Question

I am working on a pthread multi-threaded code and each thread is calling read() on a file descriptor. read() is a blocking call so it waits for data. But i want it to wait only for 3 secs to wait for data.

I thought of using alarm() and hadling SIGALRM but if I raise alarm in one thread, all the threads will got that SIGALRM signal and all of them will relinquish read. How can i do it?

Answer 1

Use the select call for that. It has one argument that allows you to specify a timeout.

The Linux man page for select has a sample usage, and you’ll find lots of examples here and elsewhere on the web.

If you’re not worried about portability, there are more modern/featureful options.

• For Linux, there’s the epoll facility. The man page has sample code, this question lists a couple of blogs with other usage information.
• For some of the *BSDs (and Mac OS X), there’s kqueue.
• Solaris has an Event Completion Framework
• AIX has a pollset interface.
• For Windows, please see: What is the best epoll/kqueue/select equvalient on Windows?

You might want to look into libraries to abstract all that out. libevent is worth a look, and wraps most of the above OS-specific interfaces.