001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.hbase.procedure2;
020
021import org.apache.yetus.audience.InterfaceAudience;
022import org.slf4j.Logger;
023import org.slf4j.LoggerFactory;
024
025/**
026 * Basic ProcedureEvent that contains an "object", which can be a description or a reference to the
027 * resource to wait on, and a queue for suspended procedures.
028 */
029@InterfaceAudience.Private
030public class ProcedureEvent<T> {
031  private static final Logger LOG = LoggerFactory.getLogger(ProcedureEvent.class);
032
033  private final T object;
034  private boolean ready = false;
035  private ProcedureDeque suspendedProcedures = new ProcedureDeque();
036
037  public ProcedureEvent(final T object) {
038    this.object = object;
039  }
040
041  public synchronized boolean isReady() {
042    return ready;
043  }
044
045  /**
046   * @return true if event is not ready and adds procedure to suspended queue, else returns false.
047   */
048  public synchronized boolean suspendIfNotReady(Procedure proc) {
049    if (!ready) {
050      suspendedProcedures.addLast(proc);
051    }
052    return !ready;
053  }
054
055  /** Mark the event as not ready. */
056  public synchronized void suspend() {
057    ready = false;
058    if (LOG.isTraceEnabled()) {
059      LOG.trace("Suspend " + toString());
060    }
061  }
062
063  /**
064   * Wakes up the suspended procedures by pushing them back into scheduler queues and sets the
065   * event as ready.
066   * See {@link #wakeInternal(AbstractProcedureScheduler)} for why this is not synchronized.
067   */
068  public void wake(AbstractProcedureScheduler procedureScheduler) {
069    procedureScheduler.wakeEvents(new ProcedureEvent[]{this});
070  }
071
072  /**
073   * Wakes up the suspended procedures only if the given {@code proc} is waiting on this event.
074   * <p/>
075   * Mainly used by region assignment to reject stale OpenRegionProcedure/CloseRegionProcedure. Use
076   * with caution as it will cause performance issue if there are lots of procedures waiting on the
077   * event.
078   */
079  public synchronized boolean wakeIfSuspended(AbstractProcedureScheduler procedureScheduler,
080      Procedure<?> proc) {
081    if (suspendedProcedures.stream().anyMatch(p -> p.getProcId() == proc.getProcId())) {
082      wake(procedureScheduler);
083      return true;
084    }
085    return false;
086  }
087
088  /**
089   * Wakes up all the given events and puts the procedures waiting on them back into
090   * ProcedureScheduler queues.
091   */
092  public static void wakeEvents(AbstractProcedureScheduler scheduler, ProcedureEvent ... events) {
093    scheduler.wakeEvents(events);
094  }
095
096  /**
097   * Only to be used by ProcedureScheduler implementations.
098   * Reason: To wake up multiple events, locking sequence is
099   * schedLock --> synchronized (event)
100   * To wake up an event, both schedLock() and synchronized(event) are required.
101   * The order is schedLock() --> synchronized(event) because when waking up multiple events
102   * simultaneously, we keep the scheduler locked until all procedures suspended on these events
103   * have been added back to the queue (Maybe it's not required? Evaluate!)
104   * To avoid deadlocks, we want to keep the locking order same even when waking up single event.
105   * That's why, {@link #wake(AbstractProcedureScheduler)} above uses the same code path as used
106   * when waking up multiple events.
107   * Access should remain package-private.
108   */
109  synchronized void wakeInternal(AbstractProcedureScheduler procedureScheduler) {
110    if (ready && !suspendedProcedures.isEmpty()) {
111      LOG.warn("Found procedures suspended in a ready event! Size=" + suspendedProcedures.size());
112    }
113    ready = true;
114    if (LOG.isTraceEnabled()) {
115      LOG.trace("Unsuspend " + toString());
116    }
117    // wakeProcedure adds to the front of queue, so we start from last in the
118    // waitQueue' queue, so that the procedure which was added first goes in the front for
119    // the scheduler queue.
120    procedureScheduler.addFront(suspendedProcedures.descendingIterator());
121    suspendedProcedures.clear();
122  }
123
124  /**
125   * Access to suspendedProcedures is 'synchronized' on this object, but it's fine to return it
126   * here for tests.
127   */
128  public ProcedureDeque getSuspendedProcedures() {
129    return suspendedProcedures;
130  }
131
132  @Override
133  public String toString() {
134    return getClass().getSimpleName() + " for " + object + ", ready=" + isReady() +
135        ", " + suspendedProcedures;
136  }
137}