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    1   package org.apache.lucene.store;
    2   
    3   /**
    4    * Licensed to the Apache Software Foundation (ASF) under one or more
    5    * contributor license agreements.  See the NOTICE file distributed with
    6    * this work for additional information regarding copyright ownership.
    7    * The ASF licenses this file to You under the Apache License, Version 2.0
    8    * (the "License"); you may not use this file except in compliance with
    9    * the License.  You may obtain a copy of the License at
   10    *
   11    *     http://www.apache.org/licenses/LICENSE-2.0
   12    *
   13    * Unless required by applicable law or agreed to in writing, software
   14    * distributed under the License is distributed on an "AS IS" BASIS,
   15    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   16    * See the License for the specific language governing permissions and
   17    * limitations under the License.
   18    */
   19   
   20   import org.apache.lucene.util.ThreadInterruptedException;
   21   import java.io.IOException;
   22   
   23   /** An interprocess mutex lock.
   24    * <p>Typical use might look like:<pre>
   25    * new Lock.With(directory.makeLock("my.lock")) {
   26    *     public Object doBody() {
   27    *       <i>... code to execute while locked ...</i>
   28    *     }
   29    *   }.run();
   30    * </pre>
   31    *
   32    * @see Directory#makeLock(String)
   33    */
   34   public abstract class Lock {
   35   
   36     /** How long {@link #obtain(long)} waits, in milliseconds,
   37      *  in between attempts to acquire the lock. */
   38     public static long LOCK_POLL_INTERVAL = 1000;
   39   
   40     /** Pass this value to {@link #obtain(long)} to try
   41      *  forever to obtain the lock. */
   42     public static final long LOCK_OBTAIN_WAIT_FOREVER = -1;
   43   
   44     /** Attempts to obtain exclusive access and immediately return
   45      *  upon success or failure.
   46      * @return true iff exclusive access is obtained
   47      */
   48     public abstract boolean obtain() throws IOException;
   49   
   50     /**
   51      * If a lock obtain called, this failureReason may be set
   52      * with the "root cause" Exception as to why the lock was
   53      * not obtained.
   54      */
   55     protected Throwable failureReason;
   56   
   57     /** Attempts to obtain an exclusive lock within amount of
   58      *  time given. Polls once per {@link #LOCK_POLL_INTERVAL}
   59      *  (currently 1000) milliseconds until lockWaitTimeout is
   60      *  passed.
   61      * @param lockWaitTimeout length of time to wait in
   62      *        milliseconds or {@link
   63      *        #LOCK_OBTAIN_WAIT_FOREVER} to retry forever
   64      * @return true if lock was obtained
   65      * @throws LockObtainFailedException if lock wait times out
   66      * @throws IllegalArgumentException if lockWaitTimeout is
   67      *         out of bounds
   68      * @throws IOException if obtain() throws IOException
   69      */
   70     public boolean obtain(long lockWaitTimeout) throws LockObtainFailedException, IOException {
   71       failureReason = null;
   72       boolean locked = obtain();
   73       if (lockWaitTimeout < 0 && lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER)
   74         throw new IllegalArgumentException("lockWaitTimeout should be LOCK_OBTAIN_WAIT_FOREVER or a non-negative number (got " + lockWaitTimeout + ")");
   75   
   76       long maxSleepCount = lockWaitTimeout / LOCK_POLL_INTERVAL;
   77       long sleepCount = 0;
   78       while (!locked) {
   79         if (lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER && sleepCount++ >= maxSleepCount) {
   80           String reason = "Lock obtain timed out: " + this.toString();
   81           if (failureReason != null) {
   82             reason += ": " + failureReason;
   83           }
   84           LockObtainFailedException e = new LockObtainFailedException(reason);
   85           if (failureReason != null) {
   86             e.initCause(failureReason);
   87           }
   88           throw e;
   89         }
   90         try {
   91           Thread.sleep(LOCK_POLL_INTERVAL);
   92         } catch (InterruptedException ie) {
   93           throw new ThreadInterruptedException(ie);
   94         }
   95         locked = obtain();
   96       }
   97       return locked;
   98     }
   99   
  100     /** Releases exclusive access. */
  101     public abstract void release() throws IOException;
  102   
  103     /** Returns true if the resource is currently locked.  Note that one must
  104      * still call {@link #obtain()} before using the resource. */
  105     public abstract boolean isLocked() throws IOException;
  106   
  107   
  108     /** Utility class for executing code with exclusive access. */
  109     public abstract static class With {
  110       private Lock lock;
  111       private long lockWaitTimeout;
  112   
  113   
  114       /** Constructs an executor that will grab the named lock. */
  115       public With(Lock lock, long lockWaitTimeout) {
  116         this.lock = lock;
  117         this.lockWaitTimeout = lockWaitTimeout;
  118       }
  119   
  120       /** Code to execute with exclusive access. */
  121       protected abstract Object doBody() throws IOException;
  122   
  123       /** Calls {@link #doBody} while <i>lock</i> is obtained.  Blocks if lock
  124        * cannot be obtained immediately.  Retries to obtain lock once per second
  125        * until it is obtained, or until it has tried ten times. Lock is released when
  126        * {@link #doBody} exits.
  127        * @throws LockObtainFailedException if lock could not
  128        * be obtained
  129        * @throws IOException if {@link Lock#obtain} throws IOException
  130        */
  131       public Object run() throws LockObtainFailedException, IOException {
  132         boolean locked = false;
  133         try {
  134            locked = lock.obtain(lockWaitTimeout);
  135            return doBody();
  136         } finally {
  137           if (locked)
  138   	      lock.release();
  139         }
  140       }
  141     }
  142   
  143   }

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