作为一个c++菜鸟，研究半天这个代码的实现原理，发现好多语法不太熟悉，因此加了一大堆注释，仅供参考。该段代码主要通过继承workthread类来实现自己的线程代码，通过thread_pool类来管理线程池，线程池不能够实现动态改变线程数目，存在一定局限性。目前可能还有缺陷，毕竟c++来封装这个东西，资源释放什么的必须想清楚，比如vector存储了基类指针实现多态，那么如何释放对象仍需要考虑，后续我可能会更进一步修改完善该代码，下面贡献一下自己的劳动成果。
#include <pthread.h>
#include <semaphore.h>
#include <iostream>
#include <vector>
using namespace std;
/*
WorkerThread class
This class needs to be sobclassed by the user.
*/
class WorkerThread{
public:
int id;
unsigned virtual executeThis()
{
return 0;
}
WorkerThread(int id) : id(id) {}
virtual ~WorkerThread(){}
};
/*
ThreadPool class manages all the ThreadPool related activities. This includes keeping track of idle threads and synchronizations between all threads.
*/
class ThreadPool{
public:
ThreadPool();
ThreadPool(int maxThreadsTemp);
virtual ~ThreadPool();
void destroyPool(int maxPollSecs);
bool assignWork(WorkerThread *worker);
bool fetchWork(WorkerThread **worker);
void initializeThreads();
static void *threadExecute(void *param); // pthread_create()调用的函数必须为静态的
static pthread_mutex_t mutexSync;
static pthread_mutex_t mutexWorkCompletion;//工作完成个数互斥量
private:
int maxThreads;
pthread_cond_t condCrit;
sem_t availableWork;
sem_t availableThreads;
vector<WorkerThread *> workerQueue;
int topIndex;
int bottomIndex;
int incompleteWork;
int queueSize;
};
#include <stdlib.h>
#include "threadpool.h"
using namespace std;
//初始化类的静态成员必须加上类型和作用域，static数据成员必须在类定义体的外部定义，不像不同数据成员可以用构造函数初始化
//应该在定义时进行初始化，注意是定义，这个定义应该放在包含类的非内联成员函数定义的文件中。
//注：静态成员函数只能使用静态变量，非静态没有限制，静态变量必须在外部定义和初始化，没初始化就为默认数值
pthread_mutex_t ThreadPool::mutexSync = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t ThreadPool::mutexWorkCompletion = PTHREAD_MUTEX_INITIALIZER;
ThreadPool::ThreadPool()
{
ThreadPool(2);
}
ThreadPool::ThreadPool(int maxThreads)
{
if (maxThreads < 1)
maxThreads=1;
pthread_mutex_lock(&mutexSync);
this->maxThreads = maxThreads;
this->queueSize = maxThreads;
workerQueue.resize(maxThreads, NULL);//调整容器大小，然后用默认构造函数初始化新的空间
topIndex = 0;
bottomIndex = 0;
incompleteWork = 0;
sem_init(&availableWork, 0, 0); //工作队列信号量，表示已经加入队列的工作，初始时没有工作
sem_init(&availableThreads, 0, queueSize); //空闲线程信号量，一开始就有quisize个线程可以使用
pthread_mutex_unlock(&mutexSync);
}
//调用pthread_create()让线程跑起来，threadExecute是类的静态函数，因为pthread_create()第三个参数必须为静态函数
void ThreadPool::initializeThreads()
{
for(int i = 0; i<maxThreads; ++i)
{
pthread_t tempThread;
pthread_create(&tempThread, NULL, ThreadPool::threadExecute, (void*)this );
}
}
ThreadPool::~ThreadPool()
{
//因为对于vector，clear并不真正释放内存(这是为优化效率所做的事)，clear实际所做的是为vector中所保存的所有对象调用析构函数(如果有的话),
//然后初始化size这些东西，让你觉得把所有的对象清除了。。。
//真正释放内存是在vector的析构函数里进行的，所以一旦超出vector的作用域（如函数返回)，首先它所保存的所有对象会被析构，
//然后会调用allocator中的deallocate函数回收对象本身的内存。。。
workerQueue.clear();
}
void ThreadPool::destroyPool(int maxPollSecs = 2)
{
while(incompleteWork>0 )
{
//cout << "Work is still incomplete=" << incompleteWork << endl;
sleep(maxPollSecs);
}
cout << "All Done!! Wow! That was a lot of work!" << endl;
sem_destroy(&availableWork);
sem_destroy(&availableThreads);
pthread_mutex_destroy(&mutexSync);
pthread_mutex_destroy(&mutexWorkCompletion);
}
//分配人物到top，然后通知有任务需要执行。
bool ThreadPool::assignWork(WorkerThread *workerThread)
{
pthread_mutex_lock(&mutexWorkCompletion);
incompleteWork++;
//cout << "assignWork...incomapleteWork=" << incompleteWork << endl;
pthread_mutex_unlock(&mutexWorkCompletion);
sem_wait(&availableThreads);
pthread_mutex_lock(&mutexSync);
//workerVec[topIndex] = workerThread;
workerQueue[topIndex] = workerThread;
//cout << "Assigning Worker[" << workerThread->id << "] Address:[" << workerThread << "] to Queue index [" << topIndex << "]" << endl;
if(queueSize !=1 )
topIndex = (topIndex+1) % (queueSize-1);
sem_post(&availableWork);
pthread_mutex_unlock(&mutexSync);
return true;
}
//当已经有人物放到队列里面后，就会受到通知，然后从底部拿走工作，在workerArg中返回
bool ThreadPool::fetchWork(WorkerThread **workerArg)
{
sem_wait(&availableWork);
pthread_mutex_lock(&mutexSync);
WorkerThread * workerThread = workerQueue[bottomIndex];
workerQueue[bottomIndex] = NULL;
*workerArg = workerThread;
if(queueSize !=1 )
bottomIndex = (bottomIndex+1) % (queueSize-1);
sem_post(&availableThreads);
pthread_mutex_unlock(&mutexSync);
return true;
}
//每个线程运行的静态函数实体，executeThis 方法将会被继承累从写，之后实现具体线程的工作。
void *ThreadPool::threadExecute(void *param)
{
WorkerThread *worker = NULL;
while(((ThreadPool *)param)->fetchWork(&worker))
{
if(worker)
{
worker->executeThis();
//cout << "worker[" << worker->id << "]\tdelete address: [" << worker << "]" << endl;
delete worker;
worker = NULL;
}
pthread_mutex_lock( &(((ThreadPool *)param)->mutexWorkCompletion) );
//cout << "Thread " << pthread_self() << " has completed a Job !" << endl;
((ThreadPool *)param)->incompleteWork--;
pthread_mutex_unlock( &(((ThreadPool *)param)->mutexWorkCompletion) );
}
return 0;
}
#include <iostream>
#include "threadpool.h"
using namespace std;
#define ITERATIONS 20
class SampleWorkerThread : public WorkerThread
{
public:
int id;
unsigned virtual executeThis()
{
// Instead of sleep() we could do anytime consuming work here.
// Using ThreadPools is advantageous only when the work to be done is really time consuming. (atleast 1 or 2 seconds)
cout<<"This is SampleWorkerThread sleep 2s"<<endl;
sleep(2);
return(0);
}
SampleWorkerThread(int id) : WorkerThread(id), id(id)
{
// cout << "Creating SampleWorkerThread " << id << "\t address=" << this << endl;
}
~SampleWorkerThread()
{
// cout << "Deleting SampleWorkerThread " << id << "\t address=" << this << endl;
}
};
int main(int argc, char **argv)
{
cout<<"Thread pool"<<endl;
ThreadPool* myPool = new ThreadPool(25);
//pthread_create()执行，开始等待任务分配
myPool->initializeThreads();
//用来计算时间间隔。
time_t t1=time(NULL);
//分配具体工作到线程池
for(unsigned int i=0;i<ITERATIONS;i++){
SampleWorkerThread* myThreathreadExecuted = new SampleWorkerThread(i);
myPool->assignWork(myThreathreadExecuted);
}
//销毁钱等待所有线程结束，等待间隔为2秒。
myPool->destroyPool(2);
time_t t2=time(NULL);
cout << t2-t1 << " seconds elapsed\n" << endl;
delete myPool;
return 0;
}
ubuntu 12.04下运行成功，编译命令如下：g++ -g main.cpp thread_pool.cpp -o thread_pool -lpthread