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Old 09-26-2016, 01:46 PM   #1
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mq_open returns "Too many open files"

Hello All,

I am using mq_open call to open a posix message queue. I am creating with below attributes.

attr.mq_flags = 0;
attr.mq_maxmsg = 50;
attr.mq_msgsize = 8192;

When I do mq_open, it fails with error "Too many open files".

If I change
attr.mq_msgsize = 8192;
attr.mq_msgsize = 4000;

It works fine. Any ideas ?

Old 09-26-2016, 02:23 PM   #2
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Generally speaking you'll get an error indicating too many open files when you've exceeded a per process, or system wide, limit on the number of open files ( or something that uses a file descriptor, even if the use of the descriptor is not evident ).

Are you repeatedly calling mq_open, or opening files again and again, without closing them, perhaps in a code loop?
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Old 09-27-2016, 10:59 AM   #3
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I suspect that the difference in number is more-or-less a "red herring." That is to say, one setting might conceal the existence of "the underlying bug in your program," but it does not address the bug itself.

Methinks that you should always be nowhere near any such architectural limit on the number of queues. Your program is probably in-error in trying to do so.

Last edited by sundialsvcs; 09-30-2016 at 08:25 AM.
Old 09-27-2016, 11:36 PM   #4
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EMFILE? Check [cat] /proc/sys/fs/mqueue/msgsize_max is 8192 (see mq_overview)
Does it work with attr.mq_maxmsg = 20? (<half total usage [*leaving* mq_msgsize 8192])

uname -rv ; grep msg /proc/self/limits

Last edited by Jjanel; 09-27-2016 at 11:43 PM.


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