Document Message Queues (and the change of data structure in Mailboxes

diff --git a/ChangeLog b/ChangeLog
index 605242b..e90432e 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,9 +6,13 @@ S4U:
  - New function NetZone::add_route(host1, host2, links) when you don't need gateways
    Also add a variant with s4u::Link, when you don't want to specify the directions
    on symmetric routes.
- - Introduce a Mailbox::get_async() with no payload parameter. You can use the new 
+ - Introduce a Mailbox::get_async() with no payload parameter. You can use the new
    Comm::get_payload() once the communication is over to retrieve the payload.
  - Implement recursive mutexes. Simply pass true to the constructor to get one.
+ - Introduce a new MessageQueue abstraction and associated Mess simulated object.
+   The behavior of a MessageQueue is similar to that of a Mailbox, but intended for
+   control messages that do not incur any simulated cost. Information is automagically
+   transported over thin air between producer and consumer. See examples/cpp/mess-wait
 
 SMPI:
  - New SMPI_app_instance_join(): wait for the completion of a started MPI instance
@@ -32,10 +36,17 @@ C API:
 Plugins:
  - Revamp the battery plugin: rewrite completely the API, for a better usability.
    The examples were updated accordingly.
- - Revamp of the Photovoltaic plugin: now called SolarPanel and complete rewrite of the API 
+ - Revamp of the Photovoltaic plugin: now called SolarPanel and complete rewrite of the API
  - Add chiller plugin: enable the management of chillers consuming electrical energy
    to compensate heat generated by hosts.
 
+Kernel:
+ - optimize an internal data structure (replace boost::circular_buffer_space_optimized by
+   std::deque to store pending and unmatched Comms in Mailboxes). It is actually a revert
+   to what was used a few years back. The boost structure had a lower memory footprint than
+   deques, but it appeared that their "space_optimized" character was generating a huge lot
+   of refcount changes on the stored Comms.
+
 ----------------------------------------------------------------------------
 
 SimGrid (3.34) June 26. 2023

diff --git a/docs/source/Release_Notes.rst b/docs/source/Release_Notes.rst
index 55b0d5a..992a1b0 100644 (file)
--- a/docs/source/Release_Notes.rst
+++ b/docs/source/Release_Notes.rst
@@ -667,7 +667,13 @@ This feature is not very usable yet, as you have to manually annotate your code,
 
 Version 3.35 (TBD)
 ------------------
-
+**On the interface front**, we introduced a new MessageQueue abstraction and associated Mess simulated object. The behavior of a
+MessageQueue is similar to that of a Mailbox, but intended for control messages that do not incur any simulated cost.
+Information is automagically transported over thin air between producer and consumer. Internally, the implementation is very
+similar to Mailboxes and Comms, only simpler. The motivation for this new abstraction came from a scalability issue observed in
+the WRENCH framework, which is heavily based on control messages. When the simulated size of these messages is set to 0, it creates
+very short lived network actions (i.e., lasting for only the route latency) that tend to overwhelm the LMM. Switching from Mailbox
+to MessageQueue for such information exchange avoid this problem and greatly improves the scalability of WRENCH-based simulators.
 
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