[Vm-dev] VM Maker: VMMaker-dtl.183.mcz

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Dave Lewis uploaded a new version of VMMaker to project VM Maker:
http://www.squeaksource.com/VMMaker/VMMaker-dtl.183.mcz

==================== Summary ====================

Name: VMMaker-dtl.183
Author: dtl
Time: 21 June 2010, 10:08:02 am
UUID: 419ddfbf-4cb4-48f1-b918-6a4663d4942b
Ancestors: VMMaker-jcg.182

VMMaker 4.2.5

Reference Mantis 0007549: 64bit VM, 32bit image, sweepPhase hangs if the first word in the heap is the start of a free chunk

Change #sweepPhase to use oop value -1 as marker for invalid oop rather than 0, because 0 may refer to a valid free chunk.

=============== Diff against VMMaker-jcg.182 ===============

Item was changed:
  ----- Method: ObjectMemory>>sweepPhase (in category 'gc -- mark and sweep') -----
  sweepPhase
  	"Sweep memory from youngStart through the end of memory. Free all 
  	inaccessible objects and coalesce adjacent free chunks. Clear the mark 
  	bits of accessible objects. Compute the starting point for the first pass of 
  	incremental compaction (compStart). Return the number of surviving 
  	objects. "
  	"Details: Each time a non-free object is encountered, decrement the 
  	number of available forward table entries. If all entries are spoken for 
  	(i.e., entriesAvailable reaches zero), set compStart to the last free 
  	chunk before that object or, if there is no free chunk before the given 
  	object, the first free chunk after it. Thus, at the end of the sweep 
  	phase, compStart through compEnd spans the highest collection of 
  	non-free objects that can be accomodated by the forwarding table. This 
  	information is used by the first pass of incremental compaction to 
  	ensure that space is initially freed at the end of memory. Note that 
  	there should always be at least one free chunk--the one at the end of 
  	the heap."
  	| entriesAvailable survivors freeChunk firstFree oop oopHeader oopHeaderType hdrBytes oopSize freeChunkSize endOfMemoryLocal |
  	self inline: false.
  	self var: #oop type: 'usqInt'.
  	self var: #endOfMemoryLocal type: 'usqInt'.
  	entriesAvailable := self fwdTableInit: self bytesPerWord * 2.
  	survivors := 0.
+ 	freeChunk := -1. "an invalid object pointer, note that 0 may refer to a meaningful slot"
+ 	firstFree := -1.
- 	freeChunk := nil.
- 	firstFree := nil.
  	"will be updated later"
  	endOfMemoryLocal := endOfMemory.
  	oop := self oopFromChunk: youngStart.
  	[oop < endOfMemoryLocal]
  		whileTrue: ["get oop's header, header type, size, and header size"
  			statSweepCount := statSweepCount + 1.
  			oopHeader := self baseHeader: oop.
  			oopHeaderType := oopHeader bitAnd: TypeMask.
  			hdrBytes := headerTypeBytes at: oopHeaderType.
  			(oopHeaderType bitAnd: 1) = 1
  				ifTrue: [oopSize := oopHeader bitAnd: self sizeMask]
  				ifFalse: [oopHeaderType = HeaderTypeSizeAndClass
  						ifTrue: [oopSize := (self sizeHeader: oop) bitAnd: self longSizeMask]
  						ifFalse: ["free chunk" oopSize := oopHeader bitAnd: self longSizeMask]].
  			(oopHeader bitAnd: self markBit) = 0
  				ifTrue: ["object is not marked; free it"
  					"<-- Finalization support: We need to mark each oop chunk as free -->"
  					self longAt: oop - hdrBytes put: HeaderTypeFree.
+ 					freeChunk ~= -1
- 					freeChunk ~= nil
  						ifTrue: ["enlarge current free chunk to include this oop"
  							freeChunkSize := freeChunkSize + oopSize + hdrBytes]
  						ifFalse: ["start a new free chunk"
  							freeChunk := oop - hdrBytes.
  							"chunk may start 4 or 8 bytes before oop"
  							freeChunkSize := oopSize + (oop - freeChunk).
  							"adjust size for possible extra header bytes"
+ 							firstFree = -1 ifTrue: [firstFree := freeChunk]]]
- 							firstFree = nil ifTrue: [firstFree := freeChunk]]]
  				ifFalse: ["object is marked; clear its mark bit and possibly adjust 
  					the compaction start"
  					self longAt: oop put: (oopHeader bitAnd: self allButMarkBit).
  					"<-- Finalization support: Check if we're running about a weak class -->"
  					(self isWeakNonInt: oop) ifTrue: [self finalizeReference: oop].
  					entriesAvailable > 0
  						ifTrue: [entriesAvailable := entriesAvailable - 1]
  						ifFalse: ["start compaction at the last free chunk before this object"
  							firstFree := freeChunk].
+ 					freeChunk ~= -1
- 					freeChunk ~= nil
  						ifTrue: ["record the size of the last free chunk"
  							self longAt: freeChunk put: ((freeChunkSize bitAnd: self longSizeMask) bitOr: HeaderTypeFree).
+ 							freeChunk := -1].
- 							freeChunk := nil].
  					survivors := survivors + 1].
  			oop := self oopFromChunk: oop + oopSize].
+ 	freeChunk ~= -1
- 	freeChunk ~= nil
  		ifTrue: ["record size of final free chunk"
  			self longAt: freeChunk put: ((freeChunkSize bitAnd: self longSizeMask) bitOr: HeaderTypeFree)].
  	oop = endOfMemory
  		ifFalse: [self error: 'sweep failed to find exact end of memory'].
+ 	firstFree = -1
- 	firstFree = nil
  		ifTrue: [self error: 'expected to find at least one free object']
  		ifFalse: [compStart := firstFree].
  
  	^ survivors!

Item was changed:
  ----- Method: VMMaker class>>versionString (in category 'version testing') -----
  versionString
  
  	"VMMaker versionString"
  
+ 	^'4.2.5'!
- 	^'4.2.4'!