Priority Messages

bootstrap/lib/kernel/include/dist.hrl

@@ -55,6 +55,8 @@
 -define(DFLAG_NAME_ME,      (16#02 bsl 32)).
 -define(DFLAG_V4_NC,        (16#04 bsl 32)).
 -define(DFLAG_ALIAS,        (16#08 bsl 32)).
+-define(DFLAG_LOCAL_EXT,    (16#10 bsl 32)). %% only used internally
+-define(DFLAG_ALTACT_MSG,   (16#20 bsl 32)).
 
 %% The following flags are mandatory in OTP 25. OTP 25 and higher
 %% will accept ?DFLAG_MANDATORY_25_DIGEST as a shorthand for all those

erts/doc/guides/erl_dist_protocol.md

@@ -819,6 +819,12 @@ following capability flags are defined:
   [`ALIAS_SEND_TT`](erl_dist_protocol.md#ALIAS_SEND_TT) control messages.
   Introduced in OTP 24.
 
+- **`-define(DFLAG_ALTACT_MSG, (1 bsl 37)).`{: #DFLAG_ALTACT_MSG }** - The node
+  supports alternate action messages (alias and priority messages) and can by
+  this handle the
+  [`ALTACT_MSG_SEND`](erl_dist_protocol.md#ALTACT_MSG_SEND) control messages.
+  Introduced in OTP 28.
+
 There is also function `dist_util:strict_order_flags/0` returning all flags
 (bitwise or:ed together) corresponding to features that require strict ordering
 of data over distribution channels.
@@ -1148,6 +1154,32 @@ distributed operation it encodes:
   Same as [`ALIAS_SEND`](erl_dist_protocol.md#ALIAS_SEND), but also with a
   sequential trace `Token`.
 
+### New Ctrlmessages for Erlang/OTP 28
+
+- **`ALTACT_MSG_SEND`{: #ALTACT_MSG_SEND }** - `{37, Flags, SenderPid, To}` or `{37, Flags, SenderPid, To, Token}`
+
+  Followed by `Message`.
+
+  This control message is used when sending an alternate action message signal
+  `Message` to the process identified by `To`. Currently defined alternate
+  action message signals are alias and priority message signals. That is,
+  message signals with an action upon reception which is different than the
+  default action to append the message to the message queue.
+
+  Currently the following bitwise flags are defined:
+  * `ALTACT_MSG_FLG_PRIO` - **`1`** - This is a priority message
+  * `ALTACT_MSG_FLG_TOKEN` - **`2`** - The control message is a 5-tuple with
+    token as element 5; otherwise, the control message is a 4-tuple.
+  * `ALTACT_MSG_FLG_ALIAS` - **`4`** - Send to an alias, i.e., `To` is a reference
+  * `ALTACT_MSG_FLG_NAME` - **`8`** - Send to a registered name, i.e., `To` is an atom
+
+  If neither `ALTACT_MSG_ALIAS` nor `ALTACT_MSG_NAME` is set, `To` is a process
+  identifier.
+
+  Nodes that can handle this control message sets the distribution flag
+  [`DFLAG_ALTACT_MSG`](erl_dist_protocol.md#dflags) in the connection setup
+  handshake.
+
 [](){: #link_protocol } [](){: #new_link_protocol } [](){: #old_link_protocol }
 
 ### Link Protocol

erts/emulator/beam/atom.names

@@ -288,6 +288,7 @@ atom exact_reductions
 atom exception_from
 atom exception_trace
 atom exclusive
+atom exit_message
 atom exit_status
 atom exited
 atom existing
@@ -424,6 +425,7 @@ atom Lt='<'
 atom machine
 atom magic_ref
 atom major
+atom marked_message
 atom match
 atom match_limit
 atom match_limit_recursion
@@ -460,6 +462,7 @@ atom module
 atom module_info
 atom monitored_by
 atom monitor
+atom monitor_message
 atom monitor_nodes
 atom monitors
 atom monotonic
@@ -571,6 +574,10 @@ atom prepare
 atom prepare_on_load
 atom print
 atom priority
+atom priority_exit_message
+atom priority_marked_message
+atom priority_messages
+atom priority_monitor_message
 atom private
 atom private_append
 atom process
@@ -704,6 +711,7 @@ atom suspending
 atom system
 atom system_flag_scheduler_wall_time
 atom system_limit
+atom system_monitor
 atom system_version
 atom system_architecture
 atom table