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/* blockinput.h - interface to blocking complicated interrupt-driven input.
Copyright (C) 1989, 1993 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 2, 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; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
/* When Emacs is using signal-driven input, the processing of those
input signals can get pretty hairy. For example, when Emacs is
running under X windows, handling an input signal can entail
retrieving events from the X event queue, or making other X calls.
If an input signal occurs while Emacs is in the midst of some
non-reentrant code, and the signal processing invokes that same
code, we lose. For example, malloc and the Xlib functions aren't
usually re-entrant, and both are used by the X input signal handler
- if we try to process an input signal in the midst of executing
any of these functions, we'll lose.
To avoid this, we make the following requirements:
* Everyone must evaluate BLOCK_INPUT before entering these functions,
and then call UNBLOCK_INPUT after performing them. Calls
BLOCK_INPUT and UNBLOCK_INPUT may be nested.
* Any complicated interrupt handling code should test
interrupt_input_blocked, and put off its work until later.
* If the interrupt handling code wishes, it may set
interrupt_input_pending to a non-zero value. If that flag is set
when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO. */
extern int interrupt_input_blocked;
/* Nonzero means an input interrupt has arrived
during the current critical section. */
extern int interrupt_input_pending;
/* Begin critical section. */
#define BLOCK_INPUT (interrupt_input_blocked++)
/* End critical section.
If doing signal-driven input, and a signal came in when input was
blocked, reinvoke the signal handler now to deal with it.
We used to have two possible definitions of this macro - one for
when SIGIO was #defined, and one for when it wasn't; when SIGIO
wasn't #defined, we wouldn't bother to check if we should re-invoke
the signal handler. But that doesn't work very well; some of the
files which use this macro don't #include the right files to get
SIGIO.
So, we always test interrupt_input_pending now; that's not too
expensive, and it'll never get set if we don't need to resignal. */
#define UNBLOCK_INPUT \
(interrupt_input_blocked--, \
(interrupt_input_blocked < 0 ? (abort (), 0) : 0), \
((interrupt_input_blocked == 0 && interrupt_input_pending != 0) \
? (reinvoke_input_signal (), 0) \
: 0))
#define TOTALLY_UNBLOCK_INPUT (interrupt_input_blocked = 0)
#define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT
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