Foundation.Process on Linux seems to inherit the Process.run()-calling thread's signal mask, creating processes that even have SIGTERM blocked #4772
Description
I spawned two processes /bin/cat -nu one from Foundation.Process (pid 15477) and one from my shell (pid 15480)
root 15477 0.0 0.0 2992 788 pts/1 S 10:30 0:00 /bin/cat -nu
root 15480 0.0 0.0 2992 784 pts/1 S+ 10:30 0:00 /bin/cat -nu
and the one from Foundation.Process is unkillable with SIGTERM:
# kill 15477
# kill -TERM 15477
# ps axuw | grep 1547[7]
root 15477 0.0 0.0 2992 788 pts/1 S 10:30 0:00 /bin/cat -nu
where as the other one will die immediately on SIGTERM. Why is that?
15477 (the one from Foundation.Process) has a lot of signals blocked (see SigBlk)
# cat /proc/15477/status | grep ^Sig
SigQ: 3/15256
SigPnd: 0000000000000000
SigBlk: fffffffe3bfbea27
SigIgn: 0000000180001000
SigCgt: 0000000000000000
fffffffe3bfbea27 is 1111111111111111111111111111111000111011111110111110101000100111 which means that all but 12 signals are actually blocked! Only 4: SIGILL, 5: SIGTRAP, 7: SIGBUS, 8: SIGFPE, 9: SIGKILL, 11: SIGSEGV, 13: SIGPIPE, 19: SIGSTOP, 27: SIGPROF and 31: SIGSYS seem not blocked.
That looks very curiously exactly like Dispatch's sigmask for its worker threads: https://github.com/apple/swift-corelibs-libdispatch/blob/9566a131de09a472790f7b69ae661326cdedf306/src/init.c#L91-L110 .
The normal /bin/cat -nu spawned from my shell has (as expected) a wholly 0 SigBlk mask (which means all signals are coming through).
# cat /proc/15480/status | grep ^Sig
SigQ: 3/15256
SigPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000