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Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!ogicse!milton!wiml
From: wiml@milton.u.washington.edu (William Lewis)
Newsgroups: comp.sys.next,comp.os.mach
Subject: Re: NXPing() in a thread
Message-ID: <19044@milton.u.washington.edu>
Date: 26 Mar 91 03:35:31 GMT
References: <00946246.F502A0C0@uno.edu>
Organization: University of Washington, Seattle
Lines: 39


  I've changed the Newsgroups: line, as the query isn't really relevant
to Objective-C ...

In article <00946246.F502A0C0@uno.edu> jrscs@uno.edu writes:
>   I have a question on the use of NXPing() in a detached thread.  The
>detached thread processes some sound data while the "main" thread handles
>the user interface.  NXPing() works fine inside the main thread but it
>hangs my NeXT if it call it inside the method for which the thread was
>launched. 

   I can't imagine how it would hang the whole NeXT, but I can see how
it could hang your application without much trouble. The trouble
stems from the fact that the DPS routines (in fact, almost all library
routines that change any sort of global state, including seemingly safe
ones as close()/open()) are not reentrant; they're not designed for a
multi-threaded environment. So when you call NXPing() in a subsidiary
thread, the main thread is probably sitting in DPSGetEvent() (assuming
it's a normal Appkit-using application), and both threads attempt to
interact with the window server simultaneously, with undesirable results.


>    ( The NXPing() inside the detached thread ( supposedly )
>coordinates the highlighting of a word in a window with the pronunciation
>of that word. )

  It would be really nice if the DPS*() routines _were_ reentrant
(or at least used mutexes or something... hello NeXT?) As far as I
know, the only way to do this is to send a Mach message to a port
registered via DPSAddPort(), which will wake up the main thread; the
handler on that port can then NXPing() or do other arbitrary
processing.  Unfortunately this seems like a whole lot more trouble
than it should be ...


-- 
 wiml@milton.acs.washington.edu       Seattle, Washington   
     (William Lewis)   |  47 41' 15" N   122 42' 58" W  
 "Just remember, wherever you go ... you're stuck there."