From c6eb41e2c63e2536f51ea6ac600dd3882983a522 Mon Sep 17 00:00:00 2001
From: prascle <prascle>
Date: Tue, 5 Oct 2004 18:36:46 +0000
Subject: [PATCH] PR: thread safe singleton

---
 src/SALOMELocalTrace/LocalTraceBufferPool.cxx | 16 ++++++++---
 src/SALOMELocalTrace/LocalTraceBufferPool.hxx |  1 +
 src/SALOMELocalTrace/LocalTraceCollector.cxx  | 28 ++++++++++---------
 src/SALOMELocalTrace/LocalTraceCollector.hxx  |  1 +
 4 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/src/SALOMELocalTrace/LocalTraceBufferPool.cxx b/src/SALOMELocalTrace/LocalTraceBufferPool.cxx
index 67791553f..49b6d32e6 100644
--- a/src/SALOMELocalTrace/LocalTraceBufferPool.cxx
+++ b/src/SALOMELocalTrace/LocalTraceBufferPool.cxx
@@ -33,18 +33,26 @@
 using namespace std;
 
 LocalTraceBufferPool* LocalTraceBufferPool::_singleton = 0;
+pthread_mutex_t LocalTraceBufferPool::_singletonMutex;
 
 // ============================================================================
 /*!
- *  guarantees a unique object instance of the class (singleton)
- *  Must be done at first because not thread safe: 
- *  _singleton is not protected by a mutex
+ *  guarantees a unique object instance of the class (singleton thread safe)
  */
 // ============================================================================
 
 LocalTraceBufferPool* LocalTraceBufferPool::instance()
 {
-  if (_singleton == 0) _singleton = new LocalTraceBufferPool();
+  if (_singleton == 0) // no need of lock when singleton already exists
+    {
+      int ret;
+      ret = pthread_mutex_lock(&_singletonMutex); // acquire lock to be alone
+      if (_singleton == 0)                     // another thread may have got
+	{                                      // the lock after the first test
+	  _singleton = new LocalTraceBufferPool(); 
+	}
+      ret = pthread_mutex_unlock(&_singletonMutex); // release lock
+    }
   return _singleton;
 }
 
diff --git a/src/SALOMELocalTrace/LocalTraceBufferPool.hxx b/src/SALOMELocalTrace/LocalTraceBufferPool.hxx
index 847478005..597b218e8 100644
--- a/src/SALOMELocalTrace/LocalTraceBufferPool.hxx
+++ b/src/SALOMELocalTrace/LocalTraceBufferPool.hxx
@@ -57,6 +57,7 @@ class LocalTraceBufferPool
 
  private:
   static LocalTraceBufferPool* _singleton;
+  static pthread_mutex_t _singletonMutex;
   LocalTrace_TraceInfo _myBuffer[TRACE_BUFFER_SIZE];
   sem_t _freeBufferSemaphore;       // to wait until there is a free buffer
   sem_t _fullBufferSemaphore;       // to wait until there is a buffer to print
diff --git a/src/SALOMELocalTrace/LocalTraceCollector.cxx b/src/SALOMELocalTrace/LocalTraceCollector.cxx
index 119722643..1bf05248e 100644
--- a/src/SALOMELocalTrace/LocalTraceCollector.cxx
+++ b/src/SALOMELocalTrace/LocalTraceCollector.cxx
@@ -32,31 +32,33 @@
 using namespace std;
 
 LocalTraceCollector* LocalTraceCollector::_singleton = 0;
+pthread_mutex_t LocalTraceCollector::_singletonMutex;
 int LocalTraceCollector::_threadToClose = 0;
 pthread_t LocalTraceCollector::_threadId = 0;
 int LocalTraceCollector::_toFile = 0;           // public, set by user
 
 // ============================================================================
 /*!
- *  guarantees a unique object instance of the class (singleton)
- *  Must be done at first because not thread safe: 
- *  _singleton is not protected by a mutex
- *  LocalTraceCollector instance is created, then LocalTraceBufferPool
- *  instance is created immediately in the same thread (not thread safe, too).
- *  After thet, a separate thread for loop to print traces is launched.
+ *  guarantees a unique object instance of the class (singleton thread safe)
+ *  a separate thread for loop to print traces is launched.
  */
 // ============================================================================
 
 LocalTraceCollector* LocalTraceCollector::instance()
 {
-  if (_singleton == 0)
+  if (_singleton == 0) // no need of lock when singleton already exists
     {
-      _singleton = new LocalTraceCollector();
-      LocalTraceBufferPool* initTraceBuffer = LocalTraceBufferPool::instance();
-      pthread_t traceThread;
-      int bid;
-      int ret = pthread_create(&traceThread, NULL,
-			       LocalTraceCollector::run, (void *)bid);
+      int ret;
+      ret = pthread_mutex_lock(&_singletonMutex); // acquire lock to be alone
+      if (_singleton == 0)                     // another thread may have got
+	{                                      // the lock after the first test
+	  _singleton = new LocalTraceCollector(); 
+	  pthread_t traceThread;
+	  int bid;
+	  int ret = pthread_create(&traceThread, NULL,
+				   LocalTraceCollector::run, (void *)bid);
+	}
+      ret = pthread_mutex_unlock(&_singletonMutex); // release lock
     }
   return _singleton;
 }
diff --git a/src/SALOMELocalTrace/LocalTraceCollector.hxx b/src/SALOMELocalTrace/LocalTraceCollector.hxx
index 5bcd75139..0b0e56ff5 100644
--- a/src/SALOMELocalTrace/LocalTraceCollector.hxx
+++ b/src/SALOMELocalTrace/LocalTraceCollector.hxx
@@ -43,6 +43,7 @@ class LocalTraceCollector
 
  private:
   static LocalTraceCollector* _singleton;
+  static pthread_mutex_t _singletonMutex;
   static pthread_t _threadId;
 };
 
-- 
2.39.2