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Class: WeakIdentityDictionary


Inheritance:

   Object
   |
   +--Collection
      |
      +--Set
         |
         +--Dictionary
            |
            +--IdentityDictionary
               |
               +--WeakIdentityDictionary
                  |
                  +--Registry
                  |
                  +--WeakDependencyDictionary

Package:
stx:libbasic
Category:
Collections-Weak
Version:
rev: 1.55 date: 2016/11/23 11:57:41
user: mawalch
file: WeakIdentityDictionary.st directory: libbasic
module: stx stc-classLibrary: libbasic
Author:
Claus Gittinger

Description:


WeakIdentityDictionaries behave like IdentityDictionaries,
as long as the keys are still referenced by some
other (non-weak) object.
However, once the last non-weak reference ceases to exist,
the object will be automatically removed from the Weakcollection
(with some delay: it will be removed after the next garbage collect).

This class was added to support keeping track of dependents without
keeping the values alive - values simply become nil when no one else
references it. The original dependency mechanism used a regular Dictionary,
which usually leads to a lot of garbage being kept due to a forgotten
release. Using a WeakDictionary may be incompatible to ST-80 but is much
more comfortable, since no manual release of dependents is needed.


Warning:


If you use this, be very careful since the collections size changes
'magically' - for example, testing for being nonEmpty and then
removing the first element may fail, since the element may vanish inbetween.
In general, never trust the value as returned by the size/isEmpty messages.

Related information:

    WeakArray
    WeakValueDictionary
    WeakIdentitySet

Instance protocol:

accessing
o  keys
return a collection containing all valid keys of the receiver

adding & removing
o  at: key ifAbsent: exceptionBlock
redefined to block interrupts
(avoid change of the dictionary while accessing)

o  at: key ifAbsentPut: replacementBlock
redefined to block interrupts
(avoid change of the dictionary while accessing)

o  at: key put: anObject
add the argument anObject under key, aKey to the receiver.
Return anObject (sigh).
Redefined to block interrupts, to avoid trouble when dependencies
are added within interrupting high prio processes.

o  removeKey: aKey ifAbsent: aBlock
remove the association under aKey from the collection,
return the value previously stored there.
If it was not in the collection return the result
from evaluating aBlock.

Redefined to avoid synchronization problems, in case
of interrupts (otherwise, there could be some other operation
on the receiver done by another process, which garbles my contents).

o  safeRemoveKey: key
redefined to block interrupts
(avoid change of the dictionary while accessing)

element disposal
o  clearDeadSlots
have to block here - dispose may be done at a low priority
from the background finalizer. If new items are added by a
higher prio process, the dictionary might get corrupted otherwise

o  update: something with: aParameter from: changedObject
an element (either key or value) died - clear out slots for
disposed keys.

enumerating
o  keysDo: aBlock
evaluate aBlock for each registered object

private
o  findKeyOrNil: key
Look for the key in the receiver.
If it is found, return the index,
otherwise the index of the first unused slot.
Grow the receiver, if key was not found, and no unused slots were present.

Warning: an empty slot MUST be filled by the sender - it is only to be sent
by at:put: / add: - like methods.

o  findKeyOrNilOrDeletedEntry: key
Look for the key in the receiver.
If it is found, return the index,
otherwise the index of the first unused slot.
Grow the receiver, if key was not found, and no unused slots were present.

o  grow: newSize
grow the receiver.
Redefined to block interrupts, to avoid trouble when dependencies
are added within interrupting high prio processes.
usage example(s):
'grow:' printCR.

o  initializeForCapacity: minSize
reset the receiver's contents.
Redefined to block interrupts, to avoid trouble when dependencies
are added within interrupting high prio processes.

o  keyContainerOfSize: n
return a container for keys of size n.
use WeakArrays here.

o  rehash
grow the receiver.
Redefined to block interrupts, to avoid trouble when dependencies
are added within interrupting high prio processes.
usage example(s):
'rehash' printCR.

testing
o  includes: anObject
redefined to block interrupts
(avoid change of the dictionary while accessing)

o  includesKey: key
redefined to block interrupts
(avoid change of the dictionary while accessing)

o  isWeakCollection
return true, if the receiver has weak references to its elements.



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