Phil, Phil Endecott wrote: > Hi Michael, > > man waitpid says under RETURN VALUE: > > waitpid(): on success, returns the process ID of the child whose > state has changed; on > error, -1 is returned; if WNOHANG was specified and no > child(ren) specified by pid has > yet changed state, then 0 is returned. > > There is a subtle case when the child has no children at all and you > call waitpid(-1,NULL,WNOHANG). To me, the existing wording implies that > it will return 0. In fact it returns -1 and ECHILD, as I have > discovered the hard way :-(. The SUS documentation is more explicit > about this, e.g. > http://www.opengroup.org/onlinepubs/007908799/xsh/wait.html: > > "If waitpid() was invoked with WNOHANG set in options, ****it has at > least one child process specified by pid for which status is not > available****, and status is not available for any process specified by > pid, 0 will be returned. Otherwise, (pid_t)-1 will be returned, and > errno will be set to indicate the error." > > I suggest the following, which is based on your existing text: > > waitpid(): on success, returns the process ID of the child whose state > has changed; > else if WNOHANG was specified and child(ren) specified by pid exist but > have not yet changed state, then 0 is returned; > else an error has occurred and -1 is returned. You are of course right that the text could be clearer. Thanks for pointing that out. For man-pages-2.77, I've changed the text to: waitpid(): on success, returns the process ID of the child whose state has changed; if WNOHANG was specified and one or more child(ren) specified by pid exist, but have not yet changed state, then 0 is returned. On error, -1 is returned. Cheers, Michael -- Michael Kerrisk Maintainer of the Linux man-pages project http://www.kernel.org/doc/man-pages/ Want to report a man-pages bug? Look here: http://www.kernel.org/doc/man-pages/reporting_bugs.html - To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
