fix race conditions in LOG_EVERY_N

* Use CMakeLists.txt to check the availability of std::atomic<>
* Declare the static integer counters as std::atomic<int> instead of int
if C++11's atomic is available

CMakeLists.txt

@@ -213,6 +213,12 @@ std::aligned_storage<sizeof(char), alignof(char)>::type data;
 int main() { }
 " HAVE_ALIGNED_STORAGE)
 
+check_cxx_source_compiles ("
+#include <atomic>
+std::atomic<int> i;
+int main() { }
+" HAVE_CXX11_ATOMIC)
+
 if (WITH_TLS)
   # Cygwin does not support the thread attribute. Don't bother.
   if (HAVE_GCC_TLS)

src/config.h.cmake.in

@@ -192,6 +192,9 @@
 /* Check whether aligned_storage and alignof present */
 #cmakedefine HAVE_ALIGNED_STORAGE ${HAVE_ALIGNED_STORAGE}
 
+/* Check whether C++11 atomic is available */
+#cmakedefine HAVE_CXX11_ATOMIC ${HAVE_CXX11_ATOMIC}
+
 /* Version number of package */
 #cmakedefine VERSION
 

src/glog/logging.h.in

@@ -86,6 +86,10 @@
 #include <gflags/gflags.h>
 #endif
 
+#if HAVE_CXX11_ATOMIC
+#include <atomic>
+#endif
+
 @ac_google_start_namespace@
 
 #if @ac_cv_have_uint16_t@      // the C99 format
@@ -896,6 +900,45 @@ PLOG_IF(FATAL, GOOGLE_PREDICT_BRANCH_NOT_TAKEN((invocation) == -1))    \
 #define LOG_OCCURRENCES LOG_EVERY_N_VARNAME(occurrences_, __LINE__)
 #define LOG_OCCURRENCES_MOD_N LOG_EVERY_N_VARNAME(occurrences_mod_n_, __LINE__)
 
+#ifdef HAVE_CXX11_ATOMIC
+#define SOME_KIND_OF_LOG_EVERY_N(severity, n, what_to_do) \
+  static std::atomic<int> LOG_OCCURRENCES(0), LOG_OCCURRENCES_MOD_N(0); \
+  ++LOG_OCCURRENCES; \
+  if (++LOG_OCCURRENCES_MOD_N > n) LOG_OCCURRENCES_MOD_N -= n; \
+  if (LOG_OCCURRENCES_MOD_N == 1) \
+    @ac_google_namespace@::LogMessage( \
+        __FILE__, __LINE__, @ac_google_namespace@::GLOG_ ## severity, LOG_OCCURRENCES, \
+        &what_to_do).stream()
+
+#define SOME_KIND_OF_LOG_IF_EVERY_N(severity, condition, n, what_to_do) \
+  static std::atomic<int> LOG_OCCURRENCES(0), LOG_OCCURRENCES_MOD_N(0); \
+  ++LOG_OCCURRENCES; \
+  if (condition && \
+      ((LOG_OCCURRENCES_MOD_N=(LOG_OCCURRENCES_MOD_N + 1) % n) == (1 % n))) \
+    @ac_google_namespace@::LogMessage( \
+        __FILE__, __LINE__, @ac_google_namespace@::GLOG_ ## severity, LOG_OCCURRENCES, \
+                 &what_to_do).stream()
+
+#define SOME_KIND_OF_PLOG_EVERY_N(severity, n, what_to_do) \
+  static std::atomic<int> LOG_OCCURRENCES(0), LOG_OCCURRENCES_MOD_N(0); \
+  ++LOG_OCCURRENCES; \
+  if (++LOG_OCCURRENCES_MOD_N > n) LOG_OCCURRENCES_MOD_N -= n; \
+  if (LOG_OCCURRENCES_MOD_N == 1) \
+    @ac_google_namespace@::ErrnoLogMessage( \
+        __FILE__, __LINE__, @ac_google_namespace@::GLOG_ ## severity, LOG_OCCURRENCES, \
+        &what_to_do).stream()
+
+#define SOME_KIND_OF_LOG_FIRST_N(severity, n, what_to_do) \
+  static std::atomic<int> LOG_OCCURRENCES(0); \
+  if (LOG_OCCURRENCES <= n) \
+    ++LOG_OCCURRENCES; \
+  if (LOG_OCCURRENCES <= n) \
+    @ac_google_namespace@::LogMessage( \
+        __FILE__, __LINE__, @ac_google_namespace@::GLOG_ ## severity, LOG_OCCURRENCES, \
+        &what_to_do).stream()
+
+#else
+
 #define SOME_KIND_OF_LOG_EVERY_N(severity, n, what_to_do) \
   static int LOG_OCCURRENCES = 0, LOG_OCCURRENCES_MOD_N = 0; \
   ++LOG_OCCURRENCES; \
@@ -931,6 +974,7 @@ PLOG_IF(FATAL, GOOGLE_PREDICT_BRANCH_NOT_TAKEN((invocation) == -1))    \
     @ac_google_namespace@::LogMessage( \
         __FILE__, __LINE__, @ac_google_namespace@::GLOG_ ## severity, LOG_OCCURRENCES, \
         &what_to_do).stream()
+#endif
 
 namespace glog_internal_namespace_ {
 template <bool>