"

 COPYRIGHT (c) 1991 by Claus Gittinger

 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' }"

ArrayedCollection variableSubclass:#WeakArray

!

!WeakArray class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1991 by Claus Gittinger

 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

"

    WeakArrays can be used to trace disposal of objects; in contrast to other

    objects, references by WeakArrays will NOT keep an object from being

    garbage collected.

    Instead, whenever an object kept in a WeakArray dies, its entry is zeroed,

    and the WeakArray is informed by the storage manager. The WeakArray itself

    then informs possible dependents via the dependency mechanism.

    WeakArrays are used to track disposal of objects which keep external

    world resources. For example, FileStreams must close their underlying

    file when disposed (otherwise you could run out of OS filedescriptors).

    This can be done by keeping the FileStream objects in a weakArray, and

    keep a parallel array of filedescriptors. Whenever a fileStream is

    freed, search both arrays for an index where the stream is zero, but the

    filedescriptor is non-nil. Then close that file, and nil the filedescriptor

    entry. Notice, that there is a class (Registry) which does exactly this in

    a more programmer friendly way.

    Another application is caching of data: keep it in a weakArray, so the

    data in that cache will not be unreclaimable due to being cached.

    (for example, the ResourcePack class uses a WeakArray to cache recently

     used resource data for a while).

    The way in which weakArrays get informed by the runtime system is via

    an interrupt (DisposeInterrupt) which is first sent to the disposeHandler

    (typically ObjectMemory). ObjectMemory then takes the required steps to

    notify all weakArrays via the #lostPointer message.

    The reason for not sending messages directly from the VM is to make it

    possible to run the finalization code at lower priority or from another class.

    Also, as a side effect, it is possible to delay finalization by blocking

    interrupts. (thus, the actual sending of the #lostPointer message is under

    control of Smalltalk code, which is modifyable).

    A weakArray notifies its dependents via normal dependency notfications.

    [hint:]

    As a possible option, we could perform the weakArray scanning only in

    the oldSpace reclamation code - this would remove most of the overhead,

    but will lead to much longer delayed finalization .... we will see.

    [instance variables:]

    [class variables:]

    [memory requirements:]

    [author:]

    [See also:]

"

! !

!WeakArray class methodsFor:'initialization'!

initialize

    "setup the private signal"

    RegistrationFailedSignal isNil ifTrue:[

    ]

! !

!WeakArray class methodsFor:'instance creation'!

basicNew:size

    "return a new weakArray with size slots"

    "This is a kludge: I would like to set the WEAK-flag in the classes

     initialize method, but (currently) the order in which the class-initialize

     methods are called is not defined ...

     ... therefore it could happen, that a WeakArray is used by other

     classes initialize method BEFORE this method is evaluated.

     To avoid this, the WEAK bit in the class is set here, when the very first

     WeakArray is created.

     [Actually, the cleanest solution was to add another class definition

      keyword (such as #variableWeakSubclass:) which sets the weak flag right

      from the start.]"

    AlreadyInitialized isNil ifTrue:[

    ].

    ^ (super basicNew:size) registerAsWeakArray

    "Modified: 25.1.1997 / 13:17:22 / cg"

! !

!WeakArray class methodsFor:'queries'!

isBuiltInClass

    "return true if this class is known by the run-time-system.

     Here, true is returned for myself, false for subclasses."

    ^ self == WeakArray

! !

!WeakArray methodsFor:'GC registration'!

registerAsWeakArray

    "register the receiver in the VM -

     i.e. tell the VM to nil disposed entries in the receiver

     and notify the disposeInterruptHandler whenever that happened."

    |ok|

%{

    OBJ __addShadowObject();

    ok = __addShadowObject(self, 0);

    if (ok == false) {

    }

%}.

    ok ifFalse:[

    ]

! !

!WeakArray methodsFor:'accessing'!

at:index

    "return the indexed instance variable with index, anInteger.

     Reimplemented here for IGC readBarrier.

     (You dont have to understand this.)"

    ^ self basicAt:index

    "Modified: 25.1.1997 / 13:41:25 / cg"

!

at:index put:someObject

    "store someObject in the weakArray at some index."

    ^ self basicAt:index put:someObject

!

basicAt:index

    "return the indexed instance variable with index, anInteger.

     Reimplemented here for IGC readBarrier.

     (You don't have to understand this.)"

%{  /* NOCONTEXT */

    REGISTER int indx;

    REGISTER unsigned int nIndex;

    OBJ el;

    if (__isSmallInteger(index)) {

    }

%}.

    ^ super basicAt:index

!

basicAt:index put:someObject

    "store someObject in the weakArray at some index."

%{  /* NOCONTEXT */

    REGISTER int indx;

    REGISTER unsigned int nIndex;

    if (__isSmallInteger(index)) {

    }

%}.

    "/ for the error-message ...

    ^ super basicAt:index put:someObject

! !

!WeakArray methodsFor:'copying'!

postCopy

    "copying alone does not really help - we have to tell

     the VM, that there is a new WeakArray around ...

     Q: who copies weakArrays ?"

    dependents := nil.

    self registerAsWeakArray.

!

postDeepCopy

    dependents := nil.

    self registerAsWeakArray.

!

skipInstvarIndexInDeepCopy:index

    "a helper for deepCopy; only indices for which this method returns

     false are copied in a deep copy."

    index == 1 ifTrue:[

    ].

    ^ false

! !

!WeakArray methodsFor:'dependents access'!

addDependent:anObject

    "make the argument, anObject be a dependent of the receiver"

    |wasBlocked|

    wasBlocked := OperatingSystem blockInterrupts.

    [

    ] ensure:[

    ]

    "Modified: 8.1.1997 / 23:40:30 / cg"

!

dependents

    "return the dependents of the receiver"

    dependents isNil ifTrue:[^ #()].

    dependents isCollection ifTrue:[

    ].

    ^ IdentitySet with:dependents

    "Modified: / 27.10.1997 / 19:37:16 / cg"

!

dependents:aCollection

    "set the dependents of the receiver"

    |dep|

    aCollection size == 1 ifTrue:[

    ].

    dependents := aCollection

!

dependentsDo:aBlock

    "evaluate aBlock for all of my dependents"

    |deps|

    deps := dependents.

    deps notNil ifTrue:[

    ]

!

removeDependent:anObject

    "make the argument, anObject be independent of the receiver"

    |wasBlocked|

    "/ must do this save from interrupts, since the dependents collection

    "/ is possibly accessed from multiple threads.

    "/ Used to use #valueUninterruptably here; inlined that code for slightly

    "/ faster execution.

    wasBlocked := OperatingSystem blockInterrupts.

    [

    ] ensure:[

    ]

! !

!WeakArray methodsFor:'enumerating'!

do:aBlock

    "evaluate the argument, aBlock for each element in the collection.

     - reimplemented for IGC readBarrier.