25. Notes About Garbage Collection In LotusScript

梦里梦外; 2022-04-05 09:08 120阅读 0赞

Garbage collection is done with three characteristics in Lotusscript.  
a) It’s done after the execution of EACH line of code.  
b) It reclaims the memory of an object when on local variable references it directly, even when another referenced object links to it.  
c) When it reclaims an object, it reclaims all the objects contained by the object. Notes does not allow free-floating objects that exist outside their container, or "owner" object. Documents, for example, must belong to a database. Items must belong to a document, and ACLEntries must belong to an ACL object.  
Point a) ensures the efficient memory usage when a sub involves the iteration of a large number of Notes objects e.g. documents.

set view = db.GetView("$all") 
    set doc = view.GetFirstDocument() 
    while not (doc is nothing) 
          ' do something... 
          set doc = view.GetNextDocument(doc) 
    wend

Point b) and c) are harmful when they work together.

dim s as new NotesSession 
    dim entry as NotesEntry 
    set entry = s.CurrentDatabase.ACL.GetFirstEntry

The entry object will be reclaimed right after the assignment statement is executed as the ACL object is not stored in any variable and thus destructed, which causes the child object ACLEntry to be reclaimed. The issue in this case can be fixed by storing the ACL object in a variable.  
Another case is as below:

Sub Initialize
    	Dim s As New NotesSession
    	Dim view As NotesView
    	Set view=TestObj()
    	Print view.Name
    End Sub
    Function TestObj As NotesView
    	Dim s As New NotesSession
    	Dim db As NotesDatabase
    	Set db=s.Getdatabase(s.Currentdatabase.Server, "log.nsf")
    	Set TestObj=db.Getview("UsageByUser")
    End function

The View object returned by the function TestObj is reclaimed before it can be used by the caller because the parent database log.nsf is reclaimed after the function ends. If the view is from the current database, it will keep alive, even if the current database object is not initialized in the caller. The current session and database objects keep alive until the whole program e.g. agent exits. To avoid the failure above, a global variable can be declared to hold the exterior database object.

Sub Initialize
    	Dim s As New NotesSession
    	‘the following two lines are optional
    	Dim db As NotesDatabase
    	Set db=s.Currentdatabase
    	Dim view As NotesView
    	Set view=TestObj()
    	Print view.Name
    End Sub
    Function TestObj As NotesView
    	Dim s As New NotesSession
    	Set TestObj=s.Currentdatabase.Getview("All")
    End function