[M3commit] CVS Update: cm3

[Jay]

How about this comment in the code:
 
(*-------------------------------------------------- raw seething windows ---*)(* NOTE: The helper procedures called by WindowProc lock VBT.mu when calling   various Trestle procedures.  They do not hold locks while calling Win32   because it knows nothing about Modula-3 locks and it can, on a whim, call   WindowProc to do something.  The only reason this scheme might work is   because we have a single Modula-3 thread that's pulling on the Win32   message queue and calling WindowProc.
 
   Similarly, we don't bother locking around updates to Child records.   They are updated by the single Modula-3/WindowProc thread.*)
?
I also need to check if any state has been modified, or cached in locals, with
the locks held that are being released.
 
 -Jay



Date: Thu, 14 Aug 2008 11:13:25 -0400From: rcoleburn at scires.comTo: jkrell at elego.de; m3commit at elegosoft.comSubject: Re: [M3commit] CVS Update: cm3

Jay:
 
I haven't studied this code in depth, but on the surface I doubt your change is "correct".  
 
I think the more telling problem is that if you look at the body of WinTrestle.Release, it is empty, save for a comment that it is not yet implemented.  So, it would seem that if WinTrestle.Acquire is called more than once, you will crash because the locks have not been released.
 
Further, I don't think it would make sense to release the locks before calling out to Windows, and then reacquire them upon return.  The locks are known to Modula-3 and not Windows.  Releasing them will allow other competing threads to acquire them while you are in the Windows subsystem and would seem to violate whatever protections were in place per holding the locks.  Upon return from Windows, the thread will be back in competition with others to reacquire the locks it gave up and upon success, there is no guarantee that the other threads didn't disturb the state the original thread depended upon.
 
I would suggest reverting these changes and looking to implement the Release procedure.
 
Regards,
Randy
>>> Jay Krell <jkrell at elego.de> 8/14/2008 4:26 PM >>>CVSROOT:/usr/cvsChanges by:jkrell at birch.08/08/14 16:26:59Modified files:cm3/m3-ui/ui/src/winvbt/: WinTrestle.m3 Log message:release locks when calling out to Win32 to prevent recursive lock acquisition. correct?
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