From 6dcd46c8d21708451bc2f25128816037f8129ceb Mon Sep 17 00:00:00 2001
From: "kenton@google.com"
 <kenton@google.com@630680e5-0e50-0410-840e-4b1c322b438d>
Date: Sat, 18 Apr 2009 01:24:27 +0000
Subject: Fix initialization ordering problem in logging code.  Based on patch
 from Wink Saville.

---
 src/google/protobuf/stubs/common.cc | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

(limited to 'src/google/protobuf/stubs/common.cc')

diff --git a/src/google/protobuf/stubs/common.cc b/src/google/protobuf/stubs/common.cc
index 54f31ba4..385ea8ae 100644
--- a/src/google/protobuf/stubs/common.cc
+++ b/src/google/protobuf/stubs/common.cc
@@ -113,7 +113,27 @@ void NullLogHandler(LogLevel level, const char* filename, int line,
 
 static LogHandler* log_handler_ = &DefaultLogHandler;
 static int log_silencer_count_ = 0;
-static Mutex log_silencer_count_mutex_;
+
+// Mutex which protects log_silencer_count_.  We provide a static function to
+// get it so that it is initialized on first use, which be during
+// initialization time.  If we just allocated it as a global variable, it might
+// not be initialized before someone tries to use it.
+static Mutex* LogSilencerMutex() {
+  static Mutex* log_silencer_count_mutex_ = new Mutex;
+  return log_silencer_count_mutex_;
+}
+
+// Forces the above mutex to be initialized during startup.  This way we don't
+// have to worry about the initialization itself being thread-safe, since no
+// threads should exist yet at startup time.  (Otherwise we'd have no way to
+// make things thread-safe here because we'd need a Mutex for that, and we'd
+// have no way to construct one safely!)
+static struct LogSilencerMutexInitializer {
+  LogSilencerMutexInitializer() {
+    LogSilencerMutex();
+  }
+} log_silencer_mutex_initializer;
+
 
 static string SimpleCtoa(char c) { return string(1, c); }
 
@@ -140,7 +160,7 @@ void LogMessage::Finish() {
   bool suppress = false;
 
   if (level_ != LOGLEVEL_FATAL) {
-    MutexLock lock(&internal::log_silencer_count_mutex_);
+    MutexLock lock(internal::LogSilencerMutex());
     suppress = internal::log_silencer_count_ > 0;
   }
 
@@ -173,12 +193,12 @@ LogHandler* SetLogHandler(LogHandler* new_func) {
 }
 
 LogSilencer::LogSilencer() {
-  MutexLock lock(&internal::log_silencer_count_mutex_);
+  MutexLock lock(internal::LogSilencerMutex());
   ++internal::log_silencer_count_;
 };
 
 LogSilencer::~LogSilencer() {
-  MutexLock lock(&internal::log_silencer_count_mutex_);
+  MutexLock lock(internal::LogSilencerMutex());
   --internal::log_silencer_count_;
 };
 
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