From 3b8d135879bd045d63174064c6879eaa6581ec00 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Tue, 23 Jun 2009 17:33:37 +0000
Subject: [PATCH] Make the lazy initialization of DefaultTimerGroup threadsafe.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73963 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Support/Timer.cpp | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/lib/Support/Timer.cpp b/lib/Support/Timer.cpp
index 3c8879bd06e..bcb27a4ab4f 100644
--- a/lib/Support/Timer.cpp
+++ b/lib/Support/Timer.cpp
@@ -52,8 +52,20 @@ namespace {
 
 static TimerGroup *DefaultTimerGroup = 0;
 static TimerGroup *getDefaultTimerGroup() {
-  if (DefaultTimerGroup) return DefaultTimerGroup;
-  return DefaultTimerGroup = new TimerGroup("Miscellaneous Ungrouped Timers");
+  TimerGroup* tmp = DefaultTimerGroup;
+  sys::MemoryFence();
+  if (!tmp) {
+    llvm_acquire_global_lock();
+    tmp = DefaultTimerGroup;
+    if (!tmp) {
+      tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
+      sys::MemoryFence();
+      DefaultTimerGroup = tmp;
+    }
+    llvm_release_global_lock();
+  }
+  
+  return tmp;
 }
 
 Timer::Timer(const std::string &N)
@@ -377,11 +389,5 @@ void TimerGroup::removeTimer() {
     if (OutStream != cerr.stream() && OutStream != cout.stream())
       delete OutStream;   // Close the file...
   }
-
-  // Delete default timer group!
-  if (NumTimers == 0 && this == DefaultTimerGroup) {
-    delete DefaultTimerGroup;
-    DefaultTimerGroup = 0;
-  }
 }