Thread: select/poll and Signal Safety

  1. #1
    Registered User
    Join Date
    Jan 2006

    select/poll and Signal Safety


    I am struggling to understand why one should use pselect()/ppoll() instead of wrapping an ordinary select() or poll() call around sigprocmask(). The linux man page talks about “race conditions”, but how would such dangers occur?

    I plan to use poll() for an application (since ppoll() isn’t widely supported) but wish to know how (if possible) it can be made signal safe? please see preliminary code scenario below.

    void foofunc() {
    	int retval;
    	sigprocmask(...); // block certain signals
    	while(1) {
    		sigprocmask(...); // set empty mask
    		// <- can something go wrong here?
    		retval = poll(...); // wait indefinitely
    		// <- and what about here?
    		sigprocmask(...); // restore old mask
    		if (retval != -1) {
    			... // handle file descriptor events
    		} else (errno == EINTR) {
    			// just signal interruptions, don't panic
    		} else {
    			... // handle error
    Any help is greatly appreciated.
    Last edited by nopcoder; 01-27-2006 at 07:27 AM.

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