> On Mar 1, 2017, at 2:44 PM, Wim Lewis <[email protected]> wrote: > > On Mar 1, 2017, at 2:23 PM, Carl Hoefs <[email protected]> wrote: >> Normally, that is sufficient. But under some circumstances, it's possible >> for an executing NSOperation to get hung up doing I/O or for some other >> reason. No means is given to forcibly stop the execution of an NSOperation, >> and there's no -thread method to obtain its thread and terminate it. > > As Ken Thomases says, this probably can't be done safely in the *general* > case. > > If you have a specific operation which might need to be asynchronously > interrupted, you can probably install a per-thread signal handler (remember > to clean it up on completion) and stash a thread identifier somewhere on the > NSOperation where your other code can find it. The handler could cancel any > blocked syscall and/or set a flag somewhere it can be cheaply checked by > cpu-intensive code. > > Truly asynchronously terminating a thread is unsafe unless you're very > careful about what might be happening in there: lots of library calls can > take out global locks temporarily (e.g., anything that uses malloc/free or > sends objc messages), and dropping one of those locks will promptly cause > your application to hang.
FWIW, pthread_cancel has historically not been implemented in any meaningful way on Darwin and this functionality is generally not useful. For example, there are no cancel points for typical file/network I/O system calls. (e.g. fread/fwrite) AFAIK, there's no way to cancel a synchronous system call via a thread (e.g. without killing the process). I would be interested to hear otherwise. I think the best you can do, as has been suggested, is to set a flag that the blocked thread can check after it wakes up again so it knows not to continue processing. Doug Hill _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
