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Fix bug #18420 with deadlocks communicating with subprocess on MS-Windows.

Browse source 
src/w32.c (fcntl): Support O_NONBLOCK fcntl on the write side of
 pipes.
 (sys_write): When a write to a non-blocking pipe returns ENOSPC,
 set errno to EAGAIN instead, to allow the caller to retry the
 write after some waiting.  Fixes deadlocks when Emacs exchanges a
 lot of data through the pipe.
This commit is contained in:
Eli Zaretskii 2014-09-14 18:18:39 +03:00
parent a6cc335aef
commit 9ed670023f
2 changed files with 55 additions and 8 deletions
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9
src/ChangeLog
View file

@ -1,3 +1,12 @@
2014-09-14 Eli Zaretskii <eliz@gnu.org>
* w32.c (fcntl): Support O_NONBLOCK fcntl on the write side of
pipes.
(sys_write): When a write to a non-blocking pipe returns ENOSPC,
set errno to EAGAIN instead, to allow the caller to retry the
write after some waiting. Fixes deadlocks when Emacs exchanges a
lot of data through the pipe. (Bug#18420)
2014-09-13 Eli Zaretskii <eliz@gnu.org>
* sound.c (Fplay_sound_internal): Encode the sound file name in

54
src/w32.c
View file

@ -7690,15 +7690,15 @@ fcntl (int s, int cmd, int options)
if (cmd == F_DUPFD_CLOEXEC)
return sys_dup (s);
if (winsock_lib == NULL)
{
errno = ENETDOWN;
return -1;
}
check_errno ();
if (fd_info[s].flags & FILE_SOCKET)
{
if (winsock_lib == NULL)
{
errno = ENETDOWN;
return -1;
}
if (cmd == F_SETFL && options == O_NONBLOCK)
{
unsigned long nblock = 1;
@ -7715,13 +7715,36 @@ fcntl (int s, int cmd, int options)
return SOCKET_ERROR;
}
}
else if ((fd_info[s].flags & (FILE_PIPE | FILE_WRITE))
== (FILE_PIPE | FILE_WRITE))
{
/* Force our writes to pipes be non-blocking. */
if (cmd == F_SETFL && options == O_NONBLOCK)
{
HANDLE h = (HANDLE)_get_osfhandle (s);
DWORD pipe_mode = PIPE_NOWAIT;
if (!SetNamedPipeHandleState (h, &pipe_mode, NULL, NULL))
{
DebPrint (("SetNamedPipeHandleState: %lu\n", GetLastError ()));
return SOCKET_ERROR;
}
fd_info[s].flags |= FILE_NDELAY;
return 0;
}
else
{
errno = EINVAL;
return SOCKET_ERROR;
}
}
errno = ENOTSOCK;
return SOCKET_ERROR;
}
/* Shadow main io functions: we need to handle pipes and sockets more
intelligently, and implement non-blocking mode as well. */
intelligently. */
int
sys_close (int fd)
@ -8206,7 +8229,6 @@ sys_read (int fd, char * buffer, unsigned int count)
/* From w32xfns.c */
extern HANDLE interrupt_handle;
/* For now, don't bother with a non-blocking mode */
int
sys_write (int fd, const void * buffer, unsigned int count)
{
@ -8341,6 +8363,22 @@ sys_write (int fd, const void * buffer, unsigned int count)
nchars += n;
if (n < 0)
{
/* When there's no buffer space in a pipe that is in the
non-blocking mode, _write returns ENOSPC. We return
EAGAIN instead, which should trigger the logic in
send_process that enters waiting loop and calls
wait_reading_process_output to allow process input to
be accepted during the wait. Those calls to
wait_reading_process_output allow sys_select to
notice when process input becomes available, thus
avoiding deadlock whereby each side of the pipe is
blocked on write, waiting for the other party to read
its end of the pipe. */
if (errno == ENOSPC
&& fd < MAXDESC
&& ((fd_info[fd].flags & (FILE_PIPE | FILE_NDELAY))
== (FILE_PIPE | FILE_NDELAY)))
errno = EAGAIN;
nchars = n;
break;
}