Fix unlikely but possible race in `WeakValueDictionary`
It may happen that value in `valueArray` could have been already
collected by the GC but #clearDeadSlots have not yet been called.
When this happened, `#at:ifAbsentPut:` returned tombstone rather
than updating the dictionary with value from block.
This commit fixes this by checking whether `valueArray` contain
the tombstone and if so, clearing up the dead slots and restarting
the operation. HTH.
"
COPYRIGHT (c) 1995 by Claus Gittinger
All Rights Reserved
This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice. This software may not
be provided or otherwise made available to, or used by, any
other person. No title to or ownership of the software is
hereby transferred.
"
"{ Package: 'stx:libbasic' }"
"{ NameSpace: Smalltalk }"
Array variableSubclass:#ImmutableArray
instanceVariableNames:''
classVariableNames:''
poolDictionaries:''
category:'System-Compiler-Support'
!
!ImmutableArray class methodsFor:'documentation'!
copyright
"
COPYRIGHT (c) 1995 by Claus Gittinger
All Rights Reserved
This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice. This software may not
be provided or otherwise made available to, or used by, any
other person. No title to or ownership of the software is
hereby transferred.
"
!
documentation
"
By default, array literals in smalltalk are mutable objects. That
may lead to some subtle (and hard to find errors), if some method passes
a literal array constant as argument to someone else, who changes the
array using at:put: like messages. Since the array object is kept in
the first methods literals, the array constant has now been changed without
having the method's sourcecode reflect this. Thus, the method will
behave differently from what its source may make you think.
To help finding this kind of 'feature/bug', the compiler can be
configured to create instances of this ImmutableArray instead of Arrays
for array literals. Instances of ImmutableArray catch storing accesses and
enter the debugger. Although useful, this feature is disabled by default
for compatibility to other smalltalk implementations.
(Also, if turned on, this makes inspecting array literals entered in
a workspace somewhat strange: you cannot modify it any longer).
Turn the ImmutableArray feature on by setting the Parsers class variable
'ArraysAreImmutable' to true or use the new launchers settings menu.
This class should be used only by the compiler.
ATTENTION:
there may be still code around which checks for explicit class being Array
(both in Smalltalk and in primitive code). All code like foo 'class == Array'
or '__isArray' will not work with ImmutableArrays; consider using '__isArrayLike'.
A somewhat better approach would be to either add a flag to the object (mutability)
and check this dynamically (expensive) or to place immutable objects into a readonly
memory segment (the good solution). We will eventually implement the second in the future...
[see also:]
ImmutableString
ImmutableByteArray
Parser Scanner
[author:]
Claus Gittinger
"
! !
!ImmutableArray class methodsFor:'queries'!
mutableClass
"answer an equivalent mustable class"
^ Array
! !
!ImmutableArray class methodsFor:'testing'!
hasImmutableInstances
^ true
! !
!ImmutableArray methodsFor:'accessing'!
at:index put:value
"Trigger an error if an immutable array is stored into.
The store will be performed (for compatibility reasons) if you continue
in the debugger."
self noModificationError.
^ super at:index put:value
"Modified: / 3.8.1998 / 14:45:23 / cg"
!
basicAt:index put:value
"Trigger an error if an immutable array is stored into.
The store will be performed (for compatibility reasons) if you continue
in the debugger."
self noModificationError.
^ super basicAt:index put:value
"Modified: / 3.8.1998 / 14:45:30 / cg"
! !
!ImmutableArray methodsFor:'converting'!
asArray
"return the receiver as an array. I am already.
Use asNewArray, or asMutableCollection if you need a copy for modification"
^ self
!
asImmutableArray
^ self
!
asMutableCollection
"return a writable copy of myself"
^ self copy changeClassTo:Array
!
asNewArray
"return the receiver as an unique new array."
^ self copy
!
beImmutable
"that's what I am"
^ self
!
beMutable
"you never go back"
^ self shouldNotImplement
! !
!ImmutableArray methodsFor:'copying'!
postCopy
"when copied, make it me a real (mutable) Array"
self changeClassTo:Array.
!
postDeepCopy
"when copied, make it me a real (mutable) Array"
self changeClassTo:Array.
!
shallowCopy
"when copying, return a real (mutable) Array"
|sz|
sz := self size.
^ (Array new:sz) replaceFrom:1 to:sz with:self startingAt:1
"
#(1 2 3 4) asImmutableArray shallowCopy
"
! !
!ImmutableArray methodsFor:'private'!
species
"Copies should be mutable"
^ Array
!
speciesForCopy
"Copies should be mutable"
^ Array
! !
!ImmutableArray methodsFor:'queries'!
isImmutable
^ true
!
isLiteral
"return true, if the receiver can be used as a literal constant in ST syntax
(i.e. can be used in constant arrays)"
"yes, I must be"
^ true
! !
!ImmutableArray methodsFor:'specials'!
become:anotherObject
"trigger an error if I should become something else
(this would be an even more tricky manipulation)"
self noModificationError.
^ super become:anotherObject
!
becomeNil
"trigger an error if I should become nil
(this would be an even more tricky manipulation)"
self noModificationError.
^ super becomeNil
!
becomeSameAs:anotherObject
"trigger an error if I should become something else
(this would be an even more tricky manipulation)"
self noModificationError.
^ super becomeSameAs:anotherObject
!
grow:newSize
"trigger an error if I should change my size"
self noModificationError.
^ super grow:newSize
! !
!ImmutableArray class methodsFor:'documentation'!
version
^ '$Header$'
!
version_CVS
^ '$Header$'
! !