mystone@mondo.engin.umich.edu (Dean Yu) (03/05/90)
I know the old litany of not moving memory from a completion routine. What
I'm wondering is if it's safe to make an asynchronous _Control call from a
completion routine. I was thinking about the AppleTalk drivers specifically;
if I have all the response and request buffers allocated beforehand, is it
safe to send an async SendResponse in the completion routine of a GetRequest?
Thanks for any thoughts on this subject.
-- Dean
_______________________________________________________________________________
Dean Yu | E-mail: mystone@caen.engin.umich.edu
Mac Support & | Real-mail: Dean Yu
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-------------------------------------------------------------------------------tim@hoptoad.uucp (Tim Maroney) (03/06/90)
In article <1990Mar5.031521.4774@caen.engin.umich.edu> mystone@mondo.engin.umich.edu (Dean Yu) writes: > I know the old litany of not moving memory from a completion routine. What >I'm wondering is if it's safe to make an asynchronous _Control call from a >completion routine. I was thinking about the AppleTalk drivers specifically; >if I have all the response and request buffers allocated beforehand, is it >safe to send an async SendResponse in the completion routine of a GetRequest? Sure, but just to be safe, use a different parameter block. And at all costs avoid the situation where you set up a possibly bottomless recursion, where the completion routine for operation A starts operation B and the completion routine for operation B starts operation A. You wouldn't think these things would complete immediately and overflow the stack, and they usually don't, but I have seen some cases where they do. -- Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, tim@toad.com "I see little divinity about them or you. You talk to me of Christianity when you are in the act of hanging your enemies. Was there ever such blasphemous nonsense!" - Shaw, "The Devil's Disciple"
jsm@Apple.COM (Jeff Miller) (03/07/90)
In article <1990Mar5.031521.4774@caen.engin.umich.edu> mystone@mondo.engin.umich.edu (Dean Yu) writes: > > I know the old litany of not moving memory from a completion routine. What >I'm wondering is if it's safe to make an asynchronous _Control call from a >completion routine. I was thinking about the AppleTalk drivers specifically; Yes, it is safe. In fact, many device drivers (including AppleTalk I believe) do this. Jeff Miller
rmh@apple.com (Rick Holzgrafe) (03/07/90)
In article <10614@hoptoad.uucp> tim@hoptoad.uucp (Tim Maroney) writes: > In article <1990Mar5.031521.4774@caen.engin.umich.edu> > mystone@mondo.engin.umich.edu (Dean Yu) writes: >> I know the old litany of not moving memory from a completion routine. What >>I'm wondering is if it's safe to make an asynchronous _Control call from a >>completion routine. I was thinking about the AppleTalk drivers specifically; >>if I have all the response and request buffers allocated beforehand, is it >>safe to send an async SendResponse in the completion routine of a GetRequest? > > Sure, but just to be safe, use a different parameter block. Not necessary to use a different parameter block. It is definitely a big no-no to use one parameter block for overlapping _Control calls. But when your completion routine is called, the original _Control call is considered "complete" by AppleTalk: it's through with the parameter block, and you can re-use it. > And at all > costs avoid the situation where you set up a possibly bottomless > recursion, where the completion routine for operation A starts > operation B and the completion routine for operation B starts operation > A. Right on! Even short recursions can be dangerous because you can't be sure whose stack you're using. We discovered that TimeKeeper has a short stack in exactly this fashion. ========================================================================== Rick Holzgrafe | {sun,voder,nsc,mtxinu,dual}!apple!rmh Software Engineer | AppleLink HOLZGRAFE1 rmh@apple.com Apple Computer, Inc. | "All opinions expressed are mine, and do 20525 Mariani Ave. MS: 67-B | not necessarily represent those of my Cupertino, CA 95014 | employer, Apple Computer Inc."