/*
* $Id$
*
* Copyright (C) 2003-2014 JNode.org
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; If not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package org.jnode.vm.scheduler;
import org.jnode.vm.Unsafe;
import org.jnode.vm.objects.VmSystemObject;
import org.jnode.annotation.Inline;
import org.jnode.annotation.MagicPermission;
import org.jnode.annotation.NoFieldAlignments;
import org.jnode.annotation.Uninterruptible;
import org.vmmagic.unboxed.Address;
import org.vmmagic.unboxed.ObjectReference;
/**
* @author Ewout Prangsma (epr@users.sourceforge.net)
*/
@NoFieldAlignments
@MagicPermission
public class SpinLock extends VmSystemObject {
/**
* Lock counter. THIS FIELD MUST BE AT OFFSET 0!!
*/
private int lockCount;
/**
* Owner used for deadlock detection
*/
private VmProcessor owner;
/**
* Claim access to this monitor. A monitor may only be locked for a small
* amount of time, since this method uses a spinlock.
*
* @see #unlock()
* @see #lockCount
*/
@Inline
@Uninterruptible
public final void lock() {
final VmProcessor current = VmProcessor.current();
// Test for obvious deadlock
if (owner == current) {
Unsafe.debugStackTrace();
Unsafe.die("Deadlock in SpinLock#lock");
}
// Do the spinlock
final Address mlAddr = ObjectReference.fromObject(this).toAddress();
while (!mlAddr.attempt(0, 1)) {
current.yield(true);
}
this.owner = current;
}
/**
* Release access to this monitor. A monitor may only be locked for a small
* amount of time, since this method uses a spinlock.
*
* @see #lock()
* @see #lockCount
*/
@Inline
@Uninterruptible
public final void unlock() {
this.owner = null;
this.lockCount = 0;
}
/**
* Is this lock locked.
*
* @return {@code true} if the lock is locked, otherwise {@code false}.
*/
@Inline
@Uninterruptible
protected final boolean isLocked() {
return (lockCount != 0);
}
}