semget() returns EAGAIN?

Corinna Vinschen
Wed Aug 7 08:12:00 GMT 2019

On Aug  7 05:02, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin wrote:
> I'm noticing that in a high-contention situation (many processes try
> to get ahold of a semaphore) semget() on Cygwin starts to return
> EAGAIN (try again) after about 62 processes has gotten to call
> semget() and are actively competing for the semaphore (i.e. using the
> semaphore ID semget() returned to them).
> EAGAIN is not documented in any of semget() API documentation that I
> can find.
> I understand that in Cygwin semget() is implemented as a connection to
> cygserver, and the error probably stems from there, but I don't think
> that such a code is appropriate as a final errno.  And why is there a
> limit, to begin with?  What exactly imposes it?

The number of parallel open pipes, for instance.  By default, 10
worker threads handle the load and up to 62 processes can be handled
in parallel.  If the numbers are too low in your scenario, try to
raise them in /etc/cygserver.conf.


Corinna Vinschen
Cygwin Maintainer
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