source: vendor/current/source3/lib/pthreadpool/pthreadpool.c

/*
 * Unix SMB/CIFS implementation.
 * thread pool implementation
 * Copyright (C) Volker Lendecke 2009
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <fcntl.h>
#include "system/time.h"
#include "system/filesys.h"
#include "replace.h"

#include "pthreadpool.h"
#include "lib/util/dlinklist.h"

struct pthreadpool_job {
        int id;
        void (*fn)(void *private_data);
        void *private_data;
};

struct pthreadpool {
        /*
         * List pthreadpools for fork safety
         */
        struct pthreadpool *prev, *next;

        /*
         * Control access to this struct
         */
        pthread_mutex_t mutex;

        /*
         * Threads waiting for work do so here
         */
        pthread_cond_t condvar;

        /*
         * Array of jobs
         */
        size_t jobs_array_len;
        struct pthreadpool_job *jobs;

        size_t head;
        size_t num_jobs;

        /*
         * pipe for signalling
         */
        int sig_pipe[2];

        /*
         * indicator to worker threads that they should shut down
         */
        int shutdown;

        /*
         * maximum number of threads
         */
        int max_threads;

        /*
         * Number of threads
         */
        int num_threads;

        /*
         * Number of idle threads
         */
        int num_idle;

        /*
         * An array of threads that require joining.
         */
        int                     num_exited;
        pthread_t               *exited; /* We alloc more */
};

static pthread_mutex_t pthreadpools_mutex = PTHREAD_MUTEX_INITIALIZER;
static struct pthreadpool *pthreadpools = NULL;
static pthread_once_t pthreadpool_atfork_initialized = PTHREAD_ONCE_INIT;

static void pthreadpool_prep_atfork(void);

/*
 * Initialize a thread pool
 */

int pthreadpool_init(unsigned max_threads, struct pthreadpool **presult)
{
        struct pthreadpool *pool;
        int ret;

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

        pool->jobs_array_len = 4;
        pool->jobs = calloc(
                pool->jobs_array_len, sizeof(struct pthreadpool_job));

        if (pool->jobs == NULL) {
                free(pool);
                return ENOMEM;
        }

        pool->head = pool->num_jobs = 0;

        ret = pipe(pool->sig_pipe);
        if (ret == -1) {
                int err = errno;
                free(pool->jobs);
                free(pool);
                return err;
        }

        ret = pthread_mutex_init(&pool->mutex, NULL);
        if (ret != 0) {
                close(pool->sig_pipe[0]);
                close(pool->sig_pipe[1]);
                free(pool->jobs);
                free(pool);
                return ret;
        }

        ret = pthread_cond_init(&pool->condvar, NULL);
        if (ret != 0) {
                pthread_mutex_destroy(&pool->mutex);
                close(pool->sig_pipe[0]);
                close(pool->sig_pipe[1]);
                free(pool->jobs);
                free(pool);
                return ret;
        }

        pool->shutdown = 0;
        pool->num_threads = 0;
        pool->num_exited = 0;
        pool->exited = NULL;
        pool->max_threads = max_threads;
        pool->num_idle = 0;

        ret = pthread_mutex_lock(&pthreadpools_mutex);
        if (ret != 0) {
                pthread_cond_destroy(&pool->condvar);
                pthread_mutex_destroy(&pool->mutex);
                close(pool->sig_pipe[0]);
                close(pool->sig_pipe[1]);
                free(pool->jobs);
                free(pool);
                return ret;
        }
        DLIST_ADD(pthreadpools, pool);

        ret = pthread_mutex_unlock(&pthreadpools_mutex);
        assert(ret == 0);

        pthread_once(&pthreadpool_atfork_initialized, pthreadpool_prep_atfork);

        *presult = pool;

        return 0;
}

static void pthreadpool_prepare(void)
{
        int ret;
        struct pthreadpool *pool;

        ret = pthread_mutex_lock(&pthreadpools_mutex);
        assert(ret == 0);

        pool = pthreadpools;

        while (pool != NULL) {
                ret = pthread_mutex_lock(&pool->mutex);
                assert(ret == 0);
                pool = pool->next;
        }
}

static void pthreadpool_parent(void)
{
        int ret;
        struct pthreadpool *pool;

        for (pool = DLIST_TAIL(pthreadpools);
             pool != NULL;
             pool = DLIST_PREV(pool)) {
                ret = pthread_mutex_unlock(&pool->mutex);
                assert(ret == 0);
        }

        ret = pthread_mutex_unlock(&pthreadpools_mutex);
        assert(ret == 0);
}

static void pthreadpool_child(void)
{
        int ret;
        struct pthreadpool *pool;

        for (pool = DLIST_TAIL(pthreadpools);
             pool != NULL;
             pool = DLIST_PREV(pool)) {

                close(pool->sig_pipe[0]);
                close(pool->sig_pipe[1]);

                ret = pipe(pool->sig_pipe);
                assert(ret == 0);

                pool->num_threads = 0;

                pool->num_exited = 0;
                free(pool->exited);
                pool->exited = NULL;

                pool->num_idle = 0;
                pool->head = 0;
                pool->num_jobs = 0;

                ret = pthread_mutex_unlock(&pool->mutex);
                assert(ret == 0);
        }

        ret = pthread_mutex_unlock(&pthreadpools_mutex);
        assert(ret == 0);
}

static void pthreadpool_prep_atfork(void)
{
        pthread_atfork(pthreadpool_prepare, pthreadpool_parent,
                       pthreadpool_child);
}

/*
 * Return the file descriptor which becomes readable when a job has
 * finished
 */

int pthreadpool_signal_fd(struct pthreadpool *pool)
{
        return pool->sig_pipe[0];
}

/*
 * Do a pthread_join() on all children that have exited, pool->mutex must be
 * locked
 */
static void pthreadpool_join_children(struct pthreadpool *pool)
{
        int i;

        for (i=0; i<pool->num_exited; i++) {
                int ret;

                ret = pthread_join(pool->exited[i], NULL);
                if (ret != 0) {
                        /*
                         * Severe internal error, we can't do much but
                         * abort here.
                         */
                        abort();
                }
        }
        pool->num_exited = 0;

        /*
         * Deliberately not free and NULL pool->exited. That will be
         * re-used by realloc later.
         */
}

/*
 * Fetch a finished job number from the signal pipe
 */

int pthreadpool_finished_jobs(struct pthreadpool *pool, int *jobids,
                              unsigned num_jobids)
{
        ssize_t to_read, nread;

        nread = -1;
        errno = EINTR;

        to_read = sizeof(int) * num_jobids;

        while ((nread == -1) && (errno == EINTR)) {
                nread = read(pool->sig_pipe[0], jobids, to_read);
        }
        if (nread == -1) {
                return -errno;
        }
        if ((nread % sizeof(int)) != 0) {
                return -EINVAL;
        }
        return nread / sizeof(int);
}

/*
 * Destroy a thread pool, finishing all threads working for it
 */

int pthreadpool_destroy(struct pthreadpool *pool)
{
        int ret, ret1;

        ret = pthread_mutex_lock(&pool->mutex);
        if (ret != 0) {
                return ret;
        }

        if ((pool->num_jobs != 0) || pool->shutdown) {
                ret = pthread_mutex_unlock(&pool->mutex);
                assert(ret == 0);
                return EBUSY;
        }

        if (pool->num_threads > 0) {
                /*
                 * We have active threads, tell them to finish, wait for that.
                 */

                pool->shutdown = 1;

                if (pool->num_idle > 0) {
                        /*
                         * Wake the idle threads. They will find
                         * pool->shutdown to be set and exit themselves
                         */
                        ret = pthread_cond_broadcast(&pool->condvar);
                        if (ret != 0) {
                                pthread_mutex_unlock(&pool->mutex);
                                return ret;
                        }
                }

                while ((pool->num_threads > 0) || (pool->num_exited > 0)) {

                        if (pool->num_exited > 0) {
                                pthreadpool_join_children(pool);
                                continue;
                        }
                        /*
                         * A thread that shuts down will also signal
                         * pool->condvar
                         */
                        ret = pthread_cond_wait(&pool->condvar, &pool->mutex);
                        if (ret != 0) {
                                pthread_mutex_unlock(&pool->mutex);
                                return ret;
                        }
                }
        }

        ret = pthread_mutex_unlock(&pool->mutex);
        if (ret != 0) {
                return ret;
        }
        ret = pthread_mutex_destroy(&pool->mutex);
        ret1 = pthread_cond_destroy(&pool->condvar);

        if (ret != 0) {
                return ret;
        }
        if (ret1 != 0) {
                return ret1;
        }

        ret = pthread_mutex_lock(&pthreadpools_mutex);
        if (ret != 0) {
                return ret;
        }
        DLIST_REMOVE(pthreadpools, pool);
        ret = pthread_mutex_unlock(&pthreadpools_mutex);
        assert(ret == 0);

        close(pool->sig_pipe[0]);
        pool->sig_pipe[0] = -1;

        close(pool->sig_pipe[1]);
        pool->sig_pipe[1] = -1;

        free(pool->exited);
        free(pool->jobs);
        free(pool);

        return 0;
}

/*
 * Prepare for pthread_exit(), pool->mutex must be locked
 */
static void pthreadpool_server_exit(struct pthreadpool *pool)
{
        pthread_t *exited;

        pool->num_threads -= 1;

        exited = (pthread_t *)realloc(
                pool->exited, sizeof(pthread_t) * (pool->num_exited + 1));

        if (exited == NULL) {
                /* lost a thread status */
                return;
        }
        pool->exited = exited;

        pool->exited[pool->num_exited] = pthread_self();
        pool->num_exited += 1;
}

static bool pthreadpool_get_job(struct pthreadpool *p,
                                struct pthreadpool_job *job)
{
        if (p->num_jobs == 0) {
                return false;
        }
        *job = p->jobs[p->head];
        p->head = (p->head+1) % p->jobs_array_len;
        p->num_jobs -= 1;
        return true;
}

static bool pthreadpool_put_job(struct pthreadpool *p,
                                int id,
                                void (*fn)(void *private_data),
                                void *private_data)
{
        struct pthreadpool_job *job;

        if (p->num_jobs == p->jobs_array_len) {
                struct pthreadpool_job *tmp;
                size_t new_len = p->jobs_array_len * 2;

                tmp = realloc(
                        p->jobs, sizeof(struct pthreadpool_job) * new_len);
                if (tmp == NULL) {
                        return false;
                }
                p->jobs = tmp;

                /*
                 * We just doubled the jobs array. The array implements a FIFO
                 * queue with a modulo-based wraparound, so we have to memcpy
                 * the jobs that are logically at the queue end but physically
                 * before the queue head into the reallocated area. The new
                 * space starts at the current jobs_array_len, and we have to
                 * copy everything before the current head job into the new
                 * area.
                 */
                memcpy(&p->jobs[p->jobs_array_len], p->jobs,
                       sizeof(struct pthreadpool_job) * p->head);

                p->jobs_array_len = new_len;
        }

        job = &p->jobs[(p->head + p->num_jobs) % p->jobs_array_len];
        job->id = id;
        job->fn = fn;
        job->private_data = private_data;

        p->num_jobs += 1;

        return true;
}

static void *pthreadpool_server(void *arg)
{
        struct pthreadpool *pool = (struct pthreadpool *)arg;
        int res;

        res = pthread_mutex_lock(&pool->mutex);
        if (res != 0) {
                return NULL;
        }

        while (1) {
                struct timespec ts;
                struct pthreadpool_job job;

                /*
                 * idle-wait at most 1 second. If nothing happens in that
                 * time, exit this thread.
                 */

                clock_gettime(CLOCK_REALTIME, &ts);
                ts.tv_sec += 1;

                while ((pool->num_jobs == 0) && (pool->shutdown == 0)) {

                        pool->num_idle += 1;
                        res = pthread_cond_timedwait(
                                &pool->condvar, &pool->mutex, &ts);
                        pool->num_idle -= 1;

                        if (res == ETIMEDOUT) {

                                if (pool->num_jobs == 0) {
                                        /*
                                         * we timed out and still no work for
                                         * us. Exit.
                                         */
                                        pthreadpool_server_exit(pool);
                                        pthread_mutex_unlock(&pool->mutex);
                                        return NULL;
                                }

                                break;
                        }
                        assert(res == 0);
                }

                if (pthreadpool_get_job(pool, &job)) {
                        ssize_t written;
                        int sig_pipe = pool->sig_pipe[1];

                        /*
                         * Do the work with the mutex unlocked
                         */

                        res = pthread_mutex_unlock(&pool->mutex);
                        assert(res == 0);

                        job.fn(job.private_data);

                        res = pthread_mutex_lock(&pool->mutex);
                        assert(res == 0);

                        written = write(sig_pipe, &job.id, sizeof(job.id));
                        if (written != sizeof(int)) {
                                pthreadpool_server_exit(pool);
                                pthread_mutex_unlock(&pool->mutex);
                                return NULL;
                        }
                }

                if ((pool->num_jobs == 0) && (pool->shutdown != 0)) {
                        /*
                         * No more work to do and we're asked to shut down, so
                         * exit
                         */
                        pthreadpool_server_exit(pool);

                        if (pool->num_threads == 0) {
                                /*
                                 * Ping the main thread waiting for all of us
                                 * workers to have quit.
                                 */
                                pthread_cond_broadcast(&pool->condvar);
                        }

                        pthread_mutex_unlock(&pool->mutex);
                        return NULL;
                }
        }
}

int pthreadpool_add_job(struct pthreadpool *pool, int job_id,
                        void (*fn)(void *private_data), void *private_data)
{
        pthread_t thread_id;
        int res;
        sigset_t mask, omask;

        res = pthread_mutex_lock(&pool->mutex);
        if (res != 0) {
                return res;
        }

        if (pool->shutdown) {
                /*
                 * Protect against the pool being shut down while
                 * trying to add a job
                 */
                res = pthread_mutex_unlock(&pool->mutex);
                assert(res == 0);
                return EINVAL;
        }

        /*
         * Just some cleanup under the mutex
         */
        pthreadpool_join_children(pool);

        /*
         * Add job to the end of the queue
         */
        if (!pthreadpool_put_job(pool, job_id, fn, private_data)) {
                pthread_mutex_unlock(&pool->mutex);
                return ENOMEM;
        }

        if (pool->num_idle > 0) {
                /*
                 * We have idle threads, wake one.
                 */
                res = pthread_cond_signal(&pool->condvar);
                pthread_mutex_unlock(&pool->mutex);
                return res;
        }

        if ((pool->max_threads != 0) &&
            (pool->num_threads >= pool->max_threads)) {
                /*
                 * No more new threads, we just queue the request
                 */
                pthread_mutex_unlock(&pool->mutex);
                return 0;
        }

        /*
         * Create a new worker thread. It should not receive any signals.
         */

        sigfillset(&mask);

        res = pthread_sigmask(SIG_BLOCK, &mask, &omask);
        if (res != 0) {
                pthread_mutex_unlock(&pool->mutex);
                return res;
        }

        res = pthread_create(&thread_id, NULL, pthreadpool_server,
                                (void *)pool);
        if (res == 0) {
                pool->num_threads += 1;
        }

        assert(pthread_sigmask(SIG_SETMASK, &omask, NULL) == 0);

        pthread_mutex_unlock(&pool->mutex);
        return res;
}