On Mon, Oct 25, 2021 at 01:41:18PM -0400, Jeff King wrote: > On Sun, Oct 24, 2021 at 07:03:49PM +0200, SZEDER Gábor wrote: > > > On Sat, Oct 23, 2021 at 05:04:42PM -0700, Junio C Hamano wrote: > > > It seems under --stress it is fairly easy to break the said test, > > > especially the one near the end > > > > I couldn't reproduce a failure with --stress, but after a cursory look > > into those tests I doubt that either that test or any of the > > preceeding SIGPIPE tests added in c24b7f6736 (pager: test for exit > > code with and without SIGPIPE, 2021-02-02) actually check what they > > are supposed to. > > Yeah, I am puzzled that they are using test_terminal in the first place > (as opposed to just "git -p"). And you are right that a raw git-log is > unlikely to be slow enough to get SIGPIPE in most cases. > > My usual test for an intentional SIGPIPE is "yes". So something like: > > git -p \ > -c core.pager='exit 0' \ > -c alias.yes='!yes' \ > yes > > will reliably trigger SIGPIPE from yes, which git.c will then translate > into an exit code of 141. Oh, that's clever. Alas it's not applicable to our tests, because 'yes' is not portable; 8648732e29 (t/test-lib.sh: provide a shell implementation of the 'yes' utility, 2009-08-28). > If you really want to see SIGPIPE from a builtin (which arguably is the > more interesting case here, though I think it behaves the same with > respect to the pager), it's a bit trickier. One way to do it is with a > command that doesn't generate output until after it gets EOF on stdin. > > So something like "git log --stdin" works, but you have to contort > yourself a bit to make it race-free: > > -- >8 -- > # The I/O setup here is: > # > # fifo:log-in stdout > # shell -----------> git-log ------> pager > # ^ / > # \-------------------------------/ > # fifo:pager-closed > # > # The pager closes its stdin, which will give git-log SIGPIPE. But the > # tricky part is that after doing so, it signals via fifo to the shell, > # which then writes to git-log's stdin, triggering it to actually > # generate output (and get SIGPIPE). > # > # You can verify that it's race-free by inserting a "sleep 3" at the > # front of the pager command (before the exec) and seeing that the > # other processes wait (and we still get SIGPIPE). > > mkfifo pager-closed > mkfifo log-in > git config core.pager 'exec 0<&-; echo ready >pager-closed; exit 0' > (git -p log --stdin <log-in; echo $? >exit-code) & > > # we have to open a descriptor rather than just "echo HEAD >log-in", because > # that will give git-log an immediate EOF on its input when echo closes it, and > # we must wait until the signal from pager-closed. Likewise we cannot wait > # for that signal before the echo, because the subshell is blocking on opening > # log-in until somebody is hooked up to the write end of the pipe. > exec 9>log-in > read ok <pager-closed > echo HEAD >&9 > exec 9>&- > > # now we can wait for the subshell to finish and retrieve any output > # it produced > wait > cat exit-code > -- >8 -- Ugh. I think this would work reliably, but... ugh :) I wonder whether we could do this as a new pair of 'test-tool' helpers, one to run the pager through the usual pager-invoking machinery and to generate a lot of output, the other to be used as the early-exiting pager, with a pipe between the two to ensure that the SIGPIPE does happen. Well, essentially the same that you outlined above but in C instead of shell, which I somehow find less "ugh".
