pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / store / Lock.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/store/Lock.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/store/Lock.java
new file mode 100644 (file)
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+++ b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/store/Lock.java
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+package org.apache.lucene.store;
+
+/**
+ * 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.
+ */
+
+import org.apache.lucene.util.ThreadInterruptedException;
+import java.io.IOException;
+
+/** An interprocess mutex lock.
+ * <p>Typical use might look like:<pre>
+ * new Lock.With(directory.makeLock("my.lock")) {
+ *     public Object doBody() {
+ *       <i>... code to execute while locked ...</i>
+ *     }
+ *   }.run();
+ * </pre>
+ *
+ * @see Directory#makeLock(String)
+ */
+public abstract class Lock {
+
+  /** How long {@link #obtain(long)} waits, in milliseconds,
+   *  in between attempts to acquire the lock. */
+  public static long LOCK_POLL_INTERVAL = 1000;
+
+  /** Pass this value to {@link #obtain(long)} to try
+   *  forever to obtain the lock. */
+  public static final long LOCK_OBTAIN_WAIT_FOREVER = -1;
+
+  /** Attempts to obtain exclusive access and immediately return
+   *  upon success or failure.
+   * @return true iff exclusive access is obtained
+   */
+  public abstract boolean obtain() throws IOException;
+
+  /**
+   * If a lock obtain called, this failureReason may be set
+   * with the "root cause" Exception as to why the lock was
+   * not obtained.
+   */
+  protected Throwable failureReason;
+
+  /** Attempts to obtain an exclusive lock within amount of
+   *  time given. Polls once per {@link #LOCK_POLL_INTERVAL}
+   *  (currently 1000) milliseconds until lockWaitTimeout is
+   *  passed.
+   * @param lockWaitTimeout length of time to wait in
+   *        milliseconds or {@link
+   *        #LOCK_OBTAIN_WAIT_FOREVER} to retry forever
+   * @return true if lock was obtained
+   * @throws LockObtainFailedException if lock wait times out
+   * @throws IllegalArgumentException if lockWaitTimeout is
+   *         out of bounds
+   * @throws IOException if obtain() throws IOException
+   */
+  public boolean obtain(long lockWaitTimeout) throws LockObtainFailedException, IOException {
+    failureReason = null;
+    boolean locked = obtain();
+    if (lockWaitTimeout < 0 && lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER)
+      throw new IllegalArgumentException("lockWaitTimeout should be LOCK_OBTAIN_WAIT_FOREVER or a non-negative number (got " + lockWaitTimeout + ")");
+
+    long maxSleepCount = lockWaitTimeout / LOCK_POLL_INTERVAL;
+    long sleepCount = 0;
+    while (!locked) {
+      if (lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER && sleepCount++ >= maxSleepCount) {
+        String reason = "Lock obtain timed out: " + this.toString();
+        if (failureReason != null) {
+          reason += ": " + failureReason;
+        }
+        LockObtainFailedException e = new LockObtainFailedException(reason);
+        if (failureReason != null) {
+          e.initCause(failureReason);
+        }
+        throw e;
+      }
+      try {
+        Thread.sleep(LOCK_POLL_INTERVAL);
+      } catch (InterruptedException ie) {
+        throw new ThreadInterruptedException(ie);
+      }
+      locked = obtain();
+    }
+    return locked;
+  }
+
+  /** Releases exclusive access. */
+  public abstract void release() throws IOException;
+
+  /** Returns true if the resource is currently locked.  Note that one must
+   * still call {@link #obtain()} before using the resource. */
+  public abstract boolean isLocked() throws IOException;
+
+
+  /** Utility class for executing code with exclusive access. */
+  public abstract static class With {
+    private Lock lock;
+    private long lockWaitTimeout;
+
+
+    /** Constructs an executor that will grab the named lock. */
+    public With(Lock lock, long lockWaitTimeout) {
+      this.lock = lock;
+      this.lockWaitTimeout = lockWaitTimeout;
+    }
+
+    /** Code to execute with exclusive access. */
+    protected abstract Object doBody() throws IOException;
+
+    /** Calls {@link #doBody} while <i>lock</i> is obtained.  Blocks if lock
+     * cannot be obtained immediately.  Retries to obtain lock once per second
+     * until it is obtained, or until it has tried ten times. Lock is released when
+     * {@link #doBody} exits.
+     * @throws LockObtainFailedException if lock could not
+     * be obtained
+     * @throws IOException if {@link Lock#obtain} throws IOException
+     */
+    public Object run() throws LockObtainFailedException, IOException {
+      boolean locked = false;
+      try {
+         locked = lock.obtain(lockWaitTimeout);
+         return doBody();
+      } finally {
+        if (locked)
+             lock.release();
+      }
+    }
+  }
+
+}