Class: Registry

• Inheritance
• Description
• Related information
• Instance protocol
  • accessing
  • element disposal
  • enumerating
  • private
  • registering objects

Inheritance:

   Object
   |
   +--Collection
      |
      +--Set
         |
         +--Dictionary
            |
            +--IdentityDictionary
               |
               +--WeakIdentityDictionary
                  |
                  +--Registry
                     |
                     +--CachingRegistry
                     |
                     +--HandleRegistry

Package:

stx:libbasic

Category:

Collections-Weak

Version:

rev: 1.72 date: 2016/11/18 15:24:51

user: stefan

file: Registry.st directory: libbasic

module: stx stc-classLibrary: libbasic

Author:

Claus Gittinger

Description:

Registries provide an easy interface to using WeakArrays.
A class, which wants to be informed of instance-death, can put a created object
into a registry. The registry will create an executor, which is a (shallow-)copy
of the object, and watch out for death of the original object. When it dies,
the executor will be sent a #finalize message.
The trick with the shallow copy is especially nice, you can think of it as
being the original object which died.

All objects, which keep external resources (such as fileDescriptors, fonts,
colormap-entries etc.) should be registered, so that the underlying resource
can be freed when the object goes away.

Of course, you too can use it to do whatever you need to do in case of the
death of an object.

Registries use #executor to acquire the copy of the original,
this can be redefined in individual classes for faster copying
(typically, not all internal state, but only some device handles are needed for
finalization). If the to-be-registered object is large, this method may also
return a stub (placeHolder) object. (i.e. there is no need for the copy to be
of the same class as the original, as long as it implements #finalize and frees
the relevant OS resources. Some classes return a specialized private-class instance,
which only holds on the handle and implements #finalize.)
Example uses are found in Form, Color, ExternalStream and Font

Related information:

    WeakArray
    WeakIdentityDictionary
    Font
    Form
    Color
    Cursor
    ExternalStream

Instance protocol:

 contents

return the collection of registered objects

 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

 informDispose: someHandle

send a dispose message - this is sent to the executor,
since the original is already gone

 update: something with: aParameter from: changedObject

an instance has been destroyed - look which one it was

 detect: aBlock ifNone: exceptionValue

detect a key, for which aBlock answers true

 do: aBlock

evaluate aBlock for each registered object

 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.

Redefined to not nil values of expired keys here.

 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.

Redefined to not nil values of expired keys here.

 register: anObject

register anObject, so that a copy of it gets the disposed message
when anObject dies (some time in the future)

 register: anObject as: aHandle

register anObject, so that I later receive informDispose: with aHandle
(some time in the future)

 registerChange: anObject

a registered object has changed, create a new executor

 unregister: anObject

remove registration of anObject, without telling the executor;
should be sent, if we are no more interested in destruction of
anObject (i.e. it no longer holds external resources).

 unregisterAllForWhich: aBlock

remove registration of all entries, for which the argument block
evaluates to true.
should be sent, if we are no more interested in destruction of
a group of objects (i.e. it no longer holds external resources).

 unregisterAllForWhichHandle: aBlock

remove registration of all handles, for which the argument block
evaluates to true.
should be sent, if we are no more interested in destruction of
a group of objects (i.e. it no longer holds external resources).