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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 17 insertions, 35 deletions

diff --git a/erts/emulator/beam/erl_node_tables.h b/erts/emulator/beam/erl_node_tables.h
index 58279017c8..9a792b10b1 100644
--- a/erts/emulator/beam/erl_node_tables.h
+++ b/erts/emulator/beam/erl_node_tables.h
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 2001-2017. All Rights Reserved.
+ * Copyright Ericsson AB 2001-2018. 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.
@@ -18,7 +18,17 @@
  * %CopyrightEnd%
  */
 
-#ifndef ERL_NODE_TABLES_H__
+#ifndef ERL_NODE_TABLES_BASIC__
+#define ERL_NODE_TABLES_BASIC__
+
+typedef struct dist_entry_ DistEntry;
+typedef struct ErtsDistOutputBuf_ ErtsDistOutputBuf;
+void erts_ref_dist_entry(DistEntry *dep);
+void erts_deref_dist_entry(DistEntry *dep);
+
+#endif
+
+#if !defined(ERL_NODE_TABLES_BASIC_ONLY) && !defined(ERL_NODE_TABLES_H__)
 #define ERL_NODE_TABLES_H__
 
 /*
@@ -42,14 +52,14 @@
 #include "sys.h"
 #include "hash.h"
 #include "erl_alloc.h"
-#include "erl_process.h"
-#include "erl_monitors.h"
 #define ERTS_PORT_TASK_ONLY_BASIC_TYPES__
 #include "erl_port_task.h"
 #undef ERTS_PORT_TASK_ONLY_BASIC_TYPES__
+#include "erl_process.h"
 #define ERTS_BINARY_TYPES_ONLY__
 #include "erl_binary.h"
 #undef ERTS_BINARY_TYPES_ONLY__
+#include "erl_monitor_link.h"
 
 #define ERTS_NODE_TAB_DELAY_GC_DEFAULT (60)
 #define ERTS_NODE_TAB_DELAY_GC_MAX (100*1000*1000)
@@ -82,7 +92,6 @@ enum dist_entry_state {
 #define ERTS_DIST_OUTPUT_BUF_DBG_PATTERN ((Uint) 0xf713f713)
 #endif
 
-typedef struct ErtsDistOutputBuf_ ErtsDistOutputBuf;
 struct ErtsDistOutputBuf_ {
 #ifdef DEBUG
     Uint dbg_pattern;
@@ -113,7 +122,7 @@ struct ErtsProcList_;
  *   unlock mutexes with higher numbers before mutexes with higher numbers.
  */
 
-typedef struct dist_entry_ {
+struct dist_entry_ {
     HashBucket hash_bucket;     /* Hash bucket */
     struct dist_entry_ *next;	/* Next entry in dist_table (not sorted) */
     struct dist_entry_ *prev;	/* Previous entry in dist_table (not sorted) */
@@ -130,18 +139,7 @@ typedef struct dist_entry_ {
 				   atom cache etc. */
     unsigned long version;	/* Protocol version */
 
-
-    erts_mtx_t lnk_mtx;         /* Protects node_links, nlinks, and
-				   monitors. */
-    ErtsLink *node_links;       /* In a dist entry, node links are kept 
-				   in a separate tree, while they are 
-				   colocted with the ordinary link tree
-				   for processes. It's not due to confusion,
-				   it's because the link tree for the dist 
-				   entry is in two levels, see erl_monitors.h 
-				*/
-    ErtsLink *nlinks;           /* Link tree with subtrees */
-    ErtsMonitor *monitors;      /* Monitor tree */
+    ErtsMonLnkDist *mld;        /* Monitors and links */
 
     erts_mtx_t qlock;           /* Protects qflgs and out_queue */
     erts_atomic32_t qflgs;
@@ -163,7 +161,7 @@ typedef struct dist_entry_ {
     ErtsThrPrgrLaterOp later_op;
 
     struct transcode_context* transcode_ctx;
-} DistEntry;
+};
 
 typedef struct erl_node_ {
   HashBucket hash_bucket;	/* Hash bucket */
@@ -219,16 +217,12 @@ int erts_dist_entry_destructor(Binary *bin);
 DistEntry *erts_dhandle_to_dist_entry(Eterm dhandle);
 Eterm erts_build_dhandle(Eterm **hpp, ErlOffHeap*, DistEntry*);
 Eterm erts_make_dhandle(Process *c_p, DistEntry *dep);
-void erts_ref_dist_entry(DistEntry *dep);
-void erts_deref_dist_entry(DistEntry *dep);
 
 ERTS_GLB_INLINE void erts_deref_node_entry(ErlNode *np);
 ERTS_GLB_INLINE void erts_de_rlock(DistEntry *dep);
 ERTS_GLB_INLINE void erts_de_runlock(DistEntry *dep);
 ERTS_GLB_INLINE void erts_de_rwlock(DistEntry *dep);
 ERTS_GLB_INLINE void erts_de_rwunlock(DistEntry *dep);
-ERTS_GLB_INLINE void erts_de_links_lock(DistEntry *dep);
-ERTS_GLB_INLINE void erts_de_links_unlock(DistEntry *dep);
 
 #if ERTS_GLB_INLINE_INCL_FUNC_DEF
 
@@ -264,18 +258,6 @@ erts_de_rwunlock(DistEntry *dep)
     erts_rwmtx_rwunlock(&dep->rwmtx);
 }
 
-ERTS_GLB_INLINE void
-erts_de_links_lock(DistEntry *dep)
-{
-    erts_mtx_lock(&dep->lnk_mtx);
-}
-
-ERTS_GLB_INLINE void
-erts_de_links_unlock(DistEntry *dep)
-{
-    erts_mtx_unlock(&dep->lnk_mtx);
-}
-
 #endif /* #if ERTS_GLB_INLINE_INCL_FUNC_DEF */
 
 void erts_debug_test_node_tab_delayed_delete(Sint64 millisecs);