项目要用线程池，网上找了很多后发现了这个开源的项目http://sourceforge.net/projects/libthreadpool/，但是测试发现这个项目代码的Bug实在太多了基本上没法用，然后就自己一点点修改调试，大约花了一周时间终于可以使用了，测试效果还不错，CPU使用率比之前能降低一大半。libthreadpool这个项目源文件只有两个，thread-pool.h和thread-pool.c现在将这两个文件修改后的代码贴在这里，方便以后使用。

TEST_LIB 宏定义的是一个小的测试代码，打开后就不用项目自带的makefile了，自己单独编译下吧。

thread-pool.h：

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <pthread.h>
#include <signal.h>
#include <errno.h>

#ifndef TPBOOL
typedef int TPBOOL;
#endif

#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif

#define BUSY_THRESHOLD 0.5	//(busy thread)/(all thread threshold)
#define MANAGE_INTERVAL 5	//tp manage thread sleep interval

typedef void* tp_work_desc;
typedef void* (*tp_work)(void *);

typedef struct tp_thread_info_s tp_thread_info;
typedef struct tp_thread_pool_s tp_thread_pool;

//thread info
struct tp_thread_info_s{
	pthread_t		thread_id;	//thread id num
	TPBOOL  		is_busy;	//thread status:true-busy;flase-idle
	pthread_cond_t  thread_cond;	
	pthread_mutex_t	thread_lock;
	tp_work			th_work;
	tp_work_desc	th_job;
	TPBOOL			exit;
	TPBOOL			is_wait; // CAUTION：在未调用pthread_cond_wait时通过pthread_cond_signal发送信号会造成信号丢失！
};

//main thread pool struct
struct tp_thread_pool_s{
	TPBOOL (*init)(tp_thread_pool *this);
	void (*close)(tp_thread_pool *this);
	void (*process_job)(tp_thread_pool *this, tp_work worker, tp_work_desc job);
	int  (*get_thread_by_id)(tp_thread_pool *this, pthread_t id);
	TPBOOL (*add_thread)(tp_thread_pool *this);
	TPBOOL (*delete_thread)(tp_thread_pool *this);
	int (*get_tp_status)(tp_thread_pool *this);
	
	int min_th_num;		//min thread number in the pool
	int cur_th_num;		//current thread number in the pool
	int max_th_num;         //max thread number in the pool
	pthread_mutex_t tp_lock;
	pthread_t manage_thread_id;	//manage thread id num
	tp_thread_info *thread_info;	//work thread relative thread info
};

tp_thread_pool *creat_thread_pool(int min_num, int max_num);

#include "thread-pool.h"

//#define TEST_LIB

#define DBG_OUT(args...) \
do{ \
	char b__[1024]; \
	sprintf(b__,args); \
	fprintf(stderr,"%u:[%s,%d] %s",(unsigned long)time(NULL),__FUNCTION__,__LINE__,b__); \
}while(0)

static void *tp_work_thread(void *pthread);
static void *tp_manage_thread(void *pthread);

static TPBOOL tp_init(tp_thread_pool *this);
static void tp_close(tp_thread_pool *this);
static void tp_process_job(tp_thread_pool *this, tp_work worker, tp_work_desc job);
static int  tp_get_thread_by_id(tp_thread_pool *this, pthread_t id);
static TPBOOL tp_add_thread(tp_thread_pool *this);
static TPBOOL tp_delete_thread(tp_thread_pool *this);
static int  tp_get_tp_status(tp_thread_pool *this);

/**
  * user interface. creat thread pool.
  * para:
  * 	num: min thread number to be created in the pool
  * return:
  * 	thread pool struct instance be created successfully
  */
tp_thread_pool *creat_thread_pool(int min_num, int max_num)
{
	tp_thread_pool *this;
	this = (tp_thread_pool*)malloc(sizeof(tp_thread_pool));	

	//init member function ponter
	this->init = tp_init;
	this->close = tp_close;
	this->process_job = tp_process_job;
	this->get_thread_by_id = tp_get_thread_by_id;
	this->add_thread = tp_add_thread;
	this->delete_thread = tp_delete_thread;
	this->get_tp_status = tp_get_tp_status;

	//init member var
	this->min_th_num = min_num;
	this->cur_th_num = this->min_th_num;
	this->max_th_num = max_num;
	pthread_mutex_init(&this->tp_lock, NULL);

	//malloc mem for num thread info struct
	this->thread_info = (tp_thread_info*)malloc(sizeof(tp_thread_info)*this->max_th_num);

	return this;
}


/**
  * member function reality. thread pool init function.
  * para:
  * 	this: thread pool struct instance ponter
  * return:
  * 	true: successful; false: failed
  */
TPBOOL tp_init(tp_thread_pool *this)
{
	int i,num = this->min_th_num;
	int err;

	//creat work thread and init work thread info
	for(i=0;i<num;i++)
	{
		pthread_cond_init(&this->thread_info[i].thread_cond, NULL);
		pthread_mutex_init(&this->thread_info[i].thread_lock, NULL);
		
		err = pthread_create(&this->thread_info[i].thread_id, NULL, tp_work_thread, &this->thread_info[i]);
		if(0 != err)
		{
			DBG_OUT("tp_init: creat work thread failed\n");
			return FALSE;
		}
		DBG_OUT("tp_init: creat work thread 0x%X\n", this->thread_info[i].thread_id);
	}

	//creat manage thread
	err = pthread_create(&this->manage_thread_id, NULL, tp_manage_thread, this);
	if(0 != err)
	{
		DBG_OUT("tp_init: creat manage thread failed\n");
		return FALSE;
	}
	DBG_OUT("tp_init: creat manage thread 0x%X\n", this->manage_thread_id);

	return TRUE;
}

/**
  * member function reality. thread pool entirely close function.
  * para:
  * 	this: thread pool struct instance ponter
  * return:
  */
void tp_close(tp_thread_pool *this)
{
	int i;
	void *status;

	//close work thread
	for(i=0;i<this->cur_th_num;i++)
	{
		if(pthread_kill(this->thread_info[i].thread_id, 0)!= ESRCH)
		{
			pthread_kill(this->thread_info[i].thread_id, SIGQUIT);
			pthread_join(this->thread_info[i].thread_id,&status);
			pthread_mutex_destroy(&this->thread_info[i].thread_lock);
			pthread_cond_destroy(&this->thread_info[i].thread_cond);
			DBG_OUT("tp_close: kill work thread 0x%X\n", this->thread_info[i].thread_id);
		}
	}

	if(pthread_kill(this->manage_thread_id, 0)!= ESRCH)
	{
		//close manage thread
		pthread_kill(this->manage_thread_id, SIGQUIT);
		pthread_join(this->manage_thread_id,&status);
		pthread_mutex_destroy(&this->tp_lock);
		DBG_OUT("tp_close: kill manage thread 0x%X\n", this->manage_thread_id);
	}
	
	//free thread struct
	free(this->thread_info);
}

/**
  * member function reality. main interface opened. 
  * after getting own worker and job, user may use the function to process the task.
  * para:
  * 	this: thread pool struct instance ponter
  *	worker: user task reality.
  *	job: user task para
  * return:
  */

// 偶尔还会出现信号丢失！检查is_wait时加上锁，锁成功时
// 一定是进入了pthread_cond_wait。
#define TP_THREAD_IS_WAIT(idx) \
do \
{ \
	while(1) \
	{ \
		pthread_mutex_lock(&this->thread_info[idx].thread_lock); \
		if(this->thread_info[idx].is_wait) \
		{ \
			pthread_mutex_unlock(&this->thread_info[idx].thread_lock); \
			break; \
		} \
		pthread_mutex_unlock(&this->thread_info[idx].thread_lock); \
		sleep(1); \
	} \
}while(0)

void tp_process_job(tp_thread_pool *this, tp_work worker, tp_work_desc job)
{
	int i;
	int tmpid;
	TPBOOL res;

	//fill this->thread_info's relative work key
	for(i=0;i<this->cur_th_num;i++)
	{
		pthread_mutex_lock(&this->thread_info[i].thread_lock);
		if(!this->thread_info[i].is_busy)
		{
			//DBG_OUT("tp_process_job: %d thread idle, thread id is %d\n", i, this->thread_info[i].thread_id);
			//thread state be set busy before work
		  	this->thread_info[i].is_busy = TRUE;
			pthread_mutex_unlock(&this->thread_info[i].thread_lock);

			this->thread_info[i].th_work = worker;
			this->thread_info[i].th_job = job;

			//DBG_OUT("tp_process_job: informing idle working thread %d, thread id is %d\n", i, this->thread_info[i].thread_id);
			TP_THREAD_IS_WAIT(i);
			pthread_cond_signal(&this->thread_info[i].thread_cond);
			return;
		}
		else
		{
			pthread_mutex_unlock(&this->thread_info[i].thread_lock);		
		}
	}//end of for

	//if all current thread are busy, new thread is created here
	pthread_mutex_lock(&this->tp_lock);
	if( res = this->add_thread(this) )
	{
		i = this->cur_th_num - 1;
		tmpid = this->thread_info[i].thread_id;
		this->thread_info[i].th_work = worker;
		this->thread_info[i].th_job = job;
	}
	pthread_mutex_unlock(&this->tp_lock);

	if (res)
	{
		TP_THREAD_IS_WAIT(i);
		pthread_cond_signal(&this->thread_info[i].thread_cond);
	}

	return;	
}

/**
  * member function reality. get real thread by thread id num.
  * para:
  * 	this: thread pool struct instance ponter
  *	id: thread id num
  * return:
  * 	seq num in thread info struct array
  */
int tp_get_thread_by_id(tp_thread_pool *this, pthread_t id){
	int i;

	for(i=0;i<this->cur_th_num;i++)
	{
		if(id == this->thread_info[i].thread_id)
		{
			return i;
		}
	}

	return -1;
}

/**
  * member function reality. add new thread into the pool.
  * para:
  * 	this: thread pool struct instance ponter
  * return:
  * 	true: successful; false: failed
  */
static TPBOOL tp_add_thread(tp_thread_pool *this)
{
	int err;
	tp_thread_info *new_thread;
	
	if( this->max_th_num <= this->cur_th_num )
	{
		DBG_OUT("Thread pool full \n");
		return FALSE;
	}

	//malloc new thread info struct
	new_thread = &this->thread_info[this->cur_th_num];
	
	//init new thread's cond & mutex
	pthread_cond_init(&new_thread->thread_cond, NULL);
	pthread_mutex_init(&new_thread->thread_lock, NULL);

	//init status is busy
	new_thread->is_busy = TRUE;
	new_thread->exit = FALSE;
	new_thread->is_wait = FALSE;

	err = pthread_create(&new_thread->thread_id, NULL, tp_work_thread, new_thread);
	if(0 != err)
	{
		pthread_mutex_destroy(&new_thread->thread_lock);
		pthread_cond_destroy(&new_thread->thread_cond);
		new_thread->is_busy = FALSE;
		DBG_OUT("ERROR:Create thread.\n");
		return FALSE;
	}

	//add current thread number in the pool.
	this->cur_th_num++;
	
	//DBG_OUT("Creat work thread %d;current threads number is %d.\n", this->thread_info[this->cur_th_num-1].thread_id,this->cur_th_num);

	return TRUE;
}

/**
  * member function reality. delete idle thread in the pool.
  * only delete last idle thread in the pool.
  * para:
  * 	this: thread pool struct instance ponter
  * return:
  * 	true: successful; false: failed
  */
static TPBOOL tp_delete_thread(tp_thread_pool *this)
{
	void* status;
	int idx = this->cur_th_num - 1;
	TPBOOL res;

	//current thread num can't < min thread num
	if(this->cur_th_num <= this->min_th_num)
	{
		DBG_OUT("current thread num can't < min thread num\n");
		return FALSE;
	}
	// check thread status
	pthread_mutex_lock(&this->thread_info[idx].thread_lock);
	//if last thread is busy, do nothing
	if(this->thread_info[idx].is_busy)
	{
		DBG_OUT("last thread is busy, do nothing.worker=%p,job=%p\n",this->thread_info[idx].th_work,this->thread_info[idx].th_job);
		res = FALSE;
		pthread_mutex_unlock(&this->thread_info[idx].thread_lock);
	}
	else
	{
		this->thread_info[idx].is_busy = TRUE;
		
		// 先锁定 tp_lock防止cur_th_num出错
		pthread_mutex_lock(&this->tp_lock);
		pthread_mutex_unlock(&this->thread_info[idx].thread_lock);
		//after deleting idle thread, current thread num -1
		this->cur_th_num--;

		//kill the idle thread and free info struct
		this->thread_info[idx].exit = 1;
		pthread_cond_signal(&this->thread_info[idx].thread_cond);
		pthread_join(this->thread_info[idx].thread_id,&status);

		pthread_mutex_destroy(&this->thread_info[idx].thread_lock);
		pthread_cond_destroy(&this->thread_info[idx].thread_cond);
		DBG_OUT("Delete thread.index = %d\n",idx);
		pthread_mutex_unlock(&this->tp_lock);
		res = TRUE;
	}

	return res;
}

/**
  * member function reality. get current thread pool status:idle, normal, busy, .etc.
  * para:
  * 	this: thread pool struct instance ponter
  * return:
  * 	0: idle; 1: normal or busy(don't process)
  */
static int  tp_get_tp_status(tp_thread_pool *this)
{
	float busy_num = 0.0;
	int i;

	//get busy thread number
	for(i=0;i<this->cur_th_num;i++)
	{
		if(this->thread_info[i].is_busy)
		{
			busy_num++;
		}
	}

	//0.2? or other num?
	busy_num = busy_num/(this->cur_th_num);

	DBG_OUT("Thread pool busy status = %f.Current thread number = %d\n",busy_num,this->cur_th_num);

	if(busy_num < BUSY_THRESHOLD)
	{
		return 0;//idle status
	}
	else
	{
		return 1;//busy or normal status	
	}
}

// 这个函数只是为了消除编译器警告
void *tp_thread_exit()
{
	pthread_exit(NULL);
}
void handle_quit(int signo)
{
	pthread_t curid;//current thread id

	//get current thread id
	curid = pthread_self();
    
    DBG_OUT("Handle sig %d,thread id = 0x%X \n", signo,curid);
    tp_thread_exit();
}

/**
  * internal interface. real work thread.
  * para:
  * 	pthread: thread pool struct ponter
  * return:
  */
static void *tp_work_thread(void *pthread)
{
	tp_thread_info *th = (tp_thread_info*)pthread;//main thread pool struct instance

	signal(SIGQUIT,handle_quit );
	//wait cond for processing real job.
	while( TRUE )
	{
		pthread_mutex_lock(&th->thread_lock);
		th->is_wait = TRUE;
		pthread_cond_wait(&th->thread_cond, &th->thread_lock);
		th->is_wait = FALSE;
		pthread_mutex_unlock(&th->thread_lock);
		
		//DBG_OUT("%d thread do work!\n", pthread_self());

		if(NULL != th->th_work)
		{
			th->th_work(th->th_job);
		}
		
		//thread state be set idle after work
		pthread_mutex_lock(&th->thread_lock);
		th->is_busy = FALSE;
		th->th_work = NULL;
		pthread_mutex_unlock(&th->thread_lock);
		
		if(th->exit)
		{
			return;
		}
		//DBG_OUT("%d thread do work over!,nseq = %d\n", pthread_self(),nseq);
	}	
}

/**
  * internal interface. manage thread pool to delete idle thread.
  * para:
  * 	pthread: thread pool struct ponter
  * return:
  */
static void *tp_manage_thread(void *pthread)
{
	tp_thread_pool *this = (tp_thread_pool*)pthread;//main thread pool struct instance

	signal(SIGQUIT,handle_quit );

	sleep(MANAGE_INTERVAL);

	do
	{
		while( this->get_tp_status(this) == 0 )
		{
			if( !this->delete_thread(this) )
			{
				break;
			}
		}
		sleep(MANAGE_INTERVAL);
	}while(TRUE);
}

#ifdef TEST_LIB
void *thread_fun(void *param)
{
	int i;
	pthread_t curid;//current thread id

	//get current thread id
	curid = pthread_self();
	for(i=0;i<100;i++)
	{
		DBG_OUT("i=%d,thread id = 0x%X,param = %d\n",i,curid,(int)param);
		sleep(1);
	}
	return NULL;
}

tp_thread_pool *g_threadpool;
int main(int argc,char *argv[])
{

	g_threadpool = creat_thread_pool(3,10);
	g_threadpool->init(g_threadpool);
	
	g_threadpool->process_job(g_threadpool,thread_fun,(void*)1);
	sleep(1);
	g_threadpool->process_job(g_threadpool,thread_fun,(void*)2);
	sleep(1);
	g_threadpool->process_job(g_threadpool,thread_fun,(void*)3);
	sleep(1);
	g_threadpool->process_job(g_threadpool,thread_fun,(void*)4);
	
	sleep(10);
	g_threadpool->close(g_threadpool);
	while(1)
	{
		sleep(2);
	}
}
#endif