/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.mmtk.plan.semispace.gctrace;
import org.mmtk.plan.Trace;
import org.mmtk.plan.semispace.*;
import org.mmtk.policy.Space;
import org.mmtk.utility.TraceGenerator;
import org.vmmagic.unboxed.*;
import org.vmmagic.pragma.*;
/**
* This plan has been modified slightly to perform the processing necessary
* for GC trace generation. To maximize performance, it attempts to remain
* as faithful as possible to semiSpace/Plan.java.
*
* The generated trace format is as follows:
* B 345678 12
* (Object 345678 was created in the boot image with a size of 12 bytes)
* U 59843 234 47298
* (Update object 59843 at the slot at offset 234 to refer to 47298)
* S 1233 12345
* (Update static slot 1233 to refer to 12345)
* T 4567 78924
* (The TIB of 4567 is set to refer to 78924)
* D 342789
* (Object 342789 became unreachable)
* A 6860 24 346648 3
* (Object 6860 was allocated, requiring 24 bytes, with fp 346648 on
* thread 3; this allocation has perfect knowledge)
* a 6884 24 346640 5
* (Object 6864 was allocated, requiring 24 bytes, with fp 346640 on
* thread 5; this allocation DOES NOT have perfect knowledge)
* I 6860 24 346648 3
* (Object 6860 was allocated into immortal space, requiring 24 bytes,
* with fp 346648 on thread 3; this allocation has perfect knowledge)
* i 6884 24 346640 5
* (Object 6864 was allocated into immortal space, requiring 24 bytes,
* with fp 346640 on thread 5; this allocation DOES NOT have perfect
* knowledge)
* 48954->[345]LObject;:blah()V:23 Ljava/lang/Foo;
* (Citation for: a) where the was allocated, fp of 48954,
* at the method with ID 345 -- or void Object.blah() -- and bytecode
* with offset 23; b) the object allocated is of type java.lang.Foo)
* D 342789 361460
* (Object 342789 became unreachable after 361460 was allocated)
*
* This class implements a simple semi-space collector. See the Jones
* & Lins GC book, section 2.2 for an overview of the basic
* algorithm. This implementation also includes a large object space
* (LOS), and an uncollected "immortal" space.<p>
*
* All plans make a clear distinction between <i>global</i> and
* <i>thread-local</i> activities. Global activities must be
* synchronized, whereas no synchronization is required for
* thread-local activities. Instances of Plan map 1:1 to "kernel
* threads" (aka CPUs). Thus instance
* methods allow fast, unsychronized access to Plan utilities such as
* allocation and collection. Each instance rests on static resources
* (such as memory and virtual memory resources) which are "global"
* and therefore "static" members of Plan. This mapping of threads to
* instances is crucial to understanding the correctness and
* performance proprties of this plan.
*/
@Uninterruptible
public final class GCTraceTraceLocal extends SSTraceLocal {
/**
* Constructor
*
* @param trace The global trace to use.
*/
public GCTraceTraceLocal(Trace trace) {
super(trace, false);
}
/****************************************************************************
*
* Object processing and tracing
*/
/**
* Trace a reference during GC. This involves determining which
* collection policy applies (such as those needed for trace generation)
* and taking the appropriate actions.
*
* @param object The object reference to be traced. In certain
* cases, this should <i>NOT</i> be an interior pointer.
* @return The possibly moved reference.
*/
@Inline
public ObjectReference traceObject(ObjectReference object) {
if (object.isNull()) return object;
if (GCTrace.traceInducedGC) {
/* We are performing a root scan following an allocation. */
TraceGenerator.rootEnumerate(object);
return object;
} else if (GCTrace.deathScan) {
/* We are performing the last scan before program termination. */
TraceGenerator.propagateDeathTime(object);
return object;
} else {
/* *gasp* We are actually performing garbage collection */
return super.traceObject(object);
}
}
/**
* Ensure that the referenced object will not move during a collection
* by 'precopying' it at the beginning.
*
* @param object The object to ensure will not move.
*/
@Inline
public ObjectReference precopyObject(ObjectReference object) {
if (object.isNull()) return object;
if (GCTrace.traceInducedGC) {
/* We are performing a root scan following an allocation. */
TraceGenerator.rootEnumerate(object);
return object;
} else if (GCTrace.deathScan) {
/* We are performing the last scan before program termination. */
TraceGenerator.propagateDeathTime(object);
return object;
} else {
return super.precopyObject(object);
}
}
/**
* If the referenced object has moved, return the new location.
*
* Some copying collectors will need to override this method.
*
* @param object The object which may have been forwarded.
* @return The new location of <code>object</code>.
*/
@Inline
public ObjectReference getForwardedReference(ObjectReference object) {
if (object.isNull()) return object;
if (SS.hi && Space.isInSpace(SS.SS0, object)) {
return SS.copySpace0.traceObject(this, object, GCTrace.ALLOC_SS);
} else if (!SS.hi && Space.isInSpace(SS.SS1, object)) {
return SS.copySpace1.traceObject(this, object, GCTrace.ALLOC_SS);
}
return object;
}
/**
* Return true if <code>obj</code> is a live object.
*
* @param object The object in question
* @return True if <code>obj</code> is a live object.
*/
public boolean isLive(ObjectReference object) {
if (object.isNull()) return false;
else if (GCTrace.traceInducedGC) return true;
else return super.isLive(object);
}
/**
* Return true if <code>obj</code> is a reachable object.
*
* @param object The object in question
* @return True if <code>obj</code> is a reachable object;
* unreachable objects may still be live, however
*/
public boolean isReachable(ObjectReference object) {
if (GCTrace.finalDead) return false;
else if (object.isNull()) return false;
else {
Space space = Space.getSpaceForObject(object);
return space.isReachable(object);
}
}
/**
* Is this object guaranteed not to move during the collection.
*
* @param object The object to check.
* @return True if the object is guaranteed not to move.
*/
public boolean willNotMoveInCurrentCollection(ObjectReference object) {
if (GCTrace.traceInducedGC) return true;
else return super.willNotMoveInCurrentCollection(object);
}
}