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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 69 insertions, 68 deletions

diff --git a/erts/emulator/beam/break.c b/erts/emulator/beam/break.c
index 3967f7f7fc..4dabac3512 100644
--- a/erts/emulator/beam/break.c
+++ b/erts/emulator/beam/break.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.
@@ -39,6 +39,7 @@
 #include "erl_instrument.h"
 #include "erl_hl_timer.h"
 #include "erl_thr_progress.h"
+#include "erl_proc_sig_queue.h"
 
 /* Forward declarations -- should really appear somewhere else */
 static void process_killer(void);
@@ -107,36 +108,11 @@ process_killer(void)
 		if ((j = sys_get_key(0)) <= 0)
 		    erts_exit(0, "");
 		switch(j) {
-		case 'k': {
-		    ErtsProcLocks rp_locks = ERTS_PROC_LOCKS_XSIG_SEND;
-		    erts_aint32_t state;
-		    erts_proc_inc_refc(rp);
-		    erts_proc_lock(rp, rp_locks);
-		    state = erts_atomic32_read_acqb(&rp->state);
-		    if (state & (ERTS_PSFLG_FREE
-				 | ERTS_PSFLG_EXITING
-				 | ERTS_PSFLG_ACTIVE
-				 | ERTS_PSFLG_ACTIVE_SYS
-				 | ERTS_PSFLG_IN_RUNQ
-				 | ERTS_PSFLG_RUNNING
-				 | ERTS_PSFLG_RUNNING_SYS
-				 | ERTS_PSFLG_DIRTY_RUNNING
-				 | ERTS_PSFLG_DIRTY_RUNNING_SYS)) {
-			erts_printf("Can only kill WAITING processes this way\n");
-		    }
-		    else {
-			(void) erts_send_exit_signal(NULL,
-						     NIL,
-						     rp,
-						     &rp_locks,
-						     am_kill,
-						     NIL,
-						     NULL,
-						     0);
-		    }
-		    erts_proc_unlock(rp, rp_locks);
-		    erts_proc_dec_refc(rp);
-		}
+		case 'k':
+                    /* Send a 'kill' exit signal from init process */
+                    erts_proc_sig_send_exit(NULL, erts_init_process_id,
+                                            rp->common.id, am_kill, NIL,
+                                            0);
 		case 'n': br = 1; break;
 		case 'r': return;
 		default: return;
@@ -161,47 +137,64 @@ static void doit_print_link(ErtsLink *lnk, void *vpcontext)
 
     if (pcontext->is_first) {
 	pcontext->is_first = 0;
-	erts_print(to, to_arg, "%T", lnk->pid);
+	erts_print(to, to_arg, "%T", lnk->other.item);
     } else {
-	erts_print(to, to_arg, ", %T", lnk->pid);
+	erts_print(to, to_arg, ", %T", lnk->other.item);
     }
 }
     
 
 static void doit_print_monitor(ErtsMonitor *mon, void *vpcontext)
 {
+    ErtsMonitorData *mdp;
     PrintMonitorContext *pcontext = vpcontext;
     fmtfn_t to = pcontext->to;
     void *to_arg = pcontext->to_arg;
     char *prefix = ", ";
  
-    if (pcontext->is_first) {
-	pcontext->is_first = 0;
-	prefix = "";
-    }
-
+    mdp = erts_monitor_to_data(mon);
     switch (mon->type) {
-    case MON_ORIGIN:
-	if (is_atom(mon->u.pid)) { /* dist by name */
-	    ASSERT(is_node_name_atom(mon->u.pid));
-	    erts_print(to, to_arg, "%s{to,{%T,%T},%T}", prefix, mon->name,
-		       mon->u.pid, mon->ref);
-	} else if (is_atom(mon->name)){ /* local by name */
-	    erts_print(to, to_arg, "%s{to,{%T,%T},%T}", prefix, mon->name,
-		       erts_this_dist_entry->sysname, mon->ref);
-	} else { /* local and distributed by pid */
-	    erts_print(to, to_arg, "%s{to,%T,%T}", prefix, mon->u.pid, mon->ref);
-	}
-	break;
-    case MON_TARGET:
-	erts_print(to, to_arg, "%s{from,%T,%T}", prefix, mon->u.pid, mon->ref);
-	break;
-    case MON_NIF_TARGET: {
-        ErtsResource* rsrc = mon->u.resource;
-        erts_print(to, to_arg, "%s{from,{%T,%T},%T}", prefix, rsrc->type->module,
-                   rsrc->type->name, mon->ref);
-	break;
-    }
+    case ERTS_MON_TYPE_PROC:
+    case ERTS_MON_TYPE_PORT:
+    case ERTS_MON_TYPE_TIME_OFFSET:
+    case ERTS_MON_TYPE_DIST_PROC:
+    case ERTS_MON_TYPE_RESOURCE:
+    case ERTS_MON_TYPE_NODE:
+
+        if (pcontext->is_first) {
+            pcontext->is_first = 0;
+            prefix = "";
+        }
+
+        if (erts_monitor_is_target(mon)) {
+            if (mon->type != ERTS_MON_TYPE_RESOURCE)
+                erts_print(to, to_arg, "%s{from,%T,%T}", prefix, mon->other.item, mdp->ref);
+            else {
+                ErtsResource* rsrc = mon->other.ptr;
+                erts_print(to, to_arg, "%s{from,{%T,%T},%T}", prefix, rsrc->type->module,
+                           rsrc->type->name, mdp->ref);
+            }
+        }
+        else {
+            if (!(mon->flags & ERTS_ML_FLG_NAME))
+                erts_print(to, to_arg, "%s{to,%T,%T}", prefix, mon->other.item, mdp->ref);
+            else {
+                ErtsMonitorDataExtended *mdep = (ErtsMonitorDataExtended *) mdp;
+                Eterm node;
+                if (mdep->dist)
+                    node = mdep->dist->nodename;
+                else
+                    node = erts_this_dist_entry->sysname;
+                erts_print(to, to_arg, "%s{to,{%T,%T},%T}", prefix, mdep->u.name,
+                           node, mdp->ref);
+            }
+        }
+
+        break;
+
+    default:
+        /* ignore other monitors... */
+        break;
     }
 }
 			       
@@ -257,15 +250,22 @@ print_process_info(fmtfn_t to, void *to_arg, Process *p)
     }
 
     erts_print(to, to_arg, "Spawned by: %T\n", p->parent);
-    ERTS_MSGQ_MV_INQ2PRIVQ(p);
-    erts_print(to, to_arg, "Message queue length: %d\n", p->msg.len);
+
+    erts_proc_lock(p, ERTS_PROC_LOCK_MSGQ);
+    erts_proc_sig_fetch(p);
+    erts_proc_unlock(p, ERTS_PROC_LOCK_MSGQ);
+    erts_print(to, to_arg, "Message queue length: %d\n", p->sig_qs.len);
 
     /* display the message queue only if there is anything in it */
-    if (!ERTS_IS_CRASH_DUMPING && p->msg.first != NULL && !garbing) {
-	ErtsMessage* mp;
+    if (!ERTS_IS_CRASH_DUMPING && p->sig_qs.first != NULL && !garbing) {
 	erts_print(to, to_arg, "Message queue: [");
-	for (mp = p->msg.first; mp; mp = mp->next)
-	    erts_print(to, to_arg, mp->next ? "%T," : "%T", ERL_MESSAGE_TERM(mp));
+        ERTS_FOREACH_SIG_PRIVQS(
+            p, mp,
+            {
+                if (ERTS_SIG_IS_NON_MSG((ErtsSignal *) mp))
+                    erts_print(to, to_arg, mp->next ? "%T," : "%T",
+                               ERL_MESSAGE_TERM(mp));
+            });
 	erts_print(to, to_arg, "]\n");
     }
 
@@ -306,11 +306,12 @@ print_process_info(fmtfn_t to, void *to_arg, Process *p)
     }
 
     /* display the links only if there are any*/
-    if (ERTS_P_LINKS(p) || ERTS_P_MONITORS(p)) {
+    if (ERTS_P_LINKS(p) || ERTS_P_MONITORS(p) || ERTS_P_LT_MONITORS(p)) {
 	PrintMonitorContext context = {1, to, to_arg};
 	erts_print(to, to_arg,"Link list: [");
-	erts_doforall_links(ERTS_P_LINKS(p), &doit_print_link, &context);	
-	erts_doforall_monitors(ERTS_P_MONITORS(p), &doit_print_monitor, &context);
+	erts_link_tree_foreach(ERTS_P_LINKS(p), doit_print_link, &context);	
+	erts_monitor_tree_foreach(ERTS_P_MONITORS(p), doit_print_monitor, &context);
+	erts_monitor_list_foreach(ERTS_P_LT_MONITORS(p), doit_print_monitor, &context);
 	erts_print(to, to_arg,"]\n");
     }