org.mmtk.plan.refcount
Class RCBaseMutator

java.lang.Object
  org.mmtk.plan.MutatorContext
      org.mmtk.plan.SimpleMutator
          org.mmtk.plan.StopTheWorldMutator
              org.mmtk.plan.refcount.RCBaseMutator

All Implemented Interfaces:

Constants

Direct Known Subclasses:

GenRCMutator, RCMutator

public class RCBaseMutator
extends StopTheWorldMutator

This class implements the mutator context for a reference counting collector. See Shahriyar et al for details of and rationale for the optimizations used here (http://dx.doi.org/10.1145/2258996.2259008). See Chapter 4 of Daniel Frampton's PhD thesis for details of and rationale for the cycle collection strategy used by this collector.

rc

private final ExplicitFreeListLocal rc

rclos

private final LargeObjectLocal rclos

modBuffer

private final ObjectReferenceDeque modBuffer

decBuffer

private final RCDecBuffer decBuffer

btSweepImmortal

private final BTSweepImmortalScanner btSweepImmortal

RCBaseMutator

public RCBaseMutator()

Constructor. One instance is created per physical processor.

alloc

public Address alloc(int bytes,
                     int align,
                     int offset,
                     int allocator,
                     int site)

Allocate memory for an object.

Overrides:

alloc in class MutatorContext

Parameters:

bytes - The number of bytes required for the object.

align - Required alignment for the object.

offset - Offset associated with the alignment.

allocator - The allocator associated with this request.

site - Allocation site

Returns:

The low address of the allocated chunk.

postAlloc

public void postAlloc(ObjectReference ref,
                      ObjectReference typeRef,
                      int bytes,
                      int allocator)

Description copied from class: MutatorContext

Perform post-allocation actions. For many allocators none are required.

Overrides:

postAlloc in class MutatorContext

Parameters:

ref - The newly allocated object

typeRef - the type reference for the instance being created

bytes - The size of the space to be allocated (in bytes)

allocator - The allocator number to be used for this allocation

getAllocatorFromSpace

public Allocator getAllocatorFromSpace(Space space)

Description copied from class: MutatorContext

Return the allocator instance associated with a space space, for this plan instance.

Overrides:

getAllocatorFromSpace in class MutatorContext

Parameters:

space - The space for which the allocator instance is desired.

Returns:

The allocator instance associated with this plan instance which is allocating into space, or null if no appropriate allocator can be established.

collectionPhase

public void collectionPhase(short phaseId,
                            boolean primary)

Perform a per-mutator collection phase. This is executed by one collector thread on behalf of a mutator thread.

Overrides:

collectionPhase in class SimpleMutator

Parameters:

phaseId - The unique phase identifier

primary - Should this thread be used to execute any single-threaded local operations?

flushRememberedSets

public final void flushRememberedSets()

Description copied from class: MutatorContext

Flush per-mutator remembered sets into the global remset pool.

Overrides:

flushRememberedSets in class MutatorContext

assertRemsetsFlushed

public final void assertRemsetsFlushed()

Description copied from class: MutatorContext

Assert that the remsets have been flushed. This is critical to correctness. We need to maintain the invariant that remset entries do not accrue during GC. If the host JVM generates barrier entries it is its own responsibility to ensure that they are flushed before returning to MMTk.

Overrides:

assertRemsetsFlushed in class MutatorContext

flush

public void flush()

Description copied from class: MutatorContext

Flush mutator context, in response to a requestMutatorFlush. Also called by the default implementation of deinitMutator.

Overrides:

flush in class MutatorContext

objectReferenceWrite

public void objectReferenceWrite(ObjectReference src,
                                 Address slot,
                                 ObjectReference tgt,
                                 Word metaDataA,
                                 Word metaDataB,
                                 int mode)

Write an object reference. Take appropriate write barrier actions.

By default do nothing, override if appropriate.

Overrides:

objectReferenceWrite in class MutatorContext

Parameters:

src - The object into which the new reference will be stored

slot - The address into which the new reference will be stored.

tgt - The value of the new reference

metaDataA - A value that assists the host VM in creating a store

metaDataB - A value that assists the host VM in creating a store

mode - The context in which the store occurred

objectReferenceTryCompareAndSwap

public boolean objectReferenceTryCompareAndSwap(ObjectReference src,
                                                Address slot,
                                                ObjectReference old,
                                                ObjectReference tgt,
                                                Word metaDataA,
                                                Word metaDataB,
                                                int mode)

Description copied from class: MutatorContext

Attempt to atomically exchange the value in the given slot with the passed replacement value. If a new reference is created, we must then take appropriate write barrier actions.

By default do nothing, override if appropriate.

Overrides:

objectReferenceTryCompareAndSwap in class MutatorContext

Parameters:

src - The object into which the new reference will be stored

slot - The address into which the new reference will be stored.

old - The old reference to be swapped out

tgt - The target of the new reference

metaDataA - A value that assists the host VM in creating a store

metaDataB - A value that assists the host VM in creating a store

mode - The context in which the store occurred

Returns:

True if the swap was successful.

objectReferenceBulkCopy

public boolean objectReferenceBulkCopy(ObjectReference src,
                                       Offset srcOffset,
                                       ObjectReference dst,
                                       Offset dstOffset,
                                       int bytes)

A number of references are about to be copied from object src to object dst (as in an array copy). Thus, dst is the mutated object. Take appropriate write barrier actions.

Overrides:

objectReferenceBulkCopy in class MutatorContext

Parameters:

src - The source of the values to be copied

srcOffset - The offset of the first source address, in bytes, relative to src (in principle, this could be negative).

dst - The mutated object, i.e. the destination of the copy.

dstOffset - The offset of the first destination address, in bytes relative to tgt (in principle, this could be negative).

bytes - The size of the region being copied, in bytes.

Returns:

True if the update was performed by the barrier, false if left to the caller (always false in this case).

coalescingWriteBarrierSlow

private void coalescingWriteBarrierSlow(ObjectReference srcObj)

Slow path of the coalescing write barrier.

Attempt to log the source object. If successful in racing for the log bit, push an entry into the modified buffer and add a decrement buffer entry for each referent object (in the RC space) before setting the header bit to indicate that it has finished logging (allowing others in the race to continue).

Parameters:

srcObj - The object being mutated

global

private static RCBase global()

Returns:

The active global plan as an RC instance.