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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 77 insertions, 35 deletions

diff --git a/erts/emulator/beam/erl_process_dump.c b/erts/emulator/beam/erl_process_dump.c
index 05e7bcdea2..00659f9f49 100644
--- a/erts/emulator/beam/erl_process_dump.c
+++ b/erts/emulator/beam/erl_process_dump.c
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 2003-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2003-2018. 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.
@@ -35,6 +35,7 @@
 #include "erl_map.h"
 #define ERTS_WANT_EXTERNAL_TAGS
 #include "external.h"
+#include "erl_proc_sig_queue.h"
 
 #define PTR_FMT "%bpX"
 #define ETERM_FMT "%beX"
@@ -96,17 +97,35 @@ erts_deep_process_dump(fmtfn_t to, void *to_arg)
     dump_binaries(to, to_arg, all_binaries);
 }
 
+static void
+monitor_size(ErtsMonitor *mon, void *vsize)
+{
+    *((Uint *) vsize) += erts_monitor_size(mon);
+}
+
+static void
+link_size(ErtsMonitor *lnk, void *vsize)
+{
+    *((Uint *) vsize) += erts_link_size(lnk);
+}
+
 Uint erts_process_memory(Process *p, int incl_msg_inq) {
-  ErtsMessage *mp;
   Uint size = 0;
   struct saved_calls *scb;
   size += sizeof(Process);
 
-  if (incl_msg_inq)
-      ERTS_MSGQ_MV_INQ2PRIVQ(p);
+  if (incl_msg_inq) {
+      erts_proc_lock(p, ERTS_PROC_LOCK_MSGQ);
+      erts_proc_sig_fetch(p);
+      erts_proc_unlock(p, ERTS_PROC_LOCK_MSGQ);
+  }
 
-  erts_doforall_links(ERTS_P_LINKS(p), &erts_one_link_size, &size);
-  erts_doforall_monitors(ERTS_P_MONITORS(p), &erts_one_mon_size, &size);
+  erts_link_tree_foreach(ERTS_P_LINKS(p),
+                         link_size, (void *) &size);
+  erts_monitor_tree_foreach(ERTS_P_MONITORS(p),
+                            monitor_size, (void *) &size);
+  erts_monitor_list_foreach(ERTS_P_LT_MONITORS(p),
+                            monitor_size, (void *) &size);
   size += (p->heap_sz + p->mbuf_sz) * sizeof(Eterm);
   if (p->abandoned_heap)
       size += (p->hend - p->heap) * sizeof(Eterm);
@@ -114,11 +133,16 @@ Uint erts_process_memory(Process *p, int incl_msg_inq) {
     size += (p->old_hend - p->old_heap) * sizeof(Eterm);
 
 
-  size += p->msg.len * sizeof(ErtsMessage);
+  size += p->sig_qs.len * sizeof(ErtsMessage);
 
-  for (mp = p->msg.first; mp; mp = mp->next)
-    if (mp->data.attached)
-      size += erts_msg_attached_data_size(mp)*sizeof(Eterm);
+  ERTS_FOREACH_SIG_PRIVQS(
+      p, mp,
+      {
+          if (ERTS_SIG_IS_NON_MSG((ErtsSignal *) mp))
+              size += erts_proc_sig_signal_size((ErtsSignal *) mp);
+          else if (mp->data.attached)
+              size += erts_msg_attached_data_size(mp) * sizeof(Eterm);
+      });
 
   if (p->arg_reg != p->def_arg_reg) {
     size += p->arity * sizeof(p->arg_reg[0]);
@@ -137,31 +161,48 @@ Uint erts_process_memory(Process *p, int incl_msg_inq) {
   return size;
 }
 
+static ERTS_INLINE void
+dump_msg(fmtfn_t to, void *to_arg, ErtsMessage *mp)
+{
+    if (ERTS_SIG_IS_MSG((ErtsSignal *) mp)) {
+        Eterm mesg = ERL_MESSAGE_TERM(mp);
+        if (is_value(mesg))
+            dump_element(to, to_arg, mesg);
+        else
+            dump_dist_ext(to, to_arg, mp->data.dist_ext);
+        mesg = ERL_MESSAGE_TOKEN(mp);
+        erts_print(to, to_arg, ":");
+        dump_element(to, to_arg, mesg);
+        erts_print(to, to_arg, "\n");
+    }
+}
+
+static ERTS_INLINE void
+heap_dump_msg(fmtfn_t to, void *to_arg, ErtsMessage *mp)
+{
+    if (ERTS_SIG_IS_MSG((ErtsSignal *) mp)) {
+        Eterm mesg = ERL_MESSAGE_TERM(mp);
+        if (is_value(mesg))
+            heap_dump(to, to_arg, mesg);
+        mesg = ERL_MESSAGE_TOKEN(mp);
+        heap_dump(to, to_arg, mesg);
+    }
+}
+
 static void
 dump_process_info(fmtfn_t to, void *to_arg, Process *p)
 {
     Eterm* sp;
-    ErtsMessage* mp;
     int yreg = -1;
 
     if (ERTS_TRACE_FLAGS(p) & F_SENSITIVE)
         return;
 
-    ERTS_MSGQ_MV_INQ2PRIVQ(p);
+    erts_proc_sig_fetch(p);
 
-    if (p->msg.first) {
+    if (p->sig_qs.first || p->sig_qs.cont) {
 	erts_print(to, to_arg, "=proc_messages:%T\n", p->common.id);
-	for (mp = p->msg.first; mp != NULL; mp = mp->next) {
-	    Eterm mesg = ERL_MESSAGE_TERM(mp);
-	    if (is_value(mesg))
-		dump_element(to, to_arg, mesg);
-	    else
-		dump_dist_ext(to, to_arg, mp->data.dist_ext);
-	    mesg = ERL_MESSAGE_TOKEN(mp);
-	    erts_print(to, to_arg, ":");
-	    dump_element(to, to_arg, mesg);
-	    erts_print(to, to_arg, "\n");
-	}
+        ERTS_FOREACH_SIG_PRIVQS(p, mp, dump_msg(to, to_arg, mp));
     }
 
     if (p->dictionary) {
@@ -183,13 +224,10 @@ dump_process_info(fmtfn_t to, void *to_arg, Process *p)
             heap_dump(to, to_arg, term);
         }
     }
-    for (mp = p->msg.first; mp != NULL; mp = mp->next) {
-        Eterm mesg = ERL_MESSAGE_TERM(mp);
-        if (is_value(mesg))
-            heap_dump(to, to_arg, mesg);
-        mesg = ERL_MESSAGE_TOKEN(mp);
-        heap_dump(to, to_arg, mesg);
-    }
+
+    if (p->sig_qs.first || p->sig_qs.cont)
+        ERTS_FOREACH_SIG_PRIVQS(p, mp, heap_dump_msg(to, to_arg, mp));
+
     if (p->dictionary) {
         erts_deep_dictionary_dump(to, to_arg, p->dictionary, heap_dump);
     }
@@ -997,8 +1035,8 @@ erts_dump_extended_process_state(fmtfn_t to, void *to_arg, erts_aint32_t psflg)
                 erts_print(to, to_arg, "FREE"); break;
             case ERTS_PSFLG_EXITING:
                 erts_print(to, to_arg, "EXITING"); break;
-            case ERTS_PSFLG_PENDING_EXIT:
-                erts_print(to, to_arg, "PENDING_EXIT"); break;
+            case ERTS_PSFLG_UNUSED:
+                erts_print(to, to_arg, "UNUSED"); break;
             case ERTS_PSFLG_ACTIVE:
                 erts_print(to, to_arg, "ACTIVE"); break;
             case ERTS_PSFLG_IN_RUNQ:
@@ -1009,8 +1047,10 @@ erts_dump_extended_process_state(fmtfn_t to, void *to_arg, erts_aint32_t psflg)
                 erts_print(to, to_arg, "SUSPENDED"); break;
             case ERTS_PSFLG_GC:
                 erts_print(to, to_arg, "GC"); break;
-            case ERTS_PSFLG_TRAP_EXIT:
-                erts_print(to, to_arg, "TRAP_EXIT"); break;
+            case ERTS_PSFLG_SYS_TASKS:
+                erts_print(to, to_arg, "SYS_TASKS"); break;
+            case ERTS_PSFLG_SIG_IN_Q:
+                erts_print(to, to_arg, "SIG_IN_Q"); break;
             case ERTS_PSFLG_ACTIVE_SYS:
                 erts_print(to, to_arg, "ACTIVE_SYS"); break;
             case ERTS_PSFLG_RUNNING_SYS:
@@ -1021,6 +1061,8 @@ erts_dump_extended_process_state(fmtfn_t to, void *to_arg, erts_aint32_t psflg)
                 erts_print(to, to_arg, "DELAYED_SYS"); break;
             case ERTS_PSFLG_OFF_HEAP_MSGQ:
                 erts_print(to, to_arg, "OFF_HEAP_MSGQ"); break;
+            case ERTS_PSFLG_SIG_Q:
+                erts_print(to, to_arg, "SIG_Q"); break;
             case ERTS_PSFLG_DIRTY_CPU_PROC:
                 erts_print(to, to_arg, "DIRTY_CPU_PROC"); break;
             case ERTS_PSFLG_DIRTY_IO_PROC: