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1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
2 Copyright (C) 1989, 1993, 2001, 2002, 2003, 2004,
3 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
4
5 This file is part of GNU Emacs.
6
7 GNU Emacs is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 GNU Emacs is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */
19
20 #ifndef EMACS_BLOCKINPUT_H
21 #define EMACS_BLOCKINPUT_H
22
23 #include "atimer.h"
24
25 /* When Emacs is using signal-driven input, the processing of those
26 input signals can get pretty hairy. For example, when Emacs is
27 running under X windows, handling an input signal can entail
28 retrieving events from the X event queue, or making other X calls.
29
30 If an input signal occurs while Emacs is in the midst of some
31 non-reentrant code, and the signal processing invokes that same
32 code, we lose. For example, malloc and the Xlib functions aren't
33 usually re-entrant, and both are used by the X input signal handler
34 - if we try to process an input signal in the midst of executing
35 any of these functions, we'll lose.
36
37 To avoid this, we make the following requirements:
38
39 * Everyone must evaluate BLOCK_INPUT before entering these functions,
40 and then call UNBLOCK_INPUT after performing them. Calls
41 BLOCK_INPUT and UNBLOCK_INPUT may be nested.
42
43 * Any complicated interrupt handling code should test
44 interrupt_input_blocked, and put off its work until later.
45
46 * If the interrupt handling code wishes, it may set
47 interrupt_input_pending to a non-zero value. If that flag is set
48 when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO. */
49
50 extern volatile int interrupt_input_blocked;
51
52 /* Nonzero means an input interrupt has arrived
53 during the current critical section. */
54 extern int interrupt_input_pending;
55
56
57 /* Non-zero means asynchronous timers should be run when input is
58 unblocked. */
59
60 extern int pending_atimers;
61
62
63 /* Begin critical section. */
64 #define BLOCK_INPUT (interrupt_input_blocked++)
65
66 /* End critical section.
67
68 If doing signal-driven input, and a signal came in when input was
69 blocked, reinvoke the signal handler now to deal with it.
70
71 We used to have two possible definitions of this macro - one for
72 when SIGIO was #defined, and one for when it wasn't; when SIGIO
73 wasn't #defined, we wouldn't bother to check if we should re-invoke
74 the signal handler. But that doesn't work very well; some of the
75 files which use this macro don't #include the right files to get
76 SIGIO.
77
78 So, we always test interrupt_input_pending now; that's not too
79 expensive, and it'll never get set if we don't need to resignal. */
80
81 #define UNBLOCK_INPUT \
82 do \
83 { \
84 --interrupt_input_blocked; \
85 if (interrupt_input_blocked == 0) \
86 { \
87 if (interrupt_input_pending) \
88 reinvoke_input_signal (); \
89 if (pending_atimers) \
90 do_pending_atimers (); \
91 } \
92 else if (interrupt_input_blocked < 0) \
93 abort (); \
94 } \
95 while (0)
96
97 /* Undo any number of BLOCK_INPUT calls,
98 and also reinvoke any pending signal. */
99
100 #define TOTALLY_UNBLOCK_INPUT \
101 do if (interrupt_input_blocked != 0) \
102 { \
103 interrupt_input_blocked = 1; \
104 UNBLOCK_INPUT; \
105 } \
106 while (0)
107
108 /* Undo any number of BLOCK_INPUT calls down to level LEVEL,
109 and also (if the level is now 0) reinvoke any pending signal. */
110
111 #define UNBLOCK_INPUT_TO(LEVEL) \
112 do \
113 { \
114 interrupt_input_blocked = (LEVEL) + 1; \
115 UNBLOCK_INPUT; \
116 } \
117 while (0)
118
119 #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT
120
121 /* In critical section ? */
122 #define INPUT_BLOCKED_P (interrupt_input_blocked > 0)
123
124 /* Defined in keyboard.c */
125 extern void reinvoke_input_signal (void);
126
127 #endif /* EMACS_BLOCKINPUT_H */
128