From ef8e45c12eed3865ec33faf5760ed19bb55e183a Mon Sep 17 00:00:00 2001
From: Martin Quinson <martin.quinson@ens-rennes.fr>
Date: Wed, 2 Mar 2022 22:23:54 +0100
Subject: [PATCH] New signal: Engine::on_simulation_start

---
 ChangeLog                      | 3 +++
 docs/source/app_s4u.rst        | 1 +
 include/simgrid/s4u/Engine.hpp | 6 +++++-
 src/s4u/s4u_Engine.cpp         | 6 ++++++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 9776b48a65..3453aea52a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,9 @@ SMPI:
    not just at the end, reducing memory cost and performance hit.
  - Update OpenMPI collectives selection logic to match current one (4.1.2)
 
+S4U:
+ - New signal: Engine::on_simulation_start_cb()
+
 XBT:
  - Drop xbt_dynar_shrink().
 
diff --git a/docs/source/app_s4u.rst b/docs/source/app_s4u.rst
index 666ac3f45b..2ff9d3a139 100644
--- a/docs/source/app_s4u.rst
+++ b/docs/source/app_s4u.rst
@@ -957,6 +957,7 @@ Signals
       .. doxygenfunction:: simgrid::s4u::Engine::on_deadlock_cb
       .. doxygenfunction:: simgrid::s4u::Engine::on_platform_created_cb
       .. doxygenfunction:: simgrid::s4u::Engine::on_platform_creation_cb
+      .. doxygenfunction:: simgrid::s4u::Engine::on_simulation_start_cb
       .. doxygenfunction:: simgrid::s4u::Engine::on_simulation_end_cb
       .. doxygenfunction:: simgrid::s4u::Engine::on_time_advance_cb
 
diff --git a/include/simgrid/s4u/Engine.hpp b/include/simgrid/s4u/Engine.hpp
index 3e620e4541..7716e47f4d 100644
--- a/include/simgrid/s4u/Engine.hpp
+++ b/include/simgrid/s4u/Engine.hpp
@@ -208,6 +208,8 @@ public:
   /** Add a callback fired when the platform is about to be created
    * (ie, after any configuration change and just before the resource creation) */
   static void on_platform_creation_cb(const std::function<void()>& cb) { on_platform_creation.connect(cb); }
+  /** Add a callback fired when the main simulation loop starts, at the beginning of the first call to Engine::run() */
+  static void on_simulation_start_cb(const std::function<void()>& cb) { on_simulation_start.connect(cb); }
   /** Add a callback fired when the main simulation loop ends, just before the end of Engine::run() */
   static void on_simulation_end_cb(const std::function<void()>& cb) { on_simulation_end.connect(cb); }
 
@@ -228,9 +230,11 @@ public:
 #endif
 
 private:
-  static xbt::signal<void()> on_simulation_end;
+  static xbt::signal<void()> on_simulation_start;
   static xbt::signal<void(double)> on_time_advance;
   static xbt::signal<void(void)> on_deadlock;
+  static xbt::signal<void()> on_simulation_end;
+
   kernel::EngineImpl* const pimpl;
   static Engine* instance_;
   void initialize(int* argc, char** argv);
diff --git a/src/s4u/s4u_Engine.cpp b/src/s4u/s4u_Engine.cpp
index 8baf07d2d8..845c3f053a 100644
--- a/src/s4u/s4u_Engine.cpp
+++ b/src/s4u/s4u_Engine.cpp
@@ -26,6 +26,7 @@ namespace simgrid {
 namespace s4u {
 xbt::signal<void()> Engine::on_platform_creation;
 xbt::signal<void()> Engine::on_platform_created;
+xbt::signal<void()> Engine::on_simulation_start;
 xbt::signal<void()> Engine::on_simulation_end;
 xbt::signal<void(double)> Engine::on_time_advance;
 xbt::signal<void(void)> Engine::on_deadlock;
@@ -333,6 +334,11 @@ void Engine::run() const
 }
 void Engine::run_until(double max_date) const
 {
+  static bool callback_called = false;
+  if (not callback_called) {
+    on_simulation_start();
+    callback_called = true;
+  }
   /* Clean IO before the run */
   fflush(stdout);
   fflush(stderr);
-- 
2.20.1