Re: Thread safe?

FROM : Jens Alfke
DATE : Sat Mar 29 18:05:14 2008

On 29 Mar '08, at 6:44 AM, Trygve Inda wrote:

> Can I call the following from a thread?


Apologies for giving an opinion instead of an answer ... but here's my 
opinion. I've always avoided calling AppKit from multiple threads. 
Instead I run the app's entire UI on the main thread, use asynchronous 
APIs as much as possible (e.g. for networking), and use background 
threads only when necessary and only for non-UI tasks.

Partly this comes from my previous experience with Java, where apps 
spawn threads promiscuously and tend to do UI tasks on many of them at 
once. This made implementing the AWT graphics library (the platform-
specific pieces of it) pretty hellish, since everything had to be 
thread-safe. This added tons of complexity to the code, and meant lots 
of race conditions and deadlocks to debug. I left that job vowing 
never to create a thread ever again :)

Multiprocessing is an unsolved problem — no one's discovered a really 
good abstraction for it that makes code simple and reliable. It's like 
memory management pre-garbage collection, or control flow pre-
structured programming. There's a great paper on the topic, "The 
Trouble With Threads" by Edward Lee of UC Berkeley:
   http://www.artist-embedded.org/docs/PositionPapers/Lee_Threads_May2006.pdf
   "For concurrent programming to become mainstream,we must discard 
threads as a
   programming model.Nondeterminism should be judiciously and carefully 
introduced
   where needed,and it should be explicit in programs."

By way of answering … I _believe_ you can create and draw into 
NSImages on background threads; but I'm not certain. Drawing into the 
same image from multiple threads at once, though, could likely get you 
into trouble.

—Jens