Messages in this thread | | | Date | Mon, 5 Feb 2007 07:13:26 -0500 | From | "Sue Alfano" <> | Subject | waitid() problem? |
| |
I didn't get any responses on this. I thought maybe the subject line was misleading, so I'm trying a different one. If I'm using the wrong mailing list, or if there's another site other than kernel.org that I should be using to search through archives and FAQs, please let me know.
I'm accessing the waitid function in the kernel using the _syscall4 macro since it's not supported in uClibc. waitid worked great, but then I started having problems when more than one child needed to be reaped.
Basically, the parent process registers a SIGCHLD signal handler via sigaction() with the SA_RESTART option and then sits on a timed select(). All the signal handler does is set a flag - the waitid processing takes place when the parent drops out of the select because of the signal or a timeout. When the waitid succeeds, the pid is used to do some processing and then is used to call waitpid to clean up the mess. This is all in a while loop, so when the waitid is called again, 0 is returned with si_pid = 0 indicating that there are no more children to reap. That's all great. The problem occurs when there's 2 or more children to reap. When this occurs, the 2nd waitid call returns -1 and si_pid = 0. The waitid continues to fail in this manner until the parent receives another SIGCHLD signal, then it works for the next zombie child in the waiting line, but only one. I can send SIGCHLD kills to the parent from the console and eventually get everything cleaned up. Sending the kill from the parent isn't enough - I suppose it wants to be blocking on the select.
I tried registering the signal handler without SA_RESRART and also via signal(), since there was a posting about SA_RESTART, but that made no difference. I also tried not having a signal handler at all, but then I couldn't reap any children on the timeout.
So, are there known issues with waitid when there are multiple children piled up waiting to be reaped? If so, is there a patch or a workaround?
The product that I'm working on is using Linux version 2.6.12-2.0.0-258
Thanks for any help, Sue - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |