C++实现的带最大最小线程数的线程池（基于ACE）

最近需要一个能根据请求数变化的线程池，JAVA有这样的东西，可是C++下好像一般只是固定大小的线程池。所以就基于ACE写了个，只做了初步测试。
主要思想是：
1. 重载ACE_Task，这相当于是个固定线程池，用一个信号量（ACE_Thread_Semaphore）来记数空闲线程数。
2. 初始化时根据用户的输入，确定最少线程数minnum和最大线程数maxnum，当多个请求到来，并且无空闲线程（信号量用光），判断总线程数小于maxnum，就开始强迫增加线程数。
3. 当线程响应完一个请求（任务）后，如果当前任务队列为空，且线程数大于minnum，就退出本线程。这里做了一个优化，就算满足条件，线程也会在队列上再等待10秒，防止线程池抖动带来不必要的开销。
使用：
重载这个类，重载service_func函数实现自己的任务处理。
start_pool初始化线程池，之后，就可以用add_task向线程池添加任务。
它会根据请求的数量自动控制池大小进行处理。
已经在LINUX下测试通过。由于ACE是跨平台的，所以这个实现也应该可以在WINDOWS下工作。
编译：
带THREAD_POOL_UNIT_TEST选项，则编译出自测程序test
gcc -g -Wall -O2 -g -Wall -I. -I../ -I../mon/comm/ACE_wrappers -g -DTHREAD_POOL_UNIT_TEST -o test thread_pool.cpp -lpthread -lm -lz -lstdc++ ../mon/comm/ACE_wrappers/ace/libACE.a -ldl
thread_pool.h头文件：

#ifndef THREAD_POOL
#define THREAD_POOL

#include "ace/Task.h"
#include "ace/Thread_Mutex.h"
#include "ace/Thread_Semaphore.h"
#include <ace/OS.h>
class thread_pool : public ACE_Task<ACE_MT_SYNCH>
{
public:
thread_pool ();

~thread_pool ();

// begin the initial threads and waiting for request
int start_pool (
int minnum = 5, // min number of thread
int maxnum = 100,  // max number of thread
int waitsize = 1024, // request queue length
int parsize = 1024); // your parameter size

// pending request in work queue
int wait_cnt ();

// add one task to thread pool
int add_task (void *arg, int size);

// user defined work thread function
virtual int service_func (void* arg);

// overide base class function for thread pool logical
virtual int svc (void);

// not use
virtual int handle_timeout (const ACE_Time_Value &tv, const void *arg);

private:
int minnum_, maxnum_;
int waitsize_, parsize_;

//    ACE_Recursive_Thread_Mutex free_thread_cnt__mutex_;

ACE_Thread_Semaphore *pfree_thread_; // for free thread count

long thread_flags_; // ace thread create flag
};

#endif /**//* THREAD_POOL */

thread_pool.cpp实现文件：

#include "thread.h"

#define THREAD_POOL_DONOT_ACQUIRE    0x1001 // do not aquire again in new added thread

thread_pool::thread_pool ()
{
thread_flags_ = THR_NEW_LWP | THR_JOINABLE | THR_INHERIT_SCHED;
pfree_thread_ = NULL;
}

thread_pool::~thread_pool ()
{
if (pfree_thread_)
delete pfree_thread_;
}

int thread_pool::wait_cnt ()
{
return this->msg_queue()->message_count ();
}

int thread_pool::handle_timeout (const ACE_Time_Value &tv, const void *arg)
{
return 0;
}

int thread_pool::start_pool (
int minnum,
int maxnum,
int waitsize,
int parsize
)
{
minnum_ = minnum;
maxnum_ = maxnum;
waitsize_ = waitsize;
parsize_ = parsize;

this->msg_queue()->high_water_mark (waitsize * parsize);

pfree_thread_ = new ACE_Thread_Semaphore (minnum);

int ret = this->activate (thread_flags_, minnum);

return ret;
}

int thread_pool::add_task (void *arg, int size)
{
ACE_Message_Block *mb = new ACE_Message_Block (parsize_);

// test free threads condition
if (pfree_thread_->tryacquire () == -1)
{ // acquire one free thread to do work
printf ("free thread used up/n");

if (this->thr_count () < maxnum_)
{
this->activate (thread_flags_, 1, 1);

printf ("new thread release/n");
pfree_thread_->release ();

printf ("new one thread, now %d/n", this->thr_count ());
} else
{
printf ("can't new more threads, queue len %d/n", wait_cnt () + 1);
}
} else
{
// pfree_thread_->release (); // restore cnt, let svc function do acquire work
printf ("new task acquire/n");
mb->set_flags (THREAD_POOL_DONOT_ACQUIRE);
}

// create msg
printf ("add msg/n");

memcpy (mb->wr_ptr (), (char*) arg, size);

this->putq (mb);

return 0;
}

int thread_pool::service_func (void* arg)
{
ACE_OS::sleep (1);
printf ("finished task %d in thread %02X/n", *(int*) arg, (int)ACE_Thread::self ());
return 0;
}

int thread_pool::svc (void)
{
printf ("thread started/n");

while (1)
{
ACE_Message_Block *b = 0;
ACE_Time_Value wait = ACE_OS::gettimeofday ();
wait.sec (wait.sec () + 10); // timeout in 10 secs to test if more tasks need to do or we'll exit

if (this->getq (b, &wait) < 0)
{
if (this->thr_count () > minnum_)
{
printf ("over task acquire/n");
pfree_thread_->acquire ();
printf ("delete one thread, now %d/n", this->thr_count ()-1);

return 0;
} else
continue; // I'm the one of last min number of threads
}

if (b->flags () & THREAD_POOL_DONOT_ACQUIRE == 0)
{
printf ("queue task acquire/n");
pfree_thread_->acquire (); // I'll use one free thread
}
else
printf ("no need to acquire/n");

this->service_func ((void*)b->rd_ptr());

printf ("finished release/n");
b->release();

pfree_thread_->release (); // added one free thread
}

return 0;
}

int main (int argc, char* argv[])
{
printf ("begin test:/n");
thread_pool t;
t.start_pool (10, 100);

for (int i=0; i<200; i++)
{
t.add_task (&i, sizeof(i));
if (i % 20 == 0)
ACE_OS::sleep (1);
}

ACE_OS::sleep (2);

ACE_Thread_Manager::instance()->wait();
return 0;
}