| Message ID | 20240518084105.111682-1-aclopte@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | [v4] Allow trap to un-ignore SIGINT/SIGQUIT in async subshells | expand |
On Sat, May 18, 2024 at 10:38:30AM +0200, Johannes Altmanninger wrote: > Unlike in Bash or Zsh, this asynchronous job ignores SIGINT, despite > builtin trap explicitly resetting the SIGINT handler. > > dash -c '( trap - INT; sleep inf ) & read _' > > POSIX Section 2.11 on [Signals] and Error Handling says about > background execution: > > > If job control is disabled (see the description of set -m) when > > the shell executes an asynchronous list, the commands in the list > > shall inherit from the shell a signal action of ignored (SIG_IGN) > > for the SIGINT and SIGQUIT signals. > > Builtin [trap] has this requirement: > > > Signals that were ignored on entry to a non-interactive shell > > cannot be trapped or reset, although no error need be reported when > > attempting to do so. > > Apparently this only applies to signals that were inherited as ignored, > not to the special case of SIGINT/SIGQUIT begin ignored in asynchronous > subshells. > > Make it so. This means that either of > > trap - INT; trap - QUIT > set -i > > in a backgrounded subshell will now un-ignore SIGINT and SIGQUIT. > > [Signals]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html > [trap]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap > > {{{ Test cases: > > shell=src/dash > > set -e > > SubshellWith() { > parent_pid=$(setsid "$shell" -c "( $1; sleep 99 ) </dev/null >/dev/null 2>&1 & echo \$\$") > sleep 1 > subshell_pid=$(ps -o pid= -$parent_pid | tail -n 1) > } > > trap 'kill -TERM -$parent_pid 2>/dev//null ||:' EXIT # Tear down after a failure. > > echo Scenario 0: '"set -i"' makes a subshell un-ignore SIGINT. > SubshellWith 'set -i' > kill -INT $subshell_pid > ! ps -p $subshell_pid | grep sleep || exit 1 > kill -TERM -$parent_pid 2>/dev//null ||: # Tear down. > > echo Scenario 1: resetting SIGINT handler. > SubshellWith 'trap - INT' > kill -INT -$parent_pid # kill the whole process group since that's the my use case > ! ps -p $subshell_pid | grep sleep || exit 1 > kill -TERM -$parent_pid 2>/dev//null ||: # Tear down. > > echo Scenario 2: ignoring SIGINT. > SubshellWith 'trap "" INT' > kill -INT $subshell_pid > ps -p $subshell_pid | grep sleep || exit 1 > kill -TERM -$parent_pid 2>/dev//null ||: # Tear down. > > }}} > > {{{ Backstory/motivation: > > The Kakoune[1] editor likes to run noninteractive shell commands that > boil down to > > mkfifo /tmp/fifo > ( > trap - INT > make > ) >/tmp/fifo 2>&1 & > > On Control-C, the editor sends SIGINT to its process group, > which should terminate the subshell running make[2]. > > We experimented with sending SIGTERM instead but found issues, > specifically if the editor is invoked (without exec) from a wrapper > script, sending SIGTERM to the whole process group would kill the > wrapper script, which in turn makes it send SIGTERM to the editor, > which then terminates. > > [1]: https://kakoune.org/ > [2]: https://lists.sr.ht/~mawww/kakoune/%3C20240307135831.1967826-3-aclopte@gmail.com%3E > > }}} > --- > src/trap.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) Patch applied. Thanks.
diff --git a/src/trap.c b/src/trap.c index f871656..90e9607 100644 --- a/src/trap.c +++ b/src/trap.c @@ -296,11 +296,11 @@ setsignal(int signo) void ignoresig(int signo) { - if (sigmode[signo - 1] != S_IGN && sigmode[signo - 1] != S_HARD_IGN) { - signal(signo, SIG_IGN); - } + if (sigmode[signo - 1] == S_IGN || sigmode[signo - 1] == S_HARD_IGN) + return; + signal(signo, SIG_IGN); if (!vforked) - sigmode[signo - 1] = S_HARD_IGN; + sigmode[signo - 1] = S_IGN; }