folly/Logging.h

   1 /*
   2  * Copyright 2017 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 #pragma once
  18
  19 #include <atomic>
  20 #include <chrono>
  21 #include <glog/logging.h>
  22
  23 #ifndef FB_LOG_EVERY_MS
  24 /**
  25  * Issues a LOG(severity) no more often than every
  26  * milliseconds. Example:
  27  *
  28  * FB_LOG_EVERY_MS(INFO, 10000) << "At least ten seconds passed"
  29  *   " since you last saw this.";
  30  *
  31  * The implementation uses for statements to introduce variables in
  32  * a nice way that doesn't mess surrounding statements.  It is thread
  33  * safe.  Non-positive intervals will always log.
  34  */
  35 #define FB_LOG_EVERY_MS(severity, milli_interval)                            \
  36   for (decltype(milli_interval) FB_LEM_once = 1,                             \
  37                                 FB_LEM_interval = (milli_interval);          \
  38        FB_LEM_once; )                                                        \
  39     for (::std::chrono::milliseconds::rep FB_LEM_prev, FB_LEM_now =          \
  40              FB_LEM_interval <= 0 ? 0 :                                      \
  41              ::std::chrono::duration_cast< ::std::chrono::milliseconds>(     \
  42                  ::std::chrono::system_clock::now().time_since_epoch()       \
  43                  ).count();                                                  \
  44          FB_LEM_once; )                                                      \
  45       for (static ::std::atomic< ::std::chrono::milliseconds::rep>           \
  46                FB_LEM_hist; FB_LEM_once; FB_LEM_once = 0)                    \
  47         if (FB_LEM_interval > 0 &&                                           \
  48             (FB_LEM_now - (FB_LEM_prev =                                     \
  49                            FB_LEM_hist.load(std::memory_order_acquire)) <    \
  50                                                           FB_LEM_interval || \
  51              !FB_LEM_hist.compare_exchange_strong(FB_LEM_prev,FB_LEM_now))) {\
  52         } else                                                               \
  53           LOG(severity)
  54
  55 #endif