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Clean up the recently added self-pipe mechanism for WINDOWSNT

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* src/process.c (child_signal_init, child_signal_read)
(child_signal_notify): #ifdef away on WINDOWSNT.
This commit is contained in:
Eli Zaretskii 2021-01-23 12:51:57 +02:00
parent cc98d0bf52
commit 8d8e1dfd05
1 changed files with 21 additions and 2 deletions
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23
src/process.c
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@ -290,7 +290,10 @@ static int child_signal_read_fd = -1;
status changes. */
static int child_signal_write_fd = -1;
static void child_signal_init (void);
#ifndef WINDOWSNT
/* FIXME: This is never used, on all platforms. */
static void child_signal_read (int, void *);
#endif
static void child_signal_notify (void);
/* Indexed by descriptor, gives the process (if any) for that descriptor. */
@ -7148,8 +7151,18 @@ process has been transmitted to the serial port. */)
have the same process ID.
To avoid a deadlock when receiving SIGCHLD while
`wait_reading_process_output' is in `pselect', the SIGCHLD handler
will notify the `pselect' using a pipe. */
'wait_reading_process_output' is in 'pselect', the SIGCHLD handler
will notify the `pselect' using a self-pipe. The deadlock could
occur if SIGCHLD is delivered outside of the 'pselect' call, in
which case 'pselect' will not be interrupted by the signal, and
will therefore wait on the process's output descriptor for the
output that will never come.
WINDOWSNT doesn't need this facility because its 'pselect'
emulation (see 'sys_select' in w32proc.c) waits on a subprocess
handle, which becomes signaled when the process exits, and also
because that emulation delays the delivery of the simulated SIGCHLD
until all the output from the subprocess has been consumed. */
/* Set up `child_signal_read_fd' and `child_signal_write_fd'. */
@ -7159,6 +7172,7 @@ child_signal_init (void)
/* Either both are initialized, or both are uninitialized. */
eassert ((child_signal_read_fd < 0) == (child_signal_write_fd < 0));
#ifndef WINDOWSNT
if (0 <= child_signal_read_fd)
return; /* already done */
@ -7185,8 +7199,10 @@ child_signal_init (void)
fd_callback_info[fds[0]].flags &= ~KEYBOARD_FD;
child_signal_read_fd = fds[0];
child_signal_write_fd = fds[1];
#endif /* !WINDOWSNT */
}
#ifndef WINDOWSNT
/* Consume a process status change. */
static void
@ -7198,6 +7214,7 @@ child_signal_read (int fd, void *data)
if (emacs_read (fd, &dummy, 1) < 0)
emacs_perror ("reading from child signal FD");
}
#endif /* !WINDOWSNT */
/* Notify `wait_reading_process_output' of a process status
change. */
@ -7205,11 +7222,13 @@ child_signal_read (int fd, void *data)
static void
child_signal_notify (void)
{
#ifndef WINDOWSNT
int fd = child_signal_write_fd;
eassert (0 <= fd);
char dummy = 0;
if (emacs_write (fd, &dummy, 1) != 1)
emacs_perror ("writing to child signal FD");
#endif
}
/* LIB_CHILD_HANDLER is a SIGCHLD handler that Emacs calls while doing