Allow the use of poll instead of selectfeature/more-fds

Increase the maximum number of open files allowed to
10 x FD_SETSIZE (which is what poll is limited to on macOS).

* configure.ac (--with-poll): New option, default off, for requesting
'poll' support.  Check for "sys/poll.h" header.
(USE_POLL): New variable.
(EMACS_CONFIG_FEATURES): Add USE_POLL.

* etc/NEWS: Document --with-poll.

* src/sysselect.h: New define EMACS_MAX_FD, defaulting to FD_SETSIZE,
for the maximum number of file descriptors Emacs can use.
* src/process.c:
* src/sysdep.c:
* src/nsterm.m (ns_select_1):
(applicationDidFinishLaunching): Use EMACS_MAX_FD instead of
FD_SETSIZE everywhere.

* src/syspoll.h (SYSPOLL_H): New file for definitions related to use
of 'poll'.

* src/sysselect.h [USE_POLL]: Set EMACS_MAX_FD to 10 x FD_SETSIZE.
(emacs_fd_set) [USE_POLL]: New type, used for bitsets of file
descriptors.
(FD_CLR, FD_ISSET, FD_SET, FD_ZERO) [USE_POLL]: Macros for
manipulating bitsets.
[USE_POLL]: Include "syspoll.h".

* src/process.c (fd_sets_to_pollfds) [USE_POLL]: New function.
Converts two 'emacs_fd_set' to an array of 'struct pollfd'
(pollfds_to_fd_sets) [USE_POLL]: New function.
Converts from an array of 'struct pollfd' to two 'emacs_fd_set'.
(timespec_to_timeout) [USE_POLL]: New function, converts a 'struct
timespec' to a timeout in milliseconds.
(emacs_pselect) [USE_POLL]: Replacement for 'pselect' that calls
'poll' and does the appropriate conversions.  Does not support
sigmask.

1 files changed, 32 insertions, 0 deletions

diff --git a/src/syspoll.h b/src/syspoll.h
new file mode 100644
index 00000000000..d133794fb13
--- /dev/null
+++ b/src/syspoll.h
@@ -0,0 +1,32 @@
+/* syspoll.h - System-dependent definitions for the poll function.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#ifndef SYSPOLL_H
+#define SYSPOLL_H 1
+
+#if !defined (DOS_NT) && !defined (WINDOWSNT)
+#include <sys/poll.h>
+
+extern int fd_sets_to_pollfds (emacs_fd_set *, emacs_fd_set *, int);
+extern void pollfds_to_fd_sets (emacs_fd_set *, emacs_fd_set *, int);
+extern int timespec_to_timeout (const struct timespec *);
+extern int emacs_pselect (int, emacs_fd_set *, emacs_fd_set *,
+			  emacs_fd_set *, const struct timespec *,
+			  const sigset_t *);
+#endif
+#endif