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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 180 insertions, 193 deletions

diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index c60cc7fecf..cd4fd7b635 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 2009-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2009-2018. 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.
@@ -57,6 +57,7 @@
 #include "erl_bif_unique.h"
 #include "erl_utils.h"
 #include "erl_io_queue.h"
+#include "erl_proc_sig_queue.h"
 #undef ERTS_WANT_NFUNC_SCHED_INTERNALS__
 #define ERTS_WANT_NFUNC_SCHED_INTERNALS__
 #include "erl_nfunc_sched.h"
@@ -658,7 +659,7 @@ int erts_flush_trace_messages(Process *c_p, ErtsProcLocks c_p_locks)
             rp_locks = 0;
             if (rp->common.id == c_p->common.id)
                 rp_locks = c_p_locks;
-            erts_queue_messages(rp, rp_locks, first, last, len, c_p->common.id);
+            erts_queue_messages(rp, rp_locks, first, last, len);
             if (rp->common.id == c_p->common.id)
                 rp_locks &= ~c_p_locks;
             if (rp_locks)
@@ -700,6 +701,7 @@ int enif_send(ErlNifEnv* env, const ErlNifPid* to_pid,
     Process* rp;
     Process* c_p;
     ErtsMessage *mp;
+    Eterm from;
     Eterm receiver = to_pid->pid;
     int scheduler;
 
@@ -778,7 +780,7 @@ int enif_send(ErlNifEnv* env, const ErlNifPid* to_pid,
         msg = copy_struct_litopt(msg, sz, &hp, ohp, &litarea);
     }
 
-    ERL_MESSAGE_TERM(mp) = msg;
+    from = c_p ? c_p->common.id : am_undefined;
 
     if (!env || !env->tracee) {
 
@@ -797,7 +799,6 @@ int enif_send(ErlNifEnv* env, const ErlNifPid* to_pid,
         ErlTraceMessageQueue *msgq;
         Process *t_p = env->tracee;
 
-
         erts_proc_lock(t_p, ERTS_PROC_LOCK_TRACE);
 
         msgq = t_p->trace_msg_q;
@@ -817,6 +818,9 @@ int enif_send(ErlNifEnv* env, const ErlNifPid* to_pid,
             rp_locks & ERTS_PROC_LOCK_MSGQ ||
             erts_proc_trylock(rp, ERTS_PROC_LOCK_MSGQ) == EBUSY) {
 
+            ERL_MESSAGE_TERM(mp) = msg;
+            ERL_MESSAGE_FROM(mp) = from;
+
             if (!msgq) {
                 msgq = erts_alloc(ERTS_ALC_T_TRACE_MSG_QUEUE,
                                   sizeof(ErlTraceMessageQueue));
@@ -846,8 +850,7 @@ int enif_send(ErlNifEnv* env, const ErlNifPid* to_pid,
         }
     }
 
-    erts_queue_message(rp, rp_locks, mp, msg,
-                       c_p ? c_p->common.id : am_undefined);
+    erts_queue_message(rp, rp_locks, mp, msg, from);
 
 done:
     if (c_p == rp)
@@ -2206,71 +2209,61 @@ static void rollback_opened_resource_types(void)
     }
 }
 
-struct destroy_monitor_ctx
-{
-    ErtsResource* resource;
-    int exiting_procs;
-    int scheduler;
-};
+#ifdef ARCH_64
+#  define ERTS_RESOURCE_DYING_FLAG (((Uint) 1) << 63)
+#else
+#  define ERTS_RESOURCE_DYING_FLAG (((Uint) 1) << 31)
+#endif
+#define ERTS_RESOURCE_REFC_MASK (~ERTS_RESOURCE_DYING_FLAG)
 
-static void destroy_one_monitor(ErtsMonitor* mon, void* context)
+static ERTS_INLINE void
+rmon_set_dying(ErtsResourceMonitors *rms)
 {
-    struct destroy_monitor_ctx* ctx = (struct destroy_monitor_ctx*) context;
-    Process* rp;
-    ErtsMonitor *rmon = NULL;
-    int is_exiting;
+    rms->refc |= ERTS_RESOURCE_DYING_FLAG;
+}
 
-    ASSERT(mon->type == MON_ORIGIN);
-    ASSERT(is_internal_pid(mon->u.pid));
-    ASSERT(is_internal_ref(mon->ref));
+static ERTS_INLINE int
+rmon_is_dying(ErtsResourceMonitors *rms)
+{
+    return !!(rms->refc & ERTS_RESOURCE_DYING_FLAG);
+}
 
-    if (ctx->scheduler > 0) { /* Normal scheduler */
-        rp = erts_proc_lookup(mon->u.pid);
-    }
-    else {
-        rp = erts_proc_lookup_inc_refc(mon->u.pid);
-    }
+static ERTS_INLINE void
+rmon_refc_inc(ErtsResourceMonitors *rms)
+{
+    rms->refc++;
+}
 
-    if (!rp) {
-        is_exiting = 1;
-    }
-    if (rp) {
-        erts_proc_lock(rp, ERTS_PROC_LOCK_LINK);
-        if (ERTS_PROC_IS_EXITING(rp)) {
-            is_exiting = 1;
-        } else {
-            rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), mon->ref);
-            ASSERT(rmon);
-            is_exiting = 0;
-        }
-        erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-        if (ctx->scheduler <= 0)
-            erts_proc_dec_refc(rp);
-    }
-    if (is_exiting) {
-        ctx->resource->monitors->pending_failed_fire++;
-    }
+static ERTS_INLINE Uint
+rmon_refc_dec_read(ErtsResourceMonitors *rms)
+{
+    Uint res;
+    ASSERT((rms->refc & ERTS_RESOURCE_REFC_MASK) != 0);
+    res = --rms->refc;
+    return res & ERTS_RESOURCE_REFC_MASK;
+}
 
-    /* ToDo: Delay destruction after monitor_locks */
-    if (rmon) {
-        ASSERT(rmon->type == MON_NIF_TARGET);
-        ASSERT(rmon->u.resource == ctx->resource);
-        erts_destroy_monitor(rmon);
-    }
-    erts_destroy_monitor(mon);
+static ERTS_INLINE void
+rmon_refc_dec(ErtsResourceMonitors *rms)
+{
+    ASSERT((rms->refc & ERTS_RESOURCE_REFC_MASK) != 0);
+    --rms->refc;
 }
 
-static void destroy_all_monitors(ErtsMonitor* monitors, ErtsResource* resource)
+static ERTS_INLINE Uint
+rmon_refc_read(ErtsResourceMonitors *rms)
 {
-    struct destroy_monitor_ctx ctx;
+    return rms->refc & ERTS_RESOURCE_REFC_MASK;
+}
 
-    execution_state(NULL, NULL, &ctx.scheduler);
+static void dtor_demonitor(ErtsMonitor* mon, void* context)
+{
+    ASSERT(erts_monitor_is_origin(mon));
+    ASSERT(is_internal_pid(mon->other.item));
 
-    ctx.resource = resource;
-    erts_sweep_monitors(monitors, &destroy_one_monitor, &ctx);
+    erts_proc_sig_send_demonitor(mon);
 }
 
-
 #  define NIF_RESOURCE_DTOR &nif_resource_dtor
 
 static int nif_resource_dtor(Binary* bin)
@@ -2281,34 +2274,36 @@ static int nif_resource_dtor(Binary* bin)
 
     if (resource->monitors) {
         ErtsResourceMonitors* rm = resource->monitors;
+        int kill;
+        ErtsMonitor *root;
+        Uint refc;
 
         ASSERT(type->down);
         erts_mtx_lock(&rm->lock);
         ASSERT(erts_refc_read(&bin->intern.refc, 0) == 0);
-        if (rm->root) {
-            ASSERT(!rm->is_dying);
-            destroy_all_monitors(rm->root, resource);
+        kill = !rmon_is_dying(rm);
+        if (kill) {
+            rmon_set_dying(rm);
+            root = rm->root;
             rm->root = NULL;
         }
-        if (rm->pending_failed_fire) {
-            /*
-             * Resource death struggle prolonged to serve exiting process(es).
-             * Destructor will be called again when last exiting process
-             * tries to fire its MON_NIF_TARGET monitor (and fails).
-             *
-             * This resource is doomed. It has no "real" references and
-             * should get not get called upon to do anything except the
-             * final destructor call.
-             *
-             * We keep refc at 0 and use a separate counter for exiting
-             * processes to avoid resource getting revived by "dec_term".
-             */
-            ASSERT(!rm->is_dying);
-            rm->is_dying = 1;
-            erts_mtx_unlock(&rm->lock);
-            return 0;
-        }
+        refc = rmon_refc_read(rm);
         erts_mtx_unlock(&rm->lock);
+
+        if (kill)
+            erts_monitor_tree_foreach_delete(&root,
+                                             dtor_demonitor,
+                                             NULL);
+
+        /*
+         * If resource->monitors->refc != 0 there are
+         * outstanding references to the resource from
+         * monitors that has not been removed yet.
+         * nif_resource_dtor() will be called again this
+         * reference count reach zero.
+         */
+        if (refc != 0)
+            return 0; /* we'll be back... */
         erts_mtx_destroy(&rm->lock);
     }
 
@@ -2338,54 +2333,82 @@ void erts_resource_stop(ErtsResource* resource, ErlNifEvent e,
     post_nif_noproc(&msg_env);
 }
 
-void erts_fire_nif_monitor(ErtsResource* resource, Eterm pid, Eterm ref)
+void erts_nif_demonitored(ErtsResource* resource)
 {
-    ErtsMonitor* rmon;
+    ErtsResourceMonitors* rmp = resource->monitors;
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
+    int free_me;
+
+    ASSERT(rmp);
+    ASSERT(resource->type->down);
+
+    erts_mtx_lock(&rmp->lock);
+    free_me = ((rmon_refc_dec_read(rmp) == 0) & !!rmon_is_dying(rmp));
+    erts_mtx_unlock(&rmp->lock);
+
+    if (free_me)
+        erts_bin_free(&bin->binary);
+}
+
+void erts_fire_nif_monitor(ErtsMonitor *tmon)
+{
+    ErtsResource* resource;
+    ErtsMonitorData *mdp;
+    ErtsMonitor *omon;
+    ErtsBinary* bin;
     struct enif_msg_environment_t msg_env;
     ErlNifPid nif_pid;
     ErlNifMonitor nif_monitor;
-    ErtsResourceMonitors* rmp = resource->monitors;
+    ErtsResourceMonitors* rmp;
+    Uint mrefc, brefc;
+    int active, is_dying;
+
+    ASSERT(tmon->type == ERTS_MON_TYPE_RESOURCE);
+    ASSERT(erts_monitor_is_target(tmon));
+
+    resource = tmon->other.ptr;
+    bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
+    rmp = resource->monitors;
+
+    mdp = erts_monitor_to_data(tmon);
+    omon = &mdp->origin;
 
     ASSERT(rmp);
     ASSERT(resource->type->down);
 
     erts_mtx_lock(&rmp->lock);
-    rmon = erts_remove_monitor(&rmp->root, ref);
-    if (!rmon) {
-        int free_me = (--rmp->pending_failed_fire == 0) && rmp->is_dying;
-        ASSERT(rmp->pending_failed_fire >= 0);
-        erts_mtx_unlock(&rmp->lock);
-
-        if (free_me) {
-            ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) == 0);
-            erts_bin_free(&bin->binary);
-        }
-        return;
+
+    mrefc = rmon_refc_dec_read(rmp);
+    is_dying = rmon_is_dying(rmp);
+    active = !is_dying && erts_monitor_is_in_table(omon);
+
+    if (active) {
+        erts_monitor_tree_delete(&rmp->root, omon);
+        brefc = (Uint) erts_refc_inc_unless(&bin->binary.intern.refc, 0, 0);
     }
-    ASSERT(!rmp->is_dying);
-    if (erts_refc_inc_unless(&bin->binary.intern.refc, 0, 0) == 0) {
-        /*
-         * Racing resource destruction. 
-         * To avoid a more complex refc-dance with destructing thread
-         * we avoid calling 'down' and just silently remove the monitor.
-         * This can happen even for non smp as destructor calls may be scheduled.
-         */
-        erts_mtx_unlock(&rmp->lock);
+
+    erts_mtx_unlock(&rmp->lock);
+
+    if (!active) {
+        ASSERT(!is_dying || erts_refc_read(&bin->binary.intern.refc, 0) == 0);
+        if (is_dying && mrefc == 0)
+            erts_bin_free(&bin->binary);
+        erts_monitor_release(tmon);
     }
     else {
-        erts_mtx_unlock(&rmp->lock);
-
-        ASSERT(rmon->u.pid == pid);
-        erts_ref_to_driver_monitor(ref, &nif_monitor);
-        nif_pid.pid = pid;
-        pre_nif_noproc(&msg_env, resource->type->owner, NULL);
-        resource->type->down(&msg_env.env, resource->data, &nif_pid, &nif_monitor);
-        post_nif_noproc(&msg_env);
+        if (brefc > 0) {
+            ASSERT(is_internal_pid(omon->other.item));
+            erts_ref_to_driver_monitor(mdp->ref, &nif_monitor);
+            nif_pid.pid = omon->other.item;
+            pre_nif_noproc(&msg_env, resource->type->owner, NULL);
+            resource->type->down(&msg_env.env, resource->data, &nif_pid, &nif_monitor);
+            post_nif_noproc(&msg_env);
+
+            erts_bin_release(&bin->binary);
+        }
 
-        erts_bin_release(&bin->binary);
+        erts_monitor_release_both(mdp);
     }
-    erts_destroy_monitor(rmon);
 }
 
 void* enif_alloc_resource(ErlNifResourceType* type, size_t data_sz)
@@ -2422,8 +2445,7 @@ void* enif_alloc_resource(ErlNifResourceType* type, size_t data_sz)
         erts_mtx_init(&resource->monitors->lock, "resource_monitors", NIL,
             ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
         resource->monitors->root = NULL;
-        resource->monitors->pending_failed_fire = 0;
-        resource->monitors->is_dying = 0;
+        resource->monitors->refc = 0;
         resource->monitors->user_data_sz = data_sz;
     }
     else {
@@ -2438,7 +2460,7 @@ void enif_release_resource(void* obj)
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
 
     ASSERT(ERTS_MAGIC_BIN_DESTRUCTOR(bin) == NIF_RESOURCE_DTOR);
-    ASSERT(!(resource->monitors && resource->monitors->is_dying));
+    ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) != 0);
 #ifdef DEBUG
     erts_refc_dec(&resource->nif_refc, 0);
 #endif
@@ -2451,7 +2473,7 @@ void enif_keep_resource(void* obj)
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
 
     ASSERT(ERTS_MAGIC_BIN_DESTRUCTOR(bin) == NIF_RESOURCE_DTOR);
-    ASSERT(!(resource->monitors && resource->monitors->is_dying));
+    ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) != 0);
 #ifdef DEBUG
     erts_refc_inc(&resource->nif_refc, 1);
 #endif
@@ -2461,7 +2483,7 @@ void enif_keep_resource(void* obj)
 Eterm erts_bld_resource_ref(Eterm** hpp, ErlOffHeap* oh, ErtsResource* resource)
 {
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
-    ASSERT(!(resource->monitors && resource->monitors->is_dying));
+    ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) != 0);
     return erts_mk_magic_ref(hpp, oh, &bin->binary);
 }
 
@@ -2470,7 +2492,7 @@ ERL_NIF_TERM enif_make_resource(ErlNifEnv* env, void* obj)
     ErtsResource* resource = DATA_TO_RESOURCE(obj);
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(resource);
     Eterm* hp = alloc_heap(env, ERTS_MAGIC_REF_THING_SIZE);
-    ASSERT(!(resource->monitors && resource->monitors->is_dying));
+    ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) != 0);
     return erts_mk_magic_ref(&hp, &MSO(env->proc), &bin->binary);
 }
 
@@ -3150,123 +3172,88 @@ int enif_map_iterator_get_pair(ErlNifEnv *env,
 int enif_monitor_process(ErlNifEnv* env, void* obj, const ErlNifPid* target_pid,
                          ErlNifMonitor* monitor)
 {
-    int scheduler;
     ErtsResource* rsrc = DATA_TO_RESOURCE(obj);
-    Process *rp;
     Eterm tmp[ERTS_REF_THING_SIZE];
     Eterm ref;
-    int retval;
+    ErtsResourceMonitors *rm;
+    ErtsMonitorData *mdp;
 
     ASSERT(ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(rsrc)->magic_binary.destructor
            == NIF_RESOURCE_DTOR);
-    ASSERT(!(rsrc->monitors && rsrc->monitors->is_dying));
+    ASSERT(erts_refc_read(&ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(rsrc)->binary.intern.refc, 0) != 0);
     ASSERT(!rsrc->monitors == !rsrc->type->down);
 
-
-    if (!rsrc->monitors) {
+    rm = rsrc->monitors;
+    if (!rm) {
         ASSERT(!rsrc->type->down);
         return -1;
     }
     ASSERT(rsrc->type->down);
 
-    execution_state(env, NULL, &scheduler);
+    ref = erts_make_ref_in_buffer(tmp);
 
-    if (scheduler > 0) /* Normal scheduler */
-        rp = erts_proc_lookup_raw(target_pid->pid);
-    else
-        rp = erts_proc_lookup_raw_inc_refc(target_pid->pid);
+    mdp = erts_monitor_create(ERTS_MON_TYPE_RESOURCE, ref,
+                              (Eterm) rsrc, target_pid->pid, NIL);
+    erts_mtx_lock(&rm->lock);
+    ASSERT(!rmon_is_dying(rm));
+    erts_monitor_tree_insert(&rm->root, &mdp->origin);
+    rmon_refc_inc(rm);
+    erts_mtx_unlock(&rm->lock);
 
-    if (!rp)
-        return 1;
+    if (!erts_proc_sig_send_monitor(&mdp->target, target_pid->pid)) {
+        /* Failed to send monitor signal; cleanup... */
+#ifdef DEBUG
+        ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(rsrc);
+#endif
 
-    ref = erts_make_ref_in_buffer(tmp);
+        erts_mtx_lock(&rm->lock);
+        ASSERT(!rmon_is_dying(rm));
+        erts_monitor_tree_delete(&rm->root, &mdp->origin);
+        rmon_refc_dec(rm);
+        ASSERT(erts_refc_read(&bin->binary.intern.refc, 1) != 0);
+        erts_mtx_unlock(&rm->lock);
+        erts_monitor_release_both(mdp);
 
-    erts_mtx_lock(&rsrc->monitors->lock);
-    erts_proc_lock(rp, ERTS_PROC_LOCK_LINK);
-    if (ERTS_PSFLG_FREE & erts_atomic32_read_nob(&rp->state)) {
-        retval = 1;
-    }
-    else {
-        erts_add_monitor(&rsrc->monitors->root, MON_ORIGIN, ref, rp->common.id, NIL);
-        erts_add_monitor(&ERTS_P_MONITORS(rp), MON_NIF_TARGET, ref, (UWord)rsrc, NIL);
-        retval = 0;
+        return 1;
     }
-    erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
-    erts_mtx_unlock(&rsrc->monitors->lock);
 
-    if (scheduler <= 0)
-        erts_proc_dec_refc(rp);
     if (monitor)
         erts_ref_to_driver_monitor(ref,monitor);
 
-    return retval;
+    return 0;
 }
 
 int enif_demonitor_process(ErlNifEnv* env, void* obj, const ErlNifMonitor* monitor)
 {
-    int scheduler;
     ErtsResource* rsrc = DATA_TO_RESOURCE(obj);
 #ifdef DEBUG
     ErtsBinary* bin = ERTS_MAGIC_BIN_FROM_UNALIGNED_DATA(rsrc);
 #endif
-    Process *rp;
+    ErtsResourceMonitors *rm;
     ErtsMonitor *mon;
-    ErtsMonitor *rmon = NULL;
     Eterm ref_heap[ERTS_REF_THING_SIZE];
     Eterm ref;
-    int is_exiting;
 
     ASSERT(bin->magic_binary.destructor == NIF_RESOURCE_DTOR);
-    ASSERT(!(rsrc->monitors && rsrc->monitors->is_dying));
-
-    execution_state(env, NULL, &scheduler);
+    ASSERT(erts_refc_read(&bin->binary.intern.refc, 0) != 0);
 
     ref = erts_driver_monitor_to_ref(ref_heap, monitor);
 
-    erts_mtx_lock(&rsrc->monitors->lock);
-    mon = erts_remove_monitor(&rsrc->monitors->root, ref);
+    rm = rsrc->monitors;
+    erts_mtx_lock(&rm->lock);
+    ASSERT(!rmon_is_dying(rm));
+    mon = erts_monitor_tree_lookup(rm->root, ref);
+    if (mon)
+        erts_monitor_tree_delete(&rm->root, mon);
+    erts_mtx_unlock(&rm->lock);
 
-    if (mon == NULL) {
-        erts_mtx_unlock(&rsrc->monitors->lock);
+    if (!mon)
         return 1;
-    }
-
-    ASSERT(mon->type == MON_ORIGIN);
-    ASSERT(is_internal_pid(mon->u.pid));
-
-    if (scheduler > 0) /* Normal scheduler */
-        rp = erts_proc_lookup(mon->u.pid);
-    else
-        rp = erts_proc_lookup_inc_refc(mon->u.pid);
-
-    if (!rp) {
-        is_exiting = 1;
-    }
-    else {
-        erts_proc_lock(rp, ERTS_PROC_LOCK_LINK);
-        if (ERTS_PROC_IS_EXITING(rp)) {
-            is_exiting = 1;
-        } else {
-            rmon = erts_remove_monitor(&ERTS_P_MONITORS(rp), ref);
-            ASSERT(rmon);
-            is_exiting = 0;
-        }
-        erts_proc_unlock(rp, ERTS_PROC_LOCK_LINK);
 
-        if (scheduler <= 0)
-            erts_proc_dec_refc(rp);
-    }
-    if (is_exiting) {
-        rsrc->monitors->pending_failed_fire++;
-    }
-    erts_mtx_unlock(&rsrc->monitors->lock);
+    ASSERT(erts_monitor_is_origin(mon));
+    ASSERT(is_internal_pid(mon->other.item));
 
-    if (rmon) {
-        ASSERT(rmon->type == MON_NIF_TARGET);
-        ASSERT(rmon->u.resource == rsrc);
-        erts_destroy_monitor(rmon);
-    }
-    erts_destroy_monitor(mon);
+    erts_proc_sig_send_demonitor(mon);
 
     return 0;
 }