Re: [PATCH] Portability: returning void

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Mar 29, 2011, 23:49 UTC
Message-ID: <20110329234955.GB14578@elie>
In-Reply-To: <20110329221652.GB23510@sigill.intra.peff.net>

Jeff King wrote:

Show 5 quoted lines

> The problem is that the sleeps hang around for 100 seconds, and they are
> connected to the test script's stdout. It works to run "./t0081-*"
> because bash sees the SIGCHLD and knows the script is done. But the
> prove program actually ignore the SIGCHLD and waits until stdout and
> stderr on the child are closed.

Strange. Why would prove tell its children to ignore SIGCHLD and SIGTERM?

> Double-weird is that if you "strace" the prove process, it will still
> hang. But if you "strace -f", it _won't_ hang.

Well, it hangs for me. :) The strangest aspect is that after 100 seconds, all is well again, which suggests that there's more happening than an unreaped process.

After lowering the sleep to 15 seconds:

| kill: 19422
| bash(19422)---sleep(19424)
|
| ok 3 - 0-length read, no input available
[...]
| kill: 19431
| bash(19431)---sleep(19434)
| ok 5 - 1-byte read, no input available
[...]
| kill: 19438
| bash(19438)---sleep(19441)
| 
| ok 6 - long read (around 8192 bytes)
[...]
| # passed all 13 test(s)
[...]
| 19398 18:31:12 exit_group(0)            = ?
| 19397 18:31:12 <... select resumed> )   = ? ERESTARTNOHAND (To be restarted)
| 19397 18:31:12 --- SIGCHLD (Child exited) @ 0 (0) ---
| 19397 18:31:12 select(8, [4 6], NULL, NULL, NULL <unfinished ...>

The test script exits, but "prove" is stuck in select and does not want to start reaping yet. So presumably the test script's children are adopted by init. We wait around 13 seconds, and then:

| 19424 18:31:25 <... nanosleep resumed> NULL) = 0
| 19424 18:31:25 close(1)                 = 0
| 19424 18:31:25 close(2)                 = 0
| 19424 18:31:25 exit_group(0)            = ?
| 19422 18:31:25 <... wait4 resumed> 0x7fff65d1ee6c, 0, NULL) = ? ERESTARTSYS (To be restarted)
| 19422 18:31:25 --- SIGTERM (Terminated) @ 0 (0) ---

The first sleep wakes up and dies. The corresponding subshell wakes up, reaps the child, and finally accepts SIGTERM.

| 19434 18:31:26 <... nanosleep resumed> NULL) = 0
[...]
| 19438 18:31:26 --- SIGTERM (Terminated) @ 0 (0) ---

Likewise for the second and third sleeps.

| 19397 18:31:26 <... select resumed> )   = 2 (in [4 6])
| 19397 18:31:26 read(4, "", 65536)       = 0
| 19397 18:31:26 read(6, "", 65536)       = 0
| 19397 18:31:26 wait4(19398, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 19398

Now "prove" wakes up again.

The analagous experiment for dash, mksh, etc shows that their subshells exec()'d /bin/sleep so the SIGTERM reaches sleep right away with no trouble.