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9ac0d9e0 | 1 | /* blockinput.h - interface to blocking complicated interrupt-driven input. |
33f9662a JB |
2 | Copyright (C) 1989, 1993 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 2, or (at your option) | |
9 | 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; see the file COPYING. If not, write to | |
18 | the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ | |
19 | ||
20 | ||
21 | /* When Emacs is using signal-driven input, the processing of those | |
22 | input signals can get pretty hairy. For example, when Emacs is | |
23 | running under X windows, handling an input signal can entail | |
24 | retrieving events from the X event queue, or making other X calls. | |
25 | ||
26 | If an input signal occurs while Emacs is in the midst of some | |
27 | non-reentrant code, and the signal processing invokes that same | |
28 | code, we lose. For example, malloc and the Xlib functions aren't | |
29 | usually re-entrant, and both are used by the X input signal handler | |
30 | - if we try to process an input signal in the midst of executing | |
31 | any of these functions, we'll lose. | |
32 | ||
33 | To avoid this, we make the following requirements: | |
34 | ||
35 | * Everyone must evaluate BLOCK_INPUT before entering these functions, | |
36 | and then call UNBLOCK_INPUT after performing them. Calls | |
37 | BLOCK_INPUT and UNBLOCK_INPUT may be nested. | |
38 | ||
39 | * Any complicated interrupt handling code should test | |
40 | interrupt_input_blocked, and put off its work until later. | |
41 | ||
42 | * If the interrupt handling code wishes, it may set | |
43 | interrupt_input_pending to a non-zero value. If that flag is set | |
44 | when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO. */ | |
45 | ||
61836955 | 46 | extern int interrupt_input_blocked; |
33f9662a JB |
47 | |
48 | /* Nonzero means an input interrupt has arrived | |
49 | during the current critical section. */ | |
50 | extern int interrupt_input_pending; | |
51 | ||
52 | /* Begin critical section. */ | |
53 | #define BLOCK_INPUT (interrupt_input_blocked++) | |
54 | ||
40a4095a JB |
55 | /* End critical section. |
56 | ||
57 | If doing signal-driven input, and a signal came in when input was | |
58 | blocked, reinvoke the signal handler now to deal with it. | |
59 | ||
60 | We used to have two possible definitions of this macro - one for | |
61 | when SIGIO was #defined, and one for when it wasn't; when SIGIO | |
62 | wasn't #defined, we wouldn't bother to check if we should re-invoke | |
63 | the signal handler. But that doesn't work very well; some of the | |
64 | files which use this macro don't #include the right files to get | |
65 | SIGIO. | |
66 | ||
67 | So, we always test interrupt_input_pending now; that's not too | |
68 | expensive, and it'll never get set if we don't need to resignal. */ | |
33f9662a JB |
69 | #define UNBLOCK_INPUT \ |
70 | (interrupt_input_blocked--, \ | |
71 | (interrupt_input_blocked < 0 ? (abort (), 0) : 0), \ | |
af56dc7e | 72 | ((interrupt_input_blocked == 0 && interrupt_input_pending != 0) \ |
40a4095a | 73 | ? (reinvoke_input_signal (), 0) \ |
33f9662a | 74 | : 0)) |
33f9662a JB |
75 | |
76 | #define TOTALLY_UNBLOCK_INPUT (interrupt_input_blocked = 0) | |
77 | #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT |