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cygserver blocking on semctl(SETVAL)
- From: Ethan Tira-Thompson <ejt at andrew dot cmu dot edu>
- To: cygwin-developers at cygwin dot com
- Date: Thu, 24 Aug 2006 18:54:07 -0400
- Subject: cygserver blocking on semctl(SETVAL)
I have a piece of code:
void SemaphoreManager::setValue(semid_t id, int x) const {
semun params;
params.val=x;
cout << "SEMCTL..." << flush;
if(semctl(semid,id,SETVAL,params)<0) {
perror("ERROR: SemaphoreManager::setValue (semctl)");
exit(EXIT_FAILURE);
}
cout << "done" << endl;
}
This is part of a function which gets called a number of times
throughout the life of the program. It works just fine up until one
particular call (with x=0) which reliably causes it to block between
the two cout's. Not just my program either -- all IPC is blocked at
this point. So bringing up new cygwin windows, running ipcs, etc.,
all hang. Once I kill any one process in the group that are using
the semaphore, it seems to jump start things a bit and may run a bit
more, but usually eventually blocks again until all of the processes
are killed.
My code runs fine under Linux and Mac OS X, it's only now that we're
nearing release that I'm testing under cygwin and finding something
has gone wrong in the past 9 months or so -- either something updated
on your end, or a change in our code tickling an unknown issue.
The kicker to note here -- is there any reason a *SETVAL* operation
could cause a block??? It should either go through or return an
error. I'm fairly convinced it's *not* this particular semctl call
that's *causing* the block, it just gets hung up because some
previous operation has blocked cygserver, and it's that operation
that's causing the trouble.
One nuisance is that when I run cygserver with -d, it doesn't block
in the same place -- something about all that debugging output
changes the race conditions. In any case, I've attached the
cygserver output leading up to a block, in hopes it means something
to you.
Thanks for taking a look -- I'm afraid I'm stumped. (doesn't help
gdb only reports '??' for all function calls when I attach to a
process, so I can't tell what any of my code is doing. And yes, I do
have -g enabled)
-ethan
This trace corresponds to the activity between entering a command in
my program to move to a new runlevel, and the block that occurs in
that runlevel.
Attachment:
cygserverout.txt
Description: Text document