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/* Copyright (c) 2001-2004, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG, 
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb;

import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;

/**
 * A LockFile variant that capitalizes upon the
 * availability of {@link java.nio.channels.FileLock FileLock}.
 *
 * @author boucherb@users
 * @version 1.7.2
 * @since HSQLDB 1.7.2
 *
 */
final class NIOLockFile extends LockFile {

    // From the java.nio.channels.FileLock API docs:
    //
    // Some network filesystems do not implement file locks on regions
    // that extend past a certain position, often 2**30 or 2**31.
    // In general, great care should be taken when locking files that
    // reside on network filesystems.
    static final long MAX_NFS_LOCK_REGION = (1L << 30);
    static final long MIN_LOCK_REGION     = MAGIC.length + 8;

    /**
     * A FileChannel object obtained from the super
     * raf attribute. 

* * The fc attribute is used to obtain this object's * {@link #fl FileLock} attribute. */ private FileChannel fc; /** * The FileLock object used to lock this object's * lock file. */ private FileLock fl; /** * Tries to obtain a valid NIO lock upon this object's lock file using * this object's {@link #fl FileLock} attribute. * * @return true if a valid lock is obtained, else false. * @throws Exception if an error occurs while attempting to obtain the lock * */ protected boolean lockImpl() throws Exception { boolean isValid; if (fl != null && fl.isValid()) { return true; } trace("lockImpl(): fc = raf.getChannel()"); fc = raf.getChannel(); trace("lockImpl(): fl = fc.tryLock()"); fl = null; try { fl = fc.tryLock(0, MIN_LOCK_REGION, false); trace("lockImpl(): fl = " + fl); } catch (Exception e) { // This will not work with a localized JVM /* if (-1 == e.toString().indexOf("No locks available")) { throw e; } else { trace(e.toString()); } */ trace(e.toString()); } // In an ideal world, maybe?: // try { // fl = fc.tryLock(); // // trace("lockImpl(): fl = " + fl); // } catch (Exception e) { // trace(e.toString()); // // try { // fl = fc.tryLock(0, MAX_NFS_LOCK_REGION, false); // // trace("lockImpl(): fl = " + fl); // trace("Warning: possibly attempting to lock on NFS"); // } catch (Exception e2) { // trace(e2.toString()); // // try { // fl = fc.tryLock(0, MIN_LOCK_REGION, false); // // trace("lockImpl(): fl = " + fl); // trace("Warning: backed off to min lock region"); // trace("Warning: lock file may be unusable on reuse"); // } catch (Exception e3) { // trace(e3.toString()); // } // } // } trace("lockImpl(): f.deleteOnExit()"); f.deleteOnExit(); isValid = fl != null && fl.isValid(); trace("lockImpl():isValid(): " + isValid); return isValid; } /** * Tries to release any valid lock held upon this object's lock file using * this object's {@link #fl FileLock} attribute. * * @return true if a valid lock is released, else false * @throws Exception if na error occurs while attempting to release the lock */ protected boolean releaseImpl() throws Exception { // PRE: we know that this method is only called // if isLocked() is true. trace("releaseImpl(): fl = " + fl); if (fl != null) { trace("releaseImpl(): fl.release()"); fl.release(); trace("tryRelease(): fl = " + fl); fl = null; } trace("releaseImpl(): fc = " + fc); if (fc != null) { trace("releaseImpl(): fc.close()"); fc.close(); fc = null; } // CHECKME: // possibly overcomes some regarding full and // true release of FileLock and maybe related // NIO resources? // System.gc(); return true; } /** * Retrieves whether this object's {@link #fl FileLock} attribute represents * a valid lock upon this object's lock file. * * @return true if this object's {@link #fl FileLock} attribute is valid, * else false */ public boolean isValid() { return super.isValid() && (fl != null && fl.isValid()); } /** * Retrieves the String value: "fl =" + fl * @return the String value: "fl =" + fl */ protected String toStringImpl() { return "fl =" + fl; } }

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