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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 10 insertions, 46 deletions

diff --git a/erts/emulator/beam/erl_process_lock.h b/erts/emulator/beam/erl_process_lock.h
index 9d5691d3c4..43f396c547 100644
--- a/erts/emulator/beam/erl_process_lock.h
+++ b/erts/emulator/beam/erl_process_lock.h
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  * 
- * Copyright Ericsson AB 2007-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2007-2018. 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.
@@ -66,7 +66,7 @@
 
 #endif
 
-#define ERTS_PROC_LOCK_MAX_BIT 5
+#define ERTS_PROC_LOCK_MAX_BIT 4
 
 typedef erts_aint32_t ErtsProcLocks;
 
@@ -82,19 +82,17 @@ typedef struct erts_proc_lock_t_ {
     /* Each erts_mtx_t has its own lock counter ^ */
 
     #define ERTS_LCNT_PROCLOCK_IDX_MAIN 0
-    #define ERTS_LCNT_PROCLOCK_IDX_LINK 1
-    #define ERTS_LCNT_PROCLOCK_IDX_MSGQ 2
-    #define ERTS_LCNT_PROCLOCK_IDX_BTM 3
-    #define ERTS_LCNT_PROCLOCK_IDX_STATUS 4
-    #define ERTS_LCNT_PROCLOCK_IDX_TRACE 5
+    #define ERTS_LCNT_PROCLOCK_IDX_MSGQ 1
+    #define ERTS_LCNT_PROCLOCK_IDX_BTM 2
+    #define ERTS_LCNT_PROCLOCK_IDX_STATUS 3
+    #define ERTS_LCNT_PROCLOCK_IDX_TRACE 4
 
-    #define ERTS_LCNT_PROCLOCK_COUNT 6
+    #define ERTS_LCNT_PROCLOCK_COUNT 5
 
     erts_lcnt_ref_t lcnt_carrier;
 #endif
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     erts_mtx_t main;
-    erts_mtx_t link;
     erts_mtx_t msgq;
     erts_mtx_t btm;
     erts_mtx_t status;
@@ -118,27 +116,18 @@ typedef struct erts_proc_lock_t_ {
 #define ERTS_PROC_LOCK_MAIN		(((ErtsProcLocks) 1) << 0)
 
 /*
- * Link lock:
- *   Protects the following fields in the process structure:
- *   * nlinks
- *   * monitors
- *   * suspend_monitors
- */
-#define ERTS_PROC_LOCK_LINK		(((ErtsProcLocks) 1) << 1)
-
-/*
  * Message queue lock:
  *   Protects the following fields in the process structure:
  *   * msg_inq
  */
-#define ERTS_PROC_LOCK_MSGQ		(((ErtsProcLocks) 1) << 2)
+#define ERTS_PROC_LOCK_MSGQ		(((ErtsProcLocks) 1) << 1)
 
 /*
  * Bif timer lock:
  *   Protects the following fields in the process structure:
  *   * bif_timers
  */
-#define ERTS_PROC_LOCK_BTM		(((ErtsProcLocks) 1) << 3)
+#define ERTS_PROC_LOCK_BTM		(((ErtsProcLocks) 1) << 2)
 
 /*
  * Status lock:
@@ -148,7 +137,7 @@ typedef struct erts_proc_lock_t_ {
  *   * sys_tasks
  *   * ...
  */
-#define ERTS_PROC_LOCK_STATUS		(((ErtsProcLocks) 1) << 4)
+#define ERTS_PROC_LOCK_STATUS		(((ErtsProcLocks) 1) << 3)
 
 /*
  * Trace message lock:
@@ -277,9 +266,6 @@ void erts_lcnt_proc_lock(erts_proc_lock_t *lock, ErtsProcLocks locks) {
         if (locks & ERTS_PROC_LOCK_MAIN) {
             erts_lcnt_lock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN);
         }
-        if (locks & ERTS_PROC_LOCK_LINK) {
-            erts_lcnt_lock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK);
-        }
         if (locks & ERTS_PROC_LOCK_MSGQ) {
             erts_lcnt_lock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ);
         }
@@ -307,9 +293,6 @@ void erts_lcnt_proc_lock_post_x(erts_proc_lock_t *lock, ErtsProcLocks locks,
         if (locks & ERTS_PROC_LOCK_MAIN) {
             erts_lcnt_lock_post_x_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN, file, line);
         }
-        if (locks & ERTS_PROC_LOCK_LINK) {
-            erts_lcnt_lock_post_x_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK, file, line);
-        }
         if (locks & ERTS_PROC_LOCK_MSGQ) {
             erts_lcnt_lock_post_x_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ, file, line);
         }
@@ -336,9 +319,6 @@ void erts_lcnt_proc_lock_unacquire(erts_proc_lock_t *lock, ErtsProcLocks locks)
         if (locks & ERTS_PROC_LOCK_MAIN) {
             erts_lcnt_lock_unacquire_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN);
         }
-        if (locks & ERTS_PROC_LOCK_LINK) {
-            erts_lcnt_lock_unacquire_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK);
-        }
         if (locks & ERTS_PROC_LOCK_MSGQ) {
             erts_lcnt_lock_unacquire_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ);
         }
@@ -365,9 +345,6 @@ void erts_lcnt_proc_unlock(erts_proc_lock_t *lock, ErtsProcLocks locks) {
         if (locks & ERTS_PROC_LOCK_MAIN) {
             erts_lcnt_unlock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN);
         }
-        if (locks & ERTS_PROC_LOCK_LINK) {
-            erts_lcnt_unlock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK);
-        }
         if (locks & ERTS_PROC_LOCK_MSGQ) {
             erts_lcnt_unlock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ);
         }
@@ -394,9 +371,6 @@ void erts_lcnt_proc_trylock(erts_proc_lock_t *lock, ErtsProcLocks locks, int res
         if (locks & ERTS_PROC_LOCK_MAIN) {
             erts_lcnt_trylock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN, res);
         }
-        if (locks & ERTS_PROC_LOCK_LINK) {
-            erts_lcnt_trylock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK, res);
-        }
         if (locks & ERTS_PROC_LOCK_MSGQ) {
             erts_lcnt_trylock_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ, res);
         }
@@ -640,9 +614,6 @@ erts_proc_raw_trylock__(Process *p, ErtsProcLocks locks)
     if (locks & ERTS_PROC_LOCK_MAIN)
 	if (erts_mtx_trylock(&p->lock.main) == EBUSY)
 	    goto busy_main;
-    if (locks & ERTS_PROC_LOCK_LINK)
-	if (erts_mtx_trylock(&p->lock.link) == EBUSY)
-	    goto busy_link;
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	if (erts_mtx_trylock(&p->lock.msgq) == EBUSY)
 	    goto busy_msgq;
@@ -668,9 +639,6 @@ busy_btm:
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_mtx_unlock(&p->lock.msgq);
 busy_msgq:
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_mtx_unlock(&p->lock.link);
-busy_link:
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_mtx_unlock(&p->lock.main);
 busy_main:
@@ -741,8 +709,6 @@ erts_proc_lock__(Process *p,
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_mtx_lock(&p->lock.main);
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_mtx_lock(&p->lock.link);
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_mtx_lock(&p->lock.msgq);
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -844,8 +810,6 @@ erts_proc_unlock__(Process *p,
 	erts_mtx_unlock(&p->lock.btm);
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_mtx_unlock(&p->lock.msgq);
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_mtx_unlock(&p->lock.link);
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_mtx_unlock(&p->lock.main);
 #endif