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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 14 insertions, 34 deletions

diff --git a/erts/emulator/beam/erl_port.h b/erts/emulator/beam/erl_port.h
index 0d148ee048..2a98a6f00b 100644
--- a/erts/emulator/beam/erl_port.h
+++ b/erts/emulator/beam/erl_port.h
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 2012-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2012-2018. 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.
@@ -373,7 +373,7 @@ Eterm erts_request_io_bytes(Process *c_p);
 
 void print_port_info(Port *, fmtfn_t, void *);
 void erts_port_free(Port *);
-void erts_fire_port_monitor(Port *prt, Eterm ref);
+void erts_fire_port_monitor(Port *prt, ErtsMonitor *tmon);
 int erts_port_handle_xports(Port *);
 
 #if defined(ERTS_ENABLE_LOCK_CHECK)
@@ -887,20 +887,20 @@ struct ErtsProc2PortSigData_ {
 	    Eterm item;
 	} info;
 	struct {
-	    Eterm port;
-	    Eterm to;
+            Eterm port_id;
+	    ErtsLink *lnk;
 	} link;
 	struct {
-	    Eterm from;
+            Eterm port_id;
+	    ErtsLink *lnk;
 	} unlink;
         struct {
-            Eterm origin;   /* who receives monitor event, pid */
-            Eterm name;     /* either name for named monitor, or port id */
+            Eterm port_id;
+            ErtsMonitor *mon;
         } monitor;
         struct {
-            Eterm origin;   /* who is at the other end of the monitor, pid */
-            Eterm name;     /* port id */
-            Uint32 ref[ERTS_MAX_REF_NUMBERS]; /* box contents of a ref */
+            Eterm port_id;
+            ErtsMonitor *mon;
         } demonitor;
     } u;
 } ;
@@ -946,7 +946,6 @@ typedef int (*ErtsProc2PortSigCallback)(Port *,
 
 typedef enum {
     ERTS_PORT_OP_BADARG,
-    ERTS_PORT_OP_CALLER_EXIT,
     ERTS_PORT_OP_BUSY,
     ERTS_PORT_OP_BUSY_SCHEDULED,
     ERTS_PORT_OP_SCHEDULED,
@@ -982,32 +981,13 @@ ErtsPortOpResult erts_port_command(Process *, int, Port *, Eterm, Eterm *);
 ErtsPortOpResult erts_port_output(Process *, int, Port *, Eterm, Eterm, Eterm *);
 ErtsPortOpResult erts_port_exit(Process *, int, Port *, Eterm, Eterm, Eterm *);
 ErtsPortOpResult erts_port_connect(Process *, int, Port *, Eterm, Eterm, Eterm *);
-ErtsPortOpResult erts_port_link(Process *, Port *, Eterm, Eterm *);
-ErtsPortOpResult erts_port_unlink(Process *, Port *, Eterm, Eterm *);
+ErtsPortOpResult erts_port_link(Process *, Port *, ErtsLink *, Eterm *);
+ErtsPortOpResult erts_port_unlink(Process *, Port *, ErtsLink *, Eterm *);
 ErtsPortOpResult erts_port_control(Process *, Port *, unsigned int, Eterm, Eterm *);
 ErtsPortOpResult erts_port_call(Process *, Port *, unsigned int, Eterm, Eterm *);
 ErtsPortOpResult erts_port_info(Process *, Port *, Eterm, Eterm *);
-
-/* Creates monitor between Origin and Target. Ref must be initialized to
- * a reference (ref may be rewritten to be used to serve additionally as a
- * signal id). Name is atom if user monitors port by name or NIL */
-ErtsPortOpResult erts_port_monitor(Process *origin, Port *target, Eterm name,
-                                   Eterm *ref);
-
-typedef enum {
-    /* Normal demonitor rules apply with locking and reductions bump */
-    ERTS_PORT_DEMONITOR_NORMAL = 1,
-    /* Relaxed demonitor rules when process is about to die, which means that
-     * pid lookup won't work, locks won't work, no reductions bump. */
-    ERTS_PORT_DEMONITOR_ORIGIN_ON_DEATHBED = 2,
-} ErtsDemonitorMode;
-
-/* Removes monitor between origin and target, identified by ref.
- * origin_is_dying can be 0 (false, normal locking rules and reductions bump
- * apply) or 1 (true, in case when we avoid origin locking) */
-ErtsPortOpResult erts_port_demonitor(Process *origin, ErtsDemonitorMode mode,
-                                    Port *target, Eterm ref,
-                                    Eterm *trap_ref);
+ErtsPortOpResult erts_port_monitor(Process *, Port *, ErtsMonitor *);
+ErtsPortOpResult erts_port_demonitor(Process *, Port *, ErtsMonitor *);
 /* defined in erl_bif_port.c */
 Port *erts_sig_lookup_port(Process *c_p, Eterm id_or_name);