// MemoryControl.java
// -------------------------------------------
// (C) 2011 by Sebastian Gaebel
// first published 22.08.2011 on http://yacy.net
//
// $LastChangedDate: 2011-08-18 00:24:17 +0200 (Do, 18. Aug 2011) $
// $LastChangedRevision: 7883 $
// $LastChangedBy: orbiter $
//
// LICENSE
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
package net.yacy.kelondro.util;
import java.util.concurrent.atomic.AtomicBoolean;
import net.yacy.cora.util.ConcurrentLog;
public abstract class MemoryStrategy {
protected final static ConcurrentLog log = new ConcurrentLog("MEMORY");
protected static long lastGC = 0l;
protected static boolean error = true;
protected static String name;
/**
* @return if an error has been detected
*/
protected final static boolean hasError() {
return error;
}
/**
* @return an identifying name
*/
protected final static String getName() {
return name;
}
/**
* Runs the garbage collector if last garbage collection is more than last millis ago
* @param last time which must be passed since lased gc
* @param info additional info for log
*/
protected synchronized boolean gc(final int last, final String info) { // thq
assert last >= 10000; // too many forced GCs will cause bad execution performance
final long elapsed = System.currentTimeMillis() - lastGC;
if (elapsed > last) {
System.gc();
lastGC = System.currentTimeMillis();
return true;
}
if (log.isFinest()) log.finest("[gc] no execute, last run: " + (elapsed / 1000) + " seconds ago, call: " + info);
return false;
}
/**
* memory that is free without increasing of total memory taken from os
* @return bytes
*/
protected abstract long free();
/**
* memory that is available including increasing total memory up to maximum
* @return bytes
*/
protected abstract long available();
/**
* memory that is currently bound in objects
* @return used bytes
*/
protected abstract long used();
/**
* currently allocated memory in the Java virtual machine; may vary over time
* @return bytes
*/
protected abstract long total();
/**
* maximum memory the Java virtual will allocate machine; may vary over time in some cases
* @return bytes
*/
protected abstract long maxMemory();
/**
* <p>Tries to free a specified amount of bytes.</p>
* <p>
* If the currently available memory is enough, the method returns <code>true</code> without
* performing additional steps. If not, the behaviour depends on the parameter <code>force</code>.
* If <code>false</code>, a Full GC is only performed if former GCs indicated that a GC should
* provide enough free memory. If former GCs didn't but <code>force</code> is set to <code>true</code>
* a Full GC is performed nevertheless.
* </p>
* <p>
* Setting the <code>force</code> parameter to false doesn't necessarily mean, that no GC may be
* performed by this method, if the currently available memory doesn't suffice!
* </p>
* <p><em>Be careful with this method as GCs should always be the last measure to take</em></p>
*
* @param size the requested amount of free memory in bytes
* @param force specifies whether a GC should be run even in case former GCs didn't provide enough memory
* @return whether enough memory could be freed (or is free) or not
*/
protected abstract boolean request(final long size, final boolean force, AtomicBoolean shortStatus);
/**
* @return if Memory seams to be in a proper state
*/
protected abstract boolean properState();
/**
* forced enable properState - StandardMemoryStrategy only
*/
protected void resetProperState() {
}
/**
* set the memory to be available for properState - StandardMemoryStrategy only
*/
protected void setProperMbyte(@SuppressWarnings("unused") final long mbyte) {
}
}