http://blog.csdn.net/denny_233/article/details/40484365 2014 所谓线程池,就是程序的初始化阶段,就预先创建一批线程,每个线程都做好准备干活;
然后初始化一个任务列表,当有任务来了,就往任务列表里面添加;
任务列表里面有任务了,这时候那些等待的线程们就要抢活干了,怎么抢,使用各种线程同步手段(互斥量,临界区等),人品好的线程抢到任务后,从任务列表取出任务,就可以开始干活了。干完以后,就又继续回到初始等待状态,准备抢夺下一个任务。
/**********************************************************************************************************************************************/
这样就好比你有一批小弟排队在那里等着,一旦有任务,他们会很守纪律的去抢着干,每个任务都会被一个小弟抢走,干完以后,小弟不用休息,继续等着抢下一个任务干活。这样当你的任务源源不断的到达,你的小弟们就一个个争先恐后的抢过来完成,绝不偷懒。
相 反,如果不使用线程池,每次等到任务来了,再临时创建线程。这样就相当于每次有任务时,你再临时招聘一个小弟过来,小弟完成任务后,就回家了。然后下次再有任务,又招聘一个小弟过来,完成任务后,回家。相比线程池,中间招聘小弟的时间就要额外耗费时间和精力了(创建和销毁线程中,cpu的时间,内存的分配)。/*********************************************************************************************************************************************/
总结来说,线程池有4个组成部分
线程池管理器(ThreadPoolManager):用于创建并管理线程池
工作线程(WorkThread): 线程池中线程
任务接口(Task):每个任务必须实现的接口,以供工作线程调度任务的执行。
任务队列:用于存放没有处理的任务。提供一种缓冲机制。
所以,使用线程池,就省去了哪些额外的线程开销,从而连续的完成所有的任务。当然,线程池中用于线程同步的操作同样也有一定的消耗,但这个消耗是相对小的。另外,还可以对线程池中的线程根据当前的任务量进行动态的调整,从而更好的节省相关资源。
什么时候适合用线程池:
1. 需要大量的线程来完成,且完成时间比较段。比如WEB服务器完成网页的请求,使用线程池技术非常适合。对于长时间的任务,如telnet链接什么的,使用线程池就没有什么有点了。
2、对性能要求苛刻的应用,比如要求服务器迅速响应客户请求。
3、接受突发性的大量请求,但不至于使服务器因此产生大量线程的应用。短时间内产生大量线程可能使内存达到极致,并出现”outofMemory”情况。
下面是一个网上的代码用例:
thpool.h代码如下:
- /**********************************
- * @author Johan Hanssen Seferidis
- * @date 12/08/2011
- * Last update: 01/11/2011
- * License: LGPL
- *
- **********************************/
-
- /* Description: Library providing a threading pool where you can add work on the fly. The number
- * of threads in the pool is adjustable when creating the pool. In most cases
- * this should equal the number of threads supported by your cpu.
- *
- * For an example on how to use the threadpool, check the main.c file or just read
- * the documentation.
- *
- * In this header file a detailed overview of the functions and the threadpool logical
- * scheme is present in case tweaking of the pool is needed.
- * */
-
- /*
- * Fast reminders:
- *
- * tp = threadpool
- * thpool = threadpool
- * thpool_t = threadpool type
- * tp_p = threadpool pointer
- * sem = semaphore
- * xN = x can be any string. N stands for amount
- *
- * */
-
- /* _______________________________________________________
- * / \
- * | JOB QUEUE | job1 | job2 | job3 | job4 | .. |
- * | |
- * | threadpool | thread1 | thread2 | .. |
- * \_______________________________________________________/
- *
- * Description: Jobs are added to the job queue. Once a thread in the pool
- * is idle, it is assigned with the first job from the queue(and
- * erased from the queue). It's each thread's job to read from
- * the queue serially(using lock) and executing each job
- * until the queue is empty.
- * 描述: 每来一个Job,会加入的队列中去,当池子中有空闲线程时,从队列中取出job
- *
- * Scheme:
- *
- * thpool______ jobqueue____ ______
- * | | | | .----------->|_job0_| Newly added job
- * | | | head------------' |_job1_|
- * | jobqueue----------------->| | |_job2_|
- * | | | tail------------. |__..__|
- * |___________| |___________| '----------->|_jobn_| Job for thread to take
- *
- *
- * job0________
- * | |
- * | function----> //Job具有通用的接口,供工作线程调度试用
- * | |
- * | arg------->
- * | | job1________
- * | next-------------->| |
- * |___________| | |..
- */
-
- #ifndef _THPOOL_
- #define _THPOOL_
-
- #include <pthread.h>
- #include <semaphore.h>
-
- /* ================================= STRUCTURES ================================================ */
- /* Individual job */
- typedef struct thpool_job_t{
- void* (*function)(void* arg); /**< function pointer */
- void* arg; /**< function's argument */
- struct thpool_job_t* next; /**< pointer to next job */
- struct thpool_job_t* prev; /**< pointer to previous job */
- }thpool_job_t;
-
- /* Job queue as doubly linked list */
- typedef struct thpool_jobqueue{
- thpool_job_t *head; /**< pointer to head of queue */
- thpool_job_t *tail; /**< pointer to tail of queue */
- int jobsN; /**< amount of jobs in queue */
- sem_t *queueSem; /**< semaphore(this is probably just holding the same as jobsN) */
- }thpool_jobqueue;
-
- /* The threadpool */
- typedef struct thpool_t{
- pthread_t* threads; /**< pointer to threads' ID */
- int threadsN; /**< amount of threads */
- thpool_jobqueue* jobqueue; /**< pointer to the job queue */
- }thpool_t;
-
- /* Container for all things that each thread is going to need */
- typedef struct thread_data{
- pthread_mutex_t *mutex_p;
- thpool_t *tp_p;
- }thread_data;
-
-
- /* =========================== FUNCTIONS ================================================ */
- /* ----------------------- Threadpool specific --------------------------- */
-
- /**
- * @brief Initialize threadpool
- *
- * Allocates memory for the threadpool, jobqueue, semaphore and fixes
- * pointers in jobqueue.
- *
- * @param number of threads to be used
- * @return threadpool struct on success,
- * NULL on error
- */
- thpool_t* thpool_init(int threadsN);
-
- /**
- * @brief What each thread is doing
- *
- * In principle this is an endless loop. The only time this loop gets interuppted is once
- * thpool_destroy() is invoked.
- *
- * @param threadpool to use
- * @return nothing
- */
- void thpool_thread_do(thpool_t* tp_p);
-
- /**
- * @brief Add work to the job queue
- *
- * Takes an action and its argument and adds it to the threadpool's job queue.
- * If you want to add to work a function with more than one arguments then
- * a way to implement this is by passing a pointer to a structure.
- *
- * ATTENTION: You have to cast both the function and argument to not get warnings.
- *
- * @param threadpool to where the work will be added to
- * @param function to add as work
- * @param argument to the above function
- * @return int
- */
- int thpool_add_work(thpool_t* tp_p, void *(*function_p)(void*), void* arg_p);
-
- /**
- * @brief Destroy the threadpool
- *
- * This will 'kill' the threadpool and free up memory. If threads are active when this
- * is called, they will finish what they are doing and then they will get destroyied.
- *
- * @param threadpool a pointer to the threadpool structure you want to destroy
- */
- void thpool_destroy(thpool_t* tp_p);
-
-
- /* ------------------------- Queue specific ------------------------------ */
- /**
- * @brief Initialize queue
- * @param pointer to threadpool
- * @return 0 on success,
- * -1 on memory allocation error
- */
- int thpool_jobqueue_init(thpool_t* tp_p);
-
- /**
- * @brief Add job to queue
- *
- * A new job will be added to the queue. The new job MUST be allocated
- * before passed to this function or else other functions like thpool_jobqueue_empty()
- * will be broken.
- *
- * @param pointer to threadpool
- * @param pointer to the new job(MUST BE ALLOCATED)
- * @return nothing
- */
- void thpool_jobqueue_add(thpool_t* tp_p, thpool_job_t* newjob_p);
-
- /**
- * @brief Remove last job from queue.
- *
- * This does not free allocated memory so be sure to have peeked() \n
- * before invoking this as else there will result lost memory pointers.
- *
- * @param pointer to threadpool
- * @return 0 on success,
- * -1 if queue is empty
- */
- int thpool_jobqueue_removelast(thpool_t* tp_p);
-
- /**
- * @brief Get last job in queue (tail)
- *
- * Gets the last job that is inside the queue. This will work even if the queue
- * is empty.
- *
- * @param pointer to threadpool structure
- * @return job a pointer to the last job in queue,
- * a pointer to NULL if the queue is empty
- */
- thpool_job_t* thpool_jobqueue_peek(thpool_t* tp_p);
-
- /**
- * @brief Remove and deallocate all jobs in queue
- *
- * This function will deallocate all jobs in the queue and set the
- * jobqueue to its initialization values, thus tail and head pointing
- * to NULL and amount of jobs equal to 0.
- *
- * @param pointer to threadpool structure
- * */
- void thpool_jobqueue_empty(thpool_t* tp_p);
-
- #endif
- </span>
thpool.c代码如下
- /* ********************************
- *
- * Author: Johan Hanssen Seferidis
- * Date: 12/08/2011
- * Update: 01/11/2011
- * License: LGPL
- *
- *
- *//** @file thpool.h *//*
- ********************************/
-
- /* Library providing a threading pool where you can add work. For an example on
- * usage you refer to the main file found in the same package */
-
- /*
- * Fast reminders:
- *
- * tp = threadpool
- * thpool = threadpool
- * thpool_t = threadpool type
- * tp_p = threadpool pointer
- * sem = semaphore
- * xN = x can be any string. N stands for amount
- *
- * */
-
- #include <stdio.h>
- #include <stdlib.h>
- #include <pthread.h>
- #include <semaphore.h>
- #include <errno.h>
-
- #include "thpool.h" /* here you can also find the interface to each function */
-
-
- static int thpool_keepalive=1;
-
- /* Create mutex variable */
- pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /* used to serialize queue access */
-
-
- /* Initialise thread pool */
- thpool_t* thpool_init(int threadsN){
- thpool_t* tp_p;
-
- if (!threadsN || threadsN<1) threadsN=1;
-
- /* Make new thread pool */
- tp_p=(thpool_t*)malloc(sizeof(thpool_t)); /* MALLOC thread pool */
- if (tp_p==NULL){
- fprintf(stderr, "thpool_init(): Could not allocate memory for thread pool\n");
- return NULL;
- }
- tp_p->threads=(pthread_t*)malloc(threadsN*sizeof(pthread_t)); /* MALLOC thread IDs */
- if (tp_p->threads==NULL){
- fprintf(stderr, "thpool_init(): Could not allocate memory for thread IDs\n");
- return NULL;
- }
- tp_p->threadsN=threadsN;
-
- /* Initialise the job queue */
- if (thpool_jobqueue_init(tp_p)==-1){
- fprintf(stderr, "thpool_init(): Could not allocate memory for job queue\n");
- return NULL;
- }
-
- /* Initialise semaphore,关于信号量的操作请参考其他*/
- tp_p->jobqueue->queueSem=(sem_t*)malloc(sizeof(sem_t)); /* MALLOC job queue semaphore */
- sem_init(tp_p->jobqueue->queueSem, 0, 0); /* no shared, initial value */
-
- /* Make threads in pool */
- int t;
- for (t=0; t<threadsN; t++){
- printf("Created thread %d in pool \n", t);
- pthread_create(&(tp_p->threads[t]), NULL, (void *)thpool_thread_do, (void *)tp_p); /* MALLOCS INSIDE PTHREAD HERE */
- }
-
- return tp_p;
- }
-
-
- /* What each individual thread is doing ,线程池的入口函数,从队列中抽取共同接口的Task;在这里即thpool_job_t的
- 前2个参数void* (*function)(void* arg) 及void *arg. */
- /* There are two scenarios here. One is everything works as it should and second if
- * the thpool is to be killed. In that manner we try to BYPASS sem_wait and end each thread. */
- void thpool_thread_do(thpool_t* tp_p){
-
- while(thpool_keepalive){
- //收到sem_post signal
- if (sem_wait(tp_p->jobqueue->queueSem)) {/* WAITING until there is work in the queue */
- perror("thpool_thread_do(): Waiting for semaphore");
- exit(1);
- }
-
- if (thpool_keepalive){
-
- /* Read job from queue and execute it */
- void*(*func_buff)(void* arg);
- void* arg_buff;
- thpool_job_t* job_p;
-
- pthread_mutex_lock(&mutex); /* LOCK */
-
- job_p = thpool_jobqueue_peek(tp_p);
- func_buff=job_p->function;
- arg_buff =job_p->arg; /*每个入队列的Task都具有的接口*/
- thpool_jobqueue_removelast(tp_p);
-
- pthread_mutex_unlock(&mutex); /* UNLOCK */
-
- func_buff(arg_buff); /* run function */
- free(job_p); /* DEALLOC job */
- }
- else
- {
- return; /* EXIT thread*/
- }
- }
- return;
- }
-
-
- /* Add work to the thread pool */
- int thpool_add_work(thpool_t* tp_p, void *(*function_p)(void*), void* arg_p){
- thpool_job_t* newJob;
-
- newJob=(thpool_job_t*)malloc(sizeof(thpool_job_t)); /* MALLOC job */
- if (newJob==NULL){
- fprintf(stderr, "thpool_add_work(): Could not allocate memory for new job\n");
- exit(1);
- }
-
- /* add function and argument */
- newJob->function=function_p;
- newJob->arg=arg_p;
-
- /* add job to queue */
- pthread_mutex_lock(&mutex); /* LOCK */
- thpool_jobqueue_add(tp_p, newJob);
- pthread_mutex_unlock(&mutex); /* UNLOCK */
-
- return 0;
- }
-
-
- /* Destroy the threadpool */
- void thpool_destroy(thpool_t* tp_p){
- int t;
-
- /* End each thread's infinite loop */
- thpool_keepalive=0;
-
- /* Awake idle threads waiting at semaphore */
- for (t=0; t<(tp_p->threadsN); t++){
- if (sem_post(tp_p->jobqueue->queueSem)){
- fprintf(stderr, "thpool_destroy(): Could not bypass sem_wait()\n");
- }
- }
-
- /* Kill semaphore */
- if (sem_destroy(tp_p->jobqueue->queueSem)!=0){
- fprintf(stderr, "thpool_destroy(): Could not destroy semaphore\n");
- }
-
- /* Wait for threads to finish */
- for (t=0; t<(tp_p->threadsN); t++){
- pthread_join(tp_p->threads[t], NULL);
- }
-
- thpool_jobqueue_empty(tp_p);
-
- /* Dealloc */
- free(tp_p->threads); /* DEALLOC threads */
- free(tp_p->jobqueue->queueSem); /* DEALLOC job queue semaphore */
- free(tp_p->jobqueue); /* DEALLOC job queue */
- free(tp_p); /* DEALLOC thread pool */
- }
-
-
-
- /* =================== JOB QUEUE OPERATIONS ===================== */
-
- /* Initialise queue */
- int thpool_jobqueue_init(thpool_t* tp_p){
- tp_p->jobqueue=(thpool_jobqueue*)malloc(sizeof(thpool_jobqueue)); /* MALLOC job queue */
- if (tp_p->jobqueue==NULL) return -1;
- tp_p->jobqueue->tail=NULL;
- tp_p->jobqueue->head=NULL;
- tp_p->jobqueue->jobsN=0;
- return 0;
- }
-
- /* Add job to queue */
- void thpool_jobqueue_add(thpool_t* tp_p, thpool_job_t* newjob_p){ /* remember that job prev and next point to NULL */
-
- newjob_p->next=NULL;
- newjob_p->prev=NULL;
-
- thpool_job_t *oldFirstJob;
- oldFirstJob = tp_p->jobqueue->head;
-
- /* fix jobs' pointers */
- switch(tp_p->jobqueue->jobsN){
-
- case 0: /* if there are no jobs in queue */
- tp_p->jobqueue->tail=newjob_p;
- tp_p->jobqueue->head=newjob_p;
- break;
-
- default: /* if there are already jobs in queue */
- oldFirstJob->prev=newjob_p;
- newjob_p->next=oldFirstJob;
- tp_p->jobqueue->head=newjob_p;
-
- }
-
- (tp_p->jobqueue->jobsN)++; /* increment amount of jobs in queue */
- sem_post(tp_p->jobqueue->queueSem);
-
- int sval;
- sem_getvalue(tp_p->jobqueue->queueSem, &sval);
- }
-
-
- /* Remove job from queue */
- int thpool_jobqueue_removelast(thpool_t* tp_p){
- thpool_job_t *oldLastJob;
- oldLastJob = tp_p->jobqueue->tail;
-
- /* fix jobs' pointers */
- switch(tp_p->jobqueue->jobsN){
-
- case 0: /* if there are no jobs in queue */
- return -1;
- break;
-
- case 1: /* if there is only one job in queue */
- tp_p->jobqueue->tail=NULL;
- tp_p->jobqueue->head=NULL;
- break;
-
- default: /* if there are more than one jobs in queue */
- oldLastJob->prev->next=NULL; /* the almost last item */
- tp_p->jobqueue->tail=oldLastJob->prev;
-
- }
-
- (tp_p->jobqueue->jobsN)--;
-
- int sval;
- sem_getvalue(tp_p->jobqueue->queueSem, &sval);
- return 0;
- }
-
-
- /* Get first element from queue */
- thpool_job_t* thpool_jobqueue_peek(thpool_t* tp_p){
- return tp_p->jobqueue->tail;
- }
-
- /* Remove and deallocate all jobs in queue */
- void thpool_jobqueue_empty(thpool_t* tp_p){
-
- thpool_job_t* curjob;
- curjob=tp_p->jobqueue->tail;
-
- while(tp_p->jobqueue->jobsN){
- tp_p->jobqueue->tail=curjob->prev;
- free(curjob);
- curjob=tp_p->jobqueue->tail;
- tp_p->jobqueue->jobsN--;
- }
-
- /* Fix head and tail */
- tp_p->jobqueue->tail=NULL;
- tp_p->jobqueue->head=NULL;
- }
- </span>
main.c 代码如下
- /*
- * This is just an example on how to use the thpool library
- *
- * We create a pool of 4 threads and then add 20 tasks to the pool(10 task1
- * functions and 10 task2 functions).
- *
- * Task1 doesn't take any arguments. Task2 takes an integer. Task2 is used to show
- * how to add work to the thread pool with an argument.
- *
- * As soon as we add the tasks to the pool, the threads will run them. One thread
- * may run x tasks in a row so if you see as output the same thread running several
- * tasks, it's not an error.
- *
- * All jobs will not be completed and in fact maybe even none will. You can add a sleep()
- * function if you want to complete all tasks in this test file to be able and see clearer
- * what is going on.
- *
- * */
-
- #include <stdio.h>
-
- #include "thpool.h"
-
-
-
- /* Some arbitrary task 1 */
- void task1(){
- printf("# Thread working: %u\n", (int)pthread_self());
- printf(" Task 1 running..\n");
- }
-
-
-
- /* Some arbitrary task 2 */
- void task2(int a){
- printf("# Thread working: %u\n", (int)pthread_self());
- printf(" Task 2 running..\n");
- printf("%d\n", a);
- }
-
-
-
- int main(){
- int i;
-
- thpool_t* threadpool; /* make a new thread pool structure */
- threadpool=thpool_init(4); /* initialise it to 4 number of threads */
-
-
- puts("Adding 20 tasks to threadpool");
- int a=54;
- for (i=0; i<10; i++){
- thpool_add_work(threadpool, (void*)task1, NULL);
- thpool_add_work(threadpool, (void*)task2, (void*)a);
- };
-
-
- puts("Will kill threadpool");
- thpool_destroy(threadpool);
-
- return 0;
- }
- </span>
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