1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
2 Copyright (C) 1989, 1993, 2001-2023 Free Software Foundation, Inc.
3
4 This file is part of GNU Emacs.
5
6 GNU Emacs is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or (at
9 your option) any later version.
10
11 GNU Emacs is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
18
19 #ifndef EMACS_BLOCKINPUT_H
20 #define EMACS_BLOCKINPUT_H
21
22 INLINE_HEADER_BEGIN
23
24 /* Emacs should avoid doing anything hairy in a signal handler, because
25 so many system functions are non-reentrant. For example, malloc
26 and the Xlib functions aren't usually re-entrant, so if they were
27 used by the SIGIO handler, we'd lose.
28
29 To avoid this, we make the following requirements:
30
31 * Everyone must evaluate BLOCK_INPUT before performing actions that
32 might conflict with a signal handler, and then call UNBLOCK_INPUT
33 after performing them. Calls BLOCK_INPUT and UNBLOCK_INPUT may be
34 nested.
35
36 * Any complicated interrupt handling code should test
37 INPUT_BLOCKED_P, and put off its work until later.
38
39 * If the interrupt handling code wishes, it may set
40 pending_signals to a non-zero value. If that flag is set
41 when input becomes unblocked, UNBLOCK_INPUT will then read
42 input and process timers.
43
44 Historically, Emacs signal handlers did much more than they do now,
45 and this caused many BLOCK_INPUT calls to be sprinkled around the code.
46 FIXME: Remove calls that aren't needed now. */
47
48 extern volatile int interrupt_input_blocked;
49
50 /* Begin critical section. */
51
52 INLINE void
53 block_input (void)
54 {
55 interrupt_input_blocked++;
56 }
57
58 extern void unblock_input (void);
59 extern void totally_unblock_input (void);
60 extern void unblock_input_to (int);
61
62 /* In critical section? */
63
64 INLINE bool
65 input_blocked_p (void)
66 {
67 return interrupt_input_blocked > 0;
68 }
69
70 INLINE_HEADER_END
71
72 #endif /* EMACS_BLOCKINPUT_H */