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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 0 insertions, 187 deletions

diff --git a/erts/emulator/beam/erl_monitors.h b/erts/emulator/beam/erl_monitors.h
deleted file mode 100644
index 1cacecd7e9..0000000000
--- a/erts/emulator/beam/erl_monitors.h
+++ /dev/null
@@ -1,187 +0,0 @@
-/*
- * %CopyrightBegin%
- * 
- * Copyright Ericsson AB 2004-2017. 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.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- * 
- * %CopyrightEnd%
- */
-
-/**********************************************************************
- * Header for monitors and links data structures.
- * Monitors are kept in an AVL tree and the data structures for
- * the four different types of monitors are like this:
- **********************************************************************
- * Local monitor by pid/port: 
- * (Ref is always same in all involved data structures)
- **********************************************************************
- *        Process/Port X     Process Y
- *       +-------------+    +-------------+
- * Type: | MON_ORIGIN  |    | MON_TARGET  |
- *       +-------------+    +-------------+
- * Pid:  | Pid(Y)      |    | Pid/Port(X) |
- *       +-------------+    +-------------+
- * Name: | []          |    | []          |
- *       +-------------+    +-------------+
- **********************************************************************
- * Local monitor by name: (Ref is always same in all involved data structures)
- **********************************************************************
- *        Process X          Process Y (name foo)
- *       +-------------+    +-------------+
- * Type: | MON_ORIGIN  |    | MON_TARGET  |
- *       +-------------+    +-------------+
- * Pid:  | Pid(Y)      |    | Pid(X)      |
- *       +-------------+    +-------------+
- * Name: | Atom(foo)   |    | Atom(foo)   |
- *       +-------------+    +-------------+
- **********************************************************************
- * Remote monitor by pid: (Ref is always same in all involved data structures)
- **********************************************************************
- *                    Node A              |           Node B
- *       ---------------------------------+----------------------------------
- *        Process X (@A)   Distentry @A       Distentry @B     Process Y (@B)
- *                         for node B         for node A 
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Type: | MON_ORIGIN  |  | MON_TARGET  |    | MON_ORIGIN  |  | MON_TARGET  |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Pid:  | Pid(Y)      |  | Pid(X)      |    | Pid(Y)      |  | Pid(X)      |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Name: | []          |  | []          |    | []          |  | []          |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- **********************************************************************
- * Remote monitor by name: (Ref is always same in all involved data structures)
- **********************************************************************
- *                    Node A              |           Node B
- *       ---------------------------------+----------------------------------
- *        Process X (@A)   Distentry @A       Distentry @B     Process Y (@B)
- *                         for node B         for node A       (name foo)
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Type: | MON_ORIGIN  |  | MON_TARGET  |    | MON_ORIGIN  |  | MON_TARGET  |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Pid:  | Atom(node B)|  | Pid(X)      |    | Pid(Y)      |  | Pid(X)      |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * Name: | Atom(foo)   |  | Atom(foo)   |    | Atom(foo)   |  | Atom(foo)   |
- *       +-------------+  +-------------+    +-------------+  +-------------+
- * The reason for the node atom in X->pid is that we don't know the actual
- * pid of the monitored process on the other node when setting the monitor
- * (which is done asyncronously).
- **********************************************************************/
-#ifndef _ERL_MONITORS_H
-#define _ERL_MONITORS_H
-
-/* Type tags for monitors */
-#define MON_ORIGIN 1
-#define MON_TARGET 2
-#define MON_NIF_TARGET 3
-#define MON_TIME_OFFSET 4
-
-/* Type tags for links */
-#define LINK_PID 1   /* ...Or port */
-#define LINK_NODE 3  /* "Node monitor" */  
-
-/* Size of a monitor without heap, in words (fixalloc) */
-#define ERTS_MONITOR_SIZE ((sizeof(ErtsMonitor) - sizeof(Uint))/sizeof(Uint))
-#define ERTS_MONITOR_SH_SIZE (ERTS_MONITOR_SIZE + ERTS_REF_THING_SIZE)
-#define ERTS_LINK_SIZE ((sizeof(ErtsLink) - sizeof(Uint))/sizeof(Uint))
-#define ERTS_LINK_SH_SIZE ERTS_LINK_SIZE /* Size of fix-alloced links */
-
-/* ErtsMonitor and ErtsLink *need* to begin in a similar way as 
-   ErtsMonitorOrLink */
-typedef struct erts_monitor_or_link {
-    struct erts_monitor_or_link *left, *right;
-    Sint16 balance;    
-} ErtsMonitorOrLink;
-
-typedef struct erts_monitor {
-    struct erts_monitor *left, *right; 
-    Sint16 balance;
-    Uint16 type;  /* MON_ORIGIN | MON_TARGET | MON_NIF_TARGET | MON_TIME_OFFSET */
-    Eterm ref;
-    union {
-        Eterm pid;  /* In case of distributed named monitor, this is the
-		     * nodename atom in MON_ORIGIN process, otherwise a pid or,
-		     * in case of a MON_TARGET, a port
-                     */
-        struct ErtsResource_* resource; /* MON_NIF_TARGET */
-    }u;
-    Eterm name;   /* When monitoring a named process: atom() else [] */
-    Uint heap[1]; /* Larger in reality */
-} ErtsMonitor;
-
-typedef struct erts_link {
-    struct erts_link *left, *right;
-    Sint16 balance;
-    Uint16 type;             /* LINK_PID | LINK_NODE */
-    Eterm pid;               /* When node monitor, 
-				the node atom is here instead */
-    union {
-	struct erts_link *root;  /* Used only in dist entries */
-	Uint refc;
-    } shared;
-    Uint heap[1];            /* Larger in reality */
-} ErtsLink;   
-
-typedef struct erts_suspend_monitor {
-    struct erts_suspend_monitor *left, *right;
-    Sint16 balance;
-
-    int pending;
-    int active;
-    Eterm pid;
-} ErtsSuspendMonitor;
-
-#define ERTS_LINK_ROOT(Linkp) ((Linkp)->shared.root)
-#define ERTS_LINK_REFC(Linkp) ((Linkp)->shared.refc) 
-
-Uint erts_tot_link_lh_size(void);
-
-
-/* Prototypes */
-void erts_destroy_monitor(ErtsMonitor *mon);
-void erts_add_monitor(ErtsMonitor **root, Uint type, Eterm ref, UWord entity,
-		      Eterm name);
-ErtsMonitor *erts_remove_monitor(ErtsMonitor **root, Eterm ref);
-ErtsMonitor *erts_lookup_monitor(ErtsMonitor *root, Eterm ref);
-void erts_sweep_monitors(ErtsMonitor *root, 
-			 void (*doit)(ErtsMonitor *, void *),
-			 void *context);
-
-void erts_destroy_link(ErtsLink *lnk);
-/* Returns 0 if OK, < 0 if already present */
-int erts_add_link(ErtsLink **root, Uint type, Eterm pid);
-ErtsLink *erts_add_or_lookup_link(ErtsLink **root, Uint type, Eterm pid);
-ErtsLink *erts_remove_link(ErtsLink **root, Eterm pid);
-ErtsLink *erts_lookup_link(ErtsLink *root, Eterm pid);
-void erts_sweep_links(ErtsLink *root, 
-		      void (*doit)(ErtsLink *, void *),
-		      void *context);
-
-void erts_destroy_suspend_monitor(ErtsSuspendMonitor *sproc);
-void erts_sweep_suspend_monitors(ErtsSuspendMonitor *root,
-				 void (*doit)(ErtsSuspendMonitor *, void *),
-				 void *context);
-ErtsSuspendMonitor *erts_add_or_lookup_suspend_monitor(ErtsSuspendMonitor **root,
-						       Eterm pid);
-ErtsSuspendMonitor *erts_lookup_suspend_monitor(ErtsSuspendMonitor *root,
-						Eterm pid);
-void erts_delete_suspend_monitor(ErtsSuspendMonitor **root, Eterm pid);
-void erts_init_monitors(void);
-void erts_one_link_size(ErtsLink *lnk, void *vpu);
-void erts_one_mon_size(ErtsMonitor *mon, void *vpu);
-
-#define erts_doforall_monitors erts_sweep_monitors
-#define erts_doforall_links erts_sweep_links
-#define erts_doforall_suspend_monitors erts_sweep_suspend_monitors
-
-#endif /* _ERL_MONITORS_H */