Move background thread creation to background_thread_0.

To avoid complications, avoid invoking pthread_create "internally", instead rely
on thread0 to launch new threads, and also terminating threads when asked.

include/jemalloc/internal/background_thread_externs.h

@@ -10,8 +10,6 @@ extern background_thread_info_t *background_thread_info;
 bool background_thread_create(tsd_t *tsd, unsigned arena_ind);
 bool background_threads_enable(tsd_t *tsd);
 bool background_threads_disable(tsd_t *tsd);
-bool background_threads_disable_single(tsd_t *tsd,
-    background_thread_info_t *info);
 void background_thread_interval_check(tsdn_t *tsdn, arena_t *arena,
     arena_decay_t *decay, size_t npages_new);
 void background_thread_prefork0(tsdn_t *tsdn);

include/jemalloc/internal/background_thread_structs.h

@@ -18,6 +18,8 @@ struct background_thread_info_s {
 	malloc_mutex_t		mtx;
 	/* Whether the thread has been created. */
 	bool			started;
+	/* Pause execution (for arena reset / destroy). */
+	bool			pause;
 	/* When true, it means no wakeup scheduled. */
 	atomic_b_t		indefinite_sleep;
 	/* Next scheduled wakeup time (absolute time in ns). */

src/background_thread.c

@@ -50,8 +50,6 @@ pthread_create_wrapper(pthread_t *__restrict thread, const pthread_attr_t *attr,
 bool background_thread_create(tsd_t *tsd, unsigned arena_ind) NOT_REACHED
 bool background_threads_enable(tsd_t *tsd) NOT_REACHED
 bool background_threads_disable(tsd_t *tsd) NOT_REACHED
-bool background_threads_disable_single(tsd_t *tsd,
-    background_thread_info_t *info) NOT_REACHED
 void background_thread_interval_check(tsdn_t *tsdn, arena_t *arena,
     arena_decay_t *decay, size_t npages_new) NOT_REACHED
 void background_thread_prefork0(tsdn_t *tsdn) NOT_REACHED
@@ -67,8 +65,9 @@ void background_thread_ctl_init(tsdn_t *tsdn) NOT_REACHED
 static bool background_thread_enabled_at_fork;
 
 static void
-background_thread_info_reinit(tsdn_t *tsdn, background_thread_info_t *info) {
+background_thread_info_init(tsdn_t *tsdn, background_thread_info_t *info) {
 	background_thread_wakeup_time_set(tsdn, info, 0);
+	info->pause = false;
 	info->npages_to_purge_new = 0;
 	if (config_stats) {
 		info->tot_n_runs = 0;
@@ -210,211 +209,107 @@ arena_decay_compute_purge_interval(tsdn_t *tsdn, arena_t *arena) {
 	return i1 < i2 ? i1 : i2;
 }
 
-static inline uint64_t
+static void
-background_work_once(tsdn_t *tsdn, unsigned ind) {
+background_thread_sleep(tsdn_t *tsdn, background_thread_info_t *info,
-	arena_t *arena;
+    uint64_t interval) {
-	unsigned i, narenas;
+	if (config_stats) {
-	uint64_t min_interval;
+		info->tot_n_runs++;
+	}
+	info->npages_to_purge_new = 0;
 
-	min_interval = BACKGROUND_THREAD_INDEFINITE_SLEEP;
+	struct timeval tv;
-	narenas = narenas_total_get();
+	/* Specific clock required by timedwait. */
-	for (i = ind; i < narenas; i += ncpus) {
+	gettimeofday(&tv, NULL);
-		arena = arena_get(tsdn, i, false);
+	nstime_t before_sleep;
+	nstime_init2(&before_sleep, tv.tv_sec, tv.tv_usec * 1000);
+
+	int ret;
+	if (interval == BACKGROUND_THREAD_INDEFINITE_SLEEP) {
+		assert(background_thread_indefinite_sleep(info));
+		ret = pthread_cond_wait(&info->cond, &info->mtx.lock);
+		assert(ret == 0);
+	} else {
+		assert(interval >= BACKGROUND_THREAD_MIN_INTERVAL_NS &&
+		    interval <= BACKGROUND_THREAD_INDEFINITE_SLEEP);
+		/* We need malloc clock (can be different from tv). */
+		nstime_t next_wakeup;
+		nstime_init(&next_wakeup, 0);
+		nstime_update(&next_wakeup);
+		nstime_iadd(&next_wakeup, interval);
+		assert(nstime_ns(&next_wakeup) <
+		    BACKGROUND_THREAD_INDEFINITE_SLEEP);
+		background_thread_wakeup_time_set(tsdn, info,
+		    nstime_ns(&next_wakeup));
+
+		nstime_t ts_wakeup;
+		nstime_copy(&ts_wakeup, &before_sleep);
+		nstime_iadd(&ts_wakeup, interval);
+		struct timespec ts;
+		ts.tv_sec = (size_t)nstime_sec(&ts_wakeup);
+		ts.tv_nsec = (size_t)nstime_nsec(&ts_wakeup);
+
+		assert(!background_thread_indefinite_sleep(info));
+		ret = pthread_cond_timedwait(&info->cond, &info->mtx.lock, &ts);
+		assert(ret == ETIMEDOUT || ret == 0);
+		background_thread_wakeup_time_set(tsdn, info,
+		    BACKGROUND_THREAD_INDEFINITE_SLEEP);
+	}
+	if (config_stats) {
+		gettimeofday(&tv, NULL);
+		nstime_t after_sleep;
+		nstime_init2(&after_sleep, tv.tv_sec, tv.tv_usec * 1000);
+		if (nstime_compare(&after_sleep, &before_sleep) > 0) {
+			nstime_subtract(&after_sleep, &before_sleep);
+			nstime_add(&info->tot_sleep_time, &after_sleep);
+		}
+	}
+	while (info->pause) {
+		malloc_mutex_unlock(tsdn, &info->mtx);
+		/* Wait on global lock to update status. */
+		malloc_mutex_lock(tsdn, &background_thread_lock);
+		malloc_mutex_unlock(tsdn, &background_thread_lock);
+		malloc_mutex_lock(tsdn, &info->mtx);
+	}
+}
+
+static inline void
+background_work_sleep_once(tsdn_t *tsdn, background_thread_info_t *info, unsigned ind) {
+	uint64_t min_interval = BACKGROUND_THREAD_INDEFINITE_SLEEP;
+	unsigned narenas = narenas_total_get();
+
+	for (unsigned i = ind; i < narenas; i += ncpus) {
+		arena_t *arena = arena_get(tsdn, i, false);
 		if (!arena) {
 			continue;
 		}
-
 		arena_decay(tsdn, arena, true, false);
+		if (min_interval == BACKGROUND_THREAD_MIN_INTERVAL_NS) {
+			/* Min interval will be used. */
+			continue;
+		}
 		uint64_t interval = arena_decay_compute_purge_interval(tsdn,
 		    arena);
-		if (interval == BACKGROUND_THREAD_MIN_INTERVAL_NS) {
+		assert(interval >= BACKGROUND_THREAD_MIN_INTERVAL_NS);
-			return interval;
-		}
-
-		assert(interval > BACKGROUND_THREAD_MIN_INTERVAL_NS);
 		if (min_interval > interval) {
 			min_interval = interval;
 		}
 	}
-
+	background_thread_sleep(tsdn, info, min_interval);
-	return min_interval;
 }
 
-static void
+static bool
-background_work(tsdn_t *tsdn, unsigned ind) {
-	int ret;
-	background_thread_info_t *info = &background_thread_info[ind];
-
-	malloc_mutex_lock(tsdn, &info->mtx);
-	background_thread_wakeup_time_set(tsdn, info,
-	    BACKGROUND_THREAD_INDEFINITE_SLEEP);
-	while (info->started) {
-		uint64_t interval = background_work_once(tsdn, ind);
-		if (config_stats) {
-			info->tot_n_runs++;
-		}
-		info->npages_to_purge_new = 0;
-
-		struct timeval tv;
-		/* Specific clock required by timedwait. */
-		gettimeofday(&tv, NULL);
-		nstime_t before_sleep;
-		nstime_init2(&before_sleep, tv.tv_sec, tv.tv_usec * 1000);
-
-		if (interval == BACKGROUND_THREAD_INDEFINITE_SLEEP) {
-			assert(background_thread_indefinite_sleep(info));
-			ret = pthread_cond_wait(&info->cond, &info->mtx.lock);
-			assert(ret == 0);
-		} else {
-			assert(interval >= BACKGROUND_THREAD_MIN_INTERVAL_NS &&
-			    interval <= BACKGROUND_THREAD_INDEFINITE_SLEEP);
-			/* We need malloc clock (can be different from tv). */
-			nstime_t next_wakeup;
-			nstime_init(&next_wakeup, 0);
-			nstime_update(&next_wakeup);
-			nstime_iadd(&next_wakeup, interval);
-			assert(nstime_ns(&next_wakeup) <
-			    BACKGROUND_THREAD_INDEFINITE_SLEEP);
-			background_thread_wakeup_time_set(tsdn, info,
-			    nstime_ns(&next_wakeup));
-
-			nstime_t ts_wakeup;
-			nstime_copy(&ts_wakeup, &before_sleep);
-			nstime_iadd(&ts_wakeup, interval);
-			struct timespec ts;
-			ts.tv_sec = (size_t)nstime_sec(&ts_wakeup);
-			ts.tv_nsec = (size_t)nstime_nsec(&ts_wakeup);
-
-			assert(!background_thread_indefinite_sleep(info));
-			ret = pthread_cond_timedwait(&info->cond,
-			    &info->mtx.lock, &ts);
-			assert(ret == ETIMEDOUT || ret == 0);
-			background_thread_wakeup_time_set(tsdn, info,
-			    BACKGROUND_THREAD_INDEFINITE_SLEEP);
-		}
-
-		if (config_stats) {
-			gettimeofday(&tv, NULL);
-			nstime_t after_sleep;
-			nstime_init2(&after_sleep, tv.tv_sec, tv.tv_usec * 1000);
-			if (nstime_compare(&after_sleep, &before_sleep) > 0) {
-				nstime_subtract(&after_sleep, &before_sleep);
-				nstime_add(&info->tot_sleep_time, &after_sleep);
-			}
-		}
-	}
-	background_thread_wakeup_time_set(tsdn, info, 0);
-	malloc_mutex_unlock(tsdn, &info->mtx);
-}
-
-static void *
-background_thread_entry(void *ind_arg) {
-	unsigned thread_ind = (unsigned)(uintptr_t)ind_arg;
-	assert(thread_ind < narenas_total_get() && thread_ind < ncpus);
-
-	if (opt_percpu_arena != percpu_arena_disabled) {
-		set_current_thread_affinity((int)thread_ind);
-	}
-	/*
-	 * Start periodic background work.  We use internal tsd which avoids
-	 * side effects, for example triggering new arena creation (which in
-	 * turn triggers another background thread creation).
-	 */
-	background_work(tsd_tsdn(tsd_internal_fetch()), thread_ind);
-	assert(pthread_equal(pthread_self(),
-	    background_thread_info[thread_ind].thread));
-
-	return NULL;
-}
-
-/* Create a new background thread if needed. */
-bool
-background_thread_create(tsd_t *tsd, unsigned arena_ind) {
-	assert(have_background_thread);
-	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
-
-	/* We create at most NCPUs threads. */
-	size_t thread_ind = arena_ind % ncpus;
-	background_thread_info_t *info = &background_thread_info[thread_ind];
-
-	bool need_new_thread;
-	malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
-	need_new_thread = background_thread_enabled() && !info->started;
-	if (need_new_thread) {
-		info->started = true;
-		background_thread_info_reinit(tsd_tsdn(tsd), info);
-		n_background_threads++;
-	}
-	malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
-	if (!need_new_thread) {
-		return false;
-	}
-
-	pre_reentrancy(tsd);
-	malloc_mutex_unlock(tsd_tsdn(tsd), &background_thread_lock);
-	/*
-	 * To avoid complications (besides reentrancy), create internal
-	 * background threads with the underlying pthread_create, and drop
-	 * background_thread_lock (pthread_create may take internal locks).
-	 */
-	int err = pthread_create_wrapper(&info->thread, NULL,
-	    background_thread_entry, (void *)thread_ind);
-	malloc_mutex_lock(tsd_tsdn(tsd), &background_thread_lock);
-	post_reentrancy(tsd);
-
-	if (err != 0) {
-		malloc_printf("<jemalloc>: arena %u background thread creation "
-		    "failed (%d).\n", arena_ind, err);
-		malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
-		info->started = false;
-		n_background_threads--;
-		malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
-
-		return true;
-	}
-	assert(info->started);
-
-	return false;
-}
-
-bool
-background_threads_enable(tsd_t *tsd) {
-	assert(n_background_threads == 0);
-	assert(background_thread_enabled());
-	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
-
-	VARIABLE_ARRAY(bool, created, ncpus);
-	unsigned i, ncreated;
-	for (i = 0; i < ncpus; i++) {
-		created[i] = false;
-	}
-	ncreated = 0;
-
-	unsigned n = narenas_total_get();
-	for (i = 0; i < n; i++) {
-		if (created[i % ncpus] ||
-		    arena_get(tsd_tsdn(tsd), i, false) == NULL) {
-			continue;
-		}
-		if (background_thread_create(tsd, i)) {
-			return true;
-		}
-		created[i % ncpus] = true;
-		if (++ncreated == ncpus) {
-			break;
-		}
-	}
-
-	return false;
-}
-
-bool
 background_threads_disable_single(tsd_t *tsd, background_thread_info_t *info) {
-	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
+	if (info == &background_thread_info[0]) {
-	pre_reentrancy(tsd);
+		malloc_mutex_assert_owner(tsd_tsdn(tsd),
+		    &background_thread_lock);
+	} else {
+		malloc_mutex_assert_not_owner(tsd_tsdn(tsd),
+		    &background_thread_lock);
+	}
 
-	bool has_thread;
+	pre_reentrancy(tsd);
 	malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+	bool has_thread;
 	if (info->started) {
 		has_thread = true;
 		info->started = false;
@@ -440,14 +335,221 @@ background_threads_disable_single(tsd_t *tsd, background_thread_info_t *info) {
 	return false;
 }
 
+static void *background_thread_entry(void *ind_arg);
+
+static void
+check_background_thread_creation(tsd_t *tsd, unsigned *n_created,
+    bool *created_threads) {
+	if (likely(*n_created == n_background_threads)) {
+		return;
+	}
+
+	for (unsigned i = 1; i < ncpus; i++) {
+		if (created_threads[i]) {
+			continue;
+		}
+		background_thread_info_t *info = &background_thread_info[i];
+		malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+		if (info->started) {
+			pre_reentrancy(tsd);
+			int err = pthread_create_wrapper(&info->thread, NULL,
+			    background_thread_entry, (void *)(uintptr_t)i);
+			post_reentrancy(tsd);
+
+			if (err == 0) {
+				(*n_created)++;
+				created_threads[i] = true;
+			} else {
+				malloc_printf("<jemalloc>: background thread "
+				    "creation failed (%d)\n", err);
+				if (opt_abort) {
+					abort();
+				}
+			}
+		}
+		malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+	}
+}
+
+static void
+background_thread0_work(tsd_t *tsd) {
+	/* Thread0 is also responsible for launching / terminating threads. */
+	VARIABLE_ARRAY(bool, created_threads, ncpus);
+	unsigned i;
+	for (i = 1; i < ncpus; i++) {
+		created_threads[i] = false;
+	}
+	/* Start working, and create more threads when asked. */
+	unsigned n_created = 1;
+	while (background_thread_info[0].started) {
+		check_background_thread_creation(tsd, &n_created,
+		    (bool *)&created_threads);
+		background_work_sleep_once(tsd_tsdn(tsd),
+		    &background_thread_info[0], 0);
+	}
+
+	/*
+	 * Shut down other threads at exit.  Note that the ctl thread is holding
+	 * the global background_thread mutex (and is waiting) for us.
+	 */
+	assert(!background_thread_enabled());
+	for (i = 1; i < ncpus; i++) {
+		background_thread_info_t *info = &background_thread_info[i];
+		if (created_threads[i]) {
+			background_threads_disable_single(tsd, info);
+		} else {
+			malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+			/* Clear in case the thread wasn't created. */
+			info->started = false;
+			malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+		}
+	}
+	background_thread_info[0].started = false;
+	assert(n_background_threads == 1);
+}
+
+static void
+background_work(tsd_t *tsd, unsigned ind) {
+	background_thread_info_t *info = &background_thread_info[ind];
+
+	malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+	background_thread_wakeup_time_set(tsd_tsdn(tsd), info,
+	    BACKGROUND_THREAD_INDEFINITE_SLEEP);
+	if (ind == 0) {
+		background_thread0_work(tsd);
+	} else {
+		while (info->started) {
+			background_work_sleep_once(tsd_tsdn(tsd), info, ind);
+		}
+	}
+	background_thread_wakeup_time_set(tsd_tsdn(tsd), info, 0);
+	malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+}
+
+static void *
+background_thread_entry(void *ind_arg) {
+	unsigned thread_ind = (unsigned)(uintptr_t)ind_arg;
+	assert(thread_ind < ncpus);
+
+	if (opt_percpu_arena != percpu_arena_disabled) {
+		set_current_thread_affinity((int)thread_ind);
+	}
+	/*
+	 * Start periodic background work.  We use internal tsd which avoids
+	 * side effects, for example triggering new arena creation (which in
+	 * turn triggers another background thread creation).
+	 */
+	background_work(tsd_internal_fetch(), thread_ind);
+	assert(pthread_equal(pthread_self(),
+	    background_thread_info[thread_ind].thread));
+
+	return NULL;
+}
+
+static void
+background_thread_init(tsd_t *tsd, background_thread_info_t *info) {
+	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
+	info->started = true;
+	background_thread_info_init(tsd_tsdn(tsd), info);
+	n_background_threads++;
+}
+
+/* Create a new background thread if needed. */
+bool
+background_thread_create(tsd_t *tsd, unsigned arena_ind) {
+	assert(have_background_thread);
+	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
+
+	/* We create at most NCPUs threads. */
+	size_t thread_ind = arena_ind % ncpus;
+	background_thread_info_t *info = &background_thread_info[thread_ind];
+
+	bool need_new_thread;
+	malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+	need_new_thread = background_thread_enabled() && !info->started;
+	if (need_new_thread) {
+		background_thread_init(tsd, info);
+	}
+	malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+	if (!need_new_thread) {
+		return false;
+	}
+	if (arena_ind != 0) {
+		/* Threads are created asynchronously by Thread 0. */
+		background_thread_info_t *t0 = &background_thread_info[0];
+		malloc_mutex_lock(tsd_tsdn(tsd), &t0->mtx);
+		assert(t0->started);
+		pthread_cond_signal(&t0->cond);
+		malloc_mutex_unlock(tsd_tsdn(tsd), &t0->mtx);
+
+		return false;
+	}
+
+	pre_reentrancy(tsd);
+	/*
+	 * To avoid complications (besides reentrancy), create internal
+	 * background threads with the underlying pthread_create.
+	 */
+	int err = pthread_create_wrapper(&info->thread, NULL,
+	    background_thread_entry, (void *)thread_ind);
+	post_reentrancy(tsd);
+
+	if (err != 0) {
+		malloc_printf("<jemalloc>: arena 0 background thread creation "
+		    "failed (%d)\n", err);
+		malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+		info->started = false;
+		n_background_threads--;
+		malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+
+		return true;
+	}
+
+	return false;
+}
+
+bool
+background_threads_enable(tsd_t *tsd) {
+	assert(n_background_threads == 0);
+	assert(background_thread_enabled());
+	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
+
+	VARIABLE_ARRAY(bool, marked, ncpus);
+	unsigned i, nmarked;
+	for (i = 0; i < ncpus; i++) {
+		marked[i] = false;
+	}
+	nmarked = 0;
+	/* Mark the threads we need to create for thread 0. */
+	unsigned n = narenas_total_get();
+	for (i = 1; i < n; i++) {
+		if (marked[i % ncpus] ||
+		    arena_get(tsd_tsdn(tsd), i, false) == NULL) {
+			continue;
+		}
+		background_thread_info_t *info = &background_thread_info[i];
+		malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+		assert(!info->started);
+		background_thread_init(tsd, info);
+		malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
+		marked[i % ncpus] = true;
+		if (++nmarked == ncpus) {
+			break;
+		}
+	}
+
+	return background_thread_create(tsd, 0);
+}
+
 bool
 background_threads_disable(tsd_t *tsd) {
 	assert(!background_thread_enabled());
-	for (unsigned i = 0; i < ncpus; i++) {
+	malloc_mutex_assert_owner(tsd_tsdn(tsd), &background_thread_lock);
-		background_thread_info_t *info = &background_thread_info[i];
+
-		if (background_threads_disable_single(tsd, info)) {
+	/* Thread 0 will be responsible for terminating other threads. */
-			return true;
+	if (background_threads_disable_single(tsd,
-		}
+	    &background_thread_info[0])) {
+		return true;
 	}
 	assert(n_background_threads == 0);
 
@@ -460,7 +562,6 @@ background_thread_interval_check(tsdn_t *tsdn, arena_t *arena,
     arena_decay_t *decay, size_t npages_new) {
 	background_thread_info_t *info = arena_background_thread_info_get(
 	    arena);
-
 	if (malloc_mutex_trylock(tsdn, &info->mtx)) {
 		/*
 		 * Background thread may hold the mutex for a long period of
@@ -474,7 +575,6 @@ background_thread_interval_check(tsdn_t *tsdn, arena_t *arena,
 	if (!info->started) {
 		goto label_done;
 	}
-	assert(background_thread_enabled());
 	if (malloc_mutex_trylock(tsdn, &decay->mtx)) {
 		goto label_done;
 	}
@@ -646,7 +746,7 @@ bool
 background_thread_boot0(void) {
 	if (!have_background_thread && opt_background_thread) {
 		malloc_printf("<jemalloc>: option background_thread currently "
-		    "supports pthread only. \n");
+		    "supports pthread only\n");
 		return true;
 	}
 
@@ -686,9 +786,10 @@ background_thread_boot1(tsdn_t *tsdn) {
 
 	for (unsigned i = 0; i < ncpus; i++) {
 		background_thread_info_t *info = &background_thread_info[i];
+		/* Thread mutex is rank_inclusive because of thread0. */
 		if (malloc_mutex_init(&info->mtx, "background_thread",
 		    WITNESS_RANK_BACKGROUND_THREAD,
-		    malloc_mutex_rank_exclusive)) {
+		    malloc_mutex_address_ordered)) {
 			return true;
 		}
 		if (pthread_cond_init(&info->cond, NULL)) {
@@ -696,7 +797,7 @@ background_thread_boot1(tsdn_t *tsdn) {
 		}
 		malloc_mutex_lock(tsdn, &info->mtx);
 		info->started = false;
-		background_thread_info_reinit(tsdn, info);
+		background_thread_info_init(tsdn, info);
 		malloc_mutex_unlock(tsdn, &info->mtx);
 	}
 #endif

src/ctl.c

@@ -1948,8 +1948,10 @@ arena_reset_prepare_background_thread(tsd_t *tsd, unsigned arena_ind) {
 			unsigned ind = arena_ind % ncpus;
 			background_thread_info_t *info =
 			    &background_thread_info[ind];
-			assert(info->started);
+			assert(info->started && !info->pause);
-			background_threads_disable_single(tsd, info);
+			malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+			info->pause = true;
+			malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
 		}
 	}
 }
@@ -1961,8 +1963,10 @@ arena_reset_finish_background_thread(tsd_t *tsd, unsigned arena_ind) {
 			unsigned ind = arena_ind % ncpus;
 			background_thread_info_t *info =
 			    &background_thread_info[ind];
-			assert(!info->started);
+			assert(info->started && info->pause);
-			background_thread_create(tsd, ind);
+			malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
+			info->pause = false;
+			malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
 		}
 		malloc_mutex_unlock(tsd_tsdn(tsd), &background_thread_lock);
 	}