From 978ba263685f9f76f4721930decccebbbf776816 Mon Sep 17 00:00:00 2001
From: Martin Quinson <martin.quinson@ens-rennes.fr>
Date: Sat, 13 Jul 2019 23:42:00 +0200
Subject: [PATCH] Introduce SG_BARRIER_SERIAL_THREAD

Fix https://framagit.org/simgrid/simgrid/issues/34
---
 ChangeLog                       |  5 +++++
 include/simgrid/s4u/Barrier.hpp | 10 +++++-----
 src/s4u/s4u_Barrier.cpp         | 24 ++++++++++++++----------
 3 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 703cc4b9fd..dc7208e70e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,10 @@
 
 SimGrid (3.23.3) NOT RELEASED YET (v3.24 expected September 23. 7:50 UTC)
 
+S4U:
+ - Barrier::wait returns SG_BARRIER_SERIAL_THREAD for (only) one actor
+   for consistency with pthread_barrier_wait()
+
 MSG:
  - convert a new set of functions to the S4U C interface and move the old MSG
    versions to legacy (MSG_process_self*, MSG_process_{un}ref, ...)
@@ -20,6 +24,7 @@ Bugs:
  - FG#28: add sg_actor_self (and other wrappers on this_actor methods)
  - FG#29 and FG#33: provide a new C API to mutexes and condition variables 
  - FG#30: convert MSG_process_{un}ref to sg_actor_{un}ref
+ - FG#34: SG_BARRIER_SERIAL_THREAD?
 
 ----------------------------------------------------------------------------
 
diff --git a/include/simgrid/s4u/Barrier.hpp b/include/simgrid/s4u/Barrier.hpp
index cd87e0729d..85e2c0564c 100644
--- a/include/simgrid/s4u/Barrier.hpp
+++ b/include/simgrid/s4u/Barrier.hpp
@@ -14,6 +14,8 @@
 #include <atomic>
 #include <future>
 
+constexpr int SG_BARRIER_SERIAL_THREAD = -1;
+
 namespace simgrid {
 namespace s4u {
 
@@ -21,8 +23,8 @@ class XBT_PUBLIC Barrier {
 private:
   MutexPtr mutex_;
   ConditionVariablePtr cond_;
-  unsigned int expected_processes_;
-  unsigned int arrived_processes_ = 0;
+  unsigned int expected_actors_;
+  unsigned int arrived_actors_ = 0;
 
   /* refcounting */
   std::atomic_int_fast32_t refcount_{0};
@@ -35,9 +37,7 @@ public:
   Barrier& operator=(Barrier const&) = delete;
 #endif
 
-  /** Constructs a new barrier */
-  static BarrierPtr create(unsigned int expected_processes);
-
+  static BarrierPtr create(unsigned int expected_actors);
   int wait();
 
 #ifndef DOXYGEN
diff --git a/src/s4u/s4u_Barrier.cpp b/src/s4u/s4u_Barrier.cpp
index 6402d774ee..be8bb6e6e1 100644
--- a/src/s4u/s4u_Barrier.cpp
+++ b/src/s4u/s4u_Barrier.cpp
@@ -17,7 +17,8 @@ XBT_LOG_NEW_DEFAULT_CATEGORY(s4u_barrier, "S4U barrier");
 namespace simgrid {
 namespace s4u {
 
-Barrier::Barrier(unsigned int expected_processes) : mutex_(Mutex::create()), cond_(ConditionVariable::create()), expected_processes_(expected_processes)
+Barrier::Barrier(unsigned int expected_processes)
+    : mutex_(Mutex::create()), cond_(ConditionVariable::create()), expected_actors_(expected_processes)
 {
 }
 
@@ -25,24 +26,27 @@ Barrier::Barrier(unsigned int expected_processes) : mutex_(Mutex::create()), con
  *
  * See @ref s4u_raii.
  */
-BarrierPtr Barrier::create(unsigned int expected_processes)
+BarrierPtr Barrier::create(unsigned int expected_actors)
 {
-    return BarrierPtr(new Barrier(expected_processes));
+  return BarrierPtr(new Barrier(expected_actors));
 }
 
-/**
- * Wait functions
+/** @brief Block the current actor until all expected actors reach the barrier.
+ *
+ * This method is meant to be somewhat consistent with the pthread_barrier_wait function.
+ *
+ * @return 0 for all actors but one: exactly one actor will get SG_BARRIER_SERIAL_THREAD as a return value.
  */
 int Barrier::wait()
 {
   mutex_->lock();
-  arrived_processes_++;
-  XBT_DEBUG("waiting %p %u/%u", this, arrived_processes_, expected_processes_);
-  if (arrived_processes_ == expected_processes_) {
+  arrived_actors_++;
+  XBT_DEBUG("waiting %p %u/%u", this, arrived_actors_, expected_actors_);
+  if (arrived_actors_ == expected_actors_) {
     cond_->notify_all();
     mutex_->unlock();
-    arrived_processes_ = 0;
-    return -1;
+    arrived_actors_ = 0;
+    return SG_BARRIER_SERIAL_THREAD;
   }
 
   cond_->wait(mutex_);
-- 
2.20.1