org.mmtk.plan.semispace.gctrace
Class GCTrace

java.lang.Object
  org.mmtk.plan.Plan
      org.mmtk.plan.Simple
          org.mmtk.plan.StopTheWorld
              org.mmtk.plan.semispace.SS
                  org.mmtk.plan.semispace.gctrace.GCTrace

All Implemented Interfaces:

Constants

public class GCTrace
extends SS

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)
 

All plans make a clear distinction between global and thread-local 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.

traceSpace

public static final RawPageSpace traceSpace

TRACE

public static final int TRACE

lastGCWasTracing

public static boolean lastGCWasTracing

traceInducedGC

public static boolean traceInducedGC

deathScan

public static boolean deathScan

finalDead

public static boolean finalDead

GCTrace

public GCTrace()

Constructor

processOptions

public void processOptions()

Description copied from class: StopTheWorld

The processOptions method is called by the runtime immediately after command-line arguments are available. Allocation must be supported prior to this point because the runtime infrastructure may require allocation in order to parse the command line arguments. For this reason all plans should operate gracefully on the default minimum heap size until the point that processOptions is called.

Overrides:

processOptions in class StopTheWorld

notifyExit

public final void notifyExit(int value)

The planExit method is called at RVM termination to allow the trace process to finish.

Overrides:

notifyExit in class Plan

Parameters:

value - The exit value

collectionRequired

public final boolean collectionRequired(boolean spaceFull,
                                        Space space)

Description copied from class: Plan

This method controls the triggering of a GC. It is called periodically during allocation. Returns true to trigger a collection.

Overrides:

collectionRequired in class Plan

Parameters:

spaceFull - Space request failed, must recover pages within 'space'.

space - TODO

Returns:

true if a collection is requested by the plan.

collectionPhase

public void collectionPhase(short phaseId)

Perform a (global) collection phase.

Overrides:

collectionPhase in class SS

Parameters:

phaseId - The unique id of the phase to perform.

isLastGCFull

public boolean isLastGCFull()

Returns:

Since trace induced collections are not called to free up memory, their failure to return memory isn't cause for concern.

global

public static GCTrace global()

Returns:

the active Plan as a GCTrace