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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 12 insertions, 86 deletions

diff --git a/erts/emulator/beam/erl_process_lock.c b/erts/emulator/beam/erl_process_lock.c
index 431867f27e..44c7892040 100644
--- a/erts/emulator/beam/erl_process_lock.c
+++ b/erts/emulator/beam/erl_process_lock.c
@@ -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.
@@ -101,7 +101,6 @@ static void cleanup_tse(void);
 #ifdef ERTS_ENABLE_LOCK_CHECK
 static struct {
     Sint16 proc_lock_main;
-    Sint16 proc_lock_link;
     Sint16 proc_lock_msgq;
     Sint16 proc_lock_btm;
     Sint16 proc_lock_status;
@@ -140,7 +139,6 @@ erts_init_proc_lock(int cpus)
 #endif
 #ifdef ERTS_ENABLE_LOCK_CHECK
     lc_id.proc_lock_main	= erts_lc_get_lock_order_id("proc_main");
-    lc_id.proc_lock_link	= erts_lc_get_lock_order_id("proc_link");
     lc_id.proc_lock_msgq	= erts_lc_get_lock_order_id("proc_msgq");
     lc_id.proc_lock_btm		= erts_lc_get_lock_order_id("proc_btm");
     lc_id.proc_lock_status	= erts_lc_get_lock_order_id("proc_status");
@@ -1055,12 +1053,6 @@ erts_proc_lock_init(Process *p)
 #ifdef ERTS_ENABLE_LOCK_CHECK
     erts_lc_trylock(1, &p->lock.main.lc);
 #endif
-    erts_mtx_init(&p->lock.link, "proc_link", p->common.id,
-        ERTS_LOCK_FLAGS_CATEGORY_PROCESS);
-    ethr_mutex_lock(&p->lock.link.mtx);
-#ifdef ERTS_ENABLE_LOCK_CHECK
-    erts_lc_trylock(1, &p->lock.link.lc);
-#endif
     erts_mtx_init(&p->lock.msgq, "proc_msgq", p->common.id,
         ERTS_LOCK_FLAGS_CATEGORY_PROCESS);
     ethr_mutex_lock(&p->lock.msgq.mtx);
@@ -1102,7 +1094,6 @@ erts_proc_lock_fin(Process *p)
 {
 #if ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     erts_mtx_destroy(&p->lock.main);
-    erts_mtx_destroy(&p->lock.link);
     erts_mtx_destroy(&p->lock.msgq);
     erts_mtx_destroy(&p->lock.btm);
     erts_mtx_destroy(&p->lock.status);
@@ -1144,8 +1135,6 @@ void erts_lcnt_enable_proc_lock_count(Process *proc, int enable) {
 
         erts_lcnt_init_lock_info_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MAIN,
             "proc_main", proc->common.id, ERTS_LOCK_TYPE_PROCLOCK);
-        erts_lcnt_init_lock_info_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_LINK,
-            "proc_link", proc->common.id, ERTS_LOCK_TYPE_PROCLOCK);
         erts_lcnt_init_lock_info_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_MSGQ,
             "proc_msgq", proc->common.id, ERTS_LOCK_TYPE_PROCLOCK);
         erts_lcnt_init_lock_info_idx(carrier, ERTS_LCNT_PROCLOCK_IDX_BTM,
@@ -1200,10 +1189,6 @@ erts_proc_lc_lock(Process *p, ErtsProcLocks locks, char *file, unsigned int line
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_lock_x(&lck,file,line);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_lock_x(&lck,file,line);
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_lock_x(&lck,file,line);
@@ -1233,10 +1218,6 @@ erts_proc_lc_trylock(Process *p, ErtsProcLocks locks, int locked,
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_trylock_x(locked, &lck, file, line);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_trylock_x(locked, &lck, file, line);
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_trylock_x(locked, &lck, file, line);
@@ -1277,10 +1258,6 @@ erts_proc_lc_unlock(Process *p, ErtsProcLocks locks)
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_unlock(&lck);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_unlock(&lck);
-    }
     if (locks & ERTS_PROC_LOCK_MAIN) {
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_unlock(&lck);
@@ -1312,10 +1289,6 @@ erts_proc_lc_might_unlock(Process *p, ErtsProcLocks locks)
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_might_unlock(&lck);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_might_unlock(&lck);
-    }
     if (locks & ERTS_PROC_LOCK_MAIN) {
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_might_unlock(&lck);
@@ -1323,8 +1296,6 @@ erts_proc_lc_might_unlock(Process *p, ErtsProcLocks locks)
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_lc_might_unlock(&p->lock.main.lc);
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_lc_might_unlock(&p->lock.link.lc);
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_lc_might_unlock(&p->lock.msgq.lc);
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -1348,10 +1319,6 @@ erts_proc_lc_require_lock(Process *p, ErtsProcLocks locks, char *file,
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_require_lock(&lck, file, line);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_require_lock(&lck, file, line);
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_require_lock(&lck, file, line);
@@ -1371,8 +1338,6 @@ erts_proc_lc_require_lock(Process *p, ErtsProcLocks locks, char *file,
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_lc_require_lock(&p->lock.main.lc, file, line);
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_lc_require_lock(&p->lock.link.lc, file, line);
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_lc_require_lock(&p->lock.msgq.lc, file, line);
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -1407,10 +1372,6 @@ erts_proc_lc_unrequire_lock(Process *p, ErtsProcLocks locks)
 	lck.id = lc_id.proc_lock_msgq;
 	erts_lc_unrequire_lock(&lck);
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	lck.id = lc_id.proc_lock_link;
-	erts_lc_unrequire_lock(&lck);
-    }
     if (locks & ERTS_PROC_LOCK_MAIN) {
 	lck.id = lc_id.proc_lock_main;
 	erts_lc_unrequire_lock(&lck);
@@ -1418,8 +1379,6 @@ erts_proc_lc_unrequire_lock(Process *p, ErtsProcLocks locks)
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
     if (locks & ERTS_PROC_LOCK_MAIN)
 	erts_lc_unrequire_lock(&p->lock.main.lc);
-    if (locks & ERTS_PROC_LOCK_LINK)
-	erts_lc_unrequire_lock(&p->lock.link.lc);
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	erts_lc_unrequire_lock(&p->lock.msgq.lc);
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -1443,8 +1402,6 @@ erts_proc_lc_trylock_force_busy(Process *p, ErtsProcLocks locks)
 
 	if (locks & ERTS_PROC_LOCK_MAIN)
 	    lck.id = lc_id.proc_lock_main;
-	else if (locks & ERTS_PROC_LOCK_LINK)
-	    lck.id = lc_id.proc_lock_link;
 	else if (locks & ERTS_PROC_LOCK_MSGQ)
 	    lck.id = lc_id.proc_lock_msgq;
 	else if (locks & ERTS_PROC_LOCK_BTM)
@@ -1487,10 +1444,6 @@ void erts_proc_lc_chk_only_proc(Process *p, ErtsProcLocks locks)
 	have_locks[have_locks_len].id = lc_id.proc_lock_main;
 	have_locks[have_locks_len++].extra = p->common.id;
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	have_locks[have_locks_len].id = lc_id.proc_lock_link;
-	have_locks[have_locks_len++].extra = p->common.id;
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	have_locks[have_locks_len].id = lc_id.proc_lock_msgq;
 	have_locks[have_locks_len++].extra = p->common.id;
@@ -1511,8 +1464,6 @@ void erts_proc_lc_chk_only_proc(Process *p, ErtsProcLocks locks)
     erts_lc_lock_t have_locks[6];
     if (locks & ERTS_PROC_LOCK_MAIN)
 	have_locks[have_locks_len++] = p->lock.main.lc;
-    if (locks & ERTS_PROC_LOCK_LINK)
-	have_locks[have_locks_len++] = p->lock.link.lc;
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	have_locks[have_locks_len++] = p->lock.msgq.lc;
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -1540,10 +1491,6 @@ erts_proc_lc_chk_have_proc_locks(Process *p, ErtsProcLocks locks)
 	have_locks[have_locks_len].id = lc_id.proc_lock_main;
 	have_locks[have_locks_len++].extra = p->common.id;
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	have_locks[have_locks_len].id = lc_id.proc_lock_link;
-	have_locks[have_locks_len++].extra = p->common.id;
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	have_locks[have_locks_len].id = lc_id.proc_lock_msgq;
 	have_locks[have_locks_len++].extra = p->common.id;
@@ -1564,8 +1511,6 @@ erts_proc_lc_chk_have_proc_locks(Process *p, ErtsProcLocks locks)
     erts_lc_lock_t have_locks[6];
     if (locks & ERTS_PROC_LOCK_MAIN)
 	have_locks[have_locks_len++] = p->lock.main.lc;
-    if (locks & ERTS_PROC_LOCK_LINK)
-	have_locks[have_locks_len++] = p->lock.link.lc;
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	have_locks[have_locks_len++] = p->lock.msgq.lc;
     if (locks & ERTS_PROC_LOCK_BTM)
@@ -1603,14 +1548,6 @@ erts_proc_lc_chk_proc_locks(Process *p, ErtsProcLocks locks)
 	have_not_locks[have_not_locks_len].id = lc_id.proc_lock_main;
 	have_not_locks[have_not_locks_len++].extra = p->common.id;
     }
-    if (locks & ERTS_PROC_LOCK_LINK) {
-	have_locks[have_locks_len].id = lc_id.proc_lock_link;
-	have_locks[have_locks_len++].extra = p->common.id;
-    }
-    else {
-	have_not_locks[have_not_locks_len].id = lc_id.proc_lock_link;
-	have_not_locks[have_not_locks_len++].extra = p->common.id;
-    }
     if (locks & ERTS_PROC_LOCK_MSGQ) {
 	have_locks[have_locks_len].id = lc_id.proc_lock_msgq;
 	have_locks[have_locks_len++].extra = p->common.id;
@@ -1651,10 +1588,6 @@ erts_proc_lc_chk_proc_locks(Process *p, ErtsProcLocks locks)
 	have_locks[have_locks_len++] = p->lock.main.lc;
     else
 	have_not_locks[have_not_locks_len++] = p->lock.main.lc;
-    if (locks & ERTS_PROC_LOCK_LINK)
-	have_locks[have_locks_len++] = p->lock.link.lc;
-    else
-	have_not_locks[have_not_locks_len++] = p->lock.link.lc;
     if (locks & ERTS_PROC_LOCK_MSGQ)
 	have_locks[have_locks_len++] = p->lock.msgq.lc;
     else
@@ -1680,13 +1613,10 @@ erts_proc_lc_chk_proc_locks(Process *p, ErtsProcLocks locks)
 ErtsProcLocks
 erts_proc_lc_my_proc_locks(Process *p)
 {
-    int resv[6];
+    int resv[5];
     ErtsProcLocks res = 0;
 #if ERTS_PROC_LOCK_OWN_IMPL
-    erts_lc_lock_t locks[6] = {ERTS_LC_LOCK_INIT(lc_id.proc_lock_main,
-						 p->common.id,
-						 ERTS_LOCK_TYPE_PROCLOCK),
-			       ERTS_LC_LOCK_INIT(lc_id.proc_lock_link,
+    erts_lc_lock_t locks[5] = {ERTS_LC_LOCK_INIT(lc_id.proc_lock_main,
 						 p->common.id,
 						 ERTS_LOCK_TYPE_PROCLOCK),
 			       ERTS_LC_LOCK_INIT(lc_id.proc_lock_msgq,
@@ -1702,26 +1632,23 @@ erts_proc_lc_my_proc_locks(Process *p)
 						 p->common.id,
 						 ERTS_LOCK_TYPE_PROCLOCK)};
 #elif ERTS_PROC_LOCK_RAW_MUTEX_IMPL
-    erts_lc_lock_t locks[6] = {p->lock.main.lc,
-			       p->lock.link.lc,
+    erts_lc_lock_t locks[5] = {p->lock.main.lc,
 			       p->lock.msgq.lc,
 			       p->lock.btm.lc,
 			       p->lock.status.lc,
 			       p->lock.trace.lc};
 #endif
 
-    erts_lc_have_locks(resv, locks, 6);
+    erts_lc_have_locks(resv, locks, 5);
     if (resv[0])
 	res |= ERTS_PROC_LOCK_MAIN;
     if (resv[1])
-	res |= ERTS_PROC_LOCK_LINK;
-    if (resv[2])
 	res |= ERTS_PROC_LOCK_MSGQ;
-    if (resv[3])
+    if (resv[2])
 	res |= ERTS_PROC_LOCK_BTM;
-    if (resv[4])
+    if (resv[3])
 	res |= ERTS_PROC_LOCK_STATUS;
-    if (resv[5])
+    if (resv[4])
 	res |= ERTS_PROC_LOCK_TRACE;
 
     return res;
@@ -1730,15 +1657,14 @@ erts_proc_lc_my_proc_locks(Process *p)
 void
 erts_proc_lc_chk_no_proc_locks(char *file, int line)
 {
-    int resv[6];
-    int ids[6] = {lc_id.proc_lock_main,
-		  lc_id.proc_lock_link,
+    int resv[5];
+    int ids[5] = {lc_id.proc_lock_main,
 		  lc_id.proc_lock_msgq,
 		  lc_id.proc_lock_btm,
 		  lc_id.proc_lock_status,
 		  lc_id.proc_lock_trace};
-    erts_lc_have_lock_ids(resv, ids, 6);
-    if (!ERTS_IS_CRASH_DUMPING && (resv[0] || resv[1] || resv[2] || resv[3] || resv[4] || resv[5])) {
+    erts_lc_have_lock_ids(resv, ids, 5);
+    if (!ERTS_IS_CRASH_DUMPING && (resv[0] || resv[1] || resv[2] || resv[3] || resv[4])) {
 	erts_lc_fail("%s:%d: Thread has process locks locked when expected "
 		     "not to have any process locks locked",
 		     file, line);