Replace system block with thread progress block

The ERTS internal system block functionality has been replaced by
new functionality for blocking the system. The old system block
functionality had contention issues and complexity issues. The
new functionality piggy-backs on thread progress tracking functionality
needed by newly introduced lock-free synchronization in the runtime
system. When the functionality for blocking the system isn't used
there is more or less no overhead at all. This since the functionality
for tracking thread progress is there and needed anyway.

1 files changed, 2 insertions, 682 deletions

diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index 3fa84bd13c..cc377b543d 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -77,6 +77,7 @@ typedef struct {
 
 #ifdef ERTS_SMP
 
+#if 0 /* Unused */
 static void 
 dispatch_profile_msg_q(profile_sched_msg_q *psmq)
 {
@@ -88,6 +89,7 @@ dispatch_profile_msg_q(profile_sched_msg_q *psmq)
 	profile_scheduler_q(make_small(msg->scheduler_id), msg->state, am_undefined, msg->Ms, msg->s, msg->us);
     }
 }
+#endif
 
 #endif
 
@@ -3338,688 +3340,6 @@ sys_alloc_stat(SysAllocStat *sasp)
 
 }
 
-#ifdef ERTS_SMP
-
-/* Local system block state */
-
-struct {
-    int emergency;
-    long emergency_timeout;
-    erts_smp_cnd_t watchdog_cnd;
-    erts_smp_tid_t watchdog_tid;
-    int threads_to_block;
-    int have_blocker;
-    erts_smp_tid_t blocker_tid;
-    int recursive_block;
-    Uint32 allowed_activities;
-    erts_smp_tsd_key_t blockable_key;
-    erts_smp_mtx_t mtx;
-    erts_smp_cnd_t cnd;
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    int activity_changing;
-    int checking;
-#endif
-} system_block_state;
-
-/* Global system block state */
-erts_system_block_state_t erts_system_block_state;
-
-
-static ERTS_INLINE int
-is_blockable_thread(void)
-{
-    return erts_smp_tsd_get(system_block_state.blockable_key) != NULL;
-}
-
-static ERTS_INLINE int
-is_blocker(void)
-{
-    return (system_block_state.have_blocker
-	    && erts_smp_equal_tids(system_block_state.blocker_tid,
-				   erts_smp_thr_self()));
-}
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-int
-erts_lc_is_blocking(void)
-{
-    int res;
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    res = erts_smp_pending_system_block() && is_blocker();
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-    return res;
-}
-#endif
-
-static ERTS_INLINE void
-block_me(void (*prepare)(void *),
-	 void (*resume)(void *),
-	 void *arg,
-	 int mtx_locked,
-	 int want_to_block,
-	 int update_act_changing,
-	 profile_sched_msg_q *psmq)
-{
-    if (prepare)
-	(*prepare)(arg);
-
-    /* Locks might be held... */
-
-    if (!mtx_locked)
-	erts_smp_mtx_lock(&system_block_state.mtx);
-
-    if (erts_smp_pending_system_block() && !is_blocker()) {
-	int is_blockable = is_blockable_thread();
-	ASSERT(is_blockable);
-
-	if (is_blockable)
-	    system_block_state.threads_to_block--;
-
-	if (erts_system_profile_flags.scheduler && psmq) {
-	    ErtsSchedulerData *esdp = erts_get_scheduler_data();
-	    if (esdp) {
-	    	profile_sched_msg *msg = NULL;
-	        
-		ASSERT(psmq->n < 2);
-		msg = &((psmq->msg)[psmq->n]);
-		msg->scheduler_id = esdp->no;
-		get_now(&(msg->Ms), &(msg->s), &(msg->us));
-		msg->no_schedulers = 0;
-		msg->state = am_inactive;
-	    	psmq->n++;
-	    }
-	}
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-	if (update_act_changing)
-	    system_block_state.activity_changing--;
-#endif
-
-	erts_smp_cnd_broadcast(&system_block_state.cnd);
-
-	do {
-	    erts_smp_cnd_wait(&system_block_state.cnd, &system_block_state.mtx);
-	} while (erts_smp_pending_system_block()
-		 && !(want_to_block && !system_block_state.have_blocker));
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-	if (update_act_changing)
-	    system_block_state.activity_changing++;
-#endif
-	if (erts_system_profile_flags.scheduler && psmq) {
-	    ErtsSchedulerData *esdp = erts_get_scheduler_data();
-	    if (esdp) {
-	    	profile_sched_msg *msg = NULL;
-	        
-		ASSERT(psmq->n < 2);
-		msg = &((psmq->msg)[psmq->n]);
-		msg->scheduler_id = esdp->no;
-		get_now(&(msg->Ms), &(msg->s), &(msg->us));
-		msg->no_schedulers = 0;
-		msg->state = am_active;
-	    	psmq->n++;
-	    }
-	}
-
-	if (is_blockable)
-	    system_block_state.threads_to_block++;
-    }
-
-    if (!mtx_locked)
-	erts_smp_mtx_unlock(&system_block_state.mtx);
-
-    if (resume)
-	(*resume)(arg);
-}
-
-void
-erts_block_me(void (*prepare)(void *),
-	      void (*resume)(void *),
-	      void *arg)
-{
-    profile_sched_msg_q psmq;
-    psmq.n = 0;
-    if (prepare)
-	(*prepare)(arg);
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    erts_lc_check_exact(NULL, 0); /* No locks should be locked */
-#endif
-
-    block_me(NULL, NULL, NULL, 0, 0, 0, &psmq);
-
-    if (erts_system_profile_flags.scheduler && psmq.n > 0) 
-    	dispatch_profile_msg_q(&psmq);
-
-    if (resume)
-	(*resume)(arg);
-}
-
-void
-erts_register_blockable_thread(void)
-{
-    profile_sched_msg_q psmq;
-    psmq.n = 0;
-    if (!is_blockable_thread()) {
-	erts_smp_mtx_lock(&system_block_state.mtx);
-	system_block_state.threads_to_block++;
-	erts_smp_tsd_set(system_block_state.blockable_key,
-			 (void *) &erts_system_block_state);
-
-	/* Someone might be waiting for us to block... */
-	if (erts_smp_pending_system_block())
-	    block_me(NULL, NULL, NULL, 1, 0, 0, &psmq);
-	erts_smp_mtx_unlock(&system_block_state.mtx);
-
-	if (erts_system_profile_flags.scheduler && psmq.n > 0)
-	    dispatch_profile_msg_q(&psmq);
-    }
-}
-
-void
-erts_unregister_blockable_thread(void)
-{
-    if (is_blockable_thread()) {
-	erts_smp_mtx_lock(&system_block_state.mtx);
-	system_block_state.threads_to_block--;
-	ASSERT(system_block_state.threads_to_block >= 0);
-	erts_smp_tsd_set(system_block_state.blockable_key, NULL);
-
-	/* Someone might be waiting for us to block... */
-	if (erts_smp_pending_system_block())
-	    erts_smp_cnd_broadcast(&system_block_state.cnd);
-	erts_smp_mtx_unlock(&system_block_state.mtx);
-    }
-}
-
-void
-erts_note_activity_begin(erts_activity_t activity)
-{
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    if (erts_smp_pending_system_block()) {
-	Uint32 broadcast = 0;
-	switch (activity) {
-	case ERTS_ACTIVITY_GC:
-	    broadcast = (system_block_state.allowed_activities
-			 & ERTS_BS_FLG_ALLOW_GC);
-	    break;
-	case ERTS_ACTIVITY_IO:
-	    broadcast = (system_block_state.allowed_activities
-			 & ERTS_BS_FLG_ALLOW_IO);
-	    break;
-	case ERTS_ACTIVITY_WAIT:
-	    broadcast = 1;
-	    break;
-	default:
-	    abort();
-	    break;
-	}
-	if (broadcast)
-	    erts_smp_cnd_broadcast(&system_block_state.cnd);
-    }
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-}
-
-void
-erts_check_block(erts_activity_t old_activity,
-		 erts_activity_t new_activity,
-		 int locked,
-		 void (*prepare)(void *),
-		 void (*resume)(void *),
-		 void *arg)
-{
-    int do_block;
-    profile_sched_msg_q psmq;
-
-    psmq.n = 0;
-    if (!locked && prepare)
-	(*prepare)(arg);
-
-    erts_smp_mtx_lock(&system_block_state.mtx);
-
-    /* First check if it is ok to block... */
-    if (!locked)
-	do_block = 1;
-    else {
-	switch (old_activity) {
-	case ERTS_ACTIVITY_UNDEFINED:
-	    do_block = 0;
-	    break;
-	case ERTS_ACTIVITY_GC:
-	    do_block = (system_block_state.allowed_activities
-			& ERTS_BS_FLG_ALLOW_GC);
-	    break;
-	case ERTS_ACTIVITY_IO:
-	    do_block = (system_block_state.allowed_activities
-			& ERTS_BS_FLG_ALLOW_IO);
-	    break;
-	case ERTS_ACTIVITY_WAIT:
-	    /* You are not allowed to leave activity waiting
-	     * without supplying the possibility to block
-	     * unlocked.
-	     */
-	    erts_set_activity_error(ERTS_ACT_ERR_LEAVE_WAIT_UNLOCKED,
-				    __FILE__, __LINE__);
-	    do_block = 0;
-	    break;
-	default:
-	    erts_set_activity_error(ERTS_ACT_ERR_LEAVE_UNKNOWN_ACTIVITY,
-				    __FILE__, __LINE__);
-	    do_block = 0;
-	    break;
-	}
-    }
-
-    if (do_block) {
-	/* ... then check if it is necessary to block... */
-
-	switch (new_activity) {
-	case ERTS_ACTIVITY_UNDEFINED:
-	    do_block = 1;
-	    break;
-	case ERTS_ACTIVITY_GC:
-	    do_block = !(system_block_state.allowed_activities
-			 & ERTS_BS_FLG_ALLOW_GC);
-	break;
-	case ERTS_ACTIVITY_IO:
-	    do_block = !(system_block_state.allowed_activities
-			 & ERTS_BS_FLG_ALLOW_IO);
-	    break;
-	case ERTS_ACTIVITY_WAIT:
-	    /* No need to block if we are going to wait */
-	    do_block = 0;
-	    break;
-	default:
-	    erts_set_activity_error(ERTS_ACT_ERR_ENTER_UNKNOWN_ACTIVITY,
-				    __FILE__, __LINE__);
-	    break;
-	}
-    }
-
-    if (do_block) {
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-	if (!locked) {
-	    /* Only system_block_state.mtx should be held */
-	    erts_lc_check_exact(&system_block_state.mtx.lc, 1);
-	}
-#endif
-
-	block_me(NULL, NULL, NULL, 1, 0, 1, &psmq);
-
-    }
-
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-
-    if (erts_system_profile_flags.scheduler && psmq.n > 0) 
-	dispatch_profile_msg_q(&psmq);	
-
-    if (!locked && resume)
-	(*resume)(arg);
-}
-
-
-
-void
-erts_set_activity_error(erts_activity_error_t error, char *file, int line)
-{
-    switch (error) {
-    case ERTS_ACT_ERR_LEAVE_WAIT_UNLOCKED:
-	erl_exit(1, "%s:%d: Fatal error: Leaving activity waiting without "
-		 "supplying the possibility to block unlocked.",
-		 file, line);
-	break;
-    case ERTS_ACT_ERR_LEAVE_UNKNOWN_ACTIVITY:
-	erl_exit(1, "%s:%d: Fatal error: Leaving unknown activity.",
-		 file, line);
-	break;
-    case ERTS_ACT_ERR_ENTER_UNKNOWN_ACTIVITY:
-	erl_exit(1, "%s:%d: Fatal error: Leaving unknown activity.",
-		 file, line);
-	break;
-    default:
-	erl_exit(1, "%s:%d: Internal error in erts_smp_set_activity()",
-		 file, line);
-	break;
-    }
-
-}
-
-
-static ERTS_INLINE erts_aint32_t
-threads_not_under_control(void)
-{
-    erts_aint32_t res = system_block_state.threads_to_block;
-
-    ERTS_THR_MEMORY_BARRIER;
-
-    /* Waiting is always an allowed activity... */
-    res -= erts_smp_atomic32_read_nob(&erts_system_block_state.in_activity.wait);
-
-    if (system_block_state.allowed_activities & ERTS_BS_FLG_ALLOW_GC)
-	res -= erts_smp_atomic32_read_nob(&erts_system_block_state.in_activity.gc);
-
-    if (system_block_state.allowed_activities & ERTS_BS_FLG_ALLOW_IO)
-	res -= erts_smp_atomic32_read_nob(&erts_system_block_state.in_activity.io);
-
-    if (res < 0) {
-	ASSERT(0);
-	return 0;
-    }
-    return res;
-}
-
-/*
- * erts_block_system() blocks all threads registered as blockable.
- * It doesn't return until either all threads have blocked (0 is returned)
- * or it has timed out (ETIMEDOUT) is returned.
- *
- * If allowed activities == 0, blocked threads will release all locks
- * before blocking.
- *
- * If allowed_activities is != 0, erts_block_system() will allow blockable
- * threads to continue executing as long as they are doing an allowed
- * activity. When they are done with the allowed activity they will block,
- * *but* they will block holding locks. Therefore, the thread calling
- * erts_block_system() must *not* try to aquire any locks that might be
- * held by blocked threads holding locks from allowed activities.
- *
- * Currently allowed_activities are:
- *	* ERTS_BS_FLG_ALLOW_GC		Thread continues with garbage
- *					collection and blocks with
- *					main process lock on current
- *					process locked.
- *	* ERTS_BS_FLG_ALLOW_IO		Thread continues with I/O
- */
-
-void
-erts_block_system(Uint32 allowed_activities)
-{
-    int do_block;
-    profile_sched_msg_q psmq;
-    
-    psmq.n = 0;
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    erts_lc_check_exact(NULL, 0); /* No locks should be locked */
-#endif
-
-    erts_smp_mtx_lock(&system_block_state.mtx);
-
-    do_block = erts_smp_pending_system_block();
-    if (do_block
-	&& system_block_state.have_blocker
-	&& erts_smp_equal_tids(system_block_state.blocker_tid,
-			       erts_smp_thr_self())) {
-	ASSERT(system_block_state.recursive_block >= 0);
-	system_block_state.recursive_block++;
-
-	/* You are not allowed to restrict allowed activites
-	   in a recursive block! */
-	ERTS_SMP_LC_ASSERT((system_block_state.allowed_activities
-			    & ~allowed_activities) == 0);
-    }
-    else {
-
-	erts_smp_atomic32_inc_nob(&erts_system_block_state.do_block);
-
-	/* Someone else might be waiting for us to block... */
-	if (do_block) {
-	do_block_me:
-	    block_me(NULL, NULL, NULL, 1, 1, 0, &psmq);
-	}
-
-	ASSERT(!system_block_state.have_blocker);
-	system_block_state.have_blocker = 1;
-	system_block_state.blocker_tid = erts_smp_thr_self();
-	system_block_state.allowed_activities = allowed_activities;
-
-	if (is_blockable_thread())
-	    system_block_state.threads_to_block--;
-
-	while (threads_not_under_control() && !system_block_state.emergency)
-	    erts_smp_cnd_wait(&system_block_state.cnd, &system_block_state.mtx);
-
-	if (system_block_state.emergency) {
-	    system_block_state.have_blocker = 0;
-	    goto do_block_me;
-	}
-    }
-
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-
-    if (erts_system_profile_flags.scheduler && psmq.n > 0 )
-    	dispatch_profile_msg_q(&psmq);
-}
-
-/*
- * erts_emergency_block_system() should only be called when we are
- * about to write a crash dump...
- */
-
-int
-erts_emergency_block_system(long timeout, Uint32 allowed_activities)
-{
-    int res = 0;
-    long another_blocker;
-
-    erts_smp_mtx_lock(&system_block_state.mtx);
-
-    if (system_block_state.emergency) {
-	 /* Argh... */
-	res = EINVAL;
-	goto done;
-    }
-
-    another_blocker = erts_smp_pending_system_block();
-    system_block_state.emergency = 1;
-    erts_smp_atomic32_inc_nob(&erts_system_block_state.do_block);
-
-    if (another_blocker) {
-	if (is_blocker()) {
-	    erts_smp_atomic32_dec_nob(&erts_system_block_state.do_block);
-	    res = 0;
-	    goto done;
-	}
-	/* kick the other blocker */
-	erts_smp_cnd_broadcast(&system_block_state.cnd);
-	while (system_block_state.have_blocker)
-	    erts_smp_cnd_wait(&system_block_state.cnd, &system_block_state.mtx);
-    }
-
-    ASSERT(!system_block_state.have_blocker);
-    system_block_state.have_blocker = 1;
-    system_block_state.blocker_tid = erts_smp_thr_self();
-    system_block_state.allowed_activities = allowed_activities;
-
-    if (is_blockable_thread())
-	system_block_state.threads_to_block--;
-
-    if (timeout < 0) {
-	while (threads_not_under_control())
-	    erts_smp_cnd_wait(&system_block_state.cnd, &system_block_state.mtx);
-    }
-    else {	
-	system_block_state.emergency_timeout = timeout;
-	erts_smp_cnd_signal(&system_block_state.watchdog_cnd);
-
-	while (system_block_state.emergency_timeout >= 0
-	       && threads_not_under_control()) {
-	    erts_smp_cnd_wait(&system_block_state.cnd,
-			      &system_block_state.mtx);
-	}
-    }
- done:
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-    return res;
-}
-
-void
-erts_release_system(void)
-{
-    long do_block;
-    profile_sched_msg_q psmq;
-    
-    psmq.n = 0;
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    erts_lc_check_exact(NULL, 0); /* No locks should be locked */
-#endif
-
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    ASSERT(is_blocker());
-
-    ASSERT(system_block_state.recursive_block >= 0);
-
-    if (system_block_state.recursive_block)
-	system_block_state.recursive_block--;
-    else {
-	do_block = erts_smp_atomic32_dec_read_nob(&erts_system_block_state.do_block);
-	system_block_state.have_blocker = 0;
-	if (is_blockable_thread())
-	    system_block_state.threads_to_block++;
-	else
-	    do_block = 0;
-
-	/* Someone else might be waiting for us to block... */
-	if (do_block)
-	    block_me(NULL, NULL, NULL, 1, 0, 0, &psmq);
-	else
-	    erts_smp_cnd_broadcast(&system_block_state.cnd);
-    }
-
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-
-    if (erts_system_profile_flags.scheduler && psmq.n > 0) 
-    	dispatch_profile_msg_q(&psmq);
-}
-
-#ifdef ERTS_ENABLE_LOCK_CHECK
-
-void
-erts_lc_activity_change_begin(void)
-{
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    system_block_state.activity_changing++;
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-}
-
-void
-erts_lc_activity_change_end(void)
-{
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    system_block_state.activity_changing--;
-    if (system_block_state.checking && !system_block_state.activity_changing)
-	erts_smp_cnd_broadcast(&system_block_state.cnd);
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-}
-
-#endif
-
-int
-erts_is_system_blocked(erts_activity_t allowed_activities)
-{
-    int blkd;
-
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    blkd = (erts_smp_pending_system_block()
-	    && system_block_state.have_blocker
-	    && erts_smp_equal_tids(system_block_state.blocker_tid,
-				   erts_smp_thr_self())
-	    && !(system_block_state.allowed_activities & ~allowed_activities));
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    if (blkd) {
-	system_block_state.checking = 1;
-	while (system_block_state.activity_changing)
-	    erts_smp_cnd_wait(&system_block_state.cnd, &system_block_state.mtx);
-	system_block_state.checking = 0;
-	blkd = !threads_not_under_control();
-    }
-#endif
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-    return blkd;
-}
-
-static void *
-emergency_watchdog(void *unused)
-{
-    erts_smp_mtx_lock(&system_block_state.mtx);
-    while (1) {
-	long timeout;
-	while (system_block_state.emergency_timeout < 0)
-	    erts_smp_cnd_wait(&system_block_state.watchdog_cnd, &system_block_state.mtx);
-	timeout = system_block_state.emergency_timeout;
-	erts_smp_mtx_unlock(&system_block_state.mtx);
-
-	if (erts_disable_tolerant_timeofday)
-	    erts_milli_sleep(timeout);
-	else {
-	    SysTimeval to;
-	    erts_get_timeval(&to);
-	    to.tv_sec += timeout / 1000;
-	    to.tv_usec += timeout % 1000;
-
-	    while (1) {
-		SysTimeval curr;
-		erts_milli_sleep(timeout);
-		erts_get_timeval(&curr);
-		if (curr.tv_sec > to.tv_sec
-		    || (curr.tv_sec == to.tv_sec && curr.tv_usec >= to.tv_usec)) {
-		    break;
-		}
-		timeout = (to.tv_sec - curr.tv_sec)*1000;
-		timeout += (to.tv_usec - curr.tv_usec)/1000;
-	    }
-	}
-
-	erts_smp_mtx_lock(&system_block_state.mtx);
-	system_block_state.emergency_timeout = -1;
-	erts_smp_cnd_broadcast(&system_block_state.cnd);
-    }
-    erts_smp_mtx_unlock(&system_block_state.mtx);
-    return NULL;
-}
-
-void
-erts_system_block_init(void)
-{
-    erts_smp_thr_opts_t thr_opts = ERTS_SMP_THR_OPTS_DEFAULT_INITER;
-    /* Local state... */
-    system_block_state.emergency = 0;
-    system_block_state.emergency_timeout = -1;
-    erts_smp_cnd_init(&system_block_state.watchdog_cnd);
-    system_block_state.threads_to_block = 0;
-    system_block_state.have_blocker = 0;
-    /* system_block_state.block_tid */
-    system_block_state.recursive_block = 0;
-    system_block_state.allowed_activities = 0;
-    erts_smp_tsd_key_create(&system_block_state.blockable_key);
-    erts_smp_mtx_init(&system_block_state.mtx, "system_block");
-    erts_smp_cnd_init(&system_block_state.cnd);
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    system_block_state.activity_changing = 0;
-    system_block_state.checking = 0;
-#endif
-
-    thr_opts.suggested_stack_size = 8;
-    erts_smp_thr_create(&system_block_state.watchdog_tid,
-			emergency_watchdog,
-			NULL,
-			&thr_opts);
-
-    /* Global state... */
-
-    erts_smp_atomic32_init_nob(&erts_system_block_state.do_block, 0);
-    erts_smp_atomic32_init_nob(&erts_system_block_state.in_activity.wait, 0);
-    erts_smp_atomic32_init_nob(&erts_system_block_state.in_activity.gc, 0);
-    erts_smp_atomic32_init_nob(&erts_system_block_state.in_activity.io, 0);
-
-    /* Make sure blockable threads unregister when exiting... */
-    erts_smp_install_exit_handler(erts_unregister_blockable_thread);
-}
-
-
-#endif /* #ifdef ERTS_SMP */
-
 char *
 erts_read_env(char *key)
 {