#3930 closed Bug (No Bug)

DllStructs created in one scope gets dropped if chained with a function that returns a re-structured-by-pointer version of it

Reported by: AutoXenon Owned by:
Milestone: Component: AutoIt
Version: Severity: None
Keywords: Cc:


Original thread:

Local $unreliable_data, $reliable_data, $intermediate_ref, $labelunreliable = GUICtrlCreateLabel('',0,0,400,25), $labelreliable = GUICtrlCreateLabel('',0,30,400,25)
While True
      $unreliable_data = parseStruct(createStruct())  ; struct technically goes out of scope, this saves a "slave struct" but the master struct gets dropped when it goes out of parseStruct's scope
      $intermediate_ref = createStruct()              ; struct scope gets transferred, this is a "master struct"
      $reliable_data = parseStruct($intermediate_ref) ; a "slave struct" of a master struct that is scoped here
      Sleep(100)                                      ; wait some time for garbage to get written into the freed memory 

Func createStruct()
     Local $struct = DllStructCreate('char[16]')
     DllStructSetData($struct,1,'hello world')
     Return $struct

Func parseStruct($struct)
     Return DllStructCreate('char msg[16]',DllStructGetPtr($struct))

Func quit()

The question is, should create-by-pointer structs count as valid references? I can imagine that if it is change to be so, it might cause headaches with ad-hoc throwaway "lens" structs unintentionally preventing the memory from being freed if the programmer is expecting it to not count as valid references. I guess it's up to you to decide on which tradeoff to pick.

Attachments (0)

Change History (4)

comment:1 Changed 21 months ago by Jpm

  • Reporter changed from anonymous to AutoXenon

comment:2 Changed 21 months ago by Jpm

In fact your concern come from the fact that parameter pass to parseStruct() is a temporary variable.
So how can you map a permanent area with the DllStructGetPtr() and get a valid result.
That the reason why you get such behavior.

I will close the ticket as No bug.


comment:3 Changed 21 months ago by anonymous

Thought so too, in which case I think this pitfall should probably be stated in the documentation, that the lifetime of DllStructs pertains to the scope where it is allocated, and so DllStructCreate when supplying a pointer will not count as valid references.

comment:4 Changed 21 months ago by Jpm

  • Resolution set to No Bug
  • Status changed from new to closed

Guidelines for posting comments:

  • You cannot re-open a ticket but you may still leave a comment if you have additional information to add.
  • In-depth discussions should take place on the forum.

For more information see the full version of the ticket guidelines here.

Add Comment

Modify Ticket

as closed The ticket will remain with no owner.

E-mail address and user name can be saved in the Preferences.

Note: See TracTickets for help on using tickets.