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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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, 6 insertions, 7 deletions

diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 0f23027752..d853b2e352 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1,7 +1,7 @@
 /*
  * %CopyrightBegin%
  *
- * Copyright Ericsson AB 1996-2017. All Rights Reserved.
+ * Copyright Ericsson AB 1996-2018. 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.
@@ -87,9 +87,7 @@ typedef struct
 {
     erts_mtx_t lock;
     ErtsMonitor* root;
-    int pending_failed_fire;
-    int is_dying;
-
+    Uint refc;
     size_t user_data_sz;
 } ErtsResourceMonitors;
 
@@ -116,7 +114,8 @@ extern void erts_pre_nif(struct enif_environment_t*, Process*,
 			 struct erl_module_nif*, Process* tracee);
 extern void erts_post_nif(struct enif_environment_t* env);
 extern void erts_resource_stop(ErtsResource*, ErlNifEvent, int is_direct_call);
-void erts_fire_nif_monitor(ErtsResource*, Eterm pid, Eterm ref);
+void erts_fire_nif_monitor(ErtsMonitor *tmon);
+void erts_nif_demonitored(ErtsResource* resource);
 extern Eterm erts_nif_taints(Process* p);
 extern void erts_print_nif_taints(fmtfn_t to, void* to_arg);
 void erts_unload_nif(struct erl_module_nif* nif);
@@ -886,6 +885,7 @@ void erts_init_trap_export(Export* ep, Eterm m, Eterm f, Uint a,
 			   Eterm (*bif)(Process*, Eterm*, BeamInstr*));
 void erts_init_bif(void);
 Eterm erl_send(Process *p, Eterm to, Eterm msg);
+int erts_set_group_leader(Process *proc, Eterm new_gl);
 
 /* erl_bif_op.c */
 
@@ -908,7 +908,6 @@ extern erts_atomic_t erts_copy_literal_area__;
 #define ERTS_COPY_LITERAL_AREA()					\
     ((ErtsLiteralArea *) erts_atomic_read_nob(&erts_copy_literal_area__))
 extern Process *erts_literal_area_collector;
-extern Process *erts_dirty_process_code_checker;
 
 extern Process *erts_code_purger;
 
@@ -1072,7 +1071,7 @@ void erts_move_multi_frags(Eterm** hpp, ErlOffHeap*, ErlHeapFragment* first,
 			   Eterm* refs, unsigned nrefs, int literals);
 
 /* Utilities */
-extern void erts_delete_nodes_monitors(Process *, ErtsProcLocks);
+void erts_monitor_nodes_delete(ErtsMonitor *);
 extern Eterm erts_monitor_nodes(Process *, Eterm, Eterm);
 extern Eterm erts_processes_monitoring_nodes(Process *);
 extern int erts_do_net_exits(DistEntry*, Eterm);