/*
* $Id$
*
* 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.VmMagic;
import org.jnode.annotation.Inline;
import org.jnode.annotation.KernelSpace;
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;
import org.vmmagic.unboxed.Word;
/**
* A ProcessorLock is a lock that grants access to a resource from a single
* processor.
*
* @author Ewout Prangsma (epr@users.sourceforge.net)
*/
@MagicPermission
@NoFieldAlignments
public class ProcessorLock {
/**
* Current owner of this lock, null if not locked. Keep this field at offset
* 0!!!
*/
private VmProcessor owner;
/**
* Number of times the lock has been locked
*/
private Word lockCount;
/**
* Claim access to this lock.
*
* @see #unlock()
* @see #lockCount
*/
@Uninterruptible
@KernelSpace
@Inline
public final void lock() {
if (this.owner == VmMagic.currentProcessor()) {
// We already own this lock, increment the lock count.
lockCount = lockCount.add(Word.one());
} else {
final Address ownerAddr = ObjectReference.fromObject(this)
.toAddress();
final ObjectReference procRef = ObjectReference.fromObject(VmMagic
.currentProcessor());
while (!ownerAddr.attempt(null, procRef)) {
// Busy wait
}
// Now I'm the owner
lockCount = lockCount.add(Word.one());
}
}
/**
* 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
*/
@Uninterruptible
@KernelSpace
@Inline
public final void unlock() {
if (this.owner == VmMagic.currentProcessor()) {
// We own this lock, decrement the lock count.
lockCount = lockCount.sub(Word.one());
if (lockCount.isZero()) {
// Release the lock
this.owner = null;
}
} else {
// We cannot unlock while we do not own the lock.
// This is a programmers error.
Unsafe.debug("Cannot unlock ProcessorLock owned by ");
Unsafe.debug(owner.getIdString());
Unsafe.die("unlock");
}
}
}