Using method in SET-CALLBACK() triggers unexpected garbage collection.

Using method in SET-CALLBACK() triggers unexpected garbage collection. Using static method as the callback will cause the static portion of a class to be garbage collected - this will manifest as static properties & variables returning to default values and static constructors being run multiple times. Using instance method causes the class instance to be garbage collected prematurely, causing various issues.

Jul 16, 2015
Knowledge

Title

URL Name

Using-method-in-SET-CALLBACK-triggers-unexpected-garbage-collection

Article Number

000175855

Environment

Product: OpenEdge Version: 11.4 and later OS: All supported platforms Other: OOABL

Question/Problem Description

Using method in SET-CALLBACK() can result in objects being garbage-collected unexpectedly. This also affects static portions of a class, which should never be garbage-collected.

If the callback is an instance method, object instance references go invalid unexpectedly, resulting in errors such as:
Invalid handle. Not initialized or points to a deleted object. (3135)
Lead attributes in a chained-attribute expression (a:b:c) must be type HANDLE or a user-defined type and valid (not UNKNOWN). (10068)

If the callback is a static method, the static portion will get collected and will be reloaded on next reference. This shows as two side effects:
- Static variables and properties get reset to default values.
- Static constructor runs multiple times in a session

Steps to Reproduce

Clarifying Information

This can happen under these circumstances:
- if a callback is registered and then unregistered for the same given event. (This can happen for buffers and queries attached to a dataset.)
- if a callback is registered only for a dynamic buffer and the dynamic buffer gets deleted (automatically) before the dynamic dataset that contains it.
- if the CLEAR() method is called on a dataset after a callback was unregistered.

Attached .zip file contains a number of sample scenarios illustrating this.

DynObjects.Class logging will also expose this:
- For object instances, there will be Delete-by-GC entries at unexpected times.
- For the static class portions there will be Delete-by-GC entries without a matching Create entry.

Error Message

Invalid handle. Not initialized or points to a deleted object. (3135) Lead attributes in a chained-attribute expression (a:b:c) must be type HANDLE or a user-defined type and valid (not UNKNOWN). (10068)

Defect Number

Defect PSC00335430

Enhancement Number

Cause

Issues managing reference counts.

Resolution

Upgrade to 11.6 or later.

Workaround

Notes

Keyword Phrase

Last Modified Date

7/8/2016 12:27 PM

Using method in SET-CALLBACK() triggers unexpected garbage collection.

Files(1)

Was this article helpful?

Was this article helpful?

Using method in SET-CALLBACK() triggers unexpected garbage collection.

Information

Related Articles