On Wed, Dec 18, 2024, 10:40 PM Kaz Kylheku <k...@kylheku.com> wrote:
> On 2024-12-18 12:48, Chet Ramey wrote: > > On 12/18/24 1:27 PM, Kaz Kylheku wrote: > > > >> What remains is the question why I somehow cannot get my > >> stuff to work with a different signal like SIGUSR1 or SIGVTALRM. > >> > >> Bash will not take them while it's sitting in the call to readline. > > > > Something is indeed messed up in your execution environment. > > > > Let's try killing an interactive shell sitting in readline() from another > > terminal: > > > > $ echo $BASH_VERSION > > 5.2.37(6)-release > > $ trap > > $ echo $$ > > 30762 > > User defined signal 1: 30 > > > > [shell terminates] > > > > Now let's try killing an interactive shell that's not sitting in > readline() > > with the same fatal signal: > > > > $ echo $BASH_VERSION > > 5.2.37(6)-release > > $ trap > > $ kill -USR1 $$ > > User defined signal 1: 30 > > > > [shell terminates]. > > Right; I didn't make the wrong claim that SIGUSR1 isn't fatal. I made > that wrong claim only about SIGALRM, and retracted that already. > > The real issue is this: > > Let's work with SIGUSR1 first: > > $ trap 'echo USR1' USR1 > $ kill -USR1 $$ > USR1 > $ kill -USR1 $$ > USR1 > > So far, so good! Now let's sit at the prompt, while sending the signal > from a background process: > > $ while sleep 1; do kill -USR1 $$; done & > [1] 22261 > $ fg > USR1 > while sleep 1; do > kill -USR1 $$; > done > ^C > USR1 > try p=$$ ; while sleep 1 ; do kill -USR1 "$p" ; done & try also trap - USR1 in the new process ( the while loop ) I waited 20 seconds before typing "fg". Nothing! > > Now, let's try it with SIGALRM: > > $ trap 'echo ALRM' ALRM > $ while sleep 1; do kill -ALRM $$; done & > [1] 21882 > $ ALRM > ALRM > ALRM > ALRM > ALRM > ALRM > ALRM > ALRM > ALRM > > The "echo ALRM" commands go off like clockwork, every second. > > Most likely because of the way Readline treats signals, SIGARLRM ends up > "blessed" for this purpose. By dumb luck, I had picked the winning signal; > it was the first one I reached for. > > I understand that Bash will die if you send a SIGUSR1, and it > has no trap set up for it; but when it does have a handler set up, > it seems that Readline may be blocking the signal (perhaps via the > sigprocmask > or whatever). I probably won't be digging into it more. > > > > > >
