linux下C语言实现的线程池

最近看到的一个很好的C语言实现的线程池。这个线程池具有比较好的动态调整能力。
https://docs.oracle.com/cd/E19120-01/open.solaris/816-5137/ggedn/index.html
外部接口：

• 构造一个线程池，注意这里并不创建线程，只是设置相关参数
  min_threads：线程池中存在的最少可用的线程数；
  max_threads：线程池中存在的最大可用的线程数；
  linger：idle工作线程退出之前存在的秒数；
  attr：创建线程相关的属性；
  调用成功返回一个线程池句柄，错误则返回NULL，且errno置错误码。

typedef struct thr_pool thr_pool_t;
thr_pool_t  *thr_pool_create(uint_t min_threads, uint_t max_threads,
                uint_t linger, pthread_attr_t *attr);

• 将工作任务加入到线程池任务队列
  void (*func)(void )：要执行的回调函数；
  arg：回调函数参数；

int thr_pool_queue(thr_pool_t *pool,
            void *(*func)(void *), void *arg);

• 等待线程池任务队列中任务完成

void    thr_pool_wait(thr_pool_t *pool);

• 取消线程池中任务，析构线程池

void    thr_pool_destroy(thr_pool_t *pool);

线程池结构体struct thr_pool如下：

- 能够在运行时创建多个线程池，通过pool_forw和pool_back两个指针域构成一个双向循环链表，来将创建的线程池链接起来。
- pool_mutex、pool_busycv、pool_workcv、pool_waitcv。互斥锁和条件变量保证线程同步。
- pool_active指针域将当前活跃的任务通过单链表链接在一起，链表尾指向NULL，注意该链表是通过活跃线程的栈空间链接起来的。
- pool_head、pool_tail指向线程中任务队列的头和尾。任务队列节点结构struct job中包含指向下一个节点的指针、任务执行的用户函数以及参数。
- pool_attr为线程属性。
- pool_flags线程池状态。
- pool_linger为idle线程退出前存活的秒数。
- minimum、maximum、pool_nthreads分别为最小线程数，最大线程数以及当前活跃的线程数。
源代码：
由于之前的实现是在solaris上的，因此做了一点修改能在linux下使用。
thr_pool.h

/*
 * Declarations for the clients of a thread pool.
 */

#include 

typedef unsigned int uint_t;

/*
 * The thr_pool_t type is opaque to the client.
 * It is created by thr_pool_create() and must be passed
 * unmodified to the remainder of the interfaces.
 */
typedef struct thr_pool thr_pool_t;

/*
 * Create a thread pool.
 *  min_threads:    the minimum number of threads kept in the pool,
 *          always available to perform work requests.
 *  max_threads:    the maximum number of threads that can be
 *          in the pool, performing work requests.
 *  linger:     the number of seconds excess idle worker threads
 *          (greater than min_threads) linger before exiting.
 *  attr:       attributes of all worker threads (can be NULL);
 *          can be destroyed after calling thr_pool_create().
 * On error, thr_pool_create() returns NULL with errno set to the error code.
 */
extern  thr_pool_t  *thr_pool_create(uint_t min_threads, uint_t max_threads,
                uint_t linger, pthread_attr_t *attr);

/*
 * Enqueue a work request to the thread pool job queue.
 * If there are idle worker threads, awaken one to perform the job.
 * Else if the maximum number of workers has not been reached,
 * create a new worker thread to perform the job.
 * Else just return after adding the job to the queue;
 * an existing worker thread will perform the job when
 * it finishes the job it is currently performing.
 *
 * The job is performed as if a new detached thread were created for it:
 *  pthread_create(NULL, attr, void *(*func)(void *), void *arg);
 *
 * On error, thr_pool_queue() returns -1 with errno set to the error code.
 */
extern  int thr_pool_queue(thr_pool_t *pool,
            void *(*func)(void *), void *arg);

/*
 * Wait for all queued jobs to complete.
 */
extern  void    thr_pool_wait(thr_pool_t *pool);

/*
 * Cancel all queued jobs and destroy the pool.
 */
extern  void    thr_pool_destroy(thr_pool_t *pool);

thr_pool.c

/*
 * Thread pool implementation.
 * See  for interface declarations.
 */

#if !defined(_REENTRANT)
#define _REENTRANT
#endif

#include "thr_pool.h"
#include <stdlib.h>
#include <signal.h>
#include <errno.h>

typedef void (*pFun)(void *);

/*
 * FIFO queued job
 */
typedef struct job job_t;
struct job {
    job_t   *job_next;      /* linked list of jobs */
    void    *(*job_func)(void *);   /* function to call */
    void    *job_arg;       /* its argument */
};

/*
 * List of active worker threads, linked through their stacks.
 */
typedef struct active active_t;
struct active {
    active_t    *active_next;   /* linked list of threads */
    pthread_t   active_tid; /* active thread id */
};

/*
 * The thread pool, opaque to the clients.
 */
struct thr_pool {
    thr_pool_t  *pool_forw; /* circular linked list */
    thr_pool_t  *pool_back; /* of all thread pools */
    pthread_mutex_t pool_mutex; /* protects the pool data */
    pthread_cond_t  pool_busycv;    /* synchronization in pool_queue */
    pthread_cond_t  pool_workcv;    /* synchronization with workers */
    pthread_cond_t  pool_waitcv;    /* synchronization in pool_wait() */
    active_t    *pool_active;   /* list of threads performing work */
    job_t       *pool_head; /* head of FIFO job queue */
    job_t       *pool_tail; /* tail of FIFO job queue */
    pthread_attr_t  pool_attr;  /* attributes of the workers */
    int     pool_flags; /* see below */
    uint_t      pool_linger;    /* seconds before idle workers exit */
    int     pool_minimum;   /* minimum number of worker threads */
    int     pool_maximum;   /* maximum number of worker threads */
    int     pool_nthreads;  /* current number of worker threads */
    int     pool_idle;  /* number of idle workers */
};

/* pool_flags */
#define POOL_WAIT   0x01        /* waiting in thr_pool_wait() */
#define POOL_DESTROY    0x02        /* pool is being destroyed */

/* the list of all created and not yet destroyed thread pools */
static thr_pool_t *thr_pools = NULL;

/* protects thr_pools */
static pthread_mutex_t thr_pool_lock = PTHREAD_MUTEX_INITIALIZER;

/* set of all signals */
static sigset_t fillset;

static void *worker_thread(void *);

static int
create_worker(thr_pool_t *pool)
{
    sigset_t oset;
    int error;
    pthread_t thread;

    (void) pthread_sigmask(SIG_SETMASK, &fillset, &oset);
    error = pthread_create(&thread, &pool->pool_attr, worker_thread, pool); //创建线程
    (void) pthread_sigmask(SIG_SETMASK, &oset, NULL);
    return (error);
}

/*
 * Worker thread is terminating.  Possible reasons:
 * - excess idle thread is terminating because there is no work.
 * - thread was cancelled (pool is being destroyed).
 * - the job function called pthread_exit().
 * In the last case, create another worker thread
 * if necessary to keep the pool populated.
 */
static void
worker_cleanup(void *vpool)
{
    thr_pool_t *pool=(thr_pool_t *)vpool;
    --pool->pool_nthreads;
    if (pool->pool_flags & POOL_DESTROY) {
        if (pool->pool_nthreads == 0)
            (void) pthread_cond_broadcast(&pool->pool_busycv);
    } else if (pool->pool_head != NULL &&
        pool->pool_nthreads < pool->pool_maximum &&
        create_worker(pool) == 0) {
        pool->pool_nthreads++;
    }
    (void) pthread_mutex_unlock(&pool->pool_mutex);
}

static void
notify_waiters(thr_pool_t *pool)
{
    if (pool->pool_head == NULL && pool->pool_active == NULL) { //任务队列和活跃线程为空
        pool->pool_flags &= ~POOL_WAIT; //清零等待状态
        (void) pthread_cond_broadcast(&pool->pool_waitcv); //激活所有线程
    }
}

/*
 * Called by a worker thread on return from a job.
 */
static void
job_cleanup(void *vpool)
{
    thr_pool_t *pool=(thr_pool_t *)vpool;
    pthread_t my_tid = pthread_self();
    active_t *activep;
    active_t **activepp;

    (void) pthread_mutex_lock(&pool->pool_mutex);
    for (activepp = &pool->pool_active;
        (activep = *activepp) != NULL;
        activepp = &activep->active_next) {
        if (activep->active_tid == my_tid) {
            *activepp = activep->active_next;
            break;
        }
    }
    if (pool->pool_flags & POOL_WAIT)
        notify_waiters(pool);
}

static void *
worker_thread(void *arg)
{
    thr_pool_t *pool = (thr_pool_t *)arg;
    int timedout;
    job_t *job;
    void *(*func)(void *);
    active_t active;
    struct timespec ts;

    /*
     * This is the worker's main loop.  It will only be left
     * if a timeout occurs or if the pool is being destroyed.
     */
    (void) pthread_mutex_lock(&pool->pool_mutex); //加锁
    pthread_cleanup_push(worker_cleanup, pool); //将工作线程清理函数压栈
    active.active_tid = pthread_self(); //获得活跃线程id
    for (;;) {
        /*
         * We don't know what this thread was doing during
         * its last job, so we reset its signal mask and
         * cancellation state back to the initial values.
         */
        (void) pthread_sigmask(SIG_SETMASK, &fillset, NULL);
        (void) pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL); //取消请求被延期直到
        (void) pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);

        timedout = 0; //超时标志清零
        pool->pool_idle++; //idle线程加1
        if (pool->pool_flags & POOL_WAIT) //线程池状态为等待状态
            notify_waiters(pool); //通知等待线程
        while (pool->pool_head == NULL &&
            !(pool->pool_flags & POOL_DESTROY)) { //任务队列为空并且线程池没有删除
            if (pool->pool_nthreads <= pool->pool_minimum) { //如果当前工作线程小于等于线程池设置最小线程数
                (void) pthread_cond_wait(&pool->pool_workcv,
                    &pool->pool_mutex); //阻塞当前线程
            } else { //否则设置定时器
                (void) clock_gettime(CLOCK_REALTIME, &ts);
                ts.tv_sec += pool->pool_linger;
                if (pool->pool_linger == 0 ||
                    pthread_cond_timedwait(&pool->pool_workcv,
                    &pool->pool_mutex, &ts) == ETIMEDOUT) {
                    timedout = 1; //超时标志置1
                    break;
                }
            }
        }
        pool->pool_idle--; //空闲线程减1
        if (pool->pool_flags & POOL_DESTROY) //线程池状态为删除态，则跳出
            break;
        if ((job = pool->pool_head) != NULL) { //任务队列不为空
            timedout = 0; //超时标志清零
            func = job->job_func;
            arg = job->job_arg;
            pool->pool_head = job->job_next; //任务出队
            if (job == pool->pool_tail) //若是任务队列最后一个任务
                pool->pool_tail = NULL;
            active.active_next = pool->pool_active; //将当期活跃工作线程加入活跃线程链表，头插,注意建立在栈中
            pool->pool_active = &active;
            (void) pthread_mutex_unlock(&pool->pool_mutex); //解锁
            pthread_cleanup_push(job_cleanup, pool); //压栈任务清零函数
            free(job); //释放当前任务
            /*
             * Call the specified job function.
             */
            (void) func(arg); //指向真正的用户函数
            /*
             * If the job function calls pthread_exit(), the thread
             * calls job_cleanup(pool) and worker_cleanup(pool);
             * the integrity of the pool is thereby maintained.
             */
            pthread_cleanup_pop(1); /* job_cleanup(pool) */
        }
        if (timedout && pool->pool_nthreads > pool->pool_minimum) { //超时并且当前工作线程大于线程池设置最小线程数
            /*
             * We timed out and there is no work to be done
             * and the number of workers exceeds the minimum.
             * Exit now to reduce the size of the pool.
             */
            break;
        }
    }
    pthread_cleanup_pop(1); /* worker_cleanup(pool) */
    return (NULL);
}

static void
clone_attributes(pthread_attr_t *new_attr, pthread_attr_t *old_attr)
{
    struct sched_param param;
    void *addr;
    size_t size;
    int value;

    (void) pthread_attr_init(new_attr);
//设置线程相关属性
    if (old_attr != NULL) {
        (void) pthread_attr_getstack(old_attr, &addr, &size);
        /* don't allow a non-NULL thread stack address */
        (void) pthread_attr_setstack(new_attr, NULL, size);

        (void) pthread_attr_getscope(old_attr, &value);
        (void) pthread_attr_setscope(new_attr, value);

        (void) pthread_attr_getinheritsched(old_attr, &value);
        (void) pthread_attr_setinheritsched(new_attr, value);

        (void) pthread_attr_getschedpolicy(old_attr, &value);
        (void) pthread_attr_setschedpolicy(new_attr, value);

        (void) pthread_attr_getschedparam(old_attr, &param);
        (void) pthread_attr_setschedparam(new_attr, &param);

        (void) pthread_attr_getguardsize(old_attr, &size);
        (void) pthread_attr_setguardsize(new_attr, size);
    }

    /* make all pool threads be detached threads */
    (void) pthread_attr_setdetachstate(new_attr, PTHREAD_CREATE_DETACHED);
}

thr_pool_t *
thr_pool_create(uint_t min_threads, uint_t max_threads, uint_t linger,
    pthread_attr_t *attr)
{
    thr_pool_t  *pool;

    (void) sigfillset(&fillset); //加入所有信号

    if (min_threads > max_threads || max_threads < 1) {
        errno = EINVAL;
        return (NULL);
    }

    if ((pool = malloc(sizeof (*pool))) == NULL) { //为线程池结构体分配内存
        errno = ENOMEM;
        return (NULL);
    }
    //初始化线程池结构体
    (void) pthread_mutex_init(&pool->pool_mutex, NULL);
    (void) pthread_cond_init(&pool->pool_busycv, NULL);
    (void) pthread_cond_init(&pool->pool_workcv, NULL);
    (void) pthread_cond_init(&pool->pool_waitcv, NULL);
    pool->pool_active = NULL;
    pool->pool_head = NULL;
    pool->pool_tail = NULL;
    pool->pool_flags = 0;
    pool->pool_linger = linger;
    pool->pool_minimum = min_threads;
    pool->pool_maximum = max_threads;
    pool->pool_nthreads = 0;
    pool->pool_idle = 0;

    /*
     * We cannot just copy the attribute pointer.
     * We need to initialize a new pthread_attr_t structure using
     * the values from the caller-supplied attribute structure.
     * If the attribute pointer is NULL, we need to initialize
     * the new pthread_attr_t structure with default values.
     */
    clone_attributes(&pool->pool_attr, attr); //设置线程创建属性

    /* insert into the global list of all thread pools */
    (void) pthread_mutex_lock(&thr_pool_lock); //加锁

    if (thr_pools == NULL) { //建立链表第一个节点
        pool->pool_forw = pool;
        pool->pool_back = pool;
        thr_pools = pool;
    } else { //后面插入
        thr_pools->pool_back->pool_forw = pool;
        pool->pool_forw = thr_pools;
        pool->pool_back = thr_pools->pool_back;
        thr_pools->pool_back = pool;
    }
    (void) pthread_mutex_unlock(&thr_pool_lock); //解锁

    return (pool);
}

int
thr_pool_queue(thr_pool_t *pool, void *(*func)(void *), void *arg)
{
    job_t *job;

    if ((job = malloc(sizeof (*job))) == NULL) { //为job节点分配空间
        errno = ENOMEM;
        return (-1);
    }
    //初始化job节点
    job->job_next = NULL;
    job->job_func = func;
    job->job_arg = arg;

    (void) pthread_mutex_lock(&pool->pool_mutex); //加锁

    //job入队，尾部入队
    if (pool->pool_head == NULL) //插入第一个job
        pool->pool_head = job;
    else 
        pool->pool_tail->job_next = job;
    pool->pool_tail = job;

    if (pool->pool_idle > 0) //有idle线程就从中唤醒一个
        (void) pthread_cond_signal(&pool->pool_workcv);
    else if (pool->pool_nthreads < pool->pool_maximum &&
        create_worker(pool) == 0) //当前线程数小于设置的总线程数，则创建一个线程
        pool->pool_nthreads++; //当前线程数加1

    (void) pthread_mutex_unlock(&pool->pool_mutex); //解锁
    return (0);
}

void
thr_pool_wait(thr_pool_t *pool)
{
    (void) pthread_mutex_lock(&pool->pool_mutex); //加锁
    pthread_cleanup_push((pFun)pthread_mutex_unlock, &pool->pool_mutex); //压栈解锁函数
    while (pool->pool_head != NULL || pool->pool_active != NULL) { //任务队列不为空或者当前活跃线程链表不为空
        pool->pool_flags |= POOL_WAIT; //置线程池状态为等待状态
        (void) pthread_cond_wait(&pool->pool_waitcv, &pool->pool_mutex); //阻塞当前线程
    }
    pthread_cleanup_pop(1); /* pthread_mutex_unlock(&pool->pool_mutex); */
}

void
thr_pool_destroy(thr_pool_t *pool)
{
    active_t *activep;
    job_t *job;

    (void) pthread_mutex_lock(&pool->pool_mutex); //加锁
    pthread_cleanup_push((pFun)pthread_mutex_unlock, &pool->pool_mutex); //压栈解锁函数

    /* mark the pool as being destroyed; wakeup idle workers */
    pool->pool_flags |= POOL_DESTROY; //线程池状态置为删除态
    (void) pthread_cond_broadcast(&pool->pool_workcv); //唤醒所有idle线程

    /* cancel all active workers */
    for (activep = pool->pool_active;
        activep != NULL;
        activep = activep->active_next) //取消所有活跃线程
        (void) pthread_cancel(activep->active_tid);

    /* wait for all active workers to finish */
    while (pool->pool_active != NULL) {
        pool->pool_flags |= POOL_WAIT;
        (void) pthread_cond_wait(&pool->pool_waitcv, &pool->pool_mutex);
    }

    /* the last worker to terminate will wake us up */
    while (pool->pool_nthreads != 0)
        (void) pthread_cond_wait(&pool->pool_busycv, &pool->pool_mutex);

    pthread_cleanup_pop(1); /* pthread_mutex_unlock(&pool->pool_mutex); */

    /*
     * Unlink the pool from the global list of all pools.
     */
    (void) pthread_mutex_lock(&thr_pool_lock);
    if (thr_pools == pool)
        thr_pools = pool->pool_forw;
    if (thr_pools == pool)
        thr_pools = NULL;
    else {
        pool->pool_back->pool_forw = pool->pool_forw;
        pool->pool_forw->pool_back = pool->pool_back;
    }
    (void) pthread_mutex_unlock(&thr_pool_lock);

    /*
     * There should be no pending jobs, but just in case...
     */
    for (job = pool->pool_head; job != NULL; job = pool->pool_head) {
        pool->pool_head = job->job_next;
        free(job);
    }
    (void) pthread_attr_destroy(&pool->pool_attr);
    free(pool);
}