FB_LOG_ONCE()

Summary: We need a thread-safe alternative to `LOG_FIRST_N(severity, n)` -- specifically when n = 1, the most common case.

Reviewed By: yfeldblum, ot, luciang

Differential Revision: D28884240

fbshipit-source-id: 41c937bf37dba036b71f1c62fd70445e79a3924a

folly/GLog.h

@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <folly/Likely.h>
+
 #include <atomic>
 #include <chrono>
 
@@ -57,3 +59,27 @@
           LOG(severity)
 
 #endif
+
+/**
+ * Issues a LOG(severity) once.
+ *
+ *   FB_LOG_ONCE(ERROR) << "Log this error only once";
+ *
+ * This macro is thread-safe and does not impact surrounding statements.
+ *
+ * NOTE: A load() is used in the fast-path scenario (steady state) in order to
+ * avoid a locked RMW operation.
+ */
+#ifndef FB_LOG_ONCE
+#define FB_LOG_ONCE(severity)                                                  \
+  for (auto __folly_detail_glog_once = true; __folly_detail_glog_once;)        \
+    for (static ::std::atomic_bool __folly_detail_glog_logged{false};          \
+         __folly_detail_glog_once;                                             \
+         __folly_detail_glog_once = false)                                     \
+      if (FOLLY_LIKELY(                                                        \
+              __folly_detail_glog_logged.load(::std::memory_order_relaxed)) || \
+          __folly_detail_glog_logged.exchange(                                 \
+              true, ::std::memory_order_relaxed)) {                            \
+      } else                                                                   \
+        LOG(severity)
+#endif

folly/detail/MemoryIdler.cpp

@@ -104,8 +104,7 @@ static void fetchStackLimits() {
   pthread_attr_t attr;
   if ((err = pthread_getattr_np(pthread_self(), &attr))) {
     // some restricted environments can't access /proc
-    FB_LOG_EVERY_MS(WARNING, 60000)
-        << "pthread_getaddr_np failed errno=" << err;
+    FB_LOG_ONCE(ERROR) << "pthread_getaddr_np failed errno=" << err;
     tls_stackSize = 1;
     return;
   }
@@ -115,7 +114,7 @@ static void fetchStackLimits() {
   size_t rawSize;
   if ((err = pthread_attr_getstack(&attr, &addr, &rawSize))) {
     // unexpected, but it is better to continue in prod than do nothing
-    FB_LOG_EVERY_MS(ERROR, 10000) << "pthread_attr_getstack error " << err;
+    FB_LOG_ONCE(ERROR) << "pthread_attr_getstack error " << err;
     assert(false);
     tls_stackSize = 1;
     return;
@@ -131,8 +130,8 @@ static void fetchStackLimits() {
     //
     // Very large stack size is a bug (hence the assert), but we can
     // carry on if we are in prod.
-    FB_LOG_EVERY_MS(ERROR, 10000)
-        << "pthread_attr_getstack returned insane stack size " << rawSize;
+    FB_LOG_ONCE(ERROR) << "pthread_attr_getstack returned insane stack size "
+                       << rawSize;
     assert(false);
     tls_stackSize = 1;
     return;

folly/io/async/Request.cpp

@@ -242,9 +242,8 @@ bool RequestContext::State::doSetContextData(
     result = doSetContextDataHelper(token, data, behaviour, safe);
   }
   if (result.unexpected) {
-    FB_LOG_EVERY_MS(WARNING, 60000)
-        << "Calling RequestContext::setContextData for "
-        << token.getDebugString() << " but it is already set";
+    FB_LOG_ONCE(WARNING) << "Calling RequestContext::setContextData for "
+                         << token.getDebugString() << " but it is already set";
   }
   if (result.replaced) {
     result.replaced->retire(); // Retire to hazptr library