Use generic lock-free queue for async threads

Queues used for communication between async threads and scheduler threads
have been replaced with lock-free queues.

Drivers using the driver_async functionality are not automatically locked
to the system anymore, and can be unloaded as any dynamically linked in
driver.

Scheduling of ready async jobs is now also interleaved in between other
jobs. Previously all ready async jobs was performed at once.

20 files changed, 939 insertions, 657 deletions

diff --git a/erts/doc/src/erl_driver.xml b/erts/doc/src/erl_driver.xml
index 2fb03954b6..8e18dd6657 100644
--- a/erts/doc/src/erl_driver.xml
+++ b/erts/doc/src/erl_driver.xml
@@ -1638,12 +1638,19 @@ ERL_DRV_EXT2TERM     char *buf, ErlDrvUInt len
       <fsummary>Cancel an asynchronous call</fsummary>
       <desc>
         <marker id="driver_async_cancel"></marker>
-        <p>This function cancels an asynchronous operation, by removing
-          it from the queue. Only functions in the queue can be
-          cancelled; if a function is executing, it's too late to
-          cancel it. The <c>async_free</c> function is also called.</p>
-        <p>The return value is 1 if the operation was removed from the
-          queue, otherwise 0.</p>
+        <p>This function used to cancel a scheduled asynchronous operation,
+	  if it was still in the queue. It returned 1 if it succeeded, and
+	  0 if it failed.</p>
+	<p>Since it could not guarantee success, it was more or less useless.
+	   The user had to implement synchronization of cancellation anyway.
+	   It also unnecessarily complicated the implementation. Therefore,
+	   as of OTP-R15B <c>driver_async_cancel()</c> is deprecated, and
+	   scheduled for removal in OTP-R16. It will currently always fail,
+	   and return 0.</p>
+	<warning><p><c>driver_async_cancel()</c> is deferred and will
+	            be removed in the OTP-R16 release.</p>
+	</warning>
+
       </desc>
     </func>
     <func>
diff --git a/erts/emulator/beam/erl_alloc.types b/erts/emulator/beam/erl_alloc.types
index 9f0cb681c0..962db8b831 100644
--- a/erts/emulator/beam/erl_alloc.types
+++ b/erts/emulator/beam/erl_alloc.types
@@ -201,7 +201,7 @@ type	LINEBUF		STANDARD	SYSTEM		line_buf
 type	IOQ		STANDARD	SYSTEM		io_queue
 type	BITS_BUF	STANDARD	SYSTEM		bits_buf
 type	TMP_DIST_BUF	TEMPORARY	SYSTEM		tmp_dist_buf
-type	ASYNC_Q		LONG_LIVED	SYSTEM		async_queue
+type	ASYNC_DATA	LONG_LIVED	SYSTEM		internal_async_data
 type	ESTACK		TEMPORARY	SYSTEM		estack
 type	PORT_CALL_BUF	TEMPORARY	SYSTEM		port_call_buf
 type	DB_TABLE	ETS		ETS		db_tab
@@ -308,12 +308,6 @@ type	ETHR_STD	STANDARD	SYSTEM		ethread_standard
 type	ETHR_SL		SHORT_LIVED	SYSTEM		ethread_short_lived
 type	ETHR_LL		LONG_LIVED	SYSTEM		ethread_long_lived
 
-+ifnot smp
-
-type	ARCALLBACK	LONG_LIVED	SYSTEM		async_ready_callback
-
-+endif
-
 +endif
 
 +if shared_heap
diff --git a/erts/emulator/beam/erl_async.c b/erts/emulator/beam/erl_async.c
index 91b64411d4..2dc7237f7c 100644
--- a/erts/emulator/beam/erl_async.c
+++ b/erts/emulator/beam/erl_async.c
@@ -24,10 +24,18 @@
 #include "erl_sys_driver.h"
 #include "global.h"
 #include "erl_threads.h"
+#include "erl_thr_queue.h"
+#include "erl_async.h"
+
+#define ERTS_MAX_ASYNC_READY_CALLS_IN_SEQ 20
+
+#define ERTS_ASYNC_PRINT_JOB 0
+
+#if !defined(ERTS_SMP) && defined(USE_THREADS) && !ERTS_USE_ASYNC_READY_Q
+#  error "Need async ready queue in non-smp case"
+#endif
 
 typedef struct _erl_async {
-    struct _erl_async* next;
-    struct _erl_async* prev;
     DE_Handle*         hndl;   /* The DE_Handle is needed when port is gone */
     Eterm              port;
     long               async_id;
@@ -35,345 +43,498 @@ typedef struct _erl_async {
     ErlDrvPDL          pdl;
     void (*async_invoke)(void*);
     void (*async_free)(void*);
-} ErlAsync;
+#if ERTS_USE_ASYNC_READY_Q
+    Uint               sched_id;
+    union {
+	ErtsThrQPrepEnQ_t *prep_enq;
+	ErtsThrQFinDeQ_t   fin_deq;
+    } q;
+#endif
+} ErtsAsync;
+
+#if ERTS_USE_ASYNC_READY_Q
+
+/*
+ * We can do without the enqueue mutex since it isn't needed for
+ * thread safety. Its only purpose is to put async threads to sleep
+ * during a blast of ready async jobs. This in order to reduce
+ * contention on the enqueue end of the async ready queues. During
+ * such a blast without the enqueue mutex much cpu time is consumed
+ * by the async threads without them doing much progress which in turn
+ * slow down progress of scheduler threads.
+ */
+#define ERTS_USE_ASYNC_READY_ENQ_MTX 1
+
+#if ERTS_USE_ASYNC_READY_ENQ_MTX
 
 typedef struct {
-    erts_mtx_t mtx;
-    erts_cnd_t cv;
-    erts_tid_t thr;
-    int   len;
-#ifndef ERTS_SMP
-    int   hndl;
+    erts_mtx_t enq_mtx;
+} ErtsAsyncReadyQXData;
+
 #endif
-    ErlAsync* head;
-    ErlAsync* tail;
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    int no;
+
+typedef struct {
+#if ERTS_USE_ASYNC_READY_ENQ_MTX
+    union {
+	ErtsAsyncReadyQXData data;
+	char align__[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(
+		sizeof(ErtsAsyncReadyQXData))];
+    } x;
 #endif
-} AsyncQueue;
+    ErtsThrQ_t thr_q;
+    ErtsThrQFinDeQ_t fin_deq;
+} ErtsAsyncReadyQ;
 
-static erts_smp_spinlock_t async_id_lock;
-static long async_id = 0;
 
+typedef union {
+    ErtsAsyncReadyQ arq;
+    char align__[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsAsyncReadyQ))];
+} ErtsAlgndAsyncReadyQ;
 
-#ifndef ERTS_SMP
+#endif /* ERTS_USE_ASYNC_READY_Q */
 
-erts_mtx_t async_ready_mtx;
-static ErlAsync* async_ready_list = NULL;
+typedef struct {
+    ErtsThrQ_t thr_q;
+    erts_tid_t thr_id;
+} ErtsAsyncQ;
+
+typedef union {
+    ErtsAsyncQ aq;
+    char align__[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsAsyncQ))];
+} ErtsAlgndAsyncQ;
 
+typedef struct {
+    int no_initialized;
+    erts_mtx_t mtx;
+    erts_cnd_t cnd;
+    erts_atomic_t id;
+} ErtsAsyncInit;
+
+typedef struct {
+    union {
+	ErtsAsyncInit data;
+	char align__[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsAsyncInit))];
+    } init;
+    ErtsAlgndAsyncQ *queue;
+#if ERTS_USE_ASYNC_READY_Q
+    ErtsAlgndAsyncReadyQ *ready_queue;
 #endif
+} ErtsAsyncData;
 
-/*
-** Initialize worker threads (if supported)
-*/
+int erts_async_max_threads; /* Initialized by erl_init.c */
+int erts_async_thread_suggested_stack_size; /* Initialized by erl_init.c */
 
-/* Detach from driver */
-static void async_detach(DE_Handle* dh)
-{
-    return;
-}
+static ErtsAsyncData *async;
 
+#ifndef USE_THREADS
 
-#ifdef USE_THREADS
+void
+erts_init_async(void)
+{
 
-static AsyncQueue* async_q;
+}
 
-static void* async_main(void*);
-static void async_add(ErlAsync*, AsyncQueue*);
+#else
 
-#ifndef ERTS_SMP
-typedef struct ErtsAsyncReadyCallback_ ErtsAsyncReadyCallback;
-struct ErtsAsyncReadyCallback_ {
-    struct ErtsAsyncReadyCallback_ *next;
-    void (*callback)(void);
-};
+static void *async_main(void *);
 
-static ErtsAsyncReadyCallback *callbacks;
-static int async_handle;
+static ERTS_INLINE ErtsAsyncQ *
+async_q(int i)
+{
+    return &async->queue[i].aq;
+}
+
+#if ERTS_USE_ASYNC_READY_Q
 
-int erts_register_async_ready_callback(void (*funcp)(void))
+static ERTS_INLINE ErtsAsyncReadyQ *
+async_ready_q(Uint sched_id)
 {
-    ErtsAsyncReadyCallback *cb = erts_alloc(ERTS_ALC_T_ARCALLBACK,
-					    sizeof(ErtsAsyncReadyCallback));
-    cb->next = callbacks;
-    cb->callback = funcp;
-    erts_mtx_lock(&async_ready_mtx);
-    callbacks = cb;
-    erts_mtx_unlock(&async_ready_mtx);
-    return async_handle;
+    return &async->ready_queue[((int)sched_id)-1].arq;
 }
+
 #endif
 
-int init_async(int hndl)
+void
+erts_init_async(void)
 {
-    erts_thr_opts_t thr_opts = ERTS_THR_OPTS_DEFAULT_INITER;
-    AsyncQueue* q;
-    int i;
+    async = NULL;
+    if (erts_async_max_threads > 0) {
+#if ERTS_USE_ASYNC_READY_Q
+	ErtsThrQInit_t qinit = ERTS_THR_Q_INIT_DEFAULT;
+#endif
+	erts_thr_opts_t thr_opts = ERTS_THR_OPTS_DEFAULT_INITER;
+	char *ptr;
+	size_t tot_size = 0;
+	int i;
+
+	tot_size += ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsAsyncData));
+	tot_size += sizeof(ErtsAlgndAsyncQ)*erts_async_max_threads;
+#if ERTS_USE_ASYNC_READY_Q
+	tot_size += sizeof(ErtsAlgndAsyncReadyQ)*erts_no_schedulers;
+#endif
 
-    thr_opts.detached = 0;
-    thr_opts.suggested_stack_size = erts_async_thread_suggested_stack_size;
-
-#ifndef ERTS_SMP
-    callbacks = NULL;
-    async_handle = hndl;
-    erts_mtx_init(&async_ready_mtx, "async_ready");
-    async_ready_list = NULL;
-#endif
-
-    async_id = 0;
-    erts_smp_spinlock_init(&async_id_lock, "async_id");
-
-    async_q = q = (AsyncQueue*)
-	(erts_async_max_threads
-	 ? erts_alloc(ERTS_ALC_T_ASYNC_Q,
-		      erts_async_max_threads * sizeof(AsyncQueue))
-	 : NULL);
-    for (i = 0; i < erts_async_max_threads; i++) {
-	q->head = NULL;
-	q->tail = NULL;
-	q->len = 0;
-#ifndef ERTS_SMP
-	q->hndl = hndl;
-#endif
-#ifdef ERTS_ENABLE_LOCK_CHECK
-	q->no = i;
-#endif
-	erts_mtx_init(&q->mtx, "asyncq");
-	erts_cnd_init(&q->cv);
-	erts_thr_create(&q->thr, async_main, (void*)q, &thr_opts);
-	q++;
-    }
-    return 0;
-}
+	ptr = erts_alloc_permanent_cache_aligned(ERTS_ALC_T_ASYNC_DATA,
+						 tot_size);
 
+	async = (ErtsAsyncData *) ptr;
+	ptr += ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsAsyncData));
 
-int exit_async()
-{
-    int i;
+	async->init.data.no_initialized = 0;
+	erts_mtx_init(&async->init.data.mtx, "async_init_mtx");
+	erts_cnd_init(&async->init.data.cnd);
+	erts_atomic_init_nob(&async->init.data.id, 0);
 
-    /* terminate threads */
-    for (i = 0; i < erts_async_max_threads; i++) {
-	ErlAsync* a = (ErlAsync*) erts_alloc(ERTS_ALC_T_ASYNC,
-					     sizeof(ErlAsync));
-	a->port = NIL;
-	async_add(a, &async_q[i]);
-    }
+	async->queue = (ErtsAlgndAsyncQ *) ptr;
+	ptr += sizeof(ErtsAlgndAsyncQ)*erts_async_max_threads;
 
-    for (i = 0; i < erts_async_max_threads; i++) {
-	erts_thr_join(async_q[i].thr, NULL);
-	erts_mtx_destroy(&async_q[i].mtx);
-	erts_cnd_destroy(&async_q[i].cv);
-    }
-#ifndef ERTS_SMP
-    erts_mtx_destroy(&async_ready_mtx);
+#if ERTS_USE_ASYNC_READY_Q
+
+	qinit.live.queue = ERTS_THR_Q_LIVE_LONG;
+	qinit.live.objects = ERTS_THR_Q_LIVE_SHORT;
+	qinit.notify = erts_notify_check_async_ready_queue;
+
+	async->ready_queue = (ErtsAlgndAsyncReadyQ *) ptr;
+	ptr += sizeof(ErtsAlgndAsyncReadyQ)*erts_no_schedulers;
+
+	for (i = 1; i <= erts_no_schedulers; i++) {
+	    ErtsAsyncReadyQ *arq = async_ready_q(i);
+#if ERTS_USE_ASYNC_READY_ENQ_MTX
+	    erts_mtx_init(&arq->x.data.enq_mtx, "async_enq_mtx");
 #endif
-    if (async_q)
-	erts_free(ERTS_ALC_T_ASYNC_Q, (void *) async_q);
-    return 0;
+	    erts_thr_q_finalize_dequeue_state_init(&arq->fin_deq);
+	    qinit.arg = (void *) (SWord) i;
+	    erts_thr_q_initialize(&arq->thr_q, &qinit);
+	}
+
+#endif
+
+	/* Create async threads... */
+
+	thr_opts.detached = 0;
+	thr_opts.suggested_stack_size
+	    = erts_async_thread_suggested_stack_size;
+
+	for (i = 0; i < erts_async_max_threads; i++) {
+	    ErtsAsyncQ *aq = async_q(i);
+	    erts_thr_create(&aq->thr_id, async_main, (void*) aq, &thr_opts);
+	}
+
+	/* Wait for async threads to initialize... */
+
+	erts_mtx_lock(&async->init.data.mtx);
+	while (async->init.data.no_initialized != erts_async_max_threads)
+	    erts_cnd_wait(&async->init.data.cnd, &async->init.data.mtx);
+	erts_mtx_unlock(&async->init.data.mtx);
+
+	erts_mtx_destroy(&async->init.data.mtx);
+	erts_cnd_destroy(&async->init.data.cnd);
+
+    }
 }
 
+#if ERTS_USE_ASYNC_READY_Q
 
-static void async_add(ErlAsync* a, AsyncQueue* q)
+void *
+erts_get_async_ready_queue(Uint sched_id)
+{
+    return (void *) async ? async_ready_q(sched_id) : NULL;
+}
+
+#endif
+
+static ERTS_INLINE void async_add(ErtsAsync *a, ErtsAsyncQ* q)
 {
     if (is_internal_port(a->port)) {
-	ERTS_LC_ASSERT(erts_drvportid2port(a->port));
+#if ERTS_USE_ASYNC_READY_Q
+	ErtsAsyncReadyQ *arq = async_ready_q(a->sched_id);
+	a->q.prep_enq = erts_thr_q_prepare_enqueue(&arq->thr_q);
+#endif
 	/* make sure the driver will stay around */
-	driver_lock_driver(internal_port_index(a->port));
+	if (a->hndl)
+	    erts_ddll_reference_referenced_driver(a->hndl);
     }
 
-    erts_mtx_lock(&q->mtx);
+#if ERTS_ASYNC_PRINT_JOB
+    erts_fprintf(stderr, "-> %ld\n", a->async_id);
+#endif
 
-    if (q->len == 0) {
-	q->head = a;
-	q->tail = a;
-	q->len = 1;
-	erts_cnd_signal(&q->cv);
-    }
-    else { /* no need to signal (since the worker is working) */
-	a->next = q->head;
-	q->head->prev = a;
-	q->head = a;
-	q->len++;
-    }
-    erts_mtx_unlock(&q->mtx);
+    erts_thr_q_enqueue(&q->thr_q, a);
 }
 
-static ErlAsync* async_get(AsyncQueue* q)
+static ERTS_INLINE ErtsAsync *async_get(ErtsThrQ_t *q,
+					erts_tse_t *tse,
+					ErtsThrQPrepEnQ_t **prep_enq)
 {
-    ErlAsync* a;
+#if ERTS_USE_ASYNC_READY_Q
+    int saved_fin_deq = 0;
+    ErtsThrQFinDeQ_t fin_deq;
+#endif
 
-    erts_mtx_lock(&q->mtx);
-    while((a = q->tail) == NULL) {
-	erts_cnd_wait(&q->cv, &q->mtx);
-    }
+    while (1) {
+	ErtsAsync *a = (ErtsAsync *) erts_thr_q_dequeue(q);
+	if (a) {
+
+#if ERTS_USE_ASYNC_READY_Q
+	    *prep_enq = a->q.prep_enq;
+	    erts_thr_q_get_finalize_dequeue_data(q, &a->q.fin_deq);
+	    if (saved_fin_deq)
+		erts_thr_q_append_finalize_dequeue_data(&a->q.fin_deq, &fin_deq);
+#endif
+
+	    return a;
+	}
+
+	if (ERTS_THR_Q_DIRTY != erts_thr_q_clean(q)) {
+	    ErtsThrQFinDeQ_t tmp_fin_deq;
+
+	    erts_tse_reset(tse);
+
+#if ERTS_USE_ASYNC_READY_Q
+	chk_fin_deq:
+	    if (erts_thr_q_get_finalize_dequeue_data(q, &tmp_fin_deq)) {
+		if (!saved_fin_deq) {
+		    erts_thr_q_finalize_dequeue_state_init(&fin_deq);
+		    saved_fin_deq = 1;
+		}
+		erts_thr_q_append_finalize_dequeue_data(&fin_deq,
+							&tmp_fin_deq);
+	    }
+#endif
+
+	    switch (erts_thr_q_inspect(q, 1)) {
+	    case ERTS_THR_Q_DIRTY:
+		break;
 #ifdef ERTS_SMP
-    ASSERT(a && q->tail == a);
+	    case ERTS_THR_Q_NEED_THR_PRGR: {
+		ErtsThrPrgrVal prgr = erts_thr_q_need_thr_progress(q);
+		erts_thr_progress_wakeup(NULL, prgr);
+		/*
+		 * We do no dequeue finalizing in hope that a new async
+		 * job will arrive before we are woken due to thread
+		 * progress...
+		 */
+		erts_tse_wait(tse);
+		break;
+	    }
 #endif
-    if (q->head == q->tail) {
-	q->head = q->tail = NULL;
-	q->len = 0;
-    }
-    else {
-	q->tail->prev->next = NULL;
-	q->tail = q->tail->prev;
-	q->len--;
+	    case ERTS_THR_Q_CLEAN:
+
+#if ERTS_USE_ASYNC_READY_Q
+		if (saved_fin_deq) {
+		    if (erts_thr_q_finalize_dequeue(&fin_deq))
+			goto chk_fin_deq;
+		    else
+			saved_fin_deq = 0;
+		}
+#endif
+
+		erts_tse_wait(tse);
+		break;
+
+	    default:
+		ASSERT(0);
+		break;
+	    }
+
+	}
     }
-    erts_mtx_unlock(&q->mtx);
-    return a;
 }
 
-
-static int async_del(long id)
+static ERTS_INLINE void call_async_ready(ErtsAsync *a)
 {
-    int i;
-    /* scan all queue for an entry with async_id == 'id' */
-
-    for (i = 0; i < erts_async_max_threads; i++) {
-	ErlAsync* a;
-	erts_mtx_lock(&async_q[i].mtx);
-	
-	a = async_q[i].head;
-	while(a != NULL) {
-	    if (a->async_id == id) {
-		if (a->prev != NULL)
-		    a->prev->next = a->next;
-		else
-		    async_q[i].head = a->next;
-		if (a->next != NULL)
-		    a->next->prev = a->prev;
-		else
-		    async_q[i].tail = a->prev;
-		async_q[i].len--;
-		erts_mtx_unlock(&async_q[i].mtx);
-		if (a->async_free != NULL)
-		    a->async_free(a->async_data);
-		async_detach(a->hndl);
-		erts_free(ERTS_ALC_T_ASYNC, a);
-		return 1;
-	    }
-	    a = a->next;
+    Port *p = erts_id2port_sflgs(a->port,
+				 NULL,
+				 0,
+				 ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP);
+    if (!p) {
+	if (a->async_free)
+	    a->async_free(a->async_data);
+    }
+    else {
+	if (async_ready(p, a->async_data)) {
+	    if (a->async_free)
+		a->async_free(a->async_data);
 	}
-	erts_mtx_unlock(&async_q[i].mtx);
+	erts_port_release(p);
     }
-    return 0;
+    if (a->hndl)
+	erts_ddll_dereference_driver(a->hndl);
 }
 
-static void* async_main(void* arg)
+static ERTS_INLINE void async_reply(ErtsAsync *a, ErtsThrQPrepEnQ_t *prep_enq)
 {
-    AsyncQueue* q = (AsyncQueue*) arg;
+#if ERTS_USE_ASYNC_READY_Q
+    ErtsAsyncReadyQ *arq;
 
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    {
-	char buf[27];
-	erts_snprintf(&buf[0], 27, "async %d", q->no);
-	erts_lc_set_thread_name(&buf[0]);
-    }
+    if (a->pdl)
+	driver_pdl_dec_refc(a->pdl);
+
+#if ERTS_ASYNC_PRINT_JOB
+    erts_fprintf(stderr, "=>> %ld\n", a->async_id);
 #endif
 
-    while(1) {
-	ErlAsync* a = async_get(q);
+    arq = async_ready_q(a->sched_id);
 
-	if (a->port == NIL) { /* TIME TO DIE SIGNAL */
-	    erts_free(ERTS_ALC_T_ASYNC, (void *) a);
-	    break;
-	}
-	else {
-	    (*a->async_invoke)(a->async_data);
-	    /* Major problem if the code for async_invoke
-	       or async_free is removed during a blocking operation */
+#if ERTS_USE_ASYNC_READY_ENQ_MTX
+	erts_mtx_lock(&arq->x.data.enq_mtx);
+#endif
+
+	erts_thr_q_enqueue_prepared(&arq->thr_q, (void *) a, prep_enq);
+
+#if ERTS_USE_ASYNC_READY_ENQ_MTX
+	erts_mtx_unlock(&arq->x.data.enq_mtx);
+#endif
+
+#else /* ERTS_USE_ASYNC_READY_Q */
+
+	call_async_ready(a);
+	if (a->pdl)
+	    driver_pdl_dec_refc(a->pdl);
+	erts_free(ERTS_ALC_T_ASYNC, (void *) a);
+
+#endif /* ERTS_USE_ASYNC_READY_Q */
+}
+
+
+static void
+async_wakeup(void *vtse)
+{
+    erts_tse_set((erts_tse_t *) vtse);
+}
+
+static erts_tse_t *async_thread_init(ErtsAsyncQ *aq)
+{
+    ErtsThrQInit_t qinit = ERTS_THR_Q_INIT_DEFAULT;
+    erts_tse_t *tse = erts_tse_fetch();
 #ifdef ERTS_SMP
-	    {
-		Port *p;
-		p = erts_id2port_sflgs(a->port,
-				       NULL,
-				       0,
-				       ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP);
-		if (!p) {
-		    if (a->async_free)
-			(*a->async_free)(a->async_data);
-		}
-		else {
-		    if (async_ready(p, a->async_data)) {
-			if (a->async_free)
-			    (*a->async_free)(a->async_data);
-		    }
-		    async_detach(a->hndl);
-		    erts_port_release(p);
-		}
-		if (a->pdl) {
-		    driver_pdl_dec_refc(a->pdl);
-		}
-		erts_free(ERTS_ALC_T_ASYNC, (void *) a);
-	    }
-#else
-	    if (a->pdl) {
-		driver_pdl_dec_refc(a->pdl);
-	    }
-	    erts_mtx_lock(&async_ready_mtx);
-	    a->next = async_ready_list;
-	    async_ready_list = a;
-	    erts_mtx_unlock(&async_ready_mtx);
-	    sys_async_ready(q->hndl);
+    ErtsThrPrgrCallbacks callbacks;
+
+    callbacks.arg = (void *) tse;
+    callbacks.wakeup = async_wakeup;
+    callbacks.prepare_wait = NULL;
+    callbacks.wait = NULL;
+
+    erts_thr_progress_register_unmanaged_thread(&callbacks);
 #endif
-	}
-    }
 
-    return NULL;
+    qinit.live.queue = ERTS_THR_Q_LIVE_LONG;
+    qinit.live.objects = ERTS_THR_Q_LIVE_SHORT;
+    qinit.arg = (void *) tse;
+    qinit.notify = async_wakeup;
+#if ERTS_USE_ASYNC_READY_Q
+    qinit.auto_finalize_dequeue = 0;
+#endif
+
+    erts_thr_q_initialize(&aq->thr_q, &qinit);
+
+    /* Inform main thread that we are done initializing... */
+    erts_mtx_lock(&async->init.data.mtx);
+    async->init.data.no_initialized++;
+    erts_cnd_signal(&async->init.data.cnd);
+    erts_mtx_unlock(&async->init.data.mtx);
+
+    return tse;
 }
 
+static void *async_main(void* arg)
+{
+    ErtsAsyncQ *aq = (ErtsAsyncQ *) arg;
+    erts_tse_t *tse = async_thread_init(aq);
+
+    while (1) {
+	ErtsThrQPrepEnQ_t *prep_enq;
+	ErtsAsync *a = async_get(&aq->thr_q, tse, &prep_enq);
+	if (is_nil(a->port))
+	    break; /* Time to die */
 
+#if ERTS_ASYNC_PRINT_JOB
+	erts_fprintf(stderr, "<- %ld\n", a->async_id);
 #endif
 
-#ifndef ERTS_SMP
+	a->async_invoke(a->async_data);
+
+	async_reply(a, prep_enq);
+    }
+
+    return NULL;
+}
+
+#endif /* USE_THREADS */
 
-int check_async_ready(void)
+void
+erts_exit_flush_async(void)
 {
 #ifdef USE_THREADS
-    ErtsAsyncReadyCallback *cbs;
+    int i;
+    ErtsAsync a;
+    a.port = NIL;
+    /*
+     * Terminate threads in order to flush queues. We do not
+     * bother to clean everything up since we are about to
+     * terminate the runtime system and a cleanup would only
+     * delay the termination.
+     */
+    for (i = 0; i < erts_async_max_threads; i++)
+	async_add(&a, async_q(i));
+    for (i = 0; i < erts_async_max_threads; i++)
+	erts_thr_join(async->queue[i].aq.thr_id, NULL);
 #endif
-    ErlAsync* a;
-    int count = 0;
+}
 
-    erts_mtx_lock(&async_ready_mtx);
-    a = async_ready_list;
-    async_ready_list = NULL;
-#ifdef USE_THREADS
-    cbs = callbacks;
-#endif
-    erts_mtx_unlock(&async_ready_mtx);
-
-    while(a != NULL) {
-	ErlAsync* a_next = a->next;
-	/* Every port not dead */
-	Port *p = erts_id2port_sflgs(a->port,
-				     NULL,
-				     0,
-				     ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP);
-	if (!p) {
-	    if (a->async_free)
-		(*a->async_free)(a->async_data);
-	}
-	else {
-	    count++;
-	    if (async_ready(p, a->async_data)) {
-		if (a->async_free != NULL)
-		    (*a->async_free)(a->async_data);
-	    }
-	    async_detach(a->hndl);
-	    erts_port_release(p);
+#if defined(USE_THREADS) && ERTS_USE_ASYNC_READY_Q
+
+int erts_check_async_ready(void *varq)
+{
+    ErtsAsyncReadyQ *arq = (ErtsAsyncReadyQ *) varq;
+    int res = 1;
+    int i;
+
+    for (i = 0; i < ERTS_MAX_ASYNC_READY_CALLS_IN_SEQ; i++) {
+	ErtsAsync *a = (ErtsAsync *) erts_thr_q_dequeue(&arq->thr_q);
+	if (!a) {
+	    res = 0;
+	    break;
 	}
+
+#if ERTS_ASYNC_PRINT_JOB
+	erts_fprintf(stderr, "<<= %ld\n", a->async_id);
+#endif
+	erts_thr_q_append_finalize_dequeue_data(&arq->fin_deq, &a->q.fin_deq);
+	call_async_ready(a);
 	erts_free(ERTS_ALC_T_ASYNC, (void *) a);
-	a = a_next;
     }
-#ifdef USE_THREADS
-    for (; cbs; cbs = cbs->next)
-	(*cbs->callback)();
-#endif
-    return count;
+
+    erts_thr_q_finalize_dequeue(&arq->fin_deq);
+    
+    return res;
 }
 
+int erts_async_ready_clean(void *varq, void *val)
+{
+    ErtsAsyncReadyQ *arq = (ErtsAsyncReadyQ *) varq;
+    ErtsThrQCleanState_t cstate;
+
+    cstate = erts_thr_q_clean(&arq->thr_q);
+
+    if (erts_thr_q_finalize_dequeue(&arq->fin_deq))
+	return ERTS_ASYNC_READY_DIRTY;
+
+    switch (cstate) {
+    case ERTS_THR_Q_DIRTY:
+	return ERTS_ASYNC_READY_DIRTY;
+#ifdef ERTS_SMP
+    case ERTS_THR_Q_NEED_THR_PRGR:
+	*((ErtsThrPrgrVal *) val)
+	    = erts_thr_q_need_thr_progress(&arq->thr_q);
+	return ERTS_ASYNC_READY_NEED_THR_PRGR;
 #endif
+    case ERTS_THR_Q_CLEAN:
+	break;
+    }
+    return ERTS_ASYNC_READY_CLEAN;
+}
 
+#endif
 
 /*
 ** Schedule async_invoke on a worker thread
@@ -393,19 +554,29 @@ long driver_async(ErlDrvPort ix, unsigned int* key,
 		  void (*async_invoke)(void*), void* async_data,
 		  void (*async_free)(void*))
 {
-    ErlAsync* a = (ErlAsync*) erts_alloc(ERTS_ALC_T_ASYNC, sizeof(ErlAsync));
-    Port* prt = erts_drvport2port(ix);
+    ErtsAsync* a;
+    Port* prt;
     long id;
     unsigned int qix;
+#if ERTS_USE_ASYNC_READY_Q
+    Uint sched_id;
 
+    sched_id = erts_get_scheduler_id();
+    if (!sched_id)
+	sched_id = 1;
+#endif
 
+    prt = erts_drvport2port(ix);
     if (!prt)
 	return -1;
 
     ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(prt));
 
-    a->next = NULL;
-    a->prev = NULL;
+    a = (ErtsAsync*) erts_alloc(ERTS_ALC_T_ASYNC, sizeof(ErtsAsync));
+
+#if ERTS_USE_ASYNC_READY_Q
+    a->sched_id = sched_id;
+#endif
     a->hndl = (DE_Handle*)prt->drv_ptr->handle;
     a->port = prt->id;
     a->pdl = NULL;
@@ -413,12 +584,16 @@ long driver_async(ErlDrvPort ix, unsigned int* key,
     a->async_invoke = async_invoke;
     a->async_free = async_free;
 
-    erts_smp_spin_lock(&async_id_lock);
-    async_id = (async_id + 1) & 0x7fffffff;
-    if (async_id == 0)
-	async_id++;
-    id = async_id;
-    erts_smp_spin_unlock(&async_id_lock);
+    if (!async)
+	id = 0;
+    else {
+	do {
+	    id = erts_atomic_inc_read_nob(&async->init.data.id);
+	} while (id == 0);
+	if (id < 0)
+	    id *= -1;
+	ASSERT(id > 0);
+    }
 
     a->async_id = id;
 
@@ -437,7 +612,7 @@ long driver_async(ErlDrvPort ix, unsigned int* key,
 	    driver_pdl_inc_refc(prt->port_data_lock);
 	    a->pdl = prt->port_data_lock;
 	}
-	async_add(a, &async_q[qix]);
+	async_add(a, async_q(qix));
 	return id;
     }
 #endif
@@ -455,10 +630,16 @@ long driver_async(ErlDrvPort ix, unsigned int* key,
 
 int driver_async_cancel(unsigned int id)
 {
-#ifdef USE_THREADS
-    if (erts_async_max_threads > 0)
-	return async_del(id);
-#endif
+    /*
+     * Not supported anymore. Always fail (which is backward
+     * compatible).
+     *
+     * This functionality could be implemented again. However,
+     * it is (and always has been) completely useless since
+     * it doesn't give you any guarantees whatsoever. The user
+     * needs to (and always have had to) synchronize in his/her
+     * own code in order to get any guarantees.
+     */
     return 0;
 }
 
diff --git a/erts/emulator/beam/erl_async.h b/erts/emulator/beam/erl_async.h
new file mode 100644
index 0000000000..95374a8fc9
--- /dev/null
+++ b/erts/emulator/beam/erl_async.h
@@ -0,0 +1,66 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2011. All Rights Reserved.
+ *
+ * The contents of this file are subject to the Erlang Public License,
+ * Version 1.1, (the "License"); you may not use this file except in
+ * compliance with the License. You should have received a copy of the
+ * Erlang Public License along with this software. If not, it can be
+ * retrieved online at http://www.erlang.org/.
+ *
+ * Software distributed under the License is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ * the License for the specific language governing rights and limitations
+ * under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+#ifndef ERL_ASYNC_H__
+#define ERL_ASYNC_H__
+
+#define ERTS_MAX_NO_OF_ASYNC_THREADS 1024
+extern int erts_async_max_threads;
+#define ERTS_ASYNC_THREAD_MIN_STACK_SIZE 16	/* Kilo words */
+#define ERTS_ASYNC_THREAD_MAX_STACK_SIZE 8192	/* Kilo words */
+extern int erts_async_thread_suggested_stack_size;
+
+#ifdef USE_THREADS
+
+#ifdef ERTS_SMP
+/*
+ * With smp support we can choose to have, or not to
+ * have an async ready queue.
+ */
+#define ERTS_USE_ASYNC_READY_Q 1
+#endif
+
+#ifndef ERTS_SMP
+/* In non-smp case we *need* the async ready queue */
+#  undef ERTS_USE_ASYNC_READY_Q
+#  define ERTS_USE_ASYNC_READY_Q 1
+#endif
+
+#ifndef ERTS_USE_ASYNC_READY_Q
+#  define ERTS_USE_ASYNC_READY_Q 0
+#endif
+
+#if ERTS_USE_ASYNC_READY_Q
+int erts_check_async_ready(void *);
+int erts_async_ready_clean(void *, void *);
+void *erts_get_async_ready_queue(Uint sched_id);
+#define ERTS_ASYNC_READY_CLEAN 0
+#define ERTS_ASYNC_READY_DIRTY 1
+#ifdef ERTS_SMP
+#define ERTS_ASYNC_READY_NEED_THR_PRGR 2
+#endif
+#endif /* ERTS_USE_ASYNC_READY_Q */
+
+#endif /* USE_THREADS */
+
+void erts_init_async(void);
+void erts_exit_flush_async(void);
+
+
+#endif /* ERL_ASYNC_H__ */
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 58eb58d1dc..d4d5691f62 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -39,6 +39,7 @@
 #include "dist.h"
 #include "erl_gc.h"
 #include "erl_cpu_topology.h"
+#include "erl_async.h"
 #include "erl_thr_progress.h"
 #ifdef HIPE
 #include "hipe_arch.h"
diff --git a/erts/emulator/beam/erl_driver.h b/erts/emulator/beam/erl_driver.h
index 401967a8de..ae0c9def90 100644
--- a/erts/emulator/beam/erl_driver.h
+++ b/erts/emulator/beam/erl_driver.h
@@ -28,6 +28,14 @@
 #  include "config.h"
 #endif
 
+#define ERL_DRV_DEPRECATED_FUNC
+#ifdef __GNUC__
+#  if __GNUC__ >= 3
+#    undef ERL_DRV_DEPRECATED_FUNC
+#    define ERL_DRV_DEPRECATED_FUNC __attribute__((deprecated))
+#  endif
+#endif
+
 #ifdef SIZEOF_CHAR
 #  define SIZEOF_CHAR_SAVED__ SIZEOF_CHAR
 #  undef SIZEOF_CHAR
@@ -582,8 +590,11 @@ EXTERN long driver_async(ErlDrvPort ix,
 			 void* async_data,
 			 void (*async_free)(void*));
 
-
-EXTERN int driver_async_cancel(unsigned int key);
+/*
+ * driver_async_cancel() is deprecated. It is scheduled for removal
+ * in OTP-R16. For more information see the erl_driver(3) documentation.
+ */
+EXTERN int driver_async_cancel(unsigned int key) ERL_DRV_DEPRECATED_FUNC;
 
 /* Locks the driver in the machine "forever", there is
    no unlock function. Note that this is almost never useful, as an open
diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 5fe44afdce..98b997583c 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -44,6 +44,7 @@
 #include "erl_cpu_topology.h"
 #include "erl_thr_progress.h"
 #include "erl_thr_queue.h"
+#include "erl_async.h"
 
 #ifdef HIPE
 #include "hipe_mode_switch.h"	/* for hipe_mode_switch_init() */
@@ -101,8 +102,6 @@ int erts_backtrace_depth;	/* How many functions to show in a backtrace
 				 * in error codes.
 				 */
 
-int erts_async_max_threads;  /* number of threads for async support */
-int erts_async_thread_suggested_stack_size;
 erts_smp_atomic32_t erts_max_gen_gcs;
 
 Eterm erts_error_logger_warnings; /* What to map warning logs to, am_error, 
@@ -279,6 +278,7 @@ erl_init(int ncpu)
     erts_init_node_tables();
     init_dist();
     erl_drv_thr_init();
+    erts_init_async();
     init_io();
     init_copy();
     init_load();
@@ -605,6 +605,8 @@ early_init(int *argc, char **argv) /*
     int max_main_threads;
     int max_reader_groups;
     int reader_groups;
+    char envbuf[21]; /* enough for any 64-bit integer */
+    size_t envbufsz;
 
     use_multi_run_queue = 1;
     erts_printf_eterm_func = erts_printf_term;
@@ -676,6 +678,16 @@ early_init(int *argc, char **argv) /*
     schdlrs = no_schedulers;
     schdlrs_onln = no_schedulers_online;
 
+    envbufsz = sizeof(envbuf);
+
+    /* erts_sys_getenv() not initialized yet; need erts_sys_getenv__() */
+    if (erts_sys_getenv__("ERL_THREAD_POOL_SIZE", envbuf, &envbufsz) == 0)
+	erts_async_max_threads = atoi(envbuf);
+    else
+	erts_async_max_threads = 0;
+    if (erts_async_max_threads > ERTS_MAX_NO_OF_ASYNC_THREADS)
+	erts_async_max_threads = ERTS_MAX_NO_OF_ASYNC_THREADS;
+
     if (argc && argv) {
 	int i = 1;
 	while (i < *argc) {
@@ -703,6 +715,20 @@ early_init(int *argc, char **argv) /*
 		    }
 		    break;
 		}
+		case 'A': {
+		    /* set number of threads in thread pool */
+		    char *arg = get_arg(argv[i]+2, argv[i+1], &i);
+		    if (((erts_async_max_threads = atoi(arg)) < 0) ||
+			(erts_async_max_threads > ERTS_MAX_NO_OF_ASYNC_THREADS)) {
+			erts_fprintf(stderr,
+				     "bad number of async threads %s\n",
+				     arg);
+			erts_usage();
+			VERBOSE(DEBUG_SYSTEM, ("using %d async-threads\n",
+					       erts_async_max_threads));
+		    }
+		    break;
+		}
 		case 'S' : {
 		    int tot, onln;
 		    char *arg = get_arg(argv[i]+2, argv[i+1], &i);
@@ -783,9 +809,12 @@ early_init(int *argc, char **argv) /*
      * ** Aux thread (see erl_process.c)
      * ** Sys message dispatcher thread (see erl_trace.c)
      *
-     * * No unmanaged threads that need to register.
+     * * Unmanaged threads that need to register:
+     * ** Async threads (see erl_async.c)
      */
-    erts_thr_progress_init(no_schedulers, no_schedulers+1, 0);
+    erts_thr_progress_init(no_schedulers,
+			   no_schedulers+2,
+			   erts_async_max_threads);
 #endif
     erts_thr_q_init();
     erts_init_utils();
@@ -867,7 +896,6 @@ erl_start(int argc, char **argv)
     int have_break_handler = 1;
     char envbuf[21]; /* enough for any 64-bit integer */
     size_t envbufsz;
-    int async_max_threads = erts_async_max_threads;
     int ncpu = early_init(&argc, argv);
 
     envbufsz = sizeof(envbuf);
@@ -883,11 +911,6 @@ erl_start(int argc, char **argv)
 				  (erts_aint32_t) max_gen_gcs);
     }
 
-    envbufsz = sizeof(envbuf);
-    if (erts_sys_getenv("ERL_THREAD_POOL_SIZE", envbuf, &envbufsz) == 0) {
-	async_max_threads = atoi(envbuf);
-    }
-
 #if (defined(__APPLE__) && defined(__MACH__)) || defined(__DARWIN__)
     /*
      * The default stack size on MacOS X is too small for pcre.
@@ -1315,17 +1338,8 @@ erl_start(int argc, char **argv)
 	    break;
 	}
 
-	case 'A':
-	    /* set number of threads in thread pool */
-	    arg = get_arg(argv[i]+2, argv[i+1], &i);
-	    if (((async_max_threads = atoi(arg)) < 0) ||
-		(async_max_threads > ERTS_MAX_NO_OF_ASYNC_THREADS)) {
-		erts_fprintf(stderr, "bad number of async threads %s\n", arg);
-		erts_usage();
-	    }
-
-	    VERBOSE(DEBUG_SYSTEM, ("using %d async-threads\n",
-				   async_max_threads));
+	case 'A': /* Was handled in early init just read past it */
+	    (void) get_arg(argv[i]+2, argv[i+1], &i);
 	    break;
 
 	case 'a':
@@ -1414,10 +1428,6 @@ erl_start(int argc, char **argv)
 	i++;
     }
 
-#ifdef USE_THREADS
-    erts_async_max_threads = async_max_threads;
-#endif
-
     /* Delayed check of +P flag */
     if (erts_max_processes < ERTS_MIN_PROCESSES
 	|| erts_max_processes > ERTS_MAX_PROCESSES
@@ -1463,6 +1473,10 @@ erl_start(int argc, char **argv)
     erts_sys_main_thread(); /* May or may not return! */
 #else
     erts_thr_set_main_status(1, 1);
+#if ERTS_USE_ASYNC_READY_Q
+    erts_get_scheduler_data()->aux_work_data.async_ready.queue
+	= erts_get_async_ready_queue(1);
+#endif
     set_main_stack_size();
     process_main();
 #endif
@@ -1535,14 +1549,7 @@ system_cleanup(int exit_code)
     erts_cleanup_incgc();
 #endif
 
-#if defined(USE_THREADS)
-    exit_async();
-#endif
-
-    /*
-     * A lot more cleaning could/should have been done...
-     */
-
+    erts_exit_flush_async();
 }
 
 /*
diff --git a/erts/emulator/beam/erl_lock_check.c b/erts/emulator/beam/erl_lock_check.c
index 633be0ef58..44da6b6c51 100644
--- a/erts/emulator/beam/erl_lock_check.c
+++ b/erts/emulator/beam/erl_lock_check.c
@@ -110,10 +110,6 @@ static erts_lc_lock_order_t erts_lock_order[] = {
     {	"fun_tab",				NULL			},
     {	"environ",				NULL			},
 #endif
-    {	"asyncq",				"address"		},
-#ifndef ERTS_SMP
-    {	"async_ready",				NULL			},
-#endif
     {	"efile_drv",				"address"		},
 #if defined(ENABLE_CHILD_WAITER_THREAD) || defined(ERTS_SMP)
     {	"child_status",				NULL			},
@@ -138,6 +134,7 @@ static erts_lc_lock_order_t erts_lock_order[] = {
     {	"alcu_init_atoms",			NULL			},
     {	"mseg_init_atoms",			NULL			},
     {	"drv_tsd",				NULL			},
+    {	"async_enq_mtx",			NULL			},
 #ifdef ERTS_SMP
     {	"sys_msg_q", 				NULL			},
     {	"atom_tab",				NULL			},
@@ -173,12 +170,12 @@ static erts_lc_lock_order_t erts_lock_order[] = {
     {	"timeofday",				NULL			},
     {	"breakpoints",				NULL			},
     {	"pollsets_lock",			NULL			},
-    {	"async_id",				NULL			},
     {	"pix_lock",				"address"		},
     {	"run_queues_lists",			NULL			},
     {	"sched_stat",				NULL			},
     {	"run_queue_sleep_list",			"address"		},
 #endif
+    {	"async_init_mtx",			NULL			},
 #ifdef ERTS_SMP
     {	"proc_lck_qs_alloc",			NULL 			},
 #endif
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 4292522fba..9db2e874c6 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -41,6 +41,7 @@
 #include "erl_cpu_topology.h"
 #include "erl_thr_progress.h"
 #include "erl_thr_queue.h"
+#include "erl_async.h"
 
 #define ERTS_RUNQ_CHECK_BALANCE_REDS_PER_SCHED (2000*CONTEXT_REDS)
 #define ERTS_RUNQ_CALL_CHECK_BALANCE_REDS \
@@ -364,6 +365,12 @@ dbg_chk_aux_work_val(erts_aint32_t value)
 #ifdef ERTS_SSI_AUX_WORK_MISC_THR_PRGR
     valid |= ERTS_SSI_AUX_WORK_MISC_THR_PRGR;
 #endif
+#ifdef ERTS_SSI_AUX_WORK_ASYNC_READY
+    valid |= ERTS_SSI_AUX_WORK_ASYNC_READY;
+#endif
+#ifdef ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN
+    valid |= ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN;
+#endif
 
 #ifdef ERTS_SSI_AUX_WORK_FIX_ALLOC_LOWER_LIM
     valid |= ERTS_SSI_AUX_WORK_FIX_ALLOC_LOWER_LIM;
@@ -870,6 +877,73 @@ erts_schedule_multi_misc_aux_work(int ignore_self,
    }
 }
 
+#if ERTS_USE_ASYNC_READY_Q
+
+void
+erts_notify_check_async_ready_queue(void *vno)
+{
+    int ix = ((int) (SWord) vno) -1;
+    set_aux_work_flags_wakeup_nob(ERTS_SCHED_SLEEP_INFO_IX(ix),
+				  ERTS_SSI_AUX_WORK_ASYNC_READY);
+}
+
+static erts_aint32_t
+handle_async_ready(ErtsAuxWorkData *awdp,
+		   erts_aint32_t aux_work)
+{
+    ErtsSchedulerSleepInfo *ssi = awdp->ssi;
+    unset_aux_work_flags(ssi, ERTS_SSI_AUX_WORK_ASYNC_READY);
+    if (erts_check_async_ready(awdp->async_ready.queue)) {
+	if (set_aux_work_flags(ssi, ERTS_SSI_AUX_WORK_ASYNC_READY)
+	    & ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN) {
+	    unset_aux_work_flags(ssi, ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN);
+	    aux_work &= ~ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN;
+	}
+	return aux_work;
+    }
+#ifdef ERTS_SMP
+    awdp->async_ready.need_thr_prgr = 0;
+#endif
+    set_aux_work_flags(ssi, ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN);
+    return ((aux_work & ~ERTS_SSI_AUX_WORK_ASYNC_READY)
+	    | ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN);
+}
+
+static erts_aint32_t
+handle_async_ready_clean(ErtsAuxWorkData *awdp,
+			 erts_aint32_t aux_work)
+{
+    void *thr_prgr_p;
+
+#ifdef ERTS_SMP
+    if (awdp->async_ready.need_thr_prgr
+	&& !erts_thr_progress_has_reached(awdp->misc.thr_prgr)) {
+	return aux_work & ~ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN;
+    }
+
+    awdp->async_ready.need_thr_prgr = 0;
+    thr_prgr_p = (void *) &awdp->async_ready.thr_prgr;
+#else
+    thr_prgr_p = NULL;
+#endif
+
+    switch (erts_async_ready_clean(awdp->async_ready.queue, thr_prgr_p)) {
+    case ERTS_ASYNC_READY_CLEAN:
+	unset_aux_work_flags(awdp->ssi, ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN);
+	return aux_work & ~ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN;
+#ifdef ERTS_SMP
+    case ERTS_ASYNC_READY_NEED_THR_PRGR:
+	erts_thr_progress_wakeup(awdp->esdp,
+				 awdp->async_ready.thr_prgr);
+	awdp->async_ready.need_thr_prgr = 1;
+#endif
+    default:
+	return aux_work;
+    }
+}
+
+#endif
+
 static erts_aint32_t
 handle_fix_alloc(ErtsAuxWorkData *awdp, erts_aint32_t aux_work)
 {
@@ -1108,6 +1182,16 @@ handle_aux_work(ErtsAuxWorkData *awdp, erts_aint32_t aux_work)
 	aux_work = handle_misc_aux_work(awdp, aux_work);
 	ERTS_DBG_CHK_AUX_WORK_VAL(aux_work);
     }
+#if ERTS_USE_ASYNC_READY_Q
+    if (aux_work & ERTS_SSI_AUX_WORK_ASYNC_READY) {
+	aux_work = handle_async_ready(awdp, aux_work);
+	ERTS_DBG_CHK_AUX_WORK_VAL(aux_work);
+    }
+    if (aux_work & ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN) {
+	aux_work = handle_async_ready_clean(awdp, aux_work);
+	ERTS_DBG_CHK_AUX_WORK_VAL(aux_work);
+    }
+#endif
 #ifdef ERTS_SMP_SCHEDULERS_NEED_TO_CHECK_CHILDREN
     if (aux_work & ERTS_SSI_AUX_WORK_CHECK_CHILDREN) {
 	aux_work = handle_check_children(awdp, aux_work);
@@ -3237,6 +3321,13 @@ init_aux_work_data(ErtsAuxWorkData *awdp, ErtsSchedulerData *esdp)
     awdp->dd.completed_callback = NULL;
     awdp->dd.completed_arg = NULL;
 #endif
+#ifdef ERTS_USE_ASYNC_READY_Q
+#ifdef ERTS_SMP
+    awdp->async_ready.need_thr_prgr = 0;
+    awdp->async_ready.thr_prgr = ERTS_THR_PRGR_VAL_WAITING;
+#endif
+    awdp->async_ready.queue = NULL;
+#endif
 }
 
 void
@@ -4448,6 +4539,9 @@ sched_thread_func(void *vesdp)
 #if HAVE_ERTS_MSEG
     erts_mseg_late_init();
 #endif
+#if ERTS_USE_ASYNC_READY_Q
+    esdp->aux_work_data.async_ready.queue = erts_get_async_ready_queue(no);
+#endif
 
     erts_sched_init_check_cpu_bind(esdp);
 
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index 895f5ae3c0..0c8204b4ce 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -54,6 +54,7 @@ typedef struct process Process;
 #include "erl_atom_table.h"
 #include "external.h"
 #include "erl_mseg.h"
+#include "erl_async.h"
 
 #ifdef HIPE
 #include "hipe_process.h"
@@ -256,11 +257,13 @@ typedef enum {
 #endif
 #define ERTS_SSI_AUX_WORK_FIX_ALLOC_LOWER_LIM	(((erts_aint32_t) 1) << 4)
 #define ERTS_SSI_AUX_WORK_FIX_ALLOC_DEALLOC	(((erts_aint32_t) 1) << 5)
+#define ERTS_SSI_AUX_WORK_ASYNC_READY		(((erts_aint32_t) 1) << 6)
+#define ERTS_SSI_AUX_WORK_ASYNC_READY_CLEAN	(((erts_aint32_t) 1) << 7)
 #ifdef ERTS_SMP
-#define ERTS_SSI_AUX_WORK_DD			(((erts_aint32_t) 1) << 6)
-#define ERTS_SSI_AUX_WORK_DD_THR_PRGR		(((erts_aint32_t) 1) << 7)
+#define ERTS_SSI_AUX_WORK_DD			(((erts_aint32_t) 1) << 8)
+#define ERTS_SSI_AUX_WORK_DD_THR_PRGR		(((erts_aint32_t) 1) << 9)
 #endif
-#define ERTS_SSI_AUX_WORK_MSEG_CACHE_CHECK	(((erts_aint32_t) 1) << 8)
+#define ERTS_SSI_AUX_WORK_MSEG_CACHE_CHECK	(((erts_aint32_t) 1) << 10)
 
 #if !HAVE_ERTS_MSEG
 #  undef ERTS_SSI_AUX_WORK_MSEG_CACHE_CHECK
@@ -418,6 +421,15 @@ typedef struct {
 	void (*completed_arg)(void *);
     } dd;
 #endif
+#ifdef ERTS_USE_ASYNC_READY_Q
+    struct {
+#ifdef ERTS_SMP
+	int need_thr_prgr;
+	ErtsThrPrgrVal thr_prgr;
+#endif
+	void *queue;
+    } async_ready;
+#endif
 } ErtsAuxWorkData;
 
 struct ErtsSchedulerData_ {
@@ -1101,6 +1113,9 @@ void erts_start_schedulers(void);
 void erts_alloc_notify_delayed_dealloc(int);
 void erts_smp_notify_check_children_needed(void);
 #endif
+#if ERTS_USE_ASYNC_READY_Q
+void erts_notify_check_async_ready_queue(void *);
+#endif
 void erts_schedule_misc_aux_work(int sched_id,
 				 void (*func)(void *),
 				 void *arg);
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 6687e02485..ba0b96870e 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -41,12 +41,6 @@
 typedef struct port Port;
 #include "erl_port_task.h"
 
-#define ERTS_MAX_NO_OF_ASYNC_THREADS 1024
-extern int erts_async_max_threads;
-#define ERTS_ASYNC_THREAD_MIN_STACK_SIZE 16	/* Kilo words */
-#define ERTS_ASYNC_THREAD_MAX_STACK_SIZE 8192	/* Kilo words */
-extern int erts_async_thread_suggested_stack_size;
-
 typedef struct erts_driver_t_ erts_driver_t;
 
 #define SMALL_IO_QUEUE 5   /* Number of fixed elements */
diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index 151c776a3d..fff720634d 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -42,6 +42,7 @@
 #include "erl_bits.h"
 #include "erl_version.h"
 #include "error.h"
+#include "erl_async.h"
 
 extern ErlDrvEntry fd_driver_entry;
 extern ErlDrvEntry vanilla_driver_entry;
@@ -4579,7 +4580,10 @@ int driver_lock_driver(ErlDrvPort ix)
 
     erts_smp_mtx_lock(&erts_driver_list_lock);
 
-    if (prt == NULL) return -1;
+    if (prt == NULL) {
+	erts_smp_mtx_unlock(&erts_driver_list_lock);
+	return -1;
+    }
 
     ERTS_SMP_LC_ASSERT(erts_lc_is_port_locked(prt));
     if ((dh = (DE_Handle*)prt->drv_ptr->handle ) == NULL) {
diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index b63fe98f27..f9cbcc5892 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -475,15 +475,6 @@ __decl_noreturn void __noreturn erl_exit(int n, char*, ...);
 #define ERTS_ABORT_EXIT	(INT_MIN + 1)	/* no crash dump; only abort() */
 #define ERTS_DUMP_EXIT	(127)		/* crash dump; then exit() */
 
-
-#ifndef ERTS_SMP
-int check_async_ready(void);
-#ifdef USE_THREADS
-void sys_async_ready(int hndl);
-int erts_register_async_ready_callback(void (*funcp)(void));
-#endif
-#endif
-
 Eterm erts_check_io_info(void *p);
 
 /* Size of misc memory allocated from system dependent code */
@@ -671,6 +662,8 @@ int erts_sys_putenv(char *key_value, int sep_ix);
    *size), a value > 0 if value buffer is too small (*size is set to needed
    size), and a value < 0 on failure. */
 int erts_sys_getenv(char *key, char *value, size_t *size);
+/* erts_sys_getenv__() is only allowed to be used in early init phase */
+int erts_sys_getenv__(char *key, char *value, size_t *size);
 
 /* Easier to use, but not as efficient, environment functions */
 char *erts_read_env(char *key);
diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 8e8d4cce61..7f851e6007 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -128,7 +128,6 @@ static ErtsSysReportExit *report_exit_list;
 static ErtsSysReportExit *report_exit_transit_list;
 #endif
 
-extern int  check_async_ready(void);
 extern int  driver_interrupt(int, int);
 extern void do_break(void);
 
@@ -1125,31 +1124,6 @@ struct erl_drv_entry vanilla_driver_entry = {
     stop_select
 };
 
-#if defined(USE_THREADS) && !defined(ERTS_SMP)
-static int  async_drv_init(void);
-static ErlDrvData async_drv_start(ErlDrvPort, char*, SysDriverOpts*);
-static void async_drv_stop(ErlDrvData);
-static void async_drv_input(ErlDrvData, ErlDrvEvent);
-
-/* INTERNAL use only */
-
-struct erl_drv_entry async_driver_entry = {
-    async_drv_init,
-    async_drv_start,
-    async_drv_stop,
-    NULL,
-    async_drv_input,
-    NULL,
-    "async",
-    NULL,
-    NULL,
-    NULL,
-    NULL,
-    NULL,
-    NULL
-};
-#endif
-
 /* Handle SIGCHLD signals. */
 #if (defined(SIG_SIGSET) || defined(SIG_SIGNAL))
 static RETSIGTYPE onchld(void)
@@ -2334,87 +2308,6 @@ static void stop_select(ErlDrvEvent fd, void* _)
     close((int)fd);
 }
 
-/*
-** Async opertation support
-*/
-#if defined(USE_THREADS) && !defined(ERTS_SMP)
-static void
-sys_async_ready_failed(int fd, int r, int err)
-{
-    char buf[120];
-    sprintf(buf, "sys_async_ready(): Fatal error: fd=%d, r=%d, errno=%d\n",
-	     fd, r, err);
-    erts_silence_warn_unused_result(write(2, buf, strlen(buf)));
-    abort();
-}
-
-/* called from threads !! */
-void sys_async_ready(int fd)
-{
-    int r;
-    while (1) {
-	r = write(fd, "0", 1);  /* signal main thread fd MUST be async_fd[1] */
-	if (r == 1) {
-	    DEBUGF(("sys_async_ready(): r = 1\r\n"));
-	    break;
-	}
-	if (r < 0 && errno == EINTR) {
-	    DEBUGF(("sys_async_ready(): r = %d\r\n", r));
-	    continue;
-	}
-	sys_async_ready_failed(fd, r, errno);
-    }
-}
-
-static int async_drv_init(void)
-{
-    async_fd[0] = -1;
-    async_fd[1] = -1;
-    return 0;
-}
-
-static ErlDrvData async_drv_start(ErlDrvPort port_num,
-				  char* name, SysDriverOpts* opts)
-{
-    if (async_fd[0] != -1)
-	return ERL_DRV_ERROR_GENERAL;
-    if (pipe(async_fd) < 0)
-	return ERL_DRV_ERROR_GENERAL;
-
-    DEBUGF(("async_drv_start: %d\r\n", port_num));
-
-    SET_NONBLOCKING(async_fd[0]);
-    driver_select(port_num, async_fd[0], ERL_DRV_READ, 1);
-
-    if (init_async(async_fd[1]) < 0)
-	return ERL_DRV_ERROR_GENERAL;
-    return (ErlDrvData)port_num;
-}
-
-static void async_drv_stop(ErlDrvData e)
-{
-    int port_num = (int)(long)e;
-
-    DEBUGF(("async_drv_stop: %d\r\n", port_num));
-
-    exit_async();
-
-    driver_select(port_num, async_fd[0], ERL_DRV_READ, 0);
-
-    close(async_fd[0]);
-    close(async_fd[1]);
-    async_fd[0] = async_fd[1] = -1;
-}
-
-
-static void async_drv_input(ErlDrvData e, ErlDrvEvent fd)
-{
-    char *buf[32];
-    DEBUGF(("async_drv_input\r\n"));
-    while (read((int) fd, (void *) buf, 32) > 0); /* fd MUST be async_fd[0] */
-    check_async_ready();  /* invoke all async_ready */
-}
-#endif
 
 void erts_do_break_handling(void)
 {
@@ -2488,12 +2381,10 @@ erts_sys_putenv(char *buffer, int sep_ix)
 }
 
 int
-erts_sys_getenv(char *key, char *value, size_t *size)
+erts_sys_getenv__(char *key, char *value, size_t *size)
 {
-    char *orig_value;
     int res;
-    erts_smp_rwmtx_rlock(&environ_rwmtx);
-    orig_value = getenv(key);
+    char *orig_value = getenv(key);
     if (!orig_value)
 	res = -1;
     else {
@@ -2508,6 +2399,15 @@ erts_sys_getenv(char *key, char *value, size_t *size)
 	    res = 0;
 	}
     }
+    return res;
+}
+
+int
+erts_sys_getenv(char *key, char *value, size_t *size)
+{
+    int res;
+    erts_smp_rwmtx_rlock(&environ_rwmtx);
+    res = erts_sys_getenv__(key, value, size);
     erts_smp_rwmtx_runlock(&environ_rwmtx);
     return res;
 }
@@ -2519,31 +2419,6 @@ sys_init_io(void)
 	erts_alloc(ERTS_ALC_T_FD_TAB, max_files * sizeof(struct fd_data));
     erts_smp_atomic_add_nob(&sys_misc_mem_sz,
 			    max_files * sizeof(struct fd_data));
-
-#ifdef USE_THREADS
-#ifdef ERTS_SMP
-    if (init_async(-1) < 0)
-	erl_exit(1, "Failed to initialize async-threads\n");
-#else
-    {
-	/* This is speical stuff, starting a driver from the 
-	 * system routines, but is a nice way of handling stuff
-	 * the erlang way
-	 */
-	SysDriverOpts dopts;
-	int ret;
-
-	sys_memset((void*)&dopts, 0, sizeof(SysDriverOpts));
-	add_driver_entry(&async_driver_entry);
-	ret = erts_open_driver(NULL, NIL, "async", &dopts, NULL);
-	DEBUGF(("open_driver = %d\n", ret));
-	if (ret < 0)
-	    erl_exit(1, "Failed to open async driver\n");
-	erts_port[ret].status |= ERTS_PORT_SFLG_IMMORTAL;
-    }
-#endif
-#endif
-
 }
 
 #if (0) /* unused? */
@@ -2770,15 +2645,7 @@ initiate_report_exit_status(ErtsSysReportExit *rep, int status)
     rep->next = report_exit_transit_list;
     rep->status = status;
     report_exit_transit_list = rep;
-    /*
-     * We need the scheduler thread to call check_children().
-     * If the scheduler thread is sleeping in a poll with a
-     * timeout, we need to wake the scheduler thread. We use the
-     * functionality of the async driver to do this, instead of
-     * implementing yet another driver doing the same thing. A
-     * little bit ugly, but it works...
-     */
-    sys_async_ready(async_fd[1]);
+    erts_sys_schedule_interrupt(1);
 }
 
 static int check_children(void)
@@ -2865,19 +2732,11 @@ erl_sys_schedule(int runnable)
 {
 #ifdef ERTS_SMP
     ERTS_CHK_IO(!runnable);
-    ERTS_SMP_LC_ASSERT(!erts_thr_progress_is_blocking());
 #else
-    if (runnable) {
-	ERTS_CHK_IO(0);		/* Poll for I/O */
-	check_async_ready();	/* Check async completions */
-    } else {
-	int wait_for_io = !check_async_ready();
-	if (wait_for_io)
-	    wait_for_io = !check_children();
-	ERTS_CHK_IO(wait_for_io);
-    }
-    (void) check_children();
+    ERTS_CHK_IO(runnable ? 0 : !check_children());
 #endif
+    ERTS_SMP_LC_ASSERT(!erts_thr_progress_is_blocking());
+    (void) check_children();
 }
 
 
diff --git a/erts/emulator/sys/vxworks/sys.c b/erts/emulator/sys/vxworks/sys.c
index 08c4f3f4e5..fc7e6cec08 100644
--- a/erts/emulator/sys/vxworks/sys.c
+++ b/erts/emulator/sys/vxworks/sys.c
@@ -1520,6 +1520,12 @@ erts_sys_getenv(char *key, char *value, size_t *size)
     return res;
 }
 
+int
+erts_sys_getenv__(char *key, char *value, size_t *size)
+{
+    return erts_sys_getenv(key, value, size);
+}
+
 void
 sys_init_io(void)
 {
diff --git a/erts/emulator/sys/win32/sys.c b/erts/emulator/sys/win32/sys.c
index ace1e1fca0..02d16b83a2 100644
--- a/erts/emulator/sys/win32/sys.c
+++ b/erts/emulator/sys/win32/sys.c
@@ -566,51 +566,6 @@ struct erl_drv_entry vanilla_driver_entry = {
     stop_select
 };
 
-#if defined(USE_THREADS) && !defined(ERTS_SMP)
-
-static int  async_drv_init(void);
-static ErlDrvData async_drv_start(ErlDrvPort, char*, SysDriverOpts*);
-static void async_drv_stop(ErlDrvData);
-static void async_drv_input(ErlDrvData, ErlDrvEvent);
-
-/* INTERNAL use only */
-
-void null_output(ErlDrvData drv_data, char* buf, int len)
-{
-}
-
-void null_ready_output(ErlDrvData drv_data, ErlDrvEvent event)
-{
-}
-
-struct erl_drv_entry async_driver_entry = {
-    async_drv_init,
-    async_drv_start,
-    async_drv_stop,
-    null_output,
-    async_drv_input,
-    null_ready_output,
-    "async",
-    NULL, /* finish */
-    NULL, /* handle */
-    NULL, /* control */
-    NULL, /* timeout */
-    NULL, /* outputv */
-    NULL, /* ready_async */
-    NULL, /* flush */
-    NULL, /* call */
-    NULL, /* event */
-    ERL_DRV_EXTENDED_MARKER,
-    ERL_DRV_EXTENDED_MAJOR_VERSION,
-    ERL_DRV_EXTENDED_MINOR_VERSION,
-    0,	/* ERL_DRV_FLAGs */
-    NULL,
-    NULL, /* process_exit */
-    stop_select
-};
-
-#endif
-
 /*
  * Initialises a DriverData structure.
  *
@@ -2825,30 +2780,6 @@ sys_init_io(void)
        We estimate the number to twice the amount of ports. 
        We really dont know on windows, do we? */
     max_files = 2*erts_max_ports;
-    
-#ifdef USE_THREADS
-#ifdef ERTS_SMP
-    if (init_async(-1) < 0)
-	erl_exit(1, "Failed to initialize async-threads\n");
-#else
-    {
-	/* This is special stuff, starting a driver from the 
-	 * system routines, but is a nice way of handling stuff
-	 * the erlang way
-	 */
-	SysDriverOpts dopts;
-	int ret;
-
-	sys_memset((void*)&dopts, 0, sizeof(SysDriverOpts));
-	add_driver_entry(&async_driver_entry);
-	ret = erts_open_driver(NULL, NIL, "async", &dopts, NULL);
-	DEBUGF(("open_driver = %d\n", ret));
-	if (ret < 0)
-	    erl_exit(1, "Failed to open async driver\n");
-	erts_port[ret].status |= ERTS_PORT_SFLG_IMMORTAL;
-    }
-#endif
-#endif
 }
 
 #ifdef ERTS_SMP
@@ -3382,75 +3313,7 @@ erts_sys_schedule_interrupt_timed(int set, long msec)
 void
 erl_sys_schedule(int runnable)
 {
-#ifdef ERTS_SMP
     erts_check_io(!runnable);
     ERTS_SMP_LC_ASSERT(!erts_thr_progress_is_blocking());
-#else
-    if (runnable) {
-	erts_check_io(0);	/* Poll for I/O */
-	check_async_ready();	/* Check async completions */
-    } else {
-	erts_check_io(check_async_ready() ? 0 : 1);
-    }
-#endif
-}
-
-#if defined(USE_THREADS) && !defined(ERTS_SMP)
-/*
- * Async operation support.
- */
-
-static ErlDrvEvent async_drv_event;
-
-void
-sys_async_ready(int fd)
-{
-    SetEvent((HANDLE)async_drv_event);
 }
 
-static int
-async_drv_init(void)
-{
-    async_drv_event = (ErlDrvEvent) NULL;
-    return 0;
-}
-
-static ErlDrvData
-async_drv_start(ErlDrvPort port_num, char* name, SysDriverOpts* opts)
-{
-    if (async_drv_event != (ErlDrvEvent) NULL) {
-	return ERL_DRV_ERROR_GENERAL;
-    }
-    if ((async_drv_event = (ErlDrvEvent)CreateAutoEvent(FALSE)) == (ErlDrvEvent) NULL) {
-	return ERL_DRV_ERROR_GENERAL;
-    }
-
-    driver_select(port_num, async_drv_event, ERL_DRV_READ|ERL_DRV_USE, 1);
-    if (init_async(async_drv_event) < 0) {
-	return ERL_DRV_ERROR_GENERAL;
-    }
-    return (ErlDrvData)port_num;
-}
-
-static void
-async_drv_stop(ErlDrvData port_num)
-{
-    exit_async();
-    driver_select((ErlDrvPort)port_num, async_drv_event, ERL_DRV_READ|ERL_DRV_USE, 0);
-    /*CloseHandle((HANDLE)async_drv_event);*/
-    async_drv_event = (ErlDrvEvent) NULL;
-}
-
-
-static void
-async_drv_input(ErlDrvData port_num, ErlDrvEvent e) 
-{
-    check_async_ready();
-
-    /*
-     * Our event is auto-resetting.
-     */
-}
-
-#endif
-
diff --git a/erts/emulator/sys/win32/sys_env.c b/erts/emulator/sys/win32/sys_env.c
index 02c8433a10..7acc7f07ee 100644
--- a/erts/emulator/sys/win32/sys_env.c
+++ b/erts/emulator/sys/win32/sys_env.c
@@ -55,19 +55,17 @@ erts_sys_putenv(char *key_value, int sep_ix)
 }
 
 int
-erts_sys_getenv(char *key, char *value, size_t *size)
+erts_sys_getenv__(char *key, char *value, size_t *size)
 {
     size_t req_size = 0;
     int res = 0;
     DWORD new_size;
 
-    erts_smp_rwmtx_rlock(&environ_rwmtx);
     SetLastError(0);
     new_size = GetEnvironmentVariable((LPCTSTR) key,
 				      (LPTSTR) value,
 				      (DWORD) *size);
     res = !new_size && GetLastError() == ERROR_ENVVAR_NOT_FOUND ? -1 : 0;
-    erts_smp_rwmtx_runlock(&environ_rwmtx);
     if (res < 0)
 	return res;
     res = new_size > *size ? 1 : 0;
@@ -75,6 +73,16 @@ erts_sys_getenv(char *key, char *value, size_t *size)
     return res;
 }
 
+int
+erts_sys_getenv(char *key, char *value, size_t *size)
+{
+    int res;
+    erts_smp_rwmtx_rlock(&environ_rwmtx);
+    res = erts_sys_getenv__(key, value, size);
+    erts_smp_rwmtx_runlock(&environ_rwmtx);
+    return res;
+}
+
 struct win32_getenv_state {
     char *env;
     char *next;
diff --git a/erts/emulator/test/driver_SUITE.erl b/erts/emulator/test/driver_SUITE.erl
index bcb0257ed1..c07dbc5871 100644
--- a/erts/emulator/test/driver_SUITE.erl
+++ b/erts/emulator/test/driver_SUITE.erl
@@ -76,7 +76,8 @@
 	 driver_select_use/1,
 	 thread_mseg_alloc_cache_clean/1,
 	 otp_9302/1,
-	 thr_free_drv/1]).
+	 thr_free_drv/1,
+	 async_blast/1]).
 
 -export([bin_prefix/2]).
 
@@ -145,7 +146,8 @@ all() ->
      smp_select, driver_select_use,
      thread_mseg_alloc_cache_clean,
      otp_9302,
-     thr_free_drv].
+     thr_free_drv,
+     async_blast].
 
 groups() -> 
     [{timer, [],
@@ -1911,17 +1913,30 @@ otp_9302(Config) when is_list(Config) ->
     ?line port_command(Port, ""),
     ?line {msg, block} = get_port_msg(Port, infinity),
     ?line {msg, job} = get_port_msg(Port, infinity),
-    ?line case erlang:system_info(thread_pool_size) of
-	      0 ->
-		  {msg, cancel} = get_port_msg(Port, infinity);
-	      _ ->
-		  ok
-	  end,
-    ?line {msg, job} = get_port_msg(Port, infinity),
+    ?line C = case erlang:system_info(thread_pool_size) of
+		  0 ->
+		      ?line {msg, cancel} = get_port_msg(Port, infinity),
+		      ?line {msg, job} = get_port_msg(Port, infinity),
+		      ?line false;
+		  _ ->
+		      case get_port_msg(Port, infinity) of
+			  {msg, cancel} -> %% Cancel always fail in Rel >= 15
+			      ?line {msg, job} = get_port_msg(Port, infinity),
+			      ?line false;
+			  {msg, job} ->
+			      ?line ok,
+			      ?line true
+		      end
+	      end,
     ?line {msg, end_of_jobs} = get_port_msg(Port, infinity),
     ?line no_msg = get_port_msg(Port, 2000),
     ?line port_close(Port),
-    ?line ok.
+    ?line case C of
+	      true ->
+		  ?line {comment, "Async job cancelled"};
+	      false ->
+		  ?line {comment, "Async job not cancelled"}
+	  end.
 
 thr_free_drv(Config) when is_list(Config) ->
     ?line Path = ?config(data_dir, Config),
@@ -1954,6 +1969,48 @@ thr_free_drv_control(Port, N) ->
 %	    io:format("N=~p, SID=~p", [N, erlang:system_info(scheduler_id)]),
 	    thr_free_drv_control(Port, N+1)
     end.
+	    
+async_blast(Config) when is_list(Config) ->
+    ?line Path = ?config(data_dir, Config),
+    ?line erl_ddll:start(),
+    ?line ok = load_driver(Path, async_blast_drv),
+    ?line SchedOnln = erlang:system_info(schedulers_online),
+    ?line MemBefore = driver_alloc_size(),
+    ?line Start = os:timestamp(),
+    ?line Blast = fun () ->
+			  Port = open_port({spawn, async_blast_drv}, []),
+			  true = is_port(Port),
+			  port_command(Port, ""),
+			  receive
+			      {Port, done} ->
+				  ok
+			  end,
+			  port_close(Port)
+		  end,
+    ?line Ps = lists:map(fun (N) ->
+				 spawn_opt(Blast,
+					   [{scheduler,
+					     (N rem SchedOnln)+ 1},
+					    monitor])
+			 end,
+			 lists:seq(1, 100)),
+    ?line MemMid = driver_alloc_size(),
+    ?line lists:foreach(fun ({Pid, Mon}) ->
+				receive
+				    {'DOWN',Mon,process,Pid,_} -> ok
+				end
+			end, Ps),
+    ?line End = os:timestamp(),
+    ?line MemAfter = driver_alloc_size(),
+    ?line io:format("MemBefore=~p, MemMid=~p, MemAfter=~p~n",
+		    [MemBefore, MemMid, MemAfter]),
+    ?line AsyncBlastTime = timer:now_diff(End,Start)/1000000,
+    ?line io:format("AsyncBlastTime=~p~n", [AsyncBlastTime]),
+    ?line MemBefore = MemAfter,
+    ?line erlang:display({async_blast_time, AsyncBlastTime}),
+    ?line ok.
+
+
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% 		Utilities
diff --git a/erts/emulator/test/driver_SUITE_data/Makefile.src b/erts/emulator/test/driver_SUITE_data/Makefile.src
index 62ab5169c0..dd48f6a0f7 100644
--- a/erts/emulator/test/driver_SUITE_data/Makefile.src
+++ b/erts/emulator/test/driver_SUITE_data/Makefile.src
@@ -13,7 +13,8 @@ MISC_DRVS =		outputv_drv@dll@ \
 			missing_callback_drv@dll@ \
 			thr_alloc_drv@dll@ \
 			otp_9302_drv@dll@ \
-			thr_free_drv@dll@
+			thr_free_drv@dll@ \
+			async_blast_drv@dll@
 
 SYS_INFO_DRVS = 	sys_info_1_0_drv@dll@ \
 			sys_info_1_1_drv@dll@ \
diff --git a/erts/emulator/test/driver_SUITE_data/async_blast_drv.c b/erts/emulator/test/driver_SUITE_data/async_blast_drv.c
new file mode 100644
index 0000000000..3821f7e3dc
--- /dev/null
+++ b/erts/emulator/test/driver_SUITE_data/async_blast_drv.c
@@ -0,0 +1,124 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2011. All Rights Reserved.
+ *
+ * The contents of this file are subject to the Erlang Public License,
+ * Version 1.1, (the "License"); you may not use this file except in
+ * compliance with the License. You should have received a copy of the
+ * Erlang Public License along with this software. If not, it can be
+ * retrieved online at http://www.erlang.org/.
+ *
+ * Software distributed under the License is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ * the License for the specific language governing rights and limitations
+ * under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+#include "erl_driver.h"
+
+#define NO_ASYNC_JOBS 10000
+
+static void stop(ErlDrvData drv_data);
+static ErlDrvData start(ErlDrvPort port,
+			char *command);
+static void output(ErlDrvData drv_data,
+		   char *buf, int len);
+static void ready_async(ErlDrvData drv_data,
+			ErlDrvThreadData thread_data);
+
+static ErlDrvEntry async_blast_drv_entry = { 
+    NULL /* init */,
+    start,
+    stop,
+    output,
+    NULL /* ready_input */,
+    NULL /* ready_output */,
+    "async_blast_drv",
+    NULL /* finish */,
+    NULL /* handle */,
+    NULL /* control */,
+    NULL /* timeout */,
+    NULL /* outputv */,
+    ready_async,
+    NULL /* flush */,
+    NULL /* call */,
+    NULL /* event */,
+    ERL_DRV_EXTENDED_MARKER,
+    ERL_DRV_EXTENDED_MAJOR_VERSION,
+    ERL_DRV_EXTENDED_MINOR_VERSION,
+    ERL_DRV_FLAG_USE_PORT_LOCKING,
+    NULL /* handle2 */,
+    NULL /* handle_monitor */
+};
+
+typedef struct {
+    ErlDrvPort port;
+    ErlDrvTermData caller;    
+    int counter;
+} async_blast_data_t;
+
+
+DRIVER_INIT(async_blast_drv)
+{
+    return &async_blast_drv_entry;
+}
+
+static void stop(ErlDrvData drv_data)
+{
+    driver_free((void *) drv_data);
+}
+
+static ErlDrvData start(ErlDrvPort port,
+			char *command)
+{
+    async_blast_data_t *abd;
+
+    abd = driver_alloc(sizeof(async_blast_data_t));
+    if (!abd)
+	return ERL_DRV_ERROR_GENERAL;
+
+    abd->port = port;
+    abd->counter = 0;
+    return (ErlDrvData) abd;
+}
+
+static void async_invoke(void *data)
+{
+
+}
+#include <stdio.h>
+
+static void ready_async(ErlDrvData drv_data,
+			ErlDrvThreadData thread_data)
+{
+    async_blast_data_t *abd = (async_blast_data_t *) drv_data;
+    if (--abd->counter == 0) {
+	ErlDrvTermData spec[] = {
+	    ERL_DRV_PORT, driver_mk_port(abd->port),
+	    ERL_DRV_ATOM, driver_mk_atom("done"),
+	    ERL_DRV_TUPLE, 2
+	};
+	driver_send_term(abd->port, abd->caller,
+			 spec, sizeof(spec)/sizeof(spec[0]));
+    }
+}
+
+static void output(ErlDrvData drv_data,
+		   char *buf, int len)
+{
+    async_blast_data_t *abd = (async_blast_data_t *) drv_data;
+    if (abd->counter == 0) {
+	int i;
+	abd->caller = driver_caller(abd->port);
+	abd->counter = NO_ASYNC_JOBS;
+	for (i = 0; i < NO_ASYNC_JOBS; i++) {
+	    if (0 > driver_async(abd->port, NULL, async_invoke, NULL, NULL)) {
+		driver_failure_atom(abd->port, "driver_async_failed");
+		break;
+	    }
+	}
+    }
+}