started
tid=2995, work thread 0 stopped
number of created threads 3
simba@ubuntu:~/Documents/build/debug/bin$

可以看到其他三个线程一直等到主线程睡眠完执行run()，在里面执行latch_.countDown() 将计数减为0，进而执行notifyall 唤醒后，才开始执行下来。

CountDownLatch_test2: C++ Code 1
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#include <muduo/base/CountDownLatch.h>
#include <muduo/base/Thread.h>

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

using namespace muduo;

class Test
{
public:
Test(int numThreads)
: latch_(numThreads),
threads_(numThreads)
{
for (int i = 0; i < numThreads; ++i)
{
char name[32];
snprintf(name, sizeof name, "work thread %d", i);
threads_.push_back(new muduo::Thread(
boost::bind(&Test::threadFunc, this), muduo::string(name)));
}
for_each(threads_.begin(), threads_.end(), boost::bind(&muduo::Thread::start, _1));
}

void wait()
{
latch_.wait();
}

void joinAll()
{
for_each(threads_.begin(), threads_.end(), boost::bind(&Thread::join, _1));
}

private:

void threadFunc()
{
sleep(3); printf("tid=%d, %s started\n",
CurrentThread::tid(),
CurrentThread::name());
latch_.countDown();


printf("tid=%d, %s stopped\n",
CurrentThread::tid(),
CurrentThread::name());
}

CountDownLatch latch_;
boost::ptr_vector<Thread> threads_;
};

int main()
{
printf("pid=%d, tid=%d\n", ::getpid(), CurrentThread::tid());
Test t(3);
t.wait();
printf("pid=%d, tid=%d %s running ...\n", ::getpid(), CurrentThread::tid(), CurrentThread::name());
t.joinAll();

printf("number of created threads %d\n", Thread::numCreated());
}



执行结果输出如下：

simba@ubuntu:~/Documents/build/debug/bin$ ./countdownlatch_test2
pid=4488, tid=4488
tid=4491, work thread 2 started
tid=4491, work thread 2 stopped
tid=4490, work thread 1 started
tid=4490, work thread 1 stopped
tid=4489, work thread 0 started
pid=4488, tid=4488 main running ...
tid=4489, work thread 0 stopped
number of created threads 3

可以看出当其他三个线程都启动后，各自执行一次 latch_.countDown()，主线程wait() 返回继续执行下去。

参考：muduo manual.pdf《linux 多线程服务器编程：使用muduo c++网络库》