linux 下c++线程池的简单实现（在老外代码上添加注释）

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 classThis 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 20class 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