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 <philippe.anctil@gmail.com>:

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 <philippe.anctil@gmail.com>:

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,

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Philippe Anctil

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Philippe Anctil

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Philippe Anctil