/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements. See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache license, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License. You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the license for the specific language governing permissions and
   * limitations under the license.
   */
  package org.apache.logging.log4j.core.async;
  
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ThreadFactory;
  
  import org.apache.logging.log4j.Level;
  import org.apache.logging.log4j.Logger;
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.impl.Log4jLogEvent;
  import org.apache.logging.log4j.core.impl.LogEventFactory;
  import org.apache.logging.log4j.core.impl.MutableLogEvent;
  import org.apache.logging.log4j.core.impl.ReusableLogEventFactory;
  import org.apache.logging.log4j.core.jmx.RingBufferAdmin;
  import org.apache.logging.log4j.message.ReusableMessage;
  import org.apache.logging.log4j.status.StatusLogger;
  
  import com.lmax.disruptor.EventFactory;
  import com.lmax.disruptor.EventTranslatorTwoArg;
  import com.lmax.disruptor.ExceptionHandler;
  import com.lmax.disruptor.RingBuffer;
  import com.lmax.disruptor.Sequence;
  import com.lmax.disruptor.SequenceReportingEventHandler;
  import com.lmax.disruptor.WaitStrategy;
  import com.lmax.disruptor.dsl.Disruptor;
  import com.lmax.disruptor.dsl.ProducerType;
  
  /**
   * Helper class decoupling the {@code AsyncLoggerConfig} class from the LMAX Disruptor library.
   * <p>
   * {@code AsyncLoggerConfig} is a plugin, and will be loaded even if users do not configure any {@code <asyncLogger>} or
   * {@code <asyncRoot>} elements in the configuration. If {@code AsyncLoggerConfig} has inner classes that extend or
   * implement classes from the Disruptor library, a {@code NoClassDefFoundError} is thrown if the Disruptor jar is not in
   * the classpath when the PluginManager loads the {@code AsyncLoggerConfig} plugin from the pre-defined plugins
   * definition file.
   * <p>
   * This class serves to make the dependency on the Disruptor optional, so that these classes are only loaded when the
   * {@code AsyncLoggerConfig} is actually used.
   */
  public class AsyncLoggerConfigDisruptor implements AsyncLoggerConfigDelegate {
  
      private static final int MAX_DRAIN_ATTEMPTS_BEFORE_SHUTDOWN = 200;
      private static final int SLEEP_MILLIS_BETWEEN_DRAIN_ATTEMPTS = 50;
      private static final Logger LOGGER = StatusLogger.getLogger();
  
      /**
       * RingBuffer events contain all information necessary to perform the work in a separate thread.
       */
      public static class Log4jEventWrapper {
          public Log4jEventWrapper() {
          }
  
          public Log4jEventWrapper(final MutableLogEvent mutableLogEvent) {
              event = mutableLogEvent;
          }
  
          private AsyncLoggerConfig loggerConfig;
          private LogEvent event;
  
          /**
           * Release references held by ring buffer to allow objects to be garbage-collected.
           */
          public void clear() {
              loggerConfig = null;
              if (event instanceof MutableLogEvent) {
                  ((MutableLogEvent) event).clear();
              } else {
                  event = null;
              }
          }
  
          @Override
          public String toString() {
              return String.valueOf(event);
          }
      }
  
      /**
       * EventHandler performs the work in a separate thread.
       */
      private static class Log4jEventWrapperHandler implements SequenceReportingEventHandler<Log4jEventWrapper> {
          private static final int NOTIFY_PROGRESS_THRESHOLD = 50;
          private Sequence sequenceCallback;
         private int counter;
 
         @Override
         public void setSequenceCallback(final Sequence sequenceCallback) {
             this.sequenceCallback = sequenceCallback;
         }
 
         @Override
         public void onEvent(final Log4jEventWrapper event, final long sequence, final boolean endOfBatch)
                 throws Exception {
             event.event.setEndOfBatch(endOfBatch);
             event.loggerConfig.asyncCallAppenders(event.event);
             event.clear();
 
             notifyIntermediateProgress(sequence);
         }
 
         /**
          * Notify the BatchEventProcessor that the sequence has progressed. Without this callback the sequence would not
          * be progressed until the batch has completely finished.
          */
         private void notifyIntermediateProgress(final long sequence) {
             if (++counter > NOTIFY_PROGRESS_THRESHOLD) {
                 sequenceCallback.set(sequence);
                 counter = 0;
             }
         }
     }
 
     /**
      * Factory used to populate the RingBuffer with events. These event objects are then re-used during the life of the
      * RingBuffer.
      */
     private static final EventFactory<Log4jEventWrapper> FACTORY = new EventFactory<Log4jEventWrapper>() {
         @Override
         public Log4jEventWrapper newInstance() {
             return new Log4jEventWrapper();
         }
     };
 
     /**
      * Factory used to populate the RingBuffer with events. These event objects are then re-used during the life of the
      * RingBuffer.
      */
     private static final EventFactory<Log4jEventWrapper> MUTABLE_FACTORY = new EventFactory<Log4jEventWrapper>() {
         @Override
         public Log4jEventWrapper newInstance() {
             return new Log4jEventWrapper(new MutableLogEvent());
         }
     };
 
     /**
      * Object responsible for passing on data to a specific RingBuffer event.
      */
     private static final EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig> TRANSLATOR =
             new EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig>() {
 
         @Override
         public void translateTo(final Log4jEventWrapper ringBufferElement, final long sequence,
                 final LogEvent logEvent, final AsyncLoggerConfig loggerConfig) {
             ringBufferElement.event = logEvent;
             ringBufferElement.loggerConfig = loggerConfig;
         }
     };
 
     /**
      * Object responsible for passing on data to a RingBuffer event with a MutableLogEvent.
      */
     private static final EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig> MUTABLE_TRANSLATOR =
             new EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig>() {
 
         @Override
         public void translateTo(final Log4jEventWrapper ringBufferElement, final long sequence,
                 final LogEvent logEvent, final AsyncLoggerConfig loggerConfig) {
             ((MutableLogEvent) ringBufferElement.event).initFrom(logEvent);
             ringBufferElement.loggerConfig = loggerConfig;
         }
     };
 
     private static final ThreadFactory THREAD_FACTORY = new DaemonThreadFactory("AsyncLoggerConfig-");
 
     private int ringBufferSize;
     private AsyncQueueFullPolicy asyncQueueFullPolicy;
     private Boolean mutable = Boolean.FALSE;
 
     private volatile Disruptor<Log4jEventWrapper> disruptor;
     private ExecutorService executor;
     private long backgroundThreadId; // LOG4J2-471
     private EventFactory<Log4jEventWrapper> factory;
     private EventTranslatorTwoArg<Log4jEventWrapper, LogEvent, AsyncLoggerConfig> translator;
 
     public AsyncLoggerConfigDisruptor() {
     }
 
     // called from AsyncLoggerConfig constructor
     @Override
     public void setLogEventFactory(final LogEventFactory logEventFactory) {
         // if any AsyncLoggerConfig uses a ReusableLogEventFactory
         // then we need to populate our ringbuffer with MutableLogEvents
         this.mutable = mutable || (logEventFactory instanceof ReusableLogEventFactory);
     }
 
     /**
      * Increases the reference count and creates and starts a new Disruptor and associated thread if none currently
      * exists.
      *
      * @see #stop()
      */
     public synchronized void start() {
         if (disruptor != null) {
             LOGGER.trace("AsyncLoggerConfigDisruptor not starting new disruptor for this configuration, "
                     + "using existing object.");
             return;
         }
         LOGGER.trace("AsyncLoggerConfigDisruptor creating new disruptor for this configuration.");
         ringBufferSize = DisruptorUtil.calculateRingBufferSize("AsyncLoggerConfig.RingBufferSize");
         final WaitStrategy waitStrategy = DisruptorUtil.createWaitStrategy("AsyncLoggerConfig.WaitStrategy");
         executor = Executors.newSingleThreadExecutor(THREAD_FACTORY);
         backgroundThreadId = DisruptorUtil.getExecutorThreadId(executor);
         asyncQueueFullPolicy = AsyncQueueFullPolicyFactory.create();
 
         translator = mutable ? MUTABLE_TRANSLATOR : TRANSLATOR;
         factory = mutable ? MUTABLE_FACTORY : FACTORY;
         disruptor = new Disruptor<>(factory, ringBufferSize, executor, ProducerType.MULTI, waitStrategy);
 
         final ExceptionHandler<Log4jEventWrapper> errorHandler = DisruptorUtil.getAsyncLoggerConfigExceptionHandler();
         disruptor.handleExceptionsWith(errorHandler);
 
         final Log4jEventWrapperHandler[] handlers = {new Log4jEventWrapperHandler()};
         disruptor.handleEventsWith(handlers);
 
         LOGGER.debug("Starting AsyncLoggerConfig disruptor for this configuration with ringbufferSize={}, "
                 + "waitStrategy={}, exceptionHandler={}...", disruptor.getRingBuffer().getBufferSize(), waitStrategy
                 .getClass().getSimpleName(), errorHandler);
         disruptor.start();
     }
 
     /**
      * Decreases the reference count. If the reference count reached zero, the Disruptor and its associated thread are
      * shut down and their references set to {@code null}.
      */
     public synchronized void stop() {
         final Disruptor<Log4jEventWrapper> temp = disruptor;
         if (temp == null) {
             LOGGER.trace("AsyncLoggerConfigDisruptor: disruptor for this configuration already shut down.");
             return; // disruptor was already shut down by another thread
         }
         LOGGER.trace("AsyncLoggerConfigDisruptor: shutting down disruptor for this configuration.");
 
         // We must guarantee that publishing to the RingBuffer has stopped before we call disruptor.shutdown().
         disruptor = null; // client code fails with NPE if log after stop = OK
 
         // Calling Disruptor.shutdown() will wait until all enqueued events are fully processed,
         // but this waiting happens in a busy-spin. To avoid (postpone) wasting CPU,
         // we sleep in short chunks, up to 10 seconds, waiting for the ringbuffer to drain.
         for (int i = 0; hasBacklog(temp) && i < MAX_DRAIN_ATTEMPTS_BEFORE_SHUTDOWN; i++) {
             try {
                 Thread.sleep(SLEEP_MILLIS_BETWEEN_DRAIN_ATTEMPTS); // give up the CPU for a while
             } catch (final InterruptedException e) { // ignored
             }
         }
         temp.shutdown(); // busy-spins until all events currently in the disruptor have been processed
 
         LOGGER.trace("AsyncLoggerConfigDisruptor: shutting down disruptor executor for this configuration.");
         executor.shutdown(); // finally, kill the processor thread
         executor = null; // release reference to allow GC
 
         if (DiscardingAsyncQueueFullPolicy.getDiscardCount(asyncQueueFullPolicy) > 0) {
             LOGGER.trace("AsyncLoggerConfigDisruptor: {} discarded {} events.", asyncQueueFullPolicy,
                     DiscardingAsyncQueueFullPolicy.getDiscardCount(asyncQueueFullPolicy));
         }
     }
 
     /**
      * Returns {@code true} if the specified disruptor still has unprocessed events.
      */
     private static boolean hasBacklog(final Disruptor<?> theDisruptor) {
         final RingBuffer<?> ringBuffer = theDisruptor.getRingBuffer();
         return !ringBuffer.hasAvailableCapacity(ringBuffer.getBufferSize());
     }
 
     @Override
     public EventRoute getEventRoute(final Level logLevel) {
         final int remainingCapacity = remainingDisruptorCapacity();
         if (remainingCapacity < 0) {
             return EventRoute.DISCARD;
         }
         return asyncQueueFullPolicy.getRoute(backgroundThreadId, logLevel);
     }
 
     private int remainingDisruptorCapacity() {
         final Disruptor<Log4jEventWrapper> temp = disruptor;
         if (hasLog4jBeenShutDown(temp)) {
             return -1;
         }
         return (int) temp.getRingBuffer().remainingCapacity();
     }
 
     /**
      * Returns {@code true} if the specified disruptor is null.
      */
     private boolean hasLog4jBeenShutDown(final Disruptor<Log4jEventWrapper> aDisruptor) {
         if (aDisruptor == null) { // LOG4J2-639
             LOGGER.warn("Ignoring log event after log4j was shut down");
             return true;
         }
         return false;
     }
 
     @Override
     public void enqueueEvent(final LogEvent event, final AsyncLoggerConfig asyncLoggerConfig) {
         // LOG4J2-639: catch NPE if disruptor field was set to null after our check above
         try {
             final LogEvent logEvent = prepareEvent(event);
             enqueue(logEvent, asyncLoggerConfig);
         } catch (final NullPointerException npe) {
             // Note: NPE prevents us from adding a log event to the disruptor after it was shut down,
             // which could cause the publishEvent method to hang and never return.
             LOGGER.warn("Ignoring log event after log4j was shut down.");
         }
     }
 
     private LogEvent prepareEvent(final LogEvent event) {
         final LogEvent logEvent = ensureImmutable(event);
         if (logEvent instanceof Log4jLogEvent && logEvent.getMessage() instanceof ReusableMessage) {
             ((Log4jLogEvent) logEvent).makeMessageImmutable();
         }
         return logEvent;
     }
 
     private void enqueue(final LogEvent logEvent, final AsyncLoggerConfig asyncLoggerConfig) {
         disruptor.getRingBuffer().publishEvent(translator, logEvent, asyncLoggerConfig);
     }
 
     @Override
     public boolean tryEnqueue(final LogEvent event, final AsyncLoggerConfig asyncLoggerConfig) {
         final LogEvent logEvent = prepareEvent(event);
         return disruptor.getRingBuffer().tryPublishEvent(translator, logEvent, asyncLoggerConfig);
     }
 
     private LogEvent ensureImmutable(final LogEvent event) {
         LogEvent result = event;
         if (event instanceof RingBufferLogEvent) {
             // Deal with special case where both types of Async Loggers are used together:
             // RingBufferLogEvents are created by the all-loggers-async type, but
             // this event is also consumed by the some-loggers-async type (this class).
             // The original event will be re-used and modified in an application thread later,
             // so take a snapshot of it, which can be safely processed in the
             // some-loggers-async background thread.
             result = ((RingBufferLogEvent) event).createMemento();
         }
         return result;
     }
 
     /*
      * (non-Javadoc)
      *
      * @see org.apache.logging.log4j.core.async.AsyncLoggerConfigDelegate#createRingBufferAdmin(java.lang.String,
      * java.lang.String)
      */
     @Override
     public RingBufferAdmin createRingBufferAdmin(final String contextName, final String loggerConfigName) {
         return RingBufferAdmin.forAsyncLoggerConfig(disruptor.getRingBuffer(), contextName, loggerConfigName);
     }
 }