folly/Logging.h

   1 /*
   2  * Copyright 2014 Facebook, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *   http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #ifndef FOLLY_LOGGING_H_
  18 #define FOLLY_LOGGING_H_
  19
  20 #include <atomic>
  21 #include <chrono>
  22 #include <glog/logging.h>
  23
  24 #ifndef FB_LOG_EVERY_MS
  25 /**
  26  * Issues a LOG(severity) no more often than every
  27  * milliseconds. Example:
  28  *
  29  * FB_LOG_EVERY_MS(INFO, 10000) << "At least ten seconds passed"
  30  *   " since you last saw this.";
  31  *
  32  * The implementation uses for statements to introduce variables in
  33  * a nice way that doesn't mess surrounding statements.  It is thread
  34  * safe.
  35  */
  36 #define FB_LOG_EVERY_MS(severity, milli_interval)                            \
  37   for (bool FB_LEM_once = true; FB_LEM_once; )                               \
  38     for (::std::chrono::milliseconds::rep FB_LEM_prev, FB_LEM_now =          \
  39              ::std::chrono::duration_cast< ::std::chrono::milliseconds>(     \
  40                  ::std::chrono::system_clock::now().time_since_epoch()       \
  41                  ).count();                                                  \
  42          FB_LEM_once; )                                                      \
  43       for (static ::std::atomic< ::std::chrono::milliseconds::rep>           \
  44                FB_LEM_hist; FB_LEM_once; FB_LEM_once = false)                \
  45         if (FB_LEM_now - (FB_LEM_prev =                                      \
  46                           FB_LEM_hist.load(std::memory_order_acquire)) <     \
  47                 milli_interval ||                                            \
  48             !FB_LEM_hist.compare_exchange_strong(FB_LEM_prev, FB_LEM_now)) { \
  49         } else                                                               \
  50           LOG(severity)
  51
  52 #endif
  53
  54 #endif  // FOLLY_LOGGING_H_