Implementation of true asynchronous signaling between processes

Communication between Erlang processes has conceptually always been
performed through asynchronous signaling. The runtime system
implementation has however previously preformed most operation
synchronously. In a system with only one true thread of execution, this
is not problematic (often the opposite). In a system with multiple threads
of execution (as current runtime system implementation with SMP support)
it becomes problematic. This since it often involves locking of structures
when updating them which in turn cause resource contention. Utilizing
true asynchronous communication often avoids these resource contention
issues.

The case that triggered this change was contention on the link lock due
to frequent updates of the monitor trees during communication with a
frequently used server. The signal order delivery guarantees of the
language makes it hard to change the implementation of only some signals
to use true asynchronous signaling. Therefore the implementations
of (almost) all signals have been changed.

Currently the following signals have been implemented as true
asynchronous signals:
- Message signals
- Exit signals
- Monitor signals
- Demonitor signals
- Monitor triggered signals (DOWN, CHANGE, etc)
- Link signals
- Unlink signals
- Group leader signals

All of the above already defined as asynchronous signals in the
language. The implementation of messages signals was quite
asynchronous to begin with, but had quite strict delivery constraints
due to the ordering guarantees of signals between a pair of processes.

The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts
that service all kinds of signals. More details regarding the signal
queue can be found in comments in the erl_proc_sig_queue.h file.

The monitor and link implementations have also been completely replaced
in order to fit the new asynchronous signaling implementation as good
as possible. More details regarding the new monitor and link
implementations can be found in the erl_monitor_link.h file.

1 files changed, 699 insertions, 1034 deletions

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 652b95105f..adea7d007e 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 1996-2017. All Rights Reserved.
+ * Copyright Ericsson AB 1996-2018. All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,8 +46,10 @@
 #include "erl_bif_unique.h"
 #include "erl_map.h"
 #include "erl_msacc.h"
+#include "erl_proc_sig_queue.h"
 
 Export *erts_await_result;
+static Export await_exit_trap;
 static Export* flush_monitor_messages_trap = NULL;
 static Export* set_cpu_topology_trap = NULL;
 static Export* await_proc_exit_trap = NULL;
@@ -92,83 +94,51 @@ BIF_RETTYPE spawn_3(BIF_ALIST_3)
 /* Utility to add a new link between processes p and another internal
  * process (rpid). Process p must be the currently executing process.
  */
-static int insert_internal_link(Process* p, Eterm rpid)
-{
-    Process *rp;
-    ErtsProcLocks rp_locks = ERTS_PROC_LOCK_LINK;
-
-    ASSERT(is_internal_pid(rpid));
-
-    if (IS_TRACED(p)
-	&& (ERTS_TRACE_FLAGS(p) & (F_TRACE_SOL|F_TRACE_SOL1))) {
-	rp_locks = ERTS_PROC_LOCKS_ALL;
-    }
-
-    erts_proc_lock(p, ERTS_PROC_LOCK_LINK);
-
-    /* get a pointer to the process struct of the linked process */
-    rp = erts_pid2proc_opt(p, ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK,
-			   rpid, rp_locks,
-			   ERTS_P2P_FLG_ALLOW_OTHER_X);
-
-    if (!rp) {
-	erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
-	return 0;
-    }
-
-    if (p != rp) {
-	erts_add_link(&ERTS_P_LINKS(p), LINK_PID, rp->common.id);
-	erts_add_link(&ERTS_P_LINKS(rp), LINK_PID, p->common.id);
-
-	ASSERT(IS_TRACER_VALID(ERTS_TRACER(p)));
-
-	if (IS_TRACED(p)) {
-	    if (ERTS_TRACE_FLAGS(p) & (F_TRACE_SOL|F_TRACE_SOL1))  {
-		ERTS_TRACE_FLAGS(rp) |= (ERTS_TRACE_FLAGS(p) & TRACEE_FLAGS);
-                erts_tracer_replace(&rp->common, ERTS_TRACER(p));
-		if (ERTS_TRACE_FLAGS(p) & F_TRACE_SOL1) { /* maybe override */
-		    ERTS_TRACE_FLAGS(rp) &= ~(F_TRACE_SOL1 | F_TRACE_SOL);
-		    ERTS_TRACE_FLAGS(p) &= ~(F_TRACE_SOL1 | F_TRACE_SOL);
-		}
-	    }
-	}
-    }
-    if (IS_TRACED_FL(rp, F_TRACE_PROCS))
-	trace_proc(p, p == rp ? rp_locks : ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK,
-                   rp, am_getting_linked, p->common.id);
-
-    if (p == rp)
-	erts_proc_unlock(p, rp_locks & ~ERTS_PROC_LOCK_MAIN);
-    else {
-	erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
-	erts_proc_unlock(rp, rp_locks);
-    }
-
-    return 1;
-}
-
 
 /* create a link to the process */
 BIF_RETTYPE link_1(BIF_ALIST_1)
 {
-    DistEntry *dep;
-
     if (IS_TRACED_FL(BIF_P, F_TRACE_PROCS)) {
 	trace_proc(BIF_P, ERTS_PROC_LOCK_MAIN, BIF_P, am_link, BIF_ARG_1);
     }
     /* check that the pid or port which is our argument is OK */
 
     if (is_internal_pid(BIF_ARG_1)) {
-	if (insert_internal_link(BIF_P, BIF_ARG_1)) {
-	    BIF_RET(am_true);
-	}
-	else {
-	    goto res_no_proc;
-	}
+        int created;
+        ErtsLinkData *ldp;
+        ErtsLink *lnk;
+
+        if (BIF_P->common.id == BIF_ARG_1)
+            BIF_RET(am_true);
+
+        if (!erts_proc_lookup(BIF_ARG_1))
+            goto res_no_proc;
+
+        lnk = erts_link_tree_lookup_create(&ERTS_P_LINKS(BIF_P),
+                                           &created,
+                                           ERTS_LNK_TYPE_PROC,
+                                           BIF_P->common.id,
+                                           BIF_ARG_1);
+        if (!created)
+            BIF_RET(am_true);
+
+        ldp = erts_link_to_data(lnk);
+        
+
+        if (erts_proc_sig_send_link(BIF_P, BIF_ARG_1, &ldp->b))
+            BIF_RET(am_true);
+
+        erts_link_tree_delete(&ERTS_P_LINKS(BIF_P), lnk);
+        erts_link_release_both(ldp);
+        goto res_no_proc;
     }
 
     if (is_internal_port(BIF_ARG_1)) {
-	int send_link_signal = 0;
+        int created;
+        ErtsLinkData *ldp;
+        ErtsLink *lnk;
+        Eterm ref;
+        Eterm *refp;
 	Port *prt = erts_port_lookup(BIF_ARG_1,
 				     (erts_port_synchronous_ops
 				      ? ERTS_PORT_SFLGS_INVALID_DRIVER_LOOKUP
@@ -177,31 +147,31 @@ BIF_RETTYPE link_1(BIF_ALIST_1)
 	    goto res_no_proc;
 	}
 
-	erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK);
-	
-	if (erts_add_link(&ERTS_P_LINKS(BIF_P), LINK_PID, BIF_ARG_1) >= 0)
-	    send_link_signal = 1;
-	/* else: already linked */
-
-	erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK);
+        lnk = erts_link_tree_lookup_create(&ERTS_P_LINKS(BIF_P),
+                                           &created,
+                                           ERTS_LNK_TYPE_PORT,
+                                           BIF_P->common.id,
+                                           BIF_ARG_1);
+        if (!created)
+            BIF_RET(am_true);
 
-	if (send_link_signal) {
-	    Eterm ref;
-	    Eterm *refp = erts_port_synchronous_ops ? &ref : NULL;
+        ldp = erts_link_to_data(lnk);
+        refp = erts_port_synchronous_ops ? &ref : NULL;
 
-	    switch (erts_port_link(BIF_P, prt, BIF_P->common.id, refp)) {
-	    case ERTS_PORT_OP_DROPPED:
-	    case ERTS_PORT_OP_BADARG:
-		goto res_no_proc;
-	    case ERTS_PORT_OP_SCHEDULED:
-		if (refp) {
-		    ASSERT(is_internal_ordinary_ref(ref));
-		    BIF_TRAP3(await_port_send_result_trap, BIF_P, ref, am_true, am_true);
-		}
-	    default:
-		break;
-	    }
-	}
+        switch (erts_port_link(BIF_P, prt, &ldp->b, refp)) {
+        case ERTS_PORT_OP_DROPPED:
+        case ERTS_PORT_OP_BADARG:
+            erts_link_tree_delete(&ERTS_P_LINKS(BIF_P), lnk);
+            erts_link_release_both(ldp);
+            goto res_no_proc;
+        case ERTS_PORT_OP_SCHEDULED:
+            if (refp) {
+                ASSERT(is_internal_ordinary_ref(ref));
+                BIF_TRAP3(await_port_send_result_trap, BIF_P, ref, am_true, am_true);
+            }
+        default:
+            break;
+        }
 	BIF_RET(am_true);
     }
     else if (is_external_port(BIF_ARG_1)
@@ -210,317 +180,203 @@ BIF_RETTYPE link_1(BIF_ALIST_1)
     }
 
     if (is_external_pid(BIF_ARG_1)) {
+        ErtsLinkData *ldp;
+        int created;
+        DistEntry *dep;
+        ErtsLink *lnk;
+        int code;
+        ErtsDSigData dsd;
+
+        dep = external_pid_dist_entry(BIF_ARG_1);
+        if (dep == erts_this_dist_entry)
+            goto res_no_proc;
 
-	erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK);
-
-	/* We may earn time by checking first that we're not linked already */
-	if (erts_lookup_link(ERTS_P_LINKS(BIF_P), BIF_ARG_1) != NULL) {
-	    erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK);
-	    BIF_RET(am_true);
-	}
-	else {
-	    ErtsLink *lnk;
-	    int code;
-	    ErtsDSigData dsd;
-	    dep = external_pid_dist_entry(BIF_ARG_1);
-	    if (dep == erts_this_dist_entry) {
-		erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK);
-		goto res_no_proc;
-	    }
-
-	    code = erts_dsig_prepare(&dsd, dep, BIF_P,
-				     (ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK),
-				     ERTS_DSP_RLOCK, 0, 1);
-	    switch (code) {
-	    case ERTS_DSIG_PREP_NOT_ALIVE:
-	    case ERTS_DSIG_PREP_NOT_CONNECTED: {
-		ErtsProcLocks locks = ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK;
-		erts_aint32_t state;
-		erts_proc_lock(BIF_P, (ERTS_PROC_LOCKS_ALL & ~locks));
-		locks = ERTS_PROC_LOCKS_ALL;
-		erts_send_exit_signal(BIF_P, BIF_ARG_1, BIF_P, &locks,
-				      am_noconnection, NIL, NULL, 0);
-		erts_proc_unlock(BIF_P, locks & ERTS_PROC_LOCKS_ALL_MINOR);
-
-		/*
-		 * Copy-paste from old dist_exit_3, not sure if we really
-		 * need erts_handle_pending_exit when exit_2 does not.
-		 */
-		state = erts_atomic32_read_acqb(&BIF_P->state);
-		if (state & (ERTS_PSFLG_EXITING|ERTS_PSFLG_PENDING_EXIT)) {
-		    if (state & ERTS_PSFLG_PENDING_EXIT)
-			erts_handle_pending_exit(BIF_P, ERTS_PROC_LOCK_MAIN);
-		    ERTS_BIF_EXITED(BIF_P);
-		}
-		BIF_RET(am_true);
-	    }
-            case ERTS_DSIG_PREP_PENDING:
-	    case ERTS_DSIG_PREP_CONNECTED:
-                /*
-                 * We have (pending) connection.
-                 * Setup link and enqueue link signal.
-                 */
-		erts_de_links_lock(dep);
-
-		erts_add_link(&ERTS_P_LINKS(BIF_P), LINK_PID, BIF_ARG_1);
-		lnk = erts_add_or_lookup_link(&(dep->nlinks),
-					      LINK_PID,
-					      BIF_P->common.id);
-		ASSERT(lnk != NULL);
-		erts_add_link(&ERTS_LINK_ROOT(lnk), LINK_PID, BIF_ARG_1);
-
-		erts_de_links_unlock(dep);
-		erts_de_runlock(dep);
-		erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK);
-
-		code = erts_dsig_send_link(&dsd, BIF_P->common.id, BIF_ARG_1);
-		if (code == ERTS_DSIG_SEND_YIELD)
-		    ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-		BIF_RET(am_true);
-	    default:
-		ERTS_ASSERT(! "Invalid dsig prepare result");
-	    }
-	}
+        lnk = erts_link_tree_lookup_create(&ERTS_P_LINKS(BIF_P),
+                                           &created,
+                                           ERTS_LNK_TYPE_DIST_PROC,
+                                           BIF_P->common.id,
+                                           BIF_ARG_1);
+
+        if (!created)
+            BIF_RET(am_true); /* Already present... */
+
+        ldp = erts_link_to_data(lnk);
+
+        code = erts_dsig_prepare(&dsd, dep, BIF_P,
+                                 ERTS_PROC_LOCK_MAIN,
+                                 ERTS_DSP_RLOCK, 0, 1);
+        switch (code) {
+        case ERTS_DSIG_PREP_NOT_ALIVE:
+        case ERTS_DSIG_PREP_NOT_CONNECTED:
+            erts_link_set_dead_dist(&ldp->b, dep->sysname);
+            erts_proc_sig_send_link_exit(NULL, BIF_ARG_1, &ldp->b,
+                                         am_noconnection, NIL);
+            BIF_RET(am_true);
+
+        case ERTS_DSIG_PREP_PENDING:
+        case ERTS_DSIG_PREP_CONNECTED: {
+            /*
+             * We have (pending) connection.
+             * Setup link and enqueue link signal.
+             */
+#ifdef DEBUG
+            int inserted =
+#endif
+                erts_link_dist_insert(&ldp->b, dep->mld);
+            ASSERT(inserted);
+            erts_de_runlock(dep);
+
+            code = erts_dsig_send_link(&dsd, BIF_P->common.id, BIF_ARG_1);
+            if (code == ERTS_DSIG_SEND_YIELD)
+                ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+            BIF_RET(am_true);
+            break;
+        }
+        default:
+            ERTS_ASSERT(! "Invalid dsig prepare result");
+        }
     }
 
     BIF_ERROR(BIF_P, BADARG);
 
-res_no_proc: {
-	erts_aint32_t state = erts_atomic32_read_nob(&BIF_P->state);
-	if (state & ERTS_PSFLG_TRAP_EXIT) {
-	    ErtsProcLocks locks = ERTS_PROC_LOCK_MAIN;
-	    erts_deliver_exit_message(BIF_ARG_1, BIF_P, &locks, am_noproc, NIL);
-	    erts_proc_unlock(BIF_P, ~ERTS_PROC_LOCK_MAIN & locks);
-	    BIF_RET(am_true);
-	}
-	else
-	    BIF_ERROR(BIF_P, EXC_NOPROC);
+res_no_proc:
+    if (BIF_P->flags & F_TRAP_EXIT) {
+        ErtsProcLocks locks = ERTS_PROC_LOCK_MAIN;
+        erts_deliver_exit_message(BIF_ARG_1, BIF_P, &locks, am_noproc, NIL);
+        erts_proc_unlock(BIF_P, ~ERTS_PROC_LOCK_MAIN & locks);
+        BIF_RET(am_true);
+    }
+    else {
+        /*
+         * This behaviour is *really* sad but link/1 has
+         * behaved like this for ages (and this behaviour is
+         * actually documented)... :'-(
+         *
+         * The proper behavior would have been to
+         * send calling process an exit signal..
+         */
+        BIF_ERROR(BIF_P, EXC_NOPROC);
     }
 }
 
-/* This function is allowed to return range of values handled by demonitor/1-2
- * Namely: atoms true, false, yield, internal_error, badarg or THE_NON_VALUE
- */
 static Eterm
-remote_demonitor(Process *c_p, DistEntry *dep, Eterm ref, Eterm to)
+demonitor(Process *c_p, Eterm ref, Eterm *multip)
 {
-    ErtsDSigData dsd;
-    ErtsMonitor *dmon;
-    ErtsMonitor *mon;
-    int code;
-    Eterm res = am_false;
-
-    ERTS_LC_ASSERT((ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK)
-		       == erts_proc_lc_my_proc_locks(c_p));
+    ErtsMonitor  *mon;  /* The monitor entry to delete */
 
-    code = erts_dsig_prepare(&dsd, dep, c_p, ERTS_PROC_LOCK_MAIN,
-			     ERTS_DSP_RLOCK, 0, 0);
-    switch (code) {
-    case ERTS_DSIG_PREP_NOT_ALIVE:
-    case ERTS_DSIG_PREP_NOT_CONNECTED:
-	/*
-	 * In the smp case this is possible if the node goes
-	 * down just before the call to demonitor.
-	 */
-	if (dep) {
-	    erts_de_links_lock(dep);
-	    dmon = erts_remove_monitor(&dep->monitors, ref);
-	    erts_de_links_unlock(dep);
-	    if (dmon)
-		erts_destroy_monitor(dmon);
-	}
-	mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
-	erts_proc_unlock(c_p, ERTS_PROC_LOCK_LINK);
-
-        res = am_true;
-	break;
-
-    case ERTS_DSIG_PREP_PENDING:
-    case ERTS_DSIG_PREP_CONNECTED:
-
-	erts_de_links_lock(dep);
-	mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
-	dmon = erts_remove_monitor(&dep->monitors, ref);
-	erts_de_links_unlock(dep);
-	erts_de_runlock(dep);
-	erts_proc_unlock(c_p, ERTS_PROC_LOCK_LINK);
-
-	if (!dmon) {
-	    /*
-	     * This is possible when smp support is enabled.
-	     * 'DOWN' message just arrived.
-	     */
-            res = am_true;
-	}
-	else {
-	    /*
-	     * Soft (no force) send, use ->data in dist slot 
-	     * monitor list since in case of monitor name 
-	     * the atom is stored there. Yield if necessary.
-	     */
-	    code = erts_dsig_send_demonitor(&dsd,
-					    c_p->common.id, 
-					    (mon->name != NIL
-					     ? mon->name
-					     : mon->u.pid), 
-					    ref,
-					    0);
-            res = (code == ERTS_DSIG_SEND_YIELD ? am_yield : am_true);
-	    erts_destroy_monitor(dmon);
-	}
-	break;
-    default:
-	ERTS_ASSERT(! "Invalid dsig prepare result");
-    }
-
-
-    /*
-     * We aren't allowed to destroy 'mon' until now, since 'to'
-     * may refer into 'mon' (external pid).
-     */
-    ASSERT(mon); /* Since link lock wasn't released between
-		    lookup and remove */
-    erts_destroy_monitor(mon);
-
-    ERTS_LC_ASSERT(ERTS_PROC_LOCK_MAIN == erts_proc_lc_my_proc_locks(c_p));
-    return res;
-}
+   *multip = am_false;
 
-static ERTS_INLINE void
-demonitor_local_process(Process *c_p, Eterm ref, Eterm to, Eterm *res)
-{
-    Process *rp = erts_pid2proc_opt(c_p,
-                           ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK,
-                           to,
-                           ERTS_PROC_LOCK_LINK,
-                           ERTS_P2P_FLG_ALLOW_OTHER_X);
-    ErtsMonitor *mon = erts_remove_monitor(&ERTS_P_MONITORS(c_p), ref);
+   if (is_not_internal_ref(ref)) {
+       if (is_external_ref(ref)
+           && (erts_this_dist_entry
+               == external_ref_dist_entry(ref))) {
+           return am_false;
+       }
+       return am_badarg; /* Not monitored by this monitor's ref */
+   }
 
-    if (!mon)
-        *res = am_false;
-    else
-    {
-        *res = am_true;
-        erts_destroy_monitor(mon);
-    }
-    if (rp) {
-        ErtsMonitor *rmon;
-        rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), ref);
-        if (rp != c_p)
-            erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-        if (rmon != NULL)
-            erts_destroy_monitor(rmon);
-    }
-    else {
-        ERTS_ASSERT_IS_NOT_EXITING(c_p);
-    }
-}
+   mon = erts_monitor_tree_lookup(ERTS_P_MONITORS(c_p), ref);
+   if (!mon)
+       return am_false;
 
-static ERTS_INLINE BIF_RETTYPE
-demonitor_local_port(Process *origin, Eterm ref, Eterm target)
-{
-    BIF_RETTYPE res = am_false;
-    Port        *port = erts_port_lookup_raw(target);
+   if (!erts_monitor_is_origin(mon))
+       return am_badarg;
 
-    if (!port) {
-        BIF_ERROR(origin, BADARG);
-    }
-    erts_proc_unlock(origin, ERTS_PROC_LOCK_LINK);
+   erts_monitor_tree_delete(&ERTS_P_MONITORS(c_p), mon);
 
-    if (port) {
-        Eterm trap_ref;
-        switch (erts_port_demonitor(origin, ERTS_PORT_DEMONITOR_NORMAL,
-                                    port, ref, &trap_ref)) {
-        case ERTS_PORT_OP_DROPPED:
-        case ERTS_PORT_OP_BADARG:
-            break;
-        case ERTS_PORT_OP_SCHEDULED:
-            BIF_TRAP3(await_port_send_result_trap, origin, trap_ref,
-                      am_busy_port, am_true);
-            /* the busy_port atom will never be returned, because it cannot be
-             * returned from erts_port_(de)monitor, but just in case if in future
-             * internal API changes - you may see this atom */
-        default:
-            break;
-        }
-    }
-    else {
-        ERTS_ASSERT_IS_NOT_EXITING(origin);
-    }
-    BIF_RET(res);
-}
+   switch (mon->type) {
 
-/* Can return atom true, false, yield, internal_error, badarg or
- * THE_NON_VALUE if error occurred or trap has been set up
- */
-static
-BIF_RETTYPE demonitor(Process *c_p, Eterm ref, Eterm *multip)
-{
-   ErtsMonitor  *mon = NULL;  /* The monitor entry to delete */
-   Eterm        to = NIL;     /* Monitor link traget */
-   DistEntry    *dep = NULL;  /* Target's distribution entry */
-   BIF_RETTYPE  res = am_false;
-   int          unlock_link = 1;
+   case ERTS_MON_TYPE_TIME_OFFSET:
+       *multip = am_true;
+       erts_demonitor_time_offset(mon);
+       return am_true;
+
+   case ERTS_MON_TYPE_PORT: {
+       Port *prt;
+       ASSERT(is_internal_port(mon->other.item));
+       prt = erts_port_lookup(mon->other.item, ERTS_PORT_SFLGS_DEAD);
+       if (!prt || erts_port_demonitor(c_p, prt, mon) == ERTS_PORT_OP_DROPPED)
+           erts_monitor_release(mon);
+       return am_true;
+   }
 
-   erts_proc_lock(c_p, ERTS_PROC_LOCK_LINK);
+   case ERTS_MON_TYPE_PROC:
+       erts_proc_sig_send_demonitor(mon);
+       return am_true;
 
-   if (is_not_internal_ref(ref)) {
-       res = am_badarg;
-       goto done; /* Cannot be this monitor's ref */
-   }
+   case ERTS_MON_TYPE_DIST_PROC: {
+       ErtsMonitorData *mdp = erts_monitor_to_data(mon);
+       Eterm to = mon->other.item;
+       DistEntry *dep;
+       int code = ERTS_DSIG_SEND_OK;
+       int deleted;
+       ErtsDSigData dsd;
 
-   mon = erts_lookup_monitor(ERTS_P_MONITORS(c_p), ref);
-   if (!mon) {
-       goto done;
-   }
+       ASSERT(is_external_pid(to) || is_node_name_atom(to));
 
-   switch (mon->type) {
-   case MON_TIME_OFFSET:
-       *multip = am_true;
-       erts_demonitor_time_offset(ref);
-       res = am_true;
-       break;
-   case MON_ORIGIN:
-       to = mon->u.pid;
-       *multip = am_false;
-       if (is_atom(to)) {
+       if (is_external_pid(to))
+           dep = external_pid_dist_entry(to);
+       else {
            /* Monitoring a name at node to */
-           ASSERT(is_node_name_atom(to));
            dep = erts_sysname_to_connected_dist_entry(to);
            ASSERT(dep != erts_this_dist_entry);
-       } else if (is_port(to)) {
-           if (port_dist_entry(to) != erts_this_dist_entry) {
-               goto badarg;
+           if (!dep) {
+               erts_monitor_release(mon);
+               return am_false;
            }
-           res = demonitor_local_port(c_p, ref, to);
-           unlock_link = 0;
-           goto done;
-       } else {
-           ASSERT(is_pid(to));
-           dep = pid_dist_entry(to);
        }
-       if (dep != erts_this_dist_entry) {
-           res = remote_demonitor(c_p, dep, ref, to);
-           /* remote_demonitor() unlocks link lock on c_p */
-           unlock_link = 0;
+
+       code = erts_dsig_prepare(&dsd, dep, c_p, ERTS_PROC_LOCK_MAIN,
+                                ERTS_DSP_RLOCK, 0, 0);
+
+       deleted = erts_monitor_dist_delete(&mdp->target);
+
+       switch (code) {
+       case ERTS_DSIG_PREP_NOT_ALIVE:
+       case ERTS_DSIG_PREP_NOT_CONNECTED:
+           /*
+            * In the smp case this is possible if the node goes
+            * down just before the call to demonitor.
+            */
+           break;
+
+       case ERTS_DSIG_PREP_PENDING:
+       case ERTS_DSIG_PREP_CONNECTED: {
+           Eterm watched;
+
+           erts_de_runlock(dep);
+
+           if (mon->flags & ERTS_ML_FLG_NAME)
+               watched = ((ErtsMonitorDataExtended *) mdp)->u.name;
+           else
+               watched = to;
+
+           /*
+            * Soft (no force) send, use ->data in dist slot 
+            * monitor list since in case of monitor name 
+            * the atom is stored there. Yield if necessary.
+            */
+           code = erts_dsig_send_demonitor(&dsd, c_p->common.id,
+                                           watched, mdp->ref, 0);
+           break;
        }
-       else { /* Local monitor */
-           demonitor_local_process(c_p, ref, to, &res);
+
+       default:
+           ERTS_INTERNAL_ERROR("invalid result from erts_dsig_prepare()");
+           break;
        }
-       break;
-    default /* case */ :
-badarg:
-       res = am_badarg; /* will be converted to error by caller */
-       *multip = am_false;
-       break;
-   }
-done:
 
-   if (unlock_link)
-       erts_proc_unlock(c_p, ERTS_PROC_LOCK_LINK);
+       if (deleted)
+           erts_monitor_release(&mdp->target);
 
-   ERTS_LC_ASSERT(ERTS_PROC_LOCK_MAIN == erts_proc_lc_my_proc_locks(c_p));
-   BIF_RET(res);
+       erts_monitor_release(mon);
+       return code == ERTS_DSIG_SEND_YIELD ? am_yield : am_true;
+   }
+
+   default:
+       ERTS_INTERNAL_ERROR("Unexpected monitor type");
+       return am_false;
+   }
 }
 
 BIF_RETTYPE demonitor_1(BIF_ALIST_1)
@@ -528,25 +384,23 @@ BIF_RETTYPE demonitor_1(BIF_ALIST_1)
     Eterm multi;
     switch (demonitor(BIF_P, BIF_ARG_1, &multi)) {
     case am_false:
-    case am_true:       BIF_RET(am_true);
-    case THE_NON_VALUE: BIF_RET(THE_NON_VALUE);
-    case am_yield:      ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-    case am_badarg:     BIF_ERROR(BIF_P, BADARG);
-
-    case am_internal_error:
+    case am_true:
+        BIF_RET(am_true);
+    case am_yield:
+        ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+    case am_badarg:
     default:
-	ASSERT(! "demonitor(): internal error");
-	BIF_ERROR(BIF_P, EXC_INTERNAL_ERROR);
+        BIF_ERROR(BIF_P, BADARG);
     }
 }
 
 BIF_RETTYPE demonitor_2(BIF_ALIST_2)
 {
-    BIF_RETTYPE res = am_true;
-    Eterm       multi = am_false;
-    int         info = 0;
-    int         flush = 0;
-    Eterm       list = BIF_ARG_2;
+    BIF_RETTYPE res;
+    Eterm multi = am_false;
+    int info = 0;
+    int flush = 0;
+    Eterm list = BIF_ARG_2;
 
     while (is_list(list)) {
 	Eterm* consp = list_val(list);
@@ -566,10 +420,9 @@ BIF_RETTYPE demonitor_2(BIF_ALIST_2)
     if (is_not_nil(list))
 	goto badarg;
 
+    res = am_true;
     switch (demonitor(BIF_P, BIF_ARG_1, &multi)) {
-    case THE_NON_VALUE:
-        /* If other error occurred or trap has been set up - pass through */
-        BIF_RET(THE_NON_VALUE);
+
     case am_false:
 	if (info)
 	    res = am_false;
@@ -578,20 +431,29 @@ flush_messages:
 	    BIF_TRAP3(flush_monitor_messages_trap, BIF_P,
 		      BIF_ARG_1, multi, res);
 	}
+        /* Fall through... */
+
     case am_true:
 	if (multi == am_true && flush)
 	    goto flush_messages;
 	BIF_RET(res);
+
     case am_yield:
-	ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+        /* return true after yield... */
+        if (flush) {
+            ERTS_VBUMP_ALL_REDS(BIF_P);
+            goto flush_messages;
+        }
+        ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
+
     case am_badarg:
-badarg:
-	BIF_ERROR(BIF_P, BADARG);
-    case am_internal_error:
     default:
-	ASSERT(! "demonitor(): internal error");
-	BIF_ERROR(BIF_P, EXC_INTERNAL_ERROR);
+        break;
+
     }
+
+badarg:
+    BIF_ERROR(BIF_P, BADARG);
 }
 
 /* Type must be atomic object! */
@@ -631,292 +493,212 @@ erts_queue_monitor_message(Process *p,
     erts_queue_message(p, *p_locksp, msgp, tup, am_system);
 }
 
-static Eterm
-local_pid_monitor(Process *p, Eterm target, Eterm mon_ref, int boolean)
+BIF_RETTYPE monitor_2(BIF_ALIST_2)
 {
-    Eterm         ret = mon_ref;
-    Process      *rp;
-    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_LINK;
-
-    if (target == p->common.id) {
-	return ret;
-    }
+    Eterm target = BIF_ARG_2;
+    Eterm tmp_heap[3];
+    Eterm ref, id, name;
+    ErtsMonitorData *mdp;
+
+    if (BIF_ARG_1 == am_process) {
+        DistEntry *dep;
+        int byname;
+
+        if (is_internal_pid(target)) {
+            name = NIL;
+            id = target;
+
+        local_process:
+
+            ref = erts_make_ref(BIF_P);
+            if (id != BIF_P->common.id) {
+                mdp = erts_monitor_create(ERTS_MON_TYPE_PROC,
+                                          ref, BIF_P->common.id,
+                                          id, name);
+                erts_monitor_tree_insert(&ERTS_P_MONITORS(BIF_P),
+                                         &mdp->origin);
+
+                if (!erts_proc_sig_send_monitor(&mdp->target, id))
+                    erts_proc_sig_send_monitor_down(&mdp->target,
+                                                    am_noproc);
+            }
+            BIF_RET(ref);
+        }
 
-    erts_proc_lock(p, ERTS_PROC_LOCK_LINK);
-    rp = erts_pid2proc_opt(p, p_locks,
-			   target, ERTS_PROC_LOCK_LINK,
-			   ERTS_P2P_FLG_ALLOW_OTHER_X);
-    if (!rp) {
-	erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
-	p_locks &= ~ERTS_PROC_LOCK_LINK;
-	if (boolean)
-	    ret = am_false;
-	else
-	    erts_queue_monitor_message(p, &p_locks,
-				       mon_ref, am_process, target, am_noproc);
-    }
-    else {
-	ASSERT(rp != p);
+        if (is_atom(target)) {
+        local_named_process:
+            name = target;
+            id = erts_whereis_name_to_id(BIF_P, target);
+            if (is_internal_pid(id))
+                goto local_process;
+            target = TUPLE2(&tmp_heap[0], name,
+                            erts_this_dist_entry->sysname);
+            goto noproc;
+        }
 
-	if (boolean)
-	    ret = am_true;
+        if (is_external_pid(target)) {
+            ErtsDSigData dsd;
+            int code;
+
+            dep = external_pid_dist_entry(target);
+            if (dep == erts_this_dist_entry)
+                goto noproc;
+
+            id = target;
+            name = NIL;
+            byname = 0;
+
+        remote_process:
+
+            ref = erts_make_ref(BIF_P);
+            mdp = erts_monitor_create(ERTS_MON_TYPE_DIST_PROC, ref,
+                                      BIF_P->common.id, id, name);
+            erts_monitor_tree_insert(&ERTS_P_MONITORS(BIF_P), &mdp->origin);
+
+            code = erts_dsig_prepare(&dsd, dep,
+                                     BIF_P, ERTS_PROC_LOCK_MAIN,
+                                     ERTS_DSP_RLOCK, 0, 1);
+            switch (code) {
+            case ERTS_DSIG_PREP_NOT_ALIVE:
+            case ERTS_DSIG_PREP_NOT_CONNECTED:
+                erts_monitor_set_dead_dist(&mdp->target, dep->sysname);
+                erts_proc_sig_send_monitor_down(&mdp->target, am_noconnection);
+                code = ERTS_DSIG_SEND_OK;
+                break;
 
-	erts_add_monitor(&ERTS_P_MONITORS(p), MON_ORIGIN, mon_ref, target, NIL);
-	erts_add_monitor(&ERTS_P_MONITORS(rp), MON_TARGET, mon_ref, p->common.id, NIL);
+            case ERTS_DSIG_PREP_PENDING:
+            case ERTS_DSIG_PREP_CONNECTED: {
+#ifdef DEBUG
+                int inserted =
+#endif
 
-	erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-    }
+                erts_monitor_dist_insert(&mdp->target, dep->mld);
+                ASSERT(inserted);
+                erts_de_runlock(dep);
 
-    erts_proc_unlock(p, p_locks & ~ERTS_PROC_LOCK_MAIN);
+                code = erts_dsig_send_monitor(&dsd, BIF_P->common.id, target, ref);
+                break;
+            }
 
-    return ret;
-}
+            default:
+                ERTS_ASSERT(! "Invalid dsig prepare result");
+                code = ERTS_DSIG_SEND_OK;
+                break;
+            }
 
-static BIF_RETTYPE
-local_port_monitor(Process *origin, Eterm target)
-{
-    BIF_RETTYPE ref = erts_make_ref(origin);
-    Port *port = erts_sig_lookup_port(origin, target);
-    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN;
+            if (byname)
+                erts_deref_dist_entry(dep);
 
-    if (!port) {
-res_no_proc:
-        /* Send the DOWN message immediately. Ref is made on the fly because
-         * caller has never seen it yet. */
-        erts_queue_monitor_message(origin, &p_locks, ref,
-                                   am_port, target, am_noproc);
-    }
-    else {
-        switch (erts_port_monitor(origin, port, target, &ref)) {
-        case ERTS_PORT_OP_DROPPED:
-        case ERTS_PORT_OP_BADARG:
-            goto res_no_proc;
-        case ERTS_PORT_OP_SCHEDULED:
-            BIF_TRAP3(await_port_send_result_trap, origin, ref,
-                      am_busy_port, ref);
-            /* the busy_port atom will never be returned, because it cannot be
-             * returned from erts_port_monitor, but just in case if in future
-             * internal API changes - you may see this atom */
-        default:
-            break;
+            if (code == ERTS_DSIG_SEND_YIELD)
+                ERTS_BIF_YIELD_RETURN(BIF_P, ref);
+            BIF_RET(ref);
         }
-    }
-    erts_proc_unlock(origin, p_locks & ~ERTS_PROC_LOCK_MAIN);
-    BIF_RET(ref);
-}
 
-/* Type = process | port :: atom(), 1st argument passed to erlang:monitor/2
- */
-static BIF_RETTYPE
-local_name_monitor(Process *self, Eterm type, Eterm target_name)
-{
-    BIF_RETTYPE ret = erts_make_ref(self);
+        if (is_tuple(target)) {
+            Eterm *tpl = tuple_val(target);
+            if (arityval(tpl[0]) != 2)
+                goto badarg;
+            if (is_not_atom(tpl[1]) || is_not_atom(tpl[2]))
+                goto badarg;
+            if (!erts_is_alive && tpl[2] != am_Noname)
+                goto badarg;
+            target = tpl[1];
+            dep = erts_find_or_insert_dist_entry(tpl[2]);
+            if (dep == erts_this_dist_entry) {
+                erts_deref_dist_entry(dep);
+                goto local_named_process;
+            }
 
-    ErtsProcLocks p_locks = ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK;
-    Process     *proc = NULL;
-    Port        *port = NULL;
+            id = dep->sysname;
+            name = target;
+            byname = 1;
+            goto remote_process;
+        }
 
-    erts_proc_lock(self, ERTS_PROC_LOCK_LINK);
+        /* badarg... */
+    }
+    else if (BIF_ARG_1 == am_port) {
+
+        if (is_internal_port(target)) {
+            Port *prt;
+            name = NIL;
+            id = target;
+        local_port:
+            ref = erts_make_ref(BIF_P);
+            mdp = erts_monitor_create(ERTS_MON_TYPE_PORT, ref,
+                                      BIF_P->common.id, id, name);
+            erts_monitor_tree_insert(&ERTS_P_MONITORS(BIF_P), &mdp->origin);
+            prt = erts_port_lookup(id, ERTS_PORT_SFLGS_INVALID_LOOKUP);
+            if (!prt || erts_port_monitor(BIF_P, prt, &mdp->target) == ERTS_PORT_OP_DROPPED)
+                erts_proc_sig_send_monitor_down(&mdp->target, am_noproc);
+            BIF_RET(ref);
+        }
 
-    erts_whereis_name(self, p_locks, target_name,
-                      &proc, ERTS_PROC_LOCK_LINK,
-                      ERTS_P2P_FLG_ALLOW_OTHER_X,
-                      &port, 0);
+        if (is_atom(target)) {
+        local_named_port:
+            name = target;
+            id = erts_whereis_name_to_id(BIF_P, target);
+            if (is_internal_port(id))
+                goto local_port;
+            target = TUPLE2(&tmp_heap[0], name,
+                            erts_this_dist_entry->sysname);
+            goto noproc;
+        }
 
-    /* If the name is not registered,
-     * or if we asked for proc and got a port,
-     * or if we asked for port and got a proc,
-     * we just send the 'DOWN' message.
-     */
-    if ((!proc && !port) ||
-        (type == am_process && port) ||
-        (type == am_port && proc)) {
-        DeclareTmpHeap(lhp,3,self);
-	Eterm item;
-        UseTmpHeap(3,self);
-
-        erts_proc_unlock(self, ERTS_PROC_LOCK_LINK);
-	p_locks &= ~ERTS_PROC_LOCK_LINK;
-
-	item = TUPLE2(lhp, target_name, erts_this_dist_entry->sysname);
-        erts_queue_monitor_message(self, &p_locks,
-                                   ret,
-                                   type, /* = process|port :: atom() */
-                                   item, am_noproc);
-        UnUseTmpHeap(3,self);
-    }
-    else if (port) {
-        erts_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
-        p_locks &= ~ERTS_PROC_LOCK_MAIN;
-
-        switch (erts_port_monitor(self, port, target_name, &ret)) {
-        case ERTS_PORT_OP_DONE:
-            return ret;
-        case ERTS_PORT_OP_SCHEDULED: { /* Scheduled a signal */
-            ASSERT(is_internal_ordinary_ref(ret));
-            BIF_TRAP3(await_port_send_result_trap, self,
-                      ret, am_true, ret);
-            /* bif_trap returns */
-        } break;
-        default:
+        if (is_external_port(target)) {
+            if (erts_this_dist_entry == external_port_dist_entry(target))
+                goto noproc;
             goto badarg;
         }
-    }
-    else if (proc != self) {
-        erts_add_monitor(&ERTS_P_MONITORS(self), MON_ORIGIN, ret,
-                         proc->common.id, target_name);
-        erts_add_monitor(&ERTS_P_MONITORS(proc), MON_TARGET, ret,
-                         self->common.id, target_name);
-        erts_proc_unlock(proc, ERTS_PROC_LOCK_LINK);
-    }
-
-    if (p_locks) {
-        erts_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
-    }
-    BIF_RET(ret);
-badarg:
-    if (p_locks) {
-        erts_proc_unlock(self, p_locks & ~ERTS_PROC_LOCK_MAIN);
-    }
-    BIF_ERROR(self, BADARG);
-}
-
-static BIF_RETTYPE
-remote_monitor(Process *p, Eterm bifarg1, Eterm bifarg2,
-	       DistEntry *dep, Eterm target, int byname)
-{
-    ErtsDSigData dsd;
-    BIF_RETTYPE ret;
-    int code;
 
-    ASSERT(dep);
-    erts_proc_lock(p, ERTS_PROC_LOCK_LINK);
-    code = erts_dsig_prepare(&dsd, dep,
-			     p, (ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK),
-			     ERTS_DSP_RLOCK, 0, 1);
-    switch (code) {
-    case ERTS_DSIG_PREP_NOT_ALIVE:
-    case ERTS_DSIG_PREP_NOT_CONNECTED:
-	erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
-	ERTS_BIF_PREP_TRAP2(ret, dmonitor_p_trap, p, bifarg1, bifarg2);
-	break;
-    case ERTS_DSIG_PREP_PENDING:
-    case ERTS_DSIG_PREP_CONNECTED:
-	{
-	    Eterm p_trgt, p_name, d_name, mon_ref;
+        if (is_tuple(target)) {
+            Eterm *tpl = tuple_val(target);
+            if (arityval(tpl[0]) != 2)
+                goto badarg;
+            if (is_not_atom(tpl[1]) || is_not_atom(tpl[2]))
+                goto badarg;
+            if (tpl[2] == erts_this_dist_entry->sysname) {
+                target = tpl[1];
+                goto local_named_port;
+            }
+        }
 
-	    mon_ref = erts_make_ref(p);
+        /* badarg... */
+    }
+    else if (BIF_ARG_1 == am_time_offset) {
 
-	    if (byname) {
-		p_trgt = dep->sysname;
-		p_name = target;
-		d_name = target;
-	    }
-	    else {
-		p_trgt = target;
-		p_name = NIL;
-		d_name = NIL;
-	    }
+        if (target != am_clock_service)
+            goto badarg;
+	ref = erts_make_ref(BIF_P);
+        mdp = erts_monitor_create(ERTS_MON_TYPE_TIME_OFFSET,
+                                  ref, BIF_P->common.id,
+                                  am_clock_service, NIL);
+        erts_monitor_tree_insert(&ERTS_P_MONITORS(BIF_P), &mdp->origin);
 
-	    erts_de_links_lock(dep);
+	erts_monitor_time_offset(&mdp->target);
 
-	    erts_add_monitor(&ERTS_P_MONITORS(p), MON_ORIGIN, mon_ref, p_trgt,
-			     p_name);
-	    erts_add_monitor(&(dep->monitors), MON_TARGET, mon_ref, p->common.id,
-			     d_name);
+        BIF_RET(ref);
+    }
 
-	    erts_de_links_unlock(dep);
-	    erts_de_runlock(dep);
-	    erts_proc_unlock(p, ERTS_PROC_LOCK_LINK);
+badarg:
 
-	    code = erts_dsig_send_monitor(&dsd, p->common.id, target, mon_ref);
-	    if (code == ERTS_DSIG_SEND_YIELD)
-		ERTS_BIF_PREP_YIELD_RETURN(ret, p, mon_ref);
-	    else
-		ERTS_BIF_PREP_RET(ret, mon_ref);
-	}
-	break;
-    default:
-	ERTS_ASSERT(! "Invalid dsig prepare result");
-    }
+    BIF_ERROR(BIF_P, BADARG);
 
-    BIF_RET(ret);
-}
-	
-BIF_RETTYPE monitor_2(BIF_ALIST_2)
-{
-    Eterm target = BIF_ARG_2;
-    BIF_RETTYPE ret;
-    DistEntry  *dep = NULL; 
+noproc: {
+        ErtsProcLocks locks = ERTS_PROC_LOCK_MAIN;
 
-    /* Only process monitors are implemented */
-    switch (BIF_ARG_1) {
-    case am_time_offset: {
-	Eterm ref;
-        if (BIF_ARG_2 != am_clock_service) {
-            goto badarg;
-        }
-	ref = erts_make_ref(BIF_P);
-	erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK);
-	erts_add_monitor(&ERTS_P_MONITORS(BIF_P), MON_TIME_OFFSET,
-			 ref, am_clock_service, NIL);
-	erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK);
-	erts_monitor_time_offset(BIF_P->common.id, ref);
-	BIF_RET(ref);
-    }
-    case am_process:
-    case am_port:
-	break;
-    default:
-        goto badarg;
-    }
+        ref = erts_make_ref(BIF_P);
+        erts_queue_monitor_message(BIF_P,
+                                   &locks,
+                                   ref,
+                                   BIF_ARG_1,
+                                   target,
+                                   am_noproc);
+        if (locks != ERTS_PROC_LOCK_MAIN)
+            erts_proc_unlock(BIF_P, locks & ~ERTS_PROC_LOCK_MAIN);
 
-    if (is_internal_pid(target) && BIF_ARG_1 == am_process) {
-local_pid:
-        ret = local_pid_monitor(BIF_P, target, erts_make_ref(BIF_P), 0);
-    } else if (is_external_pid(target) && BIF_ARG_1 == am_process) {
-	dep = external_pid_dist_entry(target);
-	if (dep == erts_this_dist_entry)
-	    goto local_pid;
-	ret = remote_monitor(BIF_P, BIF_ARG_1, BIF_ARG_2, dep, target, 0);
-    } else if (is_internal_port(target) && BIF_ARG_1 == am_port) {
-local_port:
-        ret = local_port_monitor(BIF_P, target);
-    } else if (is_external_port(target) && BIF_ARG_1 == am_port) {
-        dep = external_port_dist_entry(target);
-        if (dep == erts_this_dist_entry) {
-            goto local_port;
-        }
-        goto badarg; /* No want remote port */
-    } else if (is_atom(target)) {
-        ret = local_name_monitor(BIF_P, BIF_ARG_1, target);
-    } else if (is_tuple(target)) {
-	Eterm *tp = tuple_val(target);
-	Eterm remote_node;
-	Eterm name;
-        if (arityval(*tp) != 2) {
-            goto badarg;
-        }
-	remote_node = tp[2];
-	name = tp[1];
-	if (!is_atom(remote_node) || !is_atom(name)) {
-            goto badarg;
-	}
-	if (!erts_is_alive && remote_node != am_Noname) {
-            goto badarg; /* Remote monitor from (this) undistributed node */
-	}
-	dep = erts_find_or_insert_dist_entry(remote_node);
-	if (dep == erts_this_dist_entry) {
-            ret = local_name_monitor(BIF_P, BIF_ARG_1, name);
-	} else {
-	    ret = remote_monitor(BIF_P, BIF_ARG_1, BIF_ARG_2, dep, name, 1);
-	}
-	erts_deref_dist_entry(dep);
-    } else {
-badarg:
-	ERTS_BIF_PREP_ERROR(ret, BIF_P, BADARG);
+        BIF_RET(ref);
     }
-    return ret;
 }
 
 /**********************************************************************/
@@ -1089,91 +871,74 @@ BIF_RETTYPE spawn_opt_1(BIF_ALIST_1)
 /* remove a link from a process */
 BIF_RETTYPE unlink_1(BIF_ALIST_1)
 {
-    Process *rp;
-    DistEntry *dep;
-    ErtsLink *l = NULL, *rl = NULL;
-    ErtsProcLocks cp_locks = ERTS_PROC_LOCK_MAIN;
-
-    /*
-     * SMP specific note concerning incoming exit signals:
-     *   We have to have at least the status lock during removal of
-     *   the link half on current process, and check for and handle
-     *   a present pending exit while the status lock is held. This
-     *   in order to ensure that we wont be exited by a link after
-     *   it has been removed.
-     *
-     *   (We also have to have the link lock, of course, in order to
-     *    be allowed to remove the link...)
-     */
-
     if (IS_TRACED_FL(BIF_P, F_TRACE_PROCS)) {
-	trace_proc(BIF_P, cp_locks, BIF_P, am_unlink, BIF_ARG_1);
+        trace_proc(BIF_P, ERTS_PROC_LOCK_MAIN,
+                   BIF_P, am_unlink, BIF_ARG_1);
     }
 
-    if (is_internal_port(BIF_ARG_1)) {
-	erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
-	if (ERTS_PROC_PENDING_EXIT(BIF_P))
-	    goto handle_pending_exit;
-
-	l = erts_remove_link(&ERTS_P_LINKS(BIF_P), BIF_ARG_1);
+    if (is_internal_pid(BIF_ARG_1)) {
+        ErtsLink *lnk = erts_link_tree_lookup(ERTS_P_LINKS(BIF_P), BIF_ARG_1);
+        if (lnk) {
+            erts_link_tree_delete(&ERTS_P_LINKS(BIF_P), lnk);
+            erts_proc_sig_send_unlink(BIF_P, lnk);
+        }
+        BIF_RET(am_true);
+    }
 
-	erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
+    if (is_internal_port(BIF_ARG_1)) {
+        ErtsLink *lnk = erts_link_tree_lookup(ERTS_P_LINKS(BIF_P), BIF_ARG_1);
 
-	if (l) {
+	if (lnk) {
+            Eterm ref;
+            Eterm *refp = erts_port_synchronous_ops ? &ref : NULL;
+            ErtsPortOpResult res = ERTS_PORT_OP_DROPPED;
 	    Port *prt;
 
-	    erts_destroy_link(l);
+            erts_link_tree_delete(&ERTS_P_LINKS(BIF_P), lnk);
 
 	    /* Send unlink signal */
 	    prt = erts_port_lookup(BIF_ARG_1, ERTS_PORT_SFLGS_DEAD);
 	    if (prt) {
-		ErtsPortOpResult res;
-		Eterm ref;
-		Eterm *refp = erts_port_synchronous_ops ? &ref : NULL;
 #ifdef DEBUG
 		ref = NIL;
 #endif
-		res = erts_port_unlink(BIF_P, prt, BIF_P->common.id, refp);
+		res = erts_port_unlink(BIF_P, prt, lnk, refp);
 
-		if (refp && res == ERTS_PORT_OP_SCHEDULED) {
-		    ASSERT(is_internal_ordinary_ref(ref));
-		    BIF_TRAP3(await_port_send_result_trap, BIF_P, ref, am_true, am_true);
-		}
 	    }
+
+            if (res == ERTS_PORT_OP_DROPPED)
+                erts_link_release(lnk);
+            else if (refp && res == ERTS_PORT_OP_SCHEDULED) {
+                ASSERT(is_internal_ordinary_ref(ref));
+                BIF_TRAP3(await_port_send_result_trap, BIF_P, ref, am_true, am_true);
+            }
 	}
 
 	BIF_RET(am_true);
     }
-    else if (is_external_port(BIF_ARG_1)
-	     && external_port_dist_entry(BIF_ARG_1) == erts_this_dist_entry) {
-	BIF_RET(am_true);
-    }
-
-    if (is_not_pid(BIF_ARG_1))
-	BIF_ERROR(BIF_P, BADARG);
 
     if (is_external_pid(BIF_ARG_1)) {
-	ErtsDistLinkData dld;
+        ErtsLink *lnk, *dlnk;
+        ErtsLinkData *ldp;
+        DistEntry *dep;
 	int code;
 	ErtsDSigData dsd;
-	/* Blind removal, we might have trapped or anything, this leaves
-	   us in a state where monitors might be inconsistent, but the dist
-	   code should take care of it. */
-	erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
-	if (ERTS_PROC_PENDING_EXIT(BIF_P))
-	    goto handle_pending_exit;
-	l = erts_remove_link(&ERTS_P_LINKS(BIF_P), BIF_ARG_1);
-
-	erts_proc_unlock(BIF_P,
-			     ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
-
-	if (l)
-	    erts_destroy_link(l);
 
 	dep = external_pid_dist_entry(BIF_ARG_1);
-	if (dep == erts_this_dist_entry) {
+	if (dep == erts_this_dist_entry)
 	    BIF_RET(am_true);
-	}
+
+        lnk = erts_link_tree_lookup(ERTS_P_LINKS(BIF_P), BIF_ARG_1);
+        if (!lnk)
+            BIF_RET(am_true);
+
+        erts_link_tree_delete(&ERTS_P_LINKS(BIF_P), lnk);
+        dlnk = erts_link_to_other(lnk, &ldp);
+
+        if (erts_link_dist_delete(dlnk))
+            erts_link_release_both(ldp);
+        else
+            erts_link_release(lnk);
 
 	code = erts_dsig_prepare(&dsd, dep, BIF_P, ERTS_PROC_LOCK_MAIN,
 				 ERTS_DSP_NO_LOCK, 0, 0);
@@ -1181,74 +946,27 @@ BIF_RETTYPE unlink_1(BIF_ALIST_1)
 	case ERTS_DSIG_PREP_NOT_ALIVE:
 	case ERTS_DSIG_PREP_NOT_CONNECTED:
 	    BIF_RET(am_true);
-
 	case ERTS_DSIG_PREP_PENDING:
 	case ERTS_DSIG_PREP_CONNECTED:
-	    erts_remove_dist_link(&dld, BIF_P->common.id, BIF_ARG_1, dep);
 	    code = erts_dsig_send_unlink(&dsd, BIF_P->common.id, BIF_ARG_1);
-	    erts_destroy_dist_link(&dld);
 	    if (code == ERTS_DSIG_SEND_YIELD)
 		ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-	    BIF_RET(am_true);
-
+            break;
 	default:
 	    ASSERT(! "Invalid dsig prepare result");
 	    BIF_ERROR(BIF_P, EXC_INTERNAL_ERROR);
 	}
-    }
-
-    /* Internal pid... */
-
-    erts_proc_lock(BIF_P, ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
-
-    cp_locks |= ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS;
-
-    /* get process struct */
-    rp = erts_pid2proc_opt(BIF_P, cp_locks,
-			   BIF_ARG_1, ERTS_PROC_LOCK_LINK,
-			   ERTS_P2P_FLG_ALLOW_OTHER_X);
-
-    if (ERTS_PROC_PENDING_EXIT(BIF_P)) {
-	if (rp && rp != BIF_P)
-	    erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-	goto handle_pending_exit;
-    }
-
-    /* unlink and ignore errors */
-    l = erts_remove_link(&ERTS_P_LINKS(BIF_P), BIF_ARG_1);
-    if (l != NULL)
-	erts_destroy_link(l);
 
-    if (!rp) {
-	ERTS_ASSERT_IS_NOT_EXITING(BIF_P);
+        BIF_RET(am_true);
     }
-    else {
-	rl = erts_remove_link(&ERTS_P_LINKS(rp), BIF_P->common.id);
-	if (rl != NULL)
-	    erts_destroy_link(rl);
-
-	if (IS_TRACED_FL(rp, F_TRACE_PROCS) && rl != NULL) {
-            erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_STATUS);
-            cp_locks &= ~ERTS_PROC_LOCK_STATUS;
-	    trace_proc(BIF_P, (ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_LINK),
-                       rp, am_getting_unlinked, BIF_P->common.id);
-	}
 
-	if (rp != BIF_P)
-	    erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
+    if (is_external_port(BIF_ARG_1)) {
+        if (external_port_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
+            BIF_RET(am_true);
+        /* Links to Remote ports not supported... */
     }
- 
-    erts_proc_unlock(BIF_P, cp_locks & ~ERTS_PROC_LOCK_MAIN);
 
-    BIF_RET(am_true);
-
- handle_pending_exit:
-    erts_handle_pending_exit(BIF_P, (ERTS_PROC_LOCK_MAIN
-				     | ERTS_PROC_LOCK_LINK
-				     | ERTS_PROC_LOCK_STATUS));
-    ASSERT(ERTS_PROC_IS_EXITING(BIF_P)); 
-    erts_proc_unlock(BIF_P,	ERTS_PROC_LOCK_LINK|ERTS_PROC_LOCK_STATUS);
-    ERTS_BIF_EXITED(BIF_P);
+    BIF_ERROR(BIF_P, BADARG);
 }
 
 BIF_RETTYPE hibernate_3(BIF_ALIST_3)
@@ -1493,22 +1211,69 @@ BIF_RETTYPE raise_3(BIF_ALIST_3)
     return am_badarg;
 }
 
+static BIF_RETTYPE
+erts_internal_await_exit_trap(BIF_ALIST_0)
+{
+    /*
+     * We have sent ourselves an exit signal which will
+     * terminate ourselves. Handle all signals until
+     * terminated in order to ensure that signal order
+     * is preserved. Yield if necessary.
+     */
+    erts_aint32_t state;
+    int reds = ERTS_BIF_REDS_LEFT(BIF_P);
+    (void) erts_proc_sig_handle_incoming(BIF_P, &state, &reds,
+                                         reds, !0);
+    BUMP_REDS(BIF_P, reds);
+    if (state & ERTS_PSFLG_EXITING)
+        ERTS_BIF_EXITED(BIF_P);
+
+    ERTS_BIF_YIELD0(&await_exit_trap, BIF_P);
+}
+
 /**********************************************************************/
-/* send an exit message to another process (if trapping exits) or
-   exit the other process */
+/* send an exit signal to another process */
 
-BIF_RETTYPE exit_2(BIF_ALIST_2)
+static BIF_RETTYPE send_exit_signal_bif(Process *c_p, Eterm id, Eterm reason, int exit2)
 {
-     Process *rp;
+    BIF_RETTYPE ret_val;
 
-     /*
-      * If the first argument is not a pid, or a local port it is an error.
-      */
+    /*
+     * 'id' not a process id, nor a local port id is a 'badarg' error.
+     */
 
-     if (is_internal_port(BIF_ARG_1)) {
+     if (is_internal_pid(id)) {
+         /*
+          * Preserve the very old and *very strange* behaviour
+          * of erlang:exit/2...
+          *
+          * - terminate ourselves even though exit reason
+          *   is normal (unless we trap exit)
+          * - terminate ourselves before exit/2 return
+          */
+         int exit2_suicide = (exit2
+                              && c_p->common.id == id
+                              && (reason == am_kill
+                                  || !(c_p->flags & F_TRAP_EXIT)));
+         erts_proc_sig_send_exit(c_p, c_p->common.id, id,
+                                 reason, NIL, exit2_suicide);
+         if (!exit2_suicide)
+             ERTS_BIF_PREP_RET(ret_val, am_true);
+         else {
+             erts_proc_lock(c_p, ERTS_PROC_LOCK_MSGQ);
+             erts_proc_sig_fetch(c_p);
+             erts_proc_unlock(c_p, ERTS_PROC_LOCK_MSGQ);
+             ERTS_BIF_PREP_TRAP0(ret_val, &await_exit_trap, c_p);
+         }
+     }
+     else if (is_internal_port(id)) {
 	 Eterm ref, *refp;
 	 Uint32 invalid_flags;
 	 Port *prt;
+         ErtsPortOpResult res = ERTS_PORT_OP_DONE;
+#ifdef DEBUG
+         ref = NIL;
+#endif
 
 	 if (erts_port_synchronous_ops) {
 	     refp = &ref;
@@ -1519,108 +1284,75 @@ BIF_RETTYPE exit_2(BIF_ALIST_2)
 	     invalid_flags = ERTS_PORT_SFLGS_INVALID_LOOKUP;
 	 }
 
-	 prt = erts_port_lookup(BIF_ARG_1, invalid_flags);
-
-	 if (prt) {
-	     ErtsPortOpResult res;
-
-#ifdef DEBUG
-	     ref = NIL;
-#endif
-
-	     res = erts_port_exit(BIF_P, 0, prt, BIF_P->common.id, BIF_ARG_2, refp);
-
-	     ERTS_BIF_CHK_EXITED(BIF_P);
-
-	     if (refp && res == ERTS_PORT_OP_SCHEDULED) {
-		 ASSERT(is_internal_ordinary_ref(ref));
-		 BIF_TRAP3(await_port_send_result_trap, BIF_P, ref, am_true, am_true);
-	     }
-
-	 }
-
-	 BIF_RET(am_true);
+	 prt = erts_port_lookup(id, invalid_flags);
+	 if (prt)
+	     res = erts_port_exit(c_p, 0, prt, c_p->common.id, reason, refp);
+
+         if (!refp || res != ERTS_PORT_OP_SCHEDULED)
+             ERTS_BIF_PREP_RET(ret_val, am_true);
+         else {
+             ASSERT(is_internal_ordinary_ref(ref));
+             ERTS_BIF_PREP_TRAP3(ret_val, await_port_send_result_trap,
+                                 c_p, ref, am_true, am_true);
+         }
      }
-     else if(is_external_port(BIF_ARG_1)
-	     && external_port_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
-	 BIF_RET(am_true);
-     
-     /*
-      * If it is a remote pid, send a signal to the remote node.
-      */
-
-     if (is_external_pid(BIF_ARG_1)) {
-	 int code;
-	 ErtsDSigData dsd;
-	 DistEntry *dep;
-
-	 dep = external_pid_dist_entry(BIF_ARG_1);
-	 ERTS_ASSERT(dep);
-	 if(dep == erts_this_dist_entry)
-	     BIF_RET(am_true);
-
-	 code = erts_dsig_prepare(&dsd, dep, BIF_P, ERTS_PROC_LOCK_MAIN,
-				  ERTS_DSP_NO_LOCK, 0, 1);
-	 switch (code) {
-	 case ERTS_DSIG_PREP_NOT_ALIVE:
-	 case ERTS_DSIG_PREP_NOT_CONNECTED:
-	     BIF_RET(am_true);
-	 case ERTS_DSIG_PREP_PENDING:
-	 case ERTS_DSIG_PREP_CONNECTED:
-	     code = erts_dsig_send_exit2(&dsd, BIF_P->common.id, BIF_ARG_1, BIF_ARG_2);
-	     if (code == ERTS_DSIG_SEND_YIELD)
-		 ERTS_BIF_YIELD_RETURN(BIF_P, am_true);
-	     BIF_RET(am_true);
-	 default:
-	     ERTS_ASSERT(! "Invalid dsig prepare result");
-	 }
+     else if (is_external_pid(id)) {
+	 DistEntry *dep = external_pid_dist_entry(id);
+	 if (dep == erts_this_dist_entry)
+             ERTS_BIF_PREP_RET(ret_val, am_true); /* Old incarnation of this node... */
+         else {
+             int code;
+             ErtsDSigData dsd;
+
+             code = erts_dsig_prepare(&dsd, dep, c_p, ERTS_PROC_LOCK_MAIN,
+                                      ERTS_DSP_NO_LOCK, 0, 1);
+             switch (code) {
+             case ERTS_DSIG_PREP_NOT_ALIVE:
+             case ERTS_DSIG_PREP_NOT_CONNECTED:
+                 ERTS_BIF_PREP_RET(ret_val, am_true);
+                 break;
+             case ERTS_DSIG_PREP_PENDING:
+             case ERTS_DSIG_PREP_CONNECTED:
+                 code = erts_dsig_send_exit2(&dsd, c_p->common.id, id, reason);
+                 if (code == ERTS_DSIG_SEND_YIELD)
+                     ERTS_BIF_PREP_YIELD_RETURN(ret_val, c_p, am_true);
+                 else
+                     ERTS_BIF_PREP_RET(ret_val, am_true);
+                 break;
+             default:
+                 ASSERT(! "Invalid dsig prepare result");
+                 ERTS_BIF_PREP_ERROR(ret_val, c_p, EXC_INTERNAL_ERROR);
+                 break;
+             }
+         }
      }
-     else if (is_not_internal_pid(BIF_ARG_1)) {
-       BIF_ERROR(BIF_P, BADARG);
+     else if (is_external_port(id)) {
+	 DistEntry *dep = external_port_dist_entry(id);
+	 if(dep == erts_this_dist_entry)
+             ERTS_BIF_PREP_RET(ret_val, am_true); /* Old incarnation of this node... */
+         else
+             ERTS_BIF_PREP_ERROR(ret_val, c_p, BADARG);
      }
      else {
-	 /*
-	  * The pid is internal.  Verify that it refers to an existing process.
-	  */
-	 ErtsProcLocks rp_locks;
-
-	 if (BIF_ARG_1 == BIF_P->common.id) {
-	     rp_locks = ERTS_PROC_LOCKS_ALL;
-	     rp = BIF_P;
-	     erts_proc_lock(rp, ERTS_PROC_LOCKS_ALL_MINOR);
-	 }
-	 else {
-	     rp_locks = ERTS_PROC_LOCKS_XSIG_SEND;
-	     rp = erts_pid2proc(BIF_P, ERTS_PROC_LOCK_MAIN,
-				BIF_ARG_1, rp_locks);
-	     if (!rp) {
-		 BIF_RET(am_true);
-	     }
-	 }
+         /* Not an id of a process or a port... */
 
-	 /*
-	  * Send an exit signal.
-	  */
-	 erts_send_exit_signal(BIF_P,
-			       BIF_P->common.id,
-			       rp,
-			       &rp_locks,
-			       BIF_ARG_2,
-			       NIL,
-			       NULL,
-			       BIF_P == rp ? ERTS_XSIG_FLG_NO_IGN_NORMAL : 0);
-	 if (rp == BIF_P)
-	     rp_locks &= ~ERTS_PROC_LOCK_MAIN;
-	 if (rp_locks)
-	     erts_proc_unlock(rp, rp_locks);
-	 /*
-	  * We may have exited ourselves and may have to take action.
-	  */
-	 ERTS_BIF_CHK_EXITED(BIF_P);
-	 BIF_RET(am_true);
+         ERTS_BIF_PREP_ERROR(ret_val, c_p, BADARG);
      }
+
+     return ret_val;
 }
 
+BIF_RETTYPE exit_2(BIF_ALIST_2)
+{
+    return send_exit_signal_bif(BIF_P, BIF_ARG_1, BIF_ARG_2, !0);
+}
+
+BIF_RETTYPE exit_signal_2(BIF_ALIST_2)
+{
+    return send_exit_signal_bif(BIF_P, BIF_ARG_1, BIF_ARG_2, 0);
+}
+
+
 /**********************************************************************/
 /* this sets some process info- trapping exits or the error handler */
 
@@ -1709,36 +1441,13 @@ BIF_RETTYPE process_flag_2(BIF_ALIST_2)
        BIF_RET(old_value);
    }
    else if (BIF_ARG_1 == am_trap_exit) {
-       erts_aint32_t state;
-       Uint trap_exit;
-       if (BIF_ARG_2 == am_true) {
-	   trap_exit = 1;
-       } else if (BIF_ARG_2 == am_false) {
-	   trap_exit = 0;
-       } else {
-	   goto error;
-       }
-       /*
-	* NOTE: It is important that we check for pending exit signals
-	*       and handle them before returning if trap_exit is set to
-	*       true. For more info, see implementation of
-	*       erts_send_exit_signal().
-	*/
-       erts_proc_lock(BIF_P, ERTS_PROC_LOCKS_XSIG_SEND);
-       if (trap_exit)
-	   state = erts_atomic32_read_bor_mb(&BIF_P->state,
-						 ERTS_PSFLG_TRAP_EXIT);
+       old_value = (BIF_P->flags & F_TRAP_EXIT) ? am_true : am_false;
+       if (BIF_ARG_2 == am_true)
+           BIF_P->flags |= F_TRAP_EXIT;
+       else if (BIF_ARG_2 == am_false)
+           BIF_P->flags &= ~F_TRAP_EXIT;
        else
-	   state = erts_atomic32_read_band_mb(&BIF_P->state,
-						  ~ERTS_PSFLG_TRAP_EXIT);
-       erts_proc_unlock(BIF_P, ERTS_PROC_LOCKS_XSIG_SEND);
-
-       if (state & ERTS_PSFLG_PENDING_EXIT) {
-	   erts_handle_pending_exit(BIF_P, ERTS_PROC_LOCK_MAIN);
-	   ERTS_BIF_EXITED(BIF_P);
-       }
-
-       old_value = (state & ERTS_PSFLG_TRAP_EXIT) ? am_true : am_false;
+	   goto error;
        BIF_RET(old_value);
    }
    else if (BIF_ARG_1 == am_scheduler) {
@@ -2142,9 +1851,6 @@ do_send(Process *p, Eterm to, Eterm msg, Eterm *refp, ErtsSendContext *ctx)
             }
 
 	    switch (erts_port_command(p, ps_flags, pt, msg, refp)) {
-	    case ERTS_PORT_OP_CALLER_EXIT:
-		/* We are exiting... */
-		return SEND_USER_ERROR;
 	    case ERTS_PORT_OP_BUSY:
 		/* Nothing has been sent */
 		if (ctx->suspend)
@@ -4373,14 +4079,88 @@ BIF_RETTYPE group_leader_0(BIF_ALIST_0)
 }
 
 /**********************************************************************/
-/* arg1 == leader, arg2 == new member */
+/* set group leader */
 
-BIF_RETTYPE group_leader_2(BIF_ALIST_2)
+int
+erts_set_group_leader(Process *proc, Eterm new_gl)
 {
-    Process* new_member;
+    
+    erts_aint32_t state;
 
-    if (is_not_pid(BIF_ARG_1)) {
-	BIF_ERROR(BIF_P, BADARG);
+    ASSERT(is_pid(new_gl));
+
+    state = erts_atomic32_read_nob(&proc->state);
+
+    if (state & ERTS_PSFLG_EXITING)
+        return 0;
+        
+    ERTS_LC_ASSERT(ERTS_PROC_LOCK_MAIN & erts_proc_lc_my_proc_locks(proc));
+
+    if (!(state & ERTS_PSFLG_DIRTY_RUNNING))
+        proc->group_leader = STORE_NC_IN_PROC(proc, new_gl);
+    else {
+        ErlHeapFragment *bp;
+        Eterm *hp;
+        /*
+         * Currently executing on a dirty scheduler,
+         * so we are not allowed to write to its heap.
+         * Store group leader pid in heap fragment.
+         */
+        bp = new_message_buffer(NC_HEAP_SIZE(new_gl));
+        hp = bp->mem;
+        proc->group_leader = STORE_NC(&hp,
+                                            &proc->off_heap,
+                                            new_gl);
+        bp->next = proc->mbuf;
+        proc->mbuf = bp;
+        proc->mbuf_sz += bp->used_size;
+    }
+
+    return !0;
+}
+
+BIF_RETTYPE erts_internal_group_leader_3(BIF_ALIST_3)
+{
+    if (is_not_pid(BIF_ARG_1))
+        BIF_ERROR(BIF_P, BADARG);
+    if (is_not_internal_pid(BIF_ARG_2))
+        BIF_ERROR(BIF_P, BADARG);
+    if (is_not_internal_ref(BIF_ARG_3))
+        BIF_ERROR(BIF_P, BADARG);
+
+    erts_proc_sig_send_group_leader(BIF_P,
+                                    BIF_ARG_2,
+                                    BIF_ARG_1,
+                                    BIF_ARG_3);
+    BIF_RET(am_ok);
+}
+
+BIF_RETTYPE erts_internal_group_leader_2(BIF_ALIST_2)
+{
+    if (is_not_pid(BIF_ARG_1))
+        BIF_RET(am_badarg);
+
+    if (is_internal_pid(BIF_ARG_2)) {
+        Process *rp;
+        int res;
+
+        if (BIF_ARG_2 == BIF_P->common.id)
+            rp = BIF_P;
+        else {
+            rp = erts_try_lock_sig_free_proc(BIF_ARG_2,
+                                             ERTS_PROC_LOCK_MAIN);
+            if (!rp)
+                BIF_RET(am_badarg);
+            if (rp == ERTS_PROC_LOCK_BUSY)
+                BIF_RET(am_false);
+        }
+
+        res = erts_set_group_leader(rp, BIF_ARG_1);
+
+        if (rp != BIF_P)
+            erts_proc_unlock(rp, ERTS_PROC_LOCK_MAIN);
+
+        BIF_RET(res ? am_true : am_badarg);
     }
 
     if (is_external_pid(BIF_ARG_2)) {
@@ -4408,74 +4188,8 @@ BIF_RETTYPE group_leader_2(BIF_ALIST_2)
 	    ERTS_ASSERT(! "Invalid dsig prepare result");
 	}
     }
-    else if (is_internal_pid(BIF_ARG_2)) {
-	int await_x;
-	ErtsProcLocks locks = ERTS_PROC_LOCK_MAIN|ERTS_PROC_LOCK_STATUS;
-	new_member = erts_pid2proc_nropt(BIF_P, ERTS_PROC_LOCK_MAIN,
-					 BIF_ARG_2, locks);
-	if (!new_member)
-	    BIF_ERROR(BIF_P, BADARG);
-
-	if (new_member == ERTS_PROC_LOCK_BUSY)
-	    ERTS_BIF_YIELD2(bif_export[BIF_group_leader_2], BIF_P,
-			    BIF_ARG_1, BIF_ARG_2);
-
-	await_x = (new_member != BIF_P
-		   && ERTS_PROC_PENDING_EXIT(new_member));
-	if (!await_x) {
-	    if (is_immed(BIF_ARG_1))
-		new_member->group_leader = BIF_ARG_1;
-	    else {
-		locks &= ~ERTS_PROC_LOCK_STATUS;
-		erts_proc_unlock(new_member, ERTS_PROC_LOCK_STATUS);
-		if (new_member == BIF_P
-		    || !(erts_atomic32_read_nob(&new_member->state)
-			 & ERTS_PSFLG_DIRTY_RUNNING)) {
-		    new_member->group_leader = STORE_NC_IN_PROC(new_member,
-								BIF_ARG_1);
-		}
-		else {
-		    ErlHeapFragment *bp;
-		    Eterm *hp;
-		    /*
-		     * Other process executing on a dirty scheduler,
-		     * so we are not allowed to write to its heap.
-		     * Store in heap fragment.
-		     */
-
-		    bp = new_message_buffer(NC_HEAP_SIZE(BIF_ARG_1));
-		    hp = bp->mem;
-		    new_member->group_leader = STORE_NC(&hp,
-							&new_member->off_heap,
-							BIF_ARG_1);
-		    bp->next = new_member->mbuf;
-		    new_member->mbuf = bp;
-		    new_member->mbuf_sz += bp->used_size;
-		}
-	    }
-	}
-
-	if (new_member == BIF_P)
-	    locks &= ~ERTS_PROC_LOCK_MAIN;
-	if (locks)
-	    erts_proc_unlock(new_member, locks);
-
-	if (await_x) {
-	    /* Wait for new_member to terminate; then badarg */
-	    Eterm args[2] = {BIF_ARG_1, BIF_ARG_2};
-	    ERTS_BIF_AWAIT_X_APPLY_TRAP(BIF_P,
-					BIF_ARG_2,
-					am_erlang,
-					am_group_leader,
-					args,
-					2);
-	}
 
-	BIF_RET(am_true);
-    }
-    else {
-	BIF_ERROR(BIF_P, BADARG);
-    }
+    BIF_RET(am_badarg);
 }
 
 BIF_RETTYPE system_flag_2(BIF_ALIST_2)    
@@ -4662,7 +4376,6 @@ BIF_RETTYPE system_flag_2(BIF_ALIST_2)
         BIF_RET(ret);
     } else if (BIF_ARG_1 == make_small(1)) {
 	int i, max;
-	ErtsMessage* mp;
 	erts_proc_unlock(BIF_P, ERTS_PROC_LOCK_MAIN);
 	erts_thr_progress_block();
 
@@ -4677,16 +4390,8 @@ BIF_RETTYPE system_flag_2(BIF_ALIST_2)
 #endif
 		p->seq_trace_clock = 0;
 		p->seq_trace_lastcnt = 0;
-		ERTS_MSGQ_MV_INQ2PRIVQ(p);
-		mp = p->msg.first;
-		while(mp != NULL) {
-#ifdef USE_VM_PROBES
-		    ERL_MESSAGE_TOKEN(mp) = (ERL_MESSAGE_DT_UTAG(mp) != NIL) ? am_have_dt_utag : NIL;
-#else
-		    ERL_MESSAGE_TOKEN(mp) = NIL;
-#endif
-		    mp = mp->next;
-		}
+
+                erts_proc_sig_clear_seq_trace_tokens(p);
 	    }
 	}
 
@@ -4949,58 +4654,17 @@ static BIF_RETTYPE bif_return_trap(BIF_ALIST_2)
     BIF_RET(res);
 }
 
-/*
- * NOTE: The erts_bif_prep_await_proc_exit_*() functions are
- * tightly coupled with the implementation of erlang:await_proc_exit/3.
- * The erts_bif_prep_await_proc_exit_*() functions can safely call
- * skip_current_msgq() since they know that erlang:await_proc_exit/3
- * unconditionally will do a monitor and then unconditionally will
- * wait for the corresponding 'DOWN' message in a receive, and no other
- * receive is done before this receive. This optimization removes an
- * unnecessary scan of the currently existing message queue (which
- * can be large). If the erlang:await_proc_exit/3 implementation
- * is changed so that the above isn't true, nasty bugs in later
- * receives, etc, may appear.
- */
-
-static ERTS_INLINE int
-skip_current_msgq(Process *c_p)
-{
-    int res;
-#if defined(ERTS_ENABLE_LOCK_CHECK)
-    erts_proc_lc_chk_only_proc_main(c_p);
-#endif
-
-    erts_proc_lock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-    if (ERTS_PROC_PENDING_EXIT(c_p)) {
-	KILL_CATCHES(c_p);
-	c_p->freason = EXC_EXIT;
-	res = 0;
-    }
-    else {
-        ERTS_MSGQ_MV_INQ2PRIVQ(c_p);
-	c_p->msg.save = c_p->msg.last;
-	res = 1;
-    }
-    erts_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-    return res;
-}
-
 void
 erts_bif_prep_await_proc_exit_data_trap(Process *c_p, Eterm pid, Eterm ret)
 {
-    if (skip_current_msgq(c_p)) {
-	ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_data, ret);
-    }
+    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_data, ret);
 }
 
 void
 erts_bif_prep_await_proc_exit_reason_trap(Process *c_p, Eterm pid)
 {
-    if (skip_current_msgq(c_p)) {
-	ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p,
-			    pid, am_reason, am_undefined);
-    }
+    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p,
+                               pid, am_reason, am_undefined);
 }
 
 void
@@ -5011,21 +4675,19 @@ erts_bif_prep_await_proc_exit_apply_trap(Process *c_p,
 					 Eterm args[],
 					 int nargs)
 {
+    Eterm term;
+    Eterm *hp;
+    int i;
     ASSERT(is_atom(module) && is_atom(function));
-    if (skip_current_msgq(c_p)) {
-	Eterm term;
-	Eterm *hp;
-	int i;
 
-	hp = HAlloc(c_p, 4+2*nargs);
-	term = NIL;
-	for (i = nargs-1; i >= 0; i--) {
-	    term = CONS(hp, args[i], term);
-	    hp += 2;
-	}
-	term = TUPLE3(hp, module, function, term);
-	ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_apply, term);
+    hp = HAlloc(c_p, 4+2*nargs);
+    term = NIL;
+    for (i = nargs-1; i >= 0; i--) {
+        term = CONS(hp, args[i], term);
+        hp += 2;
     }
+    term = TUPLE3(hp, module, function, term);
+    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_apply, term);
 }
 
 Export bif_return_trap_export;
@@ -5063,6 +4725,9 @@ void erts_init_bif(void)
 			  am_erts_internal, am_dsend_continue_trap, 1,
 			  dsend_continue_trap_1);
 
+    erts_init_trap_export(&await_exit_trap, am_erts_internal,
+                          am_await_exit, 0, erts_internal_await_exit_trap);
+
     flush_monitor_messages_trap = erts_export_put(am_erts_internal,
 						  am_flush_monitor_messages,
 						  3);