asyncio_tools: add SIGHUP handling for terminal close termination

[fsagbuya]

Description

Add SIGHUP signal handling to properly terminate processes upon terminal close. Affects processes that use SignalHandler.

Tested with: artiq_ctlmgr and artiq_session

Closes m-labs/artiq#2614

[sbourdeauducq]

Tested with: artiq_ctlmgr

Did the test include checking that controllers are terminated cleanly? By ctlmgr?
Why are the controllers apparently not receiving SIGHUP themselves?

[sbourdeauducq]

and artiq_session

artiq_session is not using this sipyco signal handler itself. But some of its child processes do. Assuming this PR did make a difference, I suppose these child processes did receive SIGHUP. Why the difference with the child processes started by ctlmgr?

[sbourdeauducq]

Also, this breaks Windows. signal.SIGHUP is not even defined there.

[fsagbuya]

Did the test include checking that controllers are terminated cleanly? By ctlmgr?

Yes. Showing from this strace log:

sudo strace -p 153249 -e signal
strace: Process 153249 attached
--- SIGHUP {si_signo=SIGHUP, si_code=SI_USER, si_pid=144910, si_uid=1000} ---
--- SIGCONT {si_signo=SIGCONT, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = -1 EINTR (Interrupted system call)
--- SIGHUP {si_signo=SIGHUP, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = -1 EINTR (Interrupted system call)
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=153250, si_uid=1000, si_status=0, si_utime=14 /* 0.14 s */, si_stime=1 /* 0.01 s */} ---
rt_sigaction(SIGINT, {sa_handler=0x7ffff7951530, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, {sa_handler=0x7ffff7951530, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, 8) = 0
rt_sigaction(SIGTERM, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, {sa_handler=0x7ffff7951530, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, 8) = 0
rt_sigaction(SIGHUP, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, {sa_handler=0x7ffff7951530, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, 8) = 0
rt_sigaction(SIGINT, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, {sa_handler=0x7ffff7951530, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK, sa_restorer=0x7ffff7560620}, 8) = 0
+++ exited with 120 +++

Why are the controllers apparently not receiving SIGHUP themselves?

Most likely because of the start_new_session=True in controllers

[fsagbuya]

artiq_session is not using this sipyco signal handler itself. But some of its child processes do. Assuming this PR did make a difference, I suppose these child processes did receive SIGHUP. Why the difference with the child processes started by ctlmgr?

From another strace log, artiq_session's children (master, dashboard, ctlmgr) receive SIGHUP directly because they're created with Popen(). The controllers started by ctlmgr don't receive SIGHUP directly due to start_new_session=True, but they exit through ctlmgr's atexit handlers which now run when terminal closes with the new SIGHUP handler.