Import adapted OpenSolaris' thread pool API implementation.

The thread pool is used by libzfs to implement parallel disk scanning.
Without this change our dummy wrapper made `zpool import ZZZ` command to
scan all disks sequentially from the single thread when searching for pools.
This change makes it use two threads per CPU, same as in OpenSolaris.

On system with 200 HDDs this change reduces ZFS pool import time from 35
to 22 seconds.

1 files changed, 430 insertions, 0 deletions

diff --git a/cddl/compat/opensolaris/misc/thread_pool.c b/cddl/compat/opensolaris/misc/thread_pool.c
new file mode 100644
index 000000000000..a6a834fb2bbd
--- /dev/null
+++ b/cddl/compat/opensolaris/misc/thread_pool.c
@@ -0,0 +1,430 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#pragma ident	"%Z%%M%	%I%	%E% SMI"
+
+#include <stdlib.h>
+#include <signal.h>
+#include <errno.h>
+#include "thread_pool_impl.h"
+
+typedef void (*_Voidfp)(void*); /* pointer to extern "C" function */
+
+static void
+delete_pool(tpool_t *tpool)
+{
+	tpool_job_t *job;
+
+	/*
+	 * There should be no pending jobs, but just in case...
+	 */
+	for (job = tpool->tp_head; job != NULL; job = tpool->tp_head) {
+		tpool->tp_head = job->tpj_next;
+		free(job);
+	}
+	(void) pthread_attr_destroy(&tpool->tp_attr);
+	free(tpool);
+}
+
+/*
+ * Worker thread is terminating.
+ */
+static void
+worker_cleanup(void *arg)
+{
+	tpool_t *tpool = arg;
+
+	if (--tpool->tp_current == 0 &&
+	    (tpool->tp_flags & (TP_DESTROY | TP_ABANDON))) {
+		if (tpool->tp_flags & TP_ABANDON) {
+			pthread_mutex_unlock(&tpool->tp_mutex);
+			delete_pool(tpool);
+			return;
+		}
+		if (tpool->tp_flags & TP_DESTROY)
+			(void) pthread_cond_broadcast(&tpool->tp_busycv);
+	}
+	pthread_mutex_unlock(&tpool->tp_mutex);
+}
+
+static void
+notify_waiters(tpool_t *tpool)
+{
+	if (tpool->tp_head == NULL && tpool->tp_active == NULL) {
+		tpool->tp_flags &= ~TP_WAIT;
+		(void) pthread_cond_broadcast(&tpool->tp_waitcv);
+	}
+}
+
+/*
+ * Called by a worker thread on return from a tpool_dispatch()d job.
+ */
+static void
+job_cleanup(void *arg)
+{
+	tpool_t *tpool = arg;
+	pthread_t my_tid = pthread_self();
+	tpool_active_t *activep;
+	tpool_active_t **activepp;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	/* CSTYLED */
+	for (activepp = &tpool->tp_active;; activepp = &activep->tpa_next) {
+		activep = *activepp;
+		if (activep->tpa_tid == my_tid) {
+			*activepp = activep->tpa_next;
+			break;
+		}
+	}
+	if (tpool->tp_flags & TP_WAIT)
+		notify_waiters(tpool);
+}
+
+static void *
+tpool_worker(void *arg)
+{
+	tpool_t *tpool = (tpool_t *)arg;
+	int elapsed;
+	tpool_job_t *job;
+	void (*func)(void *);
+	tpool_active_t active;
+	sigset_t maskset;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	pthread_cleanup_push(worker_cleanup, tpool);
+
+	/*
+	 * This is the worker's main loop.
+	 * It will only be left if a timeout or an error has occured.
+	 */
+	active.tpa_tid = pthread_self();
+	for (;;) {
+		elapsed = 0;
+		tpool->tp_idle++;
+		if (tpool->tp_flags & TP_WAIT)
+			notify_waiters(tpool);
+		while ((tpool->tp_head == NULL ||
+		    (tpool->tp_flags & TP_SUSPEND)) &&
+		    !(tpool->tp_flags & (TP_DESTROY | TP_ABANDON))) {
+			if (tpool->tp_current <= tpool->tp_minimum ||
+			    tpool->tp_linger == 0) {
+				(void) pthread_cond_wait(&tpool->tp_workcv,
+				    &tpool->tp_mutex);
+			} else {
+				struct timespec timeout;
+
+				clock_gettime(CLOCK_MONOTONIC, &timeout);
+				timeout.tv_sec += tpool->tp_linger;
+				if (pthread_cond_timedwait(&tpool->tp_workcv,
+				    &tpool->tp_mutex, &timeout) != 0) {
+					elapsed = 1;
+					break;
+				}
+			}
+		}
+		tpool->tp_idle--;
+		if (tpool->tp_flags & TP_DESTROY)
+			break;
+		if (tpool->tp_flags & TP_ABANDON) {
+			/* can't abandon a suspended pool */
+			if (tpool->tp_flags & TP_SUSPEND) {
+				tpool->tp_flags &= ~TP_SUSPEND;
+				(void) pthread_cond_broadcast(&tpool->tp_workcv);
+			}
+			if (tpool->tp_head == NULL)
+				break;
+		}
+		if ((job = tpool->tp_head) != NULL &&
+		    !(tpool->tp_flags & TP_SUSPEND)) {
+			elapsed = 0;
+			func = job->tpj_func;
+			arg = job->tpj_arg;
+			tpool->tp_head = job->tpj_next;
+			if (job == tpool->tp_tail)
+				tpool->tp_tail = NULL;
+			tpool->tp_njobs--;
+			active.tpa_next = tpool->tp_active;
+			tpool->tp_active = &active;
+			pthread_mutex_unlock(&tpool->tp_mutex);
+			pthread_cleanup_push(job_cleanup, tpool);
+			free(job);
+			/*
+			 * Call the specified function.
+			 */
+			func(arg);
+			/*
+			 * We don't know what this thread has been doing,
+			 * so we reset its signal mask and cancellation
+			 * state back to the initial values.
+			 */
+			sigfillset(&maskset);
+			(void) pthread_sigmask(SIG_SETMASK, &maskset, NULL);
+			(void) pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED,
+			    NULL);
+			(void) pthread_setcancelstate(PTHREAD_CANCEL_ENABLE,
+			    NULL);
+			pthread_cleanup_pop(1);
+		}
+		if (elapsed && tpool->tp_current > tpool->tp_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);
+	return (arg);
+}
+
+/*
+ * Create a worker thread, with all signals blocked.
+ */
+static int
+create_worker(tpool_t *tpool)
+{
+	sigset_t maskset, oset;
+	pthread_t thread;
+	int error;
+
+	sigfillset(&maskset);
+	(void) pthread_sigmask(SIG_SETMASK, &maskset, &oset);
+	error = pthread_create(&thread, &tpool->tp_attr, tpool_worker, tpool);
+	(void) pthread_sigmask(SIG_SETMASK, &oset, NULL);
+	return (error);
+}
+
+tpool_t	*
+tpool_create(uint_t min_threads, uint_t max_threads, uint_t linger,
+	pthread_attr_t *attr)
+{
+	tpool_t	*tpool;
+	int error;
+
+	if (min_threads > max_threads || max_threads < 1) {
+		errno = EINVAL;
+		return (NULL);
+	}
+
+	tpool = malloc(sizeof (*tpool));
+	if (tpool == NULL) {
+		errno = ENOMEM;
+		return (NULL);
+	}
+	bzero(tpool, sizeof(*tpool));
+	(void) pthread_mutex_init(&tpool->tp_mutex, NULL);
+	(void) pthread_cond_init(&tpool->tp_busycv, NULL);
+	(void) pthread_cond_init(&tpool->tp_workcv, NULL);
+	(void) pthread_cond_init(&tpool->tp_waitcv, NULL);
+	tpool->tp_minimum = min_threads;
+	tpool->tp_maximum = max_threads;
+	tpool->tp_linger = linger;
+
+	/* make all pool threads be detached daemon threads */
+	(void) pthread_attr_init(&tpool->tp_attr);
+	(void) pthread_attr_setdetachstate(&tpool->tp_attr,
+	    PTHREAD_CREATE_DETACHED);
+
+	return (tpool);
+}
+
+/*
+ * Dispatch a work request to the thread pool.
+ * If there are idle workers, awaken one.
+ * Else, if the maximum number of workers has
+ * not been reached, spawn a new worker thread.
+ * Else just return with the job added to the queue.
+ */
+int
+tpool_dispatch(tpool_t *tpool, void (*func)(void *), void *arg)
+{
+	tpool_job_t *job;
+
+	if ((job = malloc(sizeof (*job))) == NULL)
+		return (-1);
+	bzero(job, sizeof(*job));
+	job->tpj_next = NULL;
+	job->tpj_func = func;
+	job->tpj_arg = arg;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+
+	if (tpool->tp_head == NULL)
+		tpool->tp_head = job;
+	else
+		tpool->tp_tail->tpj_next = job;
+	tpool->tp_tail = job;
+	tpool->tp_njobs++;
+
+	if (!(tpool->tp_flags & TP_SUSPEND)) {
+		if (tpool->tp_idle > 0)
+			(void) pthread_cond_signal(&tpool->tp_workcv);
+		else if (tpool->tp_current < tpool->tp_maximum &&
+		    create_worker(tpool) == 0)
+			tpool->tp_current++;
+	}
+
+	pthread_mutex_unlock(&tpool->tp_mutex);
+	return (0);
+}
+
+/*
+ * Assumes: by the time tpool_destroy() is called no one will use this
+ * thread pool in any way and no one will try to dispatch entries to it.
+ * Calling tpool_destroy() from a job in the pool will cause deadlock.
+ */
+void
+tpool_destroy(tpool_t *tpool)
+{
+	tpool_active_t *activep;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	pthread_cleanup_push((_Voidfp)pthread_mutex_unlock, &tpool->tp_mutex);
+
+	/* mark the pool as being destroyed; wakeup idle workers */
+	tpool->tp_flags |= TP_DESTROY;
+	tpool->tp_flags &= ~TP_SUSPEND;
+	(void) pthread_cond_broadcast(&tpool->tp_workcv);
+
+	/* cancel all active workers */
+	for (activep = tpool->tp_active; activep; activep = activep->tpa_next)
+		(void) pthread_cancel(activep->tpa_tid);
+
+	/* wait for all active workers to finish */
+	while (tpool->tp_active != NULL) {
+		tpool->tp_flags |= TP_WAIT;
+		(void) pthread_cond_wait(&tpool->tp_waitcv, &tpool->tp_mutex);
+	}
+
+	/* the last worker to terminate will wake us up */
+	while (tpool->tp_current != 0)
+		(void) pthread_cond_wait(&tpool->tp_busycv, &tpool->tp_mutex);
+
+	pthread_cleanup_pop(1);	/* pthread_mutex_unlock(&tpool->tp_mutex); */
+	delete_pool(tpool);
+}
+
+/*
+ * Like tpool_destroy(), but don't cancel workers or wait for them to finish.
+ * The last worker to terminate will delete the pool.
+ */
+void
+tpool_abandon(tpool_t *tpool)
+{
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	if (tpool->tp_current == 0) {
+		/* no workers, just delete the pool */
+		pthread_mutex_unlock(&tpool->tp_mutex);
+		delete_pool(tpool);
+	} else {
+		/* wake up all workers, last one will delete the pool */
+		tpool->tp_flags |= TP_ABANDON;
+		tpool->tp_flags &= ~TP_SUSPEND;
+		(void) pthread_cond_broadcast(&tpool->tp_workcv);
+		pthread_mutex_unlock(&tpool->tp_mutex);
+	}
+}
+
+/*
+ * Wait for all jobs to complete.
+ * Calling tpool_wait() from a job in the pool will cause deadlock.
+ */
+void
+tpool_wait(tpool_t *tpool)
+{
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	pthread_cleanup_push((_Voidfp)pthread_mutex_unlock, &tpool->tp_mutex);
+	while (tpool->tp_head != NULL || tpool->tp_active != NULL) {
+		tpool->tp_flags |= TP_WAIT;
+		(void) pthread_cond_wait(&tpool->tp_waitcv, &tpool->tp_mutex);
+	}
+	pthread_cleanup_pop(1);	/* pthread_mutex_unlock(&tpool->tp_mutex); */
+}
+
+void
+tpool_suspend(tpool_t *tpool)
+{
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	tpool->tp_flags |= TP_SUSPEND;
+	pthread_mutex_unlock(&tpool->tp_mutex);
+}
+
+int
+tpool_suspended(tpool_t *tpool)
+{
+	int suspended;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	suspended = (tpool->tp_flags & TP_SUSPEND) != 0;
+	pthread_mutex_unlock(&tpool->tp_mutex);
+
+	return (suspended);
+}
+
+void
+tpool_resume(tpool_t *tpool)
+{
+	int excess;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	if (!(tpool->tp_flags & TP_SUSPEND)) {
+		pthread_mutex_unlock(&tpool->tp_mutex);
+		return;
+	}
+	tpool->tp_flags &= ~TP_SUSPEND;
+	(void) pthread_cond_broadcast(&tpool->tp_workcv);
+	excess = tpool->tp_njobs - tpool->tp_idle;
+	while (excess-- > 0 && tpool->tp_current < tpool->tp_maximum) {
+		if (create_worker(tpool) != 0)
+			break;		/* pthread_create() failed */
+		tpool->tp_current++;
+	}
+	pthread_mutex_unlock(&tpool->tp_mutex);
+}
+
+int
+tpool_member(tpool_t *tpool)
+{
+	pthread_t my_tid = pthread_self();
+	tpool_active_t *activep;
+
+	pthread_mutex_lock(&tpool->tp_mutex);
+	for (activep = tpool->tp_active; activep; activep = activep->tpa_next) {
+		if (activep->tpa_tid == my_tid) {
+			pthread_mutex_unlock(&tpool->tp_mutex);
+			return (1);
+		}
+	}
+	pthread_mutex_unlock(&tpool->tp_mutex);
+	return (0);
+}