スレッドプールのコード例

この節では、スレッドプールのコード例を示します。

• 「thr_pool.h ファイル」

• 「thr_pool.c ファイル」

thr_pool.h ファイル

このファイルは、この例で使用されている関数を宣言します。

例 A–1 thr_pool.h

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

#include <pthread.h>

/*
 * 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 ファイル

このファイルは、スレッドプールを実装します。

例 A–2 thr_pool.c

/*
 * Thread pool implementation.
 * See <thr_pool.h> for interface declarations.
 */

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

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

/*
 * 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;

	(void) pthread_sigmask(SIG_SETMASK, &fillset, &oset);
	error = pthread_create(NULL, &pool->pool_attr, worker_thread, pool);
	(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(thr_pool_t *pool)
{
	--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) {
		pool->pool_flags &= ~POOL_WAIT;
		(void) pthread_cond_broadcast(&pool->pool_waitcv);
	}
}

/*
 * Called by a worker thread on return from a job.
 */
static void
job_cleanup(thr_pool_t *pool)
{
	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;
	timestruc_t 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);
	pthread_cleanup_push(worker_cleanup, pool);
	active.active_tid = pthread_self();
	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);
		(void) pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);

		timedout = 0;
		pool->pool_idle++;
		if (pool->pool_flags & POOL_WAIT)
			notify_waiters(pool);
		while (pool->pool_head == NULL &&
		    !(pool->pool_flags & POOL_DESTROY)) {
			if (pool->pool_nthreads <= pool->pool_minimum) {
				(void) pthread_cond_wait(&pool->pool_workcv,
				    &pool->pool_mutex);
			} else {
				(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;
					break;
				}
			}
		}
		pool->pool_idle--;
		if (pool->pool_flags & POOL_DESTROY)
			break;
		if ((job = pool->pool_head) != NULL) {
			timedout = 0;
			func = job->job_func;
			arg = job->job_arg;
			pool->pool_head = job->job_next;
			if (job == pool->pool_tail)
				pool->pool_tail = NULL;
			active.active_next = pool->pool_active;
			pool->pool_active = &active;
			(void) pthread_mutex_unlock(&pool->pool_mutex);
			pthread_cleanup_push(job_cleanup, pool);
			free(job);
			/*
			 * Call the specified job function.
			 */
			(void) func(arg);
			/*
			 * 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) {
			/*
			 * 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);

	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);

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

	if ((pool = malloc(sizeof (*pool))) == NULL) {
		errno = ENOMEM;
		return (NULL);
	}
	(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);

	/* insert into the global list of all thread pools */
	(void) pthread_mutex_lock(&thr_pool_lock);
	if (thr_pools == NULL) {
		pool->pool_forw = pool;
		pool->pool_back = pool;
		thr_pools = pool;
	} else {
		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);

	return (pool);
}

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

	if ((job = malloc(sizeof (*job))) == NULL) {
		errno = ENOMEM;
		return (-1);
	}
	job->job_next = NULL;
	job->job_func = func;
	job->job_arg = arg;

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

	if (pool->pool_head == NULL)
		pool->pool_head = job;
	else
		pool->pool_tail->job_next = job;
	pool->pool_tail = job;

	if (pool->pool_idle > 0)
		(void) pthread_cond_signal(&pool->pool_workcv);
	else if (pool->pool_nthreads < pool->pool_maximum &&
	    create_worker(pool) == 0)
		pool->pool_nthreads++;

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

void
thr_pool_wait(thr_pool_t *pool)
{
	(void) pthread_mutex_lock(&pool->pool_mutex);
	pthread_cleanup_push(pthread_mutex_unlock, &pool->pool_mutex);
	while (pool->pool_head != NULL || pool->pool_active != NULL) {
		pool->pool_flags |= POOL_WAIT;
		(void) pthread_cond_wait(&pool->pool_waitcv, &pool->pool_mutex);
	}
	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);
	pthread_cleanup_push(pthread_mutex_unlock, &pool->pool_mutex);

	/* mark the pool as being destroyed; wakeup idle workers */
	pool->pool_flags |= POOL_DESTROY;
	(void) pthread_cond_broadcast(&pool->pool_workcv);

	/* cancel all active workers */
	for (activep = pool->pool_active;
	    activep != NULL;
	    activep = activep->active_next)
		(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);
}