Re: grep-use-null-device

[Juri Linkov <juri@jurta.org>]

>> `compilation-start' needs to check if the process is running
>> before calling `process-send-eof':
>
> That's odd.  AFAICT no blobking operation takes place between the
> start-process and the process-send-eof, so the process-status should still
> be `run' no matter how quickly the process exits (because Emacs shouldn't
> process the SIGCHLD it receives until later).
>
> What am I missing?

The process exits during execution of create_process.  The gdb log below
with a breakpoint on sigchld_handler demonstrates what really happens:

Breakpoint 4, sigchld_handler (signo=17) at process.c:6249
6249              XSETINT (p->raw_status_low, u.i & 0xffff);
(gdb) n
6250              XSETINT (p->raw_status_high, u.i >> 16);
(gdb) n
6253              if ((WIFSIGNALED (w) || WIFEXITED (w))
(gdb) n
6260                  FD_CLR (XINT (p->infd), &input_wait_mask);
(gdb) n
6261                  FD_CLR (XINT (p->infd), &non_keyboard_wait_mask);
(gdb) p w
$1 = 512     <-- WIFEXITED
(gdb) bt
#0  sigchld_handler (signo=17) at process.c:6261
#1  <signal handler called>
#2  0x4031f784 in sigprocmask () from /lib/libc.so.6
#3  0x0817af28 in create_process (process=141365940, new_argv=0xbfffe954, current_dir=140249731) at process.c:2153
#4  0x0817a97d in Fstart_process (nargs=5, args=0xbfffea94) at process.c:1695
...
(gdb) fr 3
#3  0x0817af28 in create_process (process=141365940, new_argv=0xbfffe954, current_dir=140249731) at process.c:2153
2153      sigprocmask (SIG_SETMASK, &procmask, 0);

-- 
Juri Linkov
http://www.jurta.org/emacs/