You can get an accurate answer regarding the CPU use implication by profiling a test application using the system 
profiler.

sem_open() will have the largest overhead: you will want to avoid open()/closing() the same resource in a loop.

--
Mate

From: Lawrence Lee <community-noreply@qnx.com<mailto:community-noreply@qnx.com>>;
Reply-To: <post91301@community.qnx.com<mailto:post91301@community.qnx.com>>;
Date: Thu, 2 Feb 2012 10:46:22 -0500
To: ostech-core_os <post91301@community.qnx.com<mailto:post91301@community.qnx.com>>;
Subject: sem_xxxx APIs

QNX implemented POSIX APIs, but how does sem_xxxx APIs got implemented.

Does sem_xxxx routines actually send message to a "semaphore resource manager"? How expansive if it is sending messages 
all the time, if an application
calling sem_open, follow by sem_wait, follow by sem_post, and then sem_close all the time.




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OSTech
http://community.qnx.com/sf/go/post91301