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Windows on main thread always only sometimes?
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Windows on main thread always only sometimes?


  • Subject: Windows on main thread always only sometimes?
  • From: Jack Repenning <email@hidden>
  • Date: Thu, 2 Jul 2009 11:16:48 -0700

I've always been taught that one must only create and run AppKit objects on the main thread. Recently, though, over in objc-language,

  http://lists.apple.com/archives/Objc-language/2009/Jul/msg00002.html

it was pointed out that the threading Programming Guide seems to say otherwise:

<http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html > says:
"You can create a window on a secondary thread. The Application Kit ensures that the data structures associated with a window are deallocated on the main thread to avoid race conditions. There is some possibility that window objects may leak in an application that deals with a lot of windows concurrently. You can create a modal window on a secondary thread. The Application Kit blocks the calling secondary thread while the main thread runs the modal loop."
But now I notice this only says you can *create* windows from secondary threads; it doesn't explicitly allow any other action, and it even refers to several automatic insurances that other things happen on the main thread.

So what *are* the rules? Is the Thread Safety Summary implicitly strict, "you can create a window, but absolutely nothing else"? Or is there some set of other operations that are permitted from the secondary (and where do I learn those)?

(This may already have been discussed on this list ... surely ... I tried to search it out first, but unfortunately every message in the archives matches "thread," due to the navigation links! If so, sorry.)

-==-
Jack Repenning
email@hidden
Project Owner
SCPlugin
http://scplugin.tigris.org
"Subversion for the rest of OS X"


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