Although DELETE WIDGET-POOL is a valid statement in any ABL procedure, even one with no CREATE WIDGET-POOL statement, using this statement in an AppServer disconnect or shutdown procedure to avoid memory leaks will usually be ineffective. Here's why:
1. The AVM creates a "session widget pool" for each session. In the case of an AppServer, this is the agent runtime session that lasts from the time the agent is started until it is shut down. If no CREATE WIDGET-POOL statement is used in a procedure, all dynamic objects created in that procedure go into the session widget pool. The DELETE WIDGET-POOL statement has no effect on the session widget pool.
2. If the CREATE WIDGET-POOL statement is used without a name in a procedure, another unnamed widget pool is created that is scoped to that procedure. All objects created after the CREATE WIDGET-POOL statement is executed go into that unnamed widget pool instead of the session widget pool (unless the statement creating the object specifies a named widget pool), until the procedure goes out of scope. When the procedure goes out of scope, the unnamed pool and all the objects in it are deleted. A DELETE WIDGET-POOL statement within that procedure scope deletes the unnamed pool for that procedure, and all the objects in that pool, immediately.
The implications for an AppServer disconnect or shutdown procedure are:
1. The DELETE WIDGET-POOL statement in a disconnect or shutdown procedure deletes only those dynamic objects created within the scope of the disconnect/shutdown procedure, and only if there was a CREATE WIDGET-POOL statement to create a default unnamed widget pool scoped to the procedure. It does not delete any objects that were created in the session widget pool, even if they were created in the scope of the disconnect/shutdown procedure. It does not delete any objects created in named widget pools.
2. The DELETE WIDGET-POOL statement in a disconnect or shutdown procedure does not delete any dynamic objects that still exist from procedures that were run earlier in the session. This includes any objects that were created in startup or connect procedures.
3. Dynamic objects created in the unnamed widget pool of a procedure that has ended will have been deleted when the procedure ended. If dynamic objects are still in memory when a disconnect or shutdown procedure is run, and they were not created in the disconnect/shutdown procedure itself, they were created in one of the following ways:
a. In the session widget pool (the most likely case).
b. In a named widget pool.
c. In a widget pool that was created with the PERSISTENT option.
d. In the default widget pool of a procedure (possibly a persistent procedure) that is still running or a class-based object that is still instantiated.
A DELETE WIDGET-POOL statement in a disconnect or shutdown procedure will not delete any of the above objects.
