strip logging flag

Reviewed By: simpkins

Differential Revision: D33062040

fbshipit-source-id: a4d36cc558fc14de5929aa4ba278d394e5ca6225

folly/logging/xlog.h

@@ -57,6 +57,28 @@
  * best if you always invoke the compiler from the root directory of your
  * project repository.
  */
+
+/*
+ * The global value of FOLLY_XLOG_MIN_LEVEL. All the messages logged to
+ * XLOG(XXX) with severity less than FOLLY_XLOG_MIN_LEVEL will not be displayed.
+ * If it can be determined at compile time that the message will not be printed,
+ * the statement will be compiled out.
+ * FOLLY_XLOG_MIN_LEVEL should be below FATAL.
+ *
+ *
+ * Example: to strip out messages less than ERR, use the value of ERR below.
+ */
+#ifndef FOLLY_XLOG_MIN_LEVEL
+#define FOLLY_XLOG_MIN_LEVEL MIN_LEVEL
+#endif
+
+namespace folly {
+constexpr auto kLoggingMinLevel = LogLevel::FOLLY_XLOG_MIN_LEVEL;
+static_assert(
+    !isLogLevelFatal(kLoggingMinLevel),
+    "Cannot set FOLLY_XLOG_MIN_LEVEL to disable fatal messages");
+} // namespace folly
+
 #define XLOG(level, ...)                   \
   XLOG_IMPL(                               \
       ::folly::LogLevel::level,            \
@@ -435,7 +457,7 @@ FOLLY_EXPORT FOLLY_ALWAYS_INLINE bool xlogFirstNExactImpl(std::size_t n) {
  * See XlogLevelInfo for the implementation details.
  */
 #define XLOG_IS_ON_IMPL(level)                                \
-  ([] {                                                     \
+  ((level >= ::folly::LogLevel::FOLLY_XLOG_MIN_LEVEL) && [] { \
     static ::folly::XlogLevelInfo<XLOG_IS_IN_HEADER_FILE>     \
         folly_detail_xlog_level;                              \
     return folly_detail_xlog_level.check(                     \