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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 53 insertions, 42 deletions

diff --git a/erts/emulator/beam/msg_instrs.tab b/erts/emulator/beam/msg_instrs.tab
index d6d4d2fb49..88d2ef9fa3 100644
--- a/erts/emulator/beam/msg_instrs.tab
+++ b/erts/emulator/beam/msg_instrs.tab
@@ -2,7 +2,7 @@
 //
 // %CopyrightBegin%
 //
-// Copyright Ericsson AB 2017. All Rights Reserved.
+// Copyright Ericsson AB 2017-2018. 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.
@@ -45,23 +45,16 @@
 
 i_recv_mark() {
     /*
-     * Save the current position in message buffer.
+     * Save the current end of message queue
      */
-    c_p->msg.saved_last = c_p->msg.last;
+    ERTS_RECV_MARK_SAVE(c_p);
 }
 
 i_recv_set() {
     /*
-     * If c_p->msg.saved_last is non-zero, it points to the first
-     * message that could possibly be matched out.
-     *
-     * If c_p->msg.saved_last is zero, it means that it was invalidated
-     * because another receive was executed before this i_recv_set()
-     * instruction was reached.
+     * If previously saved recv mark, set peek position to it
      */
-    if (c_p->msg.saved_last) {
-        c_p->msg.save = c_p->msg.saved_last;
-    }
+    ERTS_RECV_MARK_SET(c_p);
     SET_I($NEXT_INSTRUCTION);
     goto loop_rec_top__;
     //| -no_next
@@ -79,7 +72,6 @@ i_loop_rec(Dest) {
 
     /* Entry point from recv_set */
  loop_rec_top__:
-    ;
 
     /*
      * We need to disable GC while matching messages
@@ -89,34 +81,59 @@ i_loop_rec(Dest) {
     ASSERT(!(c_p->flags & F_DELAY_GC));
     c_p->flags |= F_DELAY_GC;
 
-    /* Entry point from loop_rec_end */
+    /* Entry point from loop_rec_end (and locally) */
  loop_rec__:
 
+    if (FCALLS <= 0 && FCALLS <= neg_o_reds) {
+        $SET_CP_I_ABS(I);
+        c_p->flags &= ~F_DELAY_GC;
+        SWAPOUT;
+        c_p->arity = 0;
+        c_p->current = NULL;
+        goto do_schedule;
+    }
+
+    ASSERT(!ERTS_PROC_IS_EXITING(c_p));
+
     PROCESS_MAIN_CHK_LOCKS(c_p);
 
     msgp = PEEK_MESSAGE(c_p);
 
-    if (!msgp) {
-        erts_proc_lock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-        /* Make sure messages wont pass exit signals... */
-        if (ERTS_PROC_PENDING_EXIT(c_p)) {
-            erts_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-            SWAPOUT;
-            c_p->flags &= ~F_DELAY_GC;
-            c_p->arity = 0;
-            goto do_schedule; /* Will be rescheduled for exit */
-        }
-        ERTS_MSGQ_MV_INQ2PRIVQ(c_p);
-        msgp = PEEK_MESSAGE(c_p);
-        if (msgp) {
-            erts_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
-        } else {
+    if (ERTS_UNLIKELY(msgp == NULL)) {
+        int get_out;
+        SWAPOUT;
+        FCALLS -= erts_proc_sig_receive_helper(c_p, FCALLS, neg_o_reds,
+                                               &msgp, &get_out);
+        SWAPIN;
+        if (ERTS_UNLIKELY(msgp == NULL)) {
+            if (get_out) {
+                if (get_out < 0) {
+                    ASSERT(FCALLS <= 0 && FCALLS <= neg_o_reds);
+                    goto loop_rec__; /* yield */
+                }
+                else {
+                    ASSERT(ERTS_PROC_IS_EXITING(c_p));
+                    goto do_schedule; /* exit */
+                }
+            }
+
+            /*
+             * If there are no more messages in queue
+             * (and we are not yielding or exiting)
+             * erts_proc_sig_receive_helper()
+             * returns with message queue lock locked...
+             */
             c_p->flags &= ~F_DELAY_GC;
             $SET_I_REL($Dest);
             Goto(*I);		/* Jump to a wait or wait_timeout instruction */
         }
     }
-    if (is_non_value(ERL_MESSAGE_TERM(msgp))) {
+
+    ASSERT(msgp == PEEK_MESSAGE(c_p));
+    ASSERT(msgp && ERTS_SIG_IS_MSG(msgp));
+
+    if (ERTS_UNLIKELY(ERTS_SIG_IS_EXTERNAL_MSG(msgp))) {
+        FCALLS -= 10; /* FIXME: bump appropriate amount... */
         SWAPOUT; /* erts_decode_dist_message() may write to heap... */
         if (!erts_decode_dist_message(c_p, ERTS_PROC_LOCK_MAIN, msgp, 0)) {
             /*
@@ -127,13 +144,16 @@ i_loop_rec(Dest) {
             ASSERT(HTOP == c_p->htop && E == c_p->stop);
             /* TODO: Add DTrace probe for this bad message situation? */
             UNLINK_MESSAGE(c_p, msgp);
-            c_p->msg.saved_last = 0; /* Better safe than sorry. */
             msgp->next = NULL;
             erts_cleanup_messages(msgp);
             goto loop_rec__;
         }
         SWAPIN;
     }
+
+    ASSERT(msgp == PEEK_MESSAGE(c_p));
+    ASSERT(ERTS_SIG_IS_INTERNAL_MSG(msgp));
+
     r(0) = ERL_MESSAGE_TERM(msgp);
 }
 
@@ -252,17 +272,8 @@ loop_rec_end(Dest) {
 
     $SET_I_REL($Dest);
     SAVE_MESSAGE(c_p);
-    if (FCALLS > 0 || FCALLS > neg_o_reds) {
-        FCALLS--;
-        goto loop_rec__;
-    }
-
-    c_p->flags &= ~F_DELAY_GC;
-    $SET_CP_I_ABS(I);
-    SWAPOUT;
-    c_p->arity = 0;
-    c_p->current = NULL;
-    goto do_schedule;
+    FCALLS--;
+    goto loop_rec__;
 }
 
 timeout_locked() {