I am proposing the following patch.
Signal blocking effectively prevents signals from being processed by the child before it has the time to change disposition.
I re-ran my test script and the result is now correct. Signals sent to child are no longer caught by parent.
With a small program I also tested what happens with pended signals if their disposition is changed before they're delivered. They're simply delivered according to the new disposition. Example. If a SIGTERM is sent to the child right after the fork, the signal will be pended. The child will then change the signal disposition to SIG_DFL (terminate). When the child unblocks the signals, SIGTERM is delivered to the child and the child terminates.
Additional notes from http://man7.org/linux/man-pages/man7/signal.7.html: - A child created via fork(2) inherits a copy of its parent's signal mask; the signal mask is preserved across execve(2). - A child created via fork(2) initially has an empty pending signal set; the pending signal set is preserved across an execve(2).
All this is on RHEL5.11.
Regards,
2016-02-17 18:36 GMT-05:00 Philippe Anctil [email protected]:
Hi,
I have looked further into this issue. Part of the solution would be to reset signal disposition to SIG_DFL, either in the child after the fork, or around the call to create_client in accept connection for the child to inherit appropriate disposition from the start. Temporarily blocking signals could help. I have to verify exactly how it behaves.
By the way, why is SIG_CHLD set to null_handler in create_client? The default disposition for this signal is SIG_IGN.
Regards,
2016-02-16 11:45 GMT-05:00 Philippe Anctil [email protected]:
Hi,
In fork mode, sending a sigterm signal to a child is caught by the parent. I suspect it has something to do with signal_pipe being shared by the child and parent after the fork.
Here I sent a signal to the parent while a child process was also running. The parent shut down as expected. After sending sigterm, the child remains.
Processes before sigterm:
UID PID PPID C STIME TTY STAT TIME CMD user 1423 1 0 10:32 ? Ss 0:00 /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf user 1921 1423 0 10:37 ? S 0:00 _ /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf
selected pid 1423
Processes after:
UID PID PPID C STIME TTY STAT TIME CMD user 1921 1 0 10:37 ? S 0:00 /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf
Here I sent the signal to the child. The parent shut down and the child completed normally.
Processes before:
UID PID PPID C STIME TTY STAT TIME CMD user 1276 1 0 10:31 ? Ss 0:00 /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf user 1309 1276 0 10:31 ? S 0:00 _ /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf
selected pid 1309
Processes after:
UID PID PPID C STIME TTY STAT TIME CMD user 1309 1 0 10:31 ? S 0:00 /usr/local/stunnel/bin/stunnel.bin /usr/local/stunnel/etc/server.conf
I know I should be trying threads. I will eventually. I can only switch once I validate it can sustain our level of traffic. Fork has done that flawlessly for many years now.
Best regards,
-- Philippe Anctil
-- Philippe Anctil