[openldap] / libraries / libldap_r / tpool.c

/* $OpenLDAP$ */
/* This work is part of OpenLDAP Software <http://www.openldap.org/>.
 *
 * Copyright 1998-2016 The OpenLDAP Foundation.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 */

#include "portable.h"

#include <stdio.h>

#include <ac/signal.h>
#include <ac/stdarg.h>
#include <ac/stdlib.h>
#include <ac/string.h>
#include <ac/time.h>
#include <ac/errno.h>

#include "ldap-int.h"
#include "ldap_pvt_thread.h" /* Get the thread interface */
#include "ldap_queue.h"
#define LDAP_THREAD_POOL_IMPLEMENTATION
#include "ldap_thr_debug.h"  /* May rename symbols defined below */

#ifndef LDAP_THREAD_HAVE_TPOOL

/* Thread-specific key with data and optional free function */
typedef struct ldap_int_tpool_key_s {
        void *ltk_key;
        void *ltk_data;
        ldap_pvt_thread_pool_keyfree_t *ltk_free;
} ldap_int_tpool_key_t;

/* Max number of thread-specific keys we store per thread.
 * We don't expect to use many...
 */
#define MAXKEYS 32

/* Max number of threads */
#define LDAP_MAXTHR     1024    /* must be a power of 2 */

/* (Theoretical) max number of pending requests */
#define MAX_PENDING (INT_MAX/2) /* INT_MAX - (room to avoid overflow) */

/* pool->ltp_pause values */
enum { NOT_PAUSED = 0, WANT_PAUSE = 1, PAUSED = 2 };

/* Context: thread ID and thread-specific key/data pairs */
typedef struct ldap_int_thread_userctx_s {
        ldap_pvt_thread_t ltu_id;
        ldap_int_tpool_key_t ltu_key[MAXKEYS];
} ldap_int_thread_userctx_t;


/* Simple {thread ID -> context} hash table; key=ctx->ltu_id.
 * Protected by ldap_pvt_thread_pool_mutex except during pauses,
 * when it is read-only (used by pool_purgekey and pool_context).
 * Protected by tpool->ltp_mutex during pauses.
 */
static struct {
        ldap_int_thread_userctx_t *ctx;
        /* ctx is valid when not NULL or DELETED_THREAD_CTX */
#       define DELETED_THREAD_CTX (&ldap_int_main_thrctx + 1) /* dummy addr */
} thread_keys[LDAP_MAXTHR];

#define TID_HASH(tid, hash) do { \
        unsigned const char *ptr_ = (unsigned const char *)&(tid); \
        unsigned i_; \
        for (i_ = 0, (hash) = ptr_[0]; ++i_ < sizeof(tid);) \
                (hash) += ((hash) << 5) ^ ptr_[i_]; \
} while(0)


/* Task for a thread to perform */
typedef struct ldap_int_thread_task_s {
        union {
                LDAP_STAILQ_ENTRY(ldap_int_thread_task_s) q;
                LDAP_SLIST_ENTRY(ldap_int_thread_task_s) l;
        } ltt_next;
        ldap_pvt_thread_start_t *ltt_start_routine;
        void *ltt_arg;
} ldap_int_thread_task_t;

typedef LDAP_STAILQ_HEAD(tcq, ldap_int_thread_task_s) ldap_int_tpool_plist_t;

struct ldap_int_thread_pool_s {
        LDAP_STAILQ_ENTRY(ldap_int_thread_pool_s) ltp_next;

        /* protect members below, and protect thread_keys[] during pauses */
        ldap_pvt_thread_mutex_t ltp_mutex;

        /* not paused and something to do for pool_<wrapper/pause/destroy>() */
        ldap_pvt_thread_cond_t ltp_cond;

        /* ltp_active_count <= 1 && ltp_pause */
        ldap_pvt_thread_cond_t ltp_pcond;

        /* ltp_pause == 0 ? &ltp_pending_list : &empty_pending_list,
         * maintaned to reduce work for pool_wrapper()
         */
        ldap_int_tpool_plist_t *ltp_work_list;

        /* pending tasks, and unused task objects */
        ldap_int_tpool_plist_t ltp_pending_list;
        LDAP_SLIST_HEAD(tcl, ldap_int_thread_task_s) ltp_free_list;

        /* The pool is finishing, waiting for its threads to close.
         * They close when ltp_pending_list is done.  pool_submit()
         * rejects new tasks.  ltp_max_pending = -(its old value).
         */
        int ltp_finishing;

        /* Some active task needs to be the sole active task.
         * Atomic variable so ldap_pvt_thread_pool_pausing() can read it.
         * Note: Pauses adjust ltp_<open_count/vary_open_count/work_list>,
         * so pool_<submit/wrapper>() mostly can avoid testing ltp_pause.
         */
        volatile sig_atomic_t ltp_pause;

        /* Max number of threads in pool, or 0 for default (LDAP_MAXTHR) */
        int ltp_max_count;

        /* Max pending + paused + idle tasks, negated when ltp_finishing */
        int ltp_max_pending;

        int ltp_pending_count;          /* Pending + paused + idle tasks */
        int ltp_active_count;           /* Active, not paused/idle tasks */
        int ltp_open_count;                     /* Number of threads, negated when ltp_pause */
        int ltp_starting;                       /* Currenlty starting threads */

        /* >0 if paused or we may open a thread, <0 if we should close a thread.
         * Updated when ltp_<finishing/pause/max_count/open_count> change.
         * Maintained to reduce the time ltp_mutex must be locked in
         * ldap_pvt_thread_pool_<submit/wrapper>().
         */
        int ltp_vary_open_count;
#       define SET_VARY_OPEN_COUNT(pool)        \
                ((pool)->ltp_vary_open_count =  \
                 (pool)->ltp_pause      ?  1 :  \
                 (pool)->ltp_finishing  ? -1 :  \
                 ((pool)->ltp_max_count ? (pool)->ltp_max_count : LDAP_MAXTHR) \
                 - (pool)->ltp_open_count)
};

static ldap_int_tpool_plist_t empty_pending_list =
        LDAP_STAILQ_HEAD_INITIALIZER(empty_pending_list);

static int ldap_int_has_thread_pool = 0;
static LDAP_STAILQ_HEAD(tpq, ldap_int_thread_pool_s)
        ldap_int_thread_pool_list =
        LDAP_STAILQ_HEAD_INITIALIZER(ldap_int_thread_pool_list);

static ldap_pvt_thread_mutex_t ldap_pvt_thread_pool_mutex;

static void *ldap_int_thread_pool_wrapper( void *pool );

static ldap_pvt_thread_key_t    ldap_tpool_key;

/* Context of the main thread */
static ldap_int_thread_userctx_t ldap_int_main_thrctx;

int
ldap_int_thread_pool_startup ( void )
{
        ldap_int_main_thrctx.ltu_id = ldap_pvt_thread_self();
        ldap_pvt_thread_key_create( &ldap_tpool_key );
        return ldap_pvt_thread_mutex_init(&ldap_pvt_thread_pool_mutex);
}

int
ldap_int_thread_pool_shutdown ( void )
{
        struct ldap_int_thread_pool_s *pool;

        while ((pool = LDAP_STAILQ_FIRST(&ldap_int_thread_pool_list)) != NULL) {
                (ldap_pvt_thread_pool_destroy)(&pool, 0); /* ignore thr_debug macro */
        }
        ldap_pvt_thread_mutex_destroy(&ldap_pvt_thread_pool_mutex);
        ldap_pvt_thread_key_destroy( ldap_tpool_key );
        return(0);
}


/* Create a thread pool */
int
ldap_pvt_thread_pool_init (
        ldap_pvt_thread_pool_t *tpool,
        int max_threads,
        int max_pending )
{
        ldap_pvt_thread_pool_t pool;
        int rc;

        /* multiple pools are currently not supported (ITS#4943) */
        assert(!ldap_int_has_thread_pool);

        if (! (0 <= max_threads && max_threads <= LDAP_MAXTHR))
                max_threads = 0;
        if (! (1 <= max_pending && max_pending <= MAX_PENDING))
                max_pending = MAX_PENDING;

        *tpool = NULL;
        pool = (ldap_pvt_thread_pool_t) LDAP_CALLOC(1,
                sizeof(struct ldap_int_thread_pool_s));

        if (pool == NULL) return(-1);

        rc = ldap_pvt_thread_mutex_init(&pool->ltp_mutex);
        if (rc != 0) {
fail1:
                LDAP_FREE(pool);
                return(rc);
        }
        rc = ldap_pvt_thread_cond_init(&pool->ltp_cond);
        if (rc != 0) {
fail2:
                ldap_pvt_thread_mutex_destroy(&pool->ltp_mutex);
                goto fail1;
        }
        rc = ldap_pvt_thread_cond_init(&pool->ltp_pcond);
        if (rc != 0) {
                ldap_pvt_thread_cond_destroy(&pool->ltp_cond);
                goto fail2;
        }

        ldap_int_has_thread_pool = 1;

        pool->ltp_max_count = max_threads;
        SET_VARY_OPEN_COUNT(pool);
        pool->ltp_max_pending = max_pending;

        LDAP_STAILQ_INIT(&pool->ltp_pending_list);
        pool->ltp_work_list = &pool->ltp_pending_list;
        LDAP_SLIST_INIT(&pool->ltp_free_list);

        ldap_pvt_thread_mutex_lock(&ldap_pvt_thread_pool_mutex);
        LDAP_STAILQ_INSERT_TAIL(&ldap_int_thread_pool_list, pool, ltp_next);
        ldap_pvt_thread_mutex_unlock(&ldap_pvt_thread_pool_mutex);

        /* Start no threads just yet.  That can break if the process forks
         * later, as slapd does in order to daemonize.  On at least POSIX,
         * only the forking thread would survive in the child.  Yet fork()
         * can't unlock/clean up other threads' locks and data structures,
         * unless pthread_atfork() handlers have been set up to do so.
         */

        *tpool = pool;
        return(0);
}


/* Submit a task to be performed by the thread pool */
int
ldap_pvt_thread_pool_submit (
        ldap_pvt_thread_pool_t *tpool,
        ldap_pvt_thread_start_t *start_routine, void *arg )
{
        struct ldap_int_thread_pool_s *pool;
        ldap_int_thread_task_t *task;
        ldap_pvt_thread_t thr;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL)
                return(-1);

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        if (pool->ltp_pending_count >= pool->ltp_max_pending)
                goto failed;

        task = LDAP_SLIST_FIRST(&pool->ltp_free_list);
        if (task) {
                LDAP_SLIST_REMOVE_HEAD(&pool->ltp_free_list, ltt_next.l);
        } else {
                task = (ldap_int_thread_task_t *) LDAP_MALLOC(sizeof(*task));
                if (task == NULL)
                        goto failed;
        }

        task->ltt_start_routine = start_routine;
        task->ltt_arg = arg;

        pool->ltp_pending_count++;
        LDAP_STAILQ_INSERT_TAIL(&pool->ltp_pending_list, task, ltt_next.q);

        /* true if ltp_pause != 0 or we should open (create) a thread */
        if (pool->ltp_vary_open_count > 0 &&
                pool->ltp_open_count < pool->ltp_active_count+pool->ltp_pending_count)
        {
                if (pool->ltp_pause)
                        goto done;

                pool->ltp_starting++;
                pool->ltp_open_count++;
                SET_VARY_OPEN_COUNT(pool);

                if (0 != ldap_pvt_thread_create(
                        &thr, 1, ldap_int_thread_pool_wrapper, pool))
                {
                        /* couldn't create thread.  back out of
                         * ltp_open_count and check for even worse things.
                         */
                        pool->ltp_starting--;
                        pool->ltp_open_count--;
                        SET_VARY_OPEN_COUNT(pool);

                        if (pool->ltp_open_count == 0) {
                                /* no open threads at all?!?
                                 */
                                ldap_int_thread_task_t *ptr;

                                /* let pool_destroy know there are no more threads */
                                ldap_pvt_thread_cond_signal(&pool->ltp_cond);

                                LDAP_STAILQ_FOREACH(ptr, &pool->ltp_pending_list, ltt_next.q)
                                        if (ptr == task) break;
                                if (ptr == task) {
                                        /* no open threads, task not handled, so
                                         * back out of ltp_pending_count, free the task,
                                         * report the error.
                                         */
                                        pool->ltp_pending_count--;
                                        LDAP_STAILQ_REMOVE(&pool->ltp_pending_list, task,
                                                ldap_int_thread_task_s, ltt_next.q);
                                        LDAP_SLIST_INSERT_HEAD(&pool->ltp_free_list, task,
                                                ltt_next.l);
                                        goto failed;
                                }
                        }
                        /* there is another open thread, so this
                         * task will be handled eventually.
                         */
                }
        }
        ldap_pvt_thread_cond_signal(&pool->ltp_cond);

 done:
        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return(0);

 failed:
        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return(-1);
}

static void *
no_task( void *ctx, void *arg )
{
        return NULL;
}

/* Cancel a pending task that was previously submitted.
 * Return 1 if the task was successfully cancelled, 0 if
 * not found, -1 for invalid parameters
 */
int
ldap_pvt_thread_pool_retract (
        ldap_pvt_thread_pool_t *tpool,
        ldap_pvt_thread_start_t *start_routine, void *arg )
{
        struct ldap_int_thread_pool_s *pool;
        ldap_int_thread_task_t *task;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL)
                return(-1);

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);
        LDAP_STAILQ_FOREACH(task, &pool->ltp_pending_list, ltt_next.q)
                if (task->ltt_start_routine == start_routine &&
                        task->ltt_arg == arg) {
                        /* Could LDAP_STAILQ_REMOVE the task, but that
                         * walks ltp_pending_list again to find it.
                         */
                        task->ltt_start_routine = no_task;
                        task->ltt_arg = NULL;
                        break;
                }
        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return task != NULL;
}

/* Set max #threads.  value <= 0 means max supported #threads (LDAP_MAXTHR) */
int
ldap_pvt_thread_pool_maxthreads(
        ldap_pvt_thread_pool_t *tpool,
        int max_threads )
{
        struct ldap_int_thread_pool_s *pool;

        if (! (0 <= max_threads && max_threads <= LDAP_MAXTHR))
                max_threads = 0;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL)
                return(-1);

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        pool->ltp_max_count = max_threads;
        SET_VARY_OPEN_COUNT(pool);

        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return(0);
}

/* Inspect the pool */
int
ldap_pvt_thread_pool_query(
        ldap_pvt_thread_pool_t *tpool,
        ldap_pvt_thread_pool_param_t param,
        void *value )
{
        struct ldap_int_thread_pool_s   *pool;
        int                             count = -1;

        if ( tpool == NULL || value == NULL ) {
                return -1;
        }

        pool = *tpool;

        if ( pool == NULL ) {
                return 0;
        }

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);
        switch ( param ) {
        case LDAP_PVT_THREAD_POOL_PARAM_MAX:
                count = pool->ltp_max_count;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_MAX_PENDING:
                count = pool->ltp_max_pending;
                if (count < 0)
                        count = -count;
                if (count == MAX_PENDING)
                        count = 0;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_OPEN:
                count = pool->ltp_open_count;
                if (count < 0)
                        count = -count;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_STARTING:
                count = pool->ltp_starting;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_ACTIVE:
                count = pool->ltp_active_count;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_PAUSING:
                count = (pool->ltp_pause != 0);
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_PENDING:
                count = pool->ltp_pending_count;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_BACKLOAD:
                count = pool->ltp_pending_count + pool->ltp_active_count;
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_ACTIVE_MAX:
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_PENDING_MAX:
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_BACKLOAD_MAX:
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_STATE:
                *((char **)value) =
                        pool->ltp_pause ? "pausing" :
                        !pool->ltp_finishing ? "running" :
                        pool->ltp_pending_count ? "finishing" : "stopping";
                break;

        case LDAP_PVT_THREAD_POOL_PARAM_UNKNOWN:
                break;
        }
        ldap_pvt_thread_mutex_unlock( &pool->ltp_mutex );

        if ( count > -1 ) {
                *((int *)value) = count;
        }

        return ( count == -1 ? -1 : 0 );
}

/*
 * true if pool is pausing; does not lock any mutex to check.
 * 0 if not pause, 1 if pause, -1 if error or no pool.
 */
int
ldap_pvt_thread_pool_pausing( ldap_pvt_thread_pool_t *tpool )
{
        int rc = -1;
        struct ldap_int_thread_pool_s *pool;

        if ( tpool != NULL && (pool = *tpool) != NULL ) {
                rc = (pool->ltp_pause != 0);
        }

        return rc;
}

/*
 * wrapper for ldap_pvt_thread_pool_query(), left around
 * for backwards compatibility
 */
int
ldap_pvt_thread_pool_backload ( ldap_pvt_thread_pool_t *tpool )
{
        int     rc, count;

        rc = ldap_pvt_thread_pool_query( tpool,
                LDAP_PVT_THREAD_POOL_PARAM_BACKLOAD, (void *)&count );

        if ( rc == 0 ) {
                return count;
        }

        return rc;
}

/* Destroy the pool after making its threads finish */
int
ldap_pvt_thread_pool_destroy ( ldap_pvt_thread_pool_t *tpool, int run_pending )
{
        struct ldap_int_thread_pool_s *pool, *pptr;
        ldap_int_thread_task_t *task;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL) return(-1);

        ldap_pvt_thread_mutex_lock(&ldap_pvt_thread_pool_mutex);
        LDAP_STAILQ_FOREACH(pptr, &ldap_int_thread_pool_list, ltp_next)
                if (pptr == pool) break;
        if (pptr == pool)
                LDAP_STAILQ_REMOVE(&ldap_int_thread_pool_list, pool,
                        ldap_int_thread_pool_s, ltp_next);
        ldap_pvt_thread_mutex_unlock(&ldap_pvt_thread_pool_mutex);

        if (pool != pptr) return(-1);

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        pool->ltp_finishing = 1;
        SET_VARY_OPEN_COUNT(pool);
        if (pool->ltp_max_pending > 0)
                pool->ltp_max_pending = -pool->ltp_max_pending;

        if (!run_pending) {
                while ((task = LDAP_STAILQ_FIRST(&pool->ltp_pending_list)) != NULL) {
                        LDAP_STAILQ_REMOVE_HEAD(&pool->ltp_pending_list, ltt_next.q);
                        LDAP_FREE(task);
                }
                pool->ltp_pending_count = 0;
        }

        while (pool->ltp_open_count) {
                if (!pool->ltp_pause)
                        ldap_pvt_thread_cond_broadcast(&pool->ltp_cond);
                ldap_pvt_thread_cond_wait(&pool->ltp_cond, &pool->ltp_mutex);
        }

        while ((task = LDAP_SLIST_FIRST(&pool->ltp_free_list)) != NULL)
        {
                LDAP_SLIST_REMOVE_HEAD(&pool->ltp_free_list, ltt_next.l);
                LDAP_FREE(task);
        }

        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        ldap_pvt_thread_cond_destroy(&pool->ltp_pcond);
        ldap_pvt_thread_cond_destroy(&pool->ltp_cond);
        ldap_pvt_thread_mutex_destroy(&pool->ltp_mutex);
        LDAP_FREE(pool);
        *tpool = NULL;
        ldap_int_has_thread_pool = 0;
        return(0);
}

/* Thread loop.  Accept and handle submitted tasks. */
static void *
ldap_int_thread_pool_wrapper ( 
        void *xpool )
{
        struct ldap_int_thread_pool_s *pool = xpool;
        ldap_int_thread_task_t *task;
        ldap_int_tpool_plist_t *work_list;
        ldap_int_thread_userctx_t ctx, *kctx;
        unsigned i, keyslot, hash;

        assert(pool != NULL);

        for ( i=0; i<MAXKEYS; i++ ) {
                ctx.ltu_key[i].ltk_key = NULL;
        }

        ctx.ltu_id = ldap_pvt_thread_self();
        TID_HASH(ctx.ltu_id, hash);

        ldap_pvt_thread_key_setdata( ldap_tpool_key, &ctx );

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        /* thread_keys[] is read-only when paused */
        while (pool->ltp_pause)
                ldap_pvt_thread_cond_wait(&pool->ltp_cond, &pool->ltp_mutex);

        /* find a key slot to give this thread ID and store a
         * pointer to our keys there; start at the thread ID
         * itself (mod LDAP_MAXTHR) and look for an empty slot.
         */
        ldap_pvt_thread_mutex_lock(&ldap_pvt_thread_pool_mutex);
        for (keyslot = hash & (LDAP_MAXTHR-1);
                (kctx = thread_keys[keyslot].ctx) && kctx != DELETED_THREAD_CTX;
                keyslot = (keyslot+1) & (LDAP_MAXTHR-1));
        thread_keys[keyslot].ctx = &ctx;
        ldap_pvt_thread_mutex_unlock(&ldap_pvt_thread_pool_mutex);

        pool->ltp_starting--;
        pool->ltp_active_count++;

        for (;;) {
                work_list = pool->ltp_work_list; /* help the compiler a bit */
                task = LDAP_STAILQ_FIRST(work_list);
                if (task == NULL) {     /* paused or no pending tasks */
                        if (--(pool->ltp_active_count) < 2) {
                                /* Notify pool_pause it is the sole active thread. */
                                ldap_pvt_thread_cond_signal(&pool->ltp_pcond);
                        }

                        do {
                                if (pool->ltp_vary_open_count < 0) {
                                        /* Not paused, and either finishing or too many
                                         * threads running (can happen if ltp_max_count
                                         * was reduced).  Let this thread die.
                                         */
                                        goto done;
                                }

                                /* We could check an idle timer here, and let the
                                 * thread die if it has been inactive for a while.
                                 * Only die if there are other open threads (i.e.,
                                 * always have at least one thread open).
                                 * The check should be like this:
                                 *   if (pool->ltp_open_count>1 && pool->ltp_starting==0)
                                 *       check timer, wait if ltp_pause, leave thread;
                                 *
                                 * Just use pthread_cond_timedwait() if we want to
                                 * check idle time.
                                 */
                                ldap_pvt_thread_cond_wait(&pool->ltp_cond, &pool->ltp_mutex);

                                work_list = pool->ltp_work_list;
                                task = LDAP_STAILQ_FIRST(work_list);
                        } while (task == NULL);

                        pool->ltp_active_count++;
                }

                LDAP_STAILQ_REMOVE_HEAD(work_list, ltt_next.q);
                pool->ltp_pending_count--;
                ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);

                task->ltt_start_routine(&ctx, task->ltt_arg);

                ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);
                LDAP_SLIST_INSERT_HEAD(&pool->ltp_free_list, task, ltt_next.l);
        }
 done:

        assert(!pool->ltp_pause); /* thread_keys writable, ltp_open_count >= 0 */

        /* The ltp_mutex lock protects ctx->ltu_key from pool_purgekey()
         * during this call, since it prevents new pauses. */
        ldap_pvt_thread_pool_context_reset(&ctx);

        ldap_pvt_thread_mutex_lock(&ldap_pvt_thread_pool_mutex);
        thread_keys[keyslot].ctx = DELETED_THREAD_CTX;
        ldap_pvt_thread_mutex_unlock(&ldap_pvt_thread_pool_mutex);

        pool->ltp_open_count--;
        SET_VARY_OPEN_COUNT(pool);
        /* let pool_destroy know we're all done */
        if (pool->ltp_open_count == 0)
                ldap_pvt_thread_cond_signal(&pool->ltp_cond);

        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);

        ldap_pvt_thread_exit(NULL);
        return(NULL);
}

/* Arguments > ltp_pause to handle_pause(,PAUSE_ARG()).  arg=PAUSE_ARG
 * ensures (arg-ltp_pause) sets GO_* at need and keeps DO_PAUSE/GO_*.
 */
#define GO_IDLE         8
#define GO_UNIDLE       16
#define CHECK_PAUSE     32      /* if ltp_pause: GO_IDLE; wait; GO_UNIDLE */
#define DO_PAUSE        64      /* CHECK_PAUSE; pause the pool */
#define PAUSE_ARG(a) \
                ((a) | ((a) & (GO_IDLE|GO_UNIDLE) ? GO_IDLE-1 : CHECK_PAUSE))

static int
handle_pause( ldap_pvt_thread_pool_t *tpool, int pause_type )
{
        struct ldap_int_thread_pool_s *pool;
        int ret = 0, pause, max_ltp_pause;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL)
                return(0);

        if (pause_type == CHECK_PAUSE && !pool->ltp_pause)
                return(0);

        /* Let pool_unidle() ignore requests for new pauses */
        max_ltp_pause = pause_type==PAUSE_ARG(GO_UNIDLE) ? WANT_PAUSE : NOT_PAUSED;

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        pause = pool->ltp_pause;        /* NOT_PAUSED, WANT_PAUSE or PAUSED */

        /* If ltp_pause and not GO_IDLE|GO_UNIDLE: Set GO_IDLE,GO_UNIDLE */
        pause_type -= pause;

        if (pause_type & GO_IDLE) {
                pool->ltp_pending_count++;
                pool->ltp_active_count--;
                if (pause && pool->ltp_active_count < 2) {
                        /* Tell the task waiting to DO_PAUSE it can proceed */
                        ldap_pvt_thread_cond_signal(&pool->ltp_pcond);
                }
        }

        if (pause_type & GO_UNIDLE) {
                /* Wait out pause if any, then cancel GO_IDLE */
                if (pause > max_ltp_pause) {
                        ret = 1;
                        do {
                                ldap_pvt_thread_cond_wait(&pool->ltp_cond, &pool->ltp_mutex);
                        } while (pool->ltp_pause > max_ltp_pause);
                }
                pool->ltp_pending_count--;
                pool->ltp_active_count++;
        }

        if (pause_type & DO_PAUSE) {
                /* Tell everyone else to pause or finish, then await that */
                ret = 0;
                assert(!pool->ltp_pause);
                pool->ltp_pause = WANT_PAUSE;
                /* Let ldap_pvt_thread_pool_submit() through to its ltp_pause test,
                 * and do not finish threads in ldap_pvt_thread_pool_wrapper() */
                pool->ltp_open_count = -pool->ltp_open_count;
                SET_VARY_OPEN_COUNT(pool);
                /* Hide pending tasks from ldap_pvt_thread_pool_wrapper() */
                pool->ltp_work_list = &empty_pending_list;
                /* Wait for this task to become the sole active task */
                while (pool->ltp_active_count > 1) {
                        ldap_pvt_thread_cond_wait(&pool->ltp_pcond, &pool->ltp_mutex);
                }
                assert(pool->ltp_pause == WANT_PAUSE);
                pool->ltp_pause = PAUSED;
        }

        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return(ret);
}

/* Consider this task idle: It will not block pool_pause() in other tasks. */
void
ldap_pvt_thread_pool_idle( ldap_pvt_thread_pool_t *tpool )
{
        handle_pause(tpool, PAUSE_ARG(GO_IDLE));
}

/* Cancel pool_idle(). If the pool is paused, wait it out first. */
void
ldap_pvt_thread_pool_unidle( ldap_pvt_thread_pool_t *tpool )
{
        handle_pause(tpool, PAUSE_ARG(GO_UNIDLE));
}

/*
 * If a pause was requested, wait for it.  If several threads
 * are waiting to pause, let through one or more pauses.
 * The calling task must be active, not idle.
 * Return 1 if we waited, 0 if not, -1 at parameter error.
 */
int
ldap_pvt_thread_pool_pausecheck( ldap_pvt_thread_pool_t *tpool )
{
        return handle_pause(tpool, PAUSE_ARG(CHECK_PAUSE));
}

/*
 * Pause the pool.  The calling task must be active, not idle.
 * Return when all other tasks are paused or idle.
 */
int
ldap_pvt_thread_pool_pause( ldap_pvt_thread_pool_t *tpool )
{
        return handle_pause(tpool, PAUSE_ARG(DO_PAUSE));
}

/* End a pause */
int
ldap_pvt_thread_pool_resume ( 
        ldap_pvt_thread_pool_t *tpool )
{
        struct ldap_int_thread_pool_s *pool;

        if (tpool == NULL)
                return(-1);

        pool = *tpool;

        if (pool == NULL)
                return(0);

        ldap_pvt_thread_mutex_lock(&pool->ltp_mutex);

        assert(pool->ltp_pause == PAUSED);
        pool->ltp_pause = 0;
        if (pool->ltp_open_count <= 0) /* true when paused, but be paranoid */
                pool->ltp_open_count = -pool->ltp_open_count;
        SET_VARY_OPEN_COUNT(pool);
        pool->ltp_work_list = &pool->ltp_pending_list;

        ldap_pvt_thread_cond_broadcast(&pool->ltp_cond);

        ldap_pvt_thread_mutex_unlock(&pool->ltp_mutex);
        return(0);
}

/*
 * Get the key's data and optionally free function in the given context.
 */
int ldap_pvt_thread_pool_getkey(
        void *xctx,
        void *key,
        void **data,
        ldap_pvt_thread_pool_keyfree_t **kfree )
{
        ldap_int_thread_userctx_t *ctx = xctx;
        int i;

        if ( !ctx || !key || !data ) return EINVAL;

        for ( i=0; i<MAXKEYS && ctx->ltu_key[i].ltk_key; i++ ) {
                if ( ctx->ltu_key[i].ltk_key == key ) {
                        *data = ctx->ltu_key[i].ltk_data;
                        if ( kfree ) *kfree = ctx->ltu_key[i].ltk_free;
                        return 0;
                }
        }
        return ENOENT;
}

static void
clear_key_idx( ldap_int_thread_userctx_t *ctx, int i )
{
        for ( ; i < MAXKEYS-1 && ctx->ltu_key[i+1].ltk_key; i++ )
                ctx->ltu_key[i] = ctx->ltu_key[i+1];
        ctx->ltu_key[i].ltk_key = NULL;
}

/*
 * Set or remove data for the key in the given context.
 * key can be any unique pointer.
 * kfree() is an optional function to free the data (but not the key):
 *   pool_context_reset() and pool_purgekey() call kfree(key, data),
 *   but pool_setkey() does not.  For pool_setkey() it is the caller's
 *   responsibility to free any existing data with the same key.
 *   kfree() must not call functions taking a tpool argument.
 */
int ldap_pvt_thread_pool_setkey(
        void *xctx,
        void *key,
        void *data,
        ldap_pvt_thread_pool_keyfree_t *kfree,
        void **olddatap,
        ldap_pvt_thread_pool_keyfree_t **oldkfreep )
{
        ldap_int_thread_userctx_t *ctx = xctx;
        int i, found;

        if ( !ctx || !key ) return EINVAL;

        for ( i=found=0; i<MAXKEYS; i++ ) {
                if ( ctx->ltu_key[i].ltk_key == key ) {
                        found = 1;
                        break;
                } else if ( !ctx->ltu_key[i].ltk_key ) {
                        break;
                }
        }

        if ( olddatap ) {
                if ( found ) {
                        *olddatap = ctx->ltu_key[i].ltk_data;
                } else {
                        *olddatap = NULL;
                }
        }

        if ( oldkfreep ) {
                if ( found ) {
                        *oldkfreep = ctx->ltu_key[i].ltk_free;
                } else {
                        *oldkfreep = 0;
                }
        }

        if ( data || kfree ) {
                if ( i>=MAXKEYS )
                        return ENOMEM;
                ctx->ltu_key[i].ltk_key = key;
                ctx->ltu_key[i].ltk_data = data;
                ctx->ltu_key[i].ltk_free = kfree;
        } else if ( found ) {
                clear_key_idx( ctx, i );
        }

        return 0;
}

/* Free all elements with this key, no matter which thread they're in.
 * May only be called while the pool is paused.
 */
void ldap_pvt_thread_pool_purgekey( void *key )
{
        int i, j;
        ldap_int_thread_userctx_t *ctx;

        assert ( key != NULL );

        for ( i=0; i<LDAP_MAXTHR; i++ ) {
                ctx = thread_keys[i].ctx;
                if ( ctx && ctx != DELETED_THREAD_CTX ) {
                        for ( j=0; j<MAXKEYS && ctx->ltu_key[j].ltk_key; j++ ) {
                                if ( ctx->ltu_key[j].ltk_key == key ) {
                                        if (ctx->ltu_key[j].ltk_free)
                                                ctx->ltu_key[j].ltk_free( ctx->ltu_key[j].ltk_key,
                                                ctx->ltu_key[j].ltk_data );
                                        clear_key_idx( ctx, j );
                                        break;
                                }
                        }
                }
        }
}

/*
 * Find the context of the current thread.
 * This is necessary if the caller does not have access to the
 * thread context handle (for example, a slapd plugin calling
 * slapi_search_internal()). No doubt it is more efficient
 * for the application to keep track of the thread context
 * handles itself.
 */
void *ldap_pvt_thread_pool_context( )
{
        void *ctx = NULL;

        ldap_pvt_thread_key_getdata( ldap_tpool_key, &ctx );
        return ctx ? ctx : (void *) &ldap_int_main_thrctx;
}

/*
 * Free the context's keys.
 * Must not call functions taking a tpool argument (because this
 * thread already holds ltp_mutex when called from pool_wrapper()).
 */
void ldap_pvt_thread_pool_context_reset( void *vctx )
{
        ldap_int_thread_userctx_t *ctx = vctx;
        int i;

        for ( i=MAXKEYS-1; i>=0; i--) {
                if ( !ctx->ltu_key[i].ltk_key )
                        continue;
                if ( ctx->ltu_key[i].ltk_free )
                        ctx->ltu_key[i].ltk_free( ctx->ltu_key[i].ltk_key,
                        ctx->ltu_key[i].ltk_data );
                ctx->ltu_key[i].ltk_key = NULL;
        }
}

ldap_pvt_thread_t ldap_pvt_thread_pool_tid( void *vctx )
{
        ldap_int_thread_userctx_t *ctx = vctx;

        return ctx->ltu_id;
}
#endif /* LDAP_THREAD_HAVE_TPOOL */