src/blockinput.h

   1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
   2    Copyright (C) 1989, 1993, 2001-2011  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
   9 (at 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 <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef EMACS_BLOCKINPUT_H
  20 #define EMACS_BLOCKINPUT_H
  21
  22 #include "atimer.h"
  23
  24 /* When Emacs is using signal-driven input, the processing of those
  25    input signals can get pretty hairy.  For example, when Emacs is
  26    running under X windows, handling an input signal can entail
  27    retrieving events from the X event queue, or making other X calls.
  28
  29    If an input signal occurs while Emacs is in the midst of some
  30    non-reentrant code, and the signal processing invokes that same
  31    code, we lose.  For example, malloc and the Xlib functions aren't
  32    usually re-entrant, and both are used by the X input signal handler
  33    - if we try to process an input signal in the midst of executing
  34    any of these functions, we'll lose.
  35
  36    To avoid this, we make the following requirements:
  37
  38    * Everyone must evaluate BLOCK_INPUT before entering these functions,
  39    and then call UNBLOCK_INPUT after performing them.  Calls
  40    BLOCK_INPUT and UNBLOCK_INPUT may be nested.
  41
  42    * Any complicated interrupt handling code should test
  43    interrupt_input_blocked, and put off its work until later.
  44
  45    * If the interrupt handling code wishes, it may set
  46    interrupt_input_pending to a non-zero value.  If that flag is set
  47    when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO.  */
  48
  49 extern volatile int interrupt_input_blocked;
  50
  51 /* Nonzero means an input interrupt has arrived
  52    during the current critical section.  */
  53 extern int interrupt_input_pending;
  54
  55
  56 /* Non-zero means asynchronous timers should be run when input is
  57    unblocked.  */
  58
  59 extern int pending_atimers;
  60
  61
  62 /* Begin critical section. */
  63 #define BLOCK_INPUT (interrupt_input_blocked++)
  64
  65 /* End critical section.
  66
  67    If doing signal-driven input, and a signal came in when input was
  68    blocked, reinvoke the signal handler now to deal with it.
  69
  70    We used to have two possible definitions of this macro - one for
  71    when SIGIO was #defined, and one for when it wasn't; when SIGIO
  72    wasn't #defined, we wouldn't bother to check if we should re-invoke
  73    the signal handler.  But that doesn't work very well; some of the
  74    files which use this macro don't #include the right files to get
  75    SIGIO.
  76
  77    So, we always test interrupt_input_pending now; that's not too
  78    expensive, and it'll never get set if we don't need to resignal.  */
  79
  80 #define UNBLOCK_INPUT                           \
  81   do                                            \
  82     {                                           \
  83       --interrupt_input_blocked;                \
  84       if (interrupt_input_blocked == 0)         \
  85         {                                       \
  86           if (interrupt_input_pending)          \
  87             reinvoke_input_signal ();           \
  88           if (pending_atimers)                  \
  89             do_pending_atimers ();              \
  90         }                                       \
  91       else if (interrupt_input_blocked < 0)     \
  92         abort ();                               \
  93     }                                           \
  94   while (0)
  95
  96 /* Undo any number of BLOCK_INPUT calls,
  97    and also reinvoke any pending signal.  */
  98
  99 #define TOTALLY_UNBLOCK_INPUT                   \
 100   do if (interrupt_input_blocked != 0)          \
 101     {                                           \
 102       interrupt_input_blocked = 1;              \
 103       UNBLOCK_INPUT;                            \
 104     }                                           \
 105   while (0)
 106
 107 /* Undo any number of BLOCK_INPUT calls down to level LEVEL,
 108    and also (if the level is now 0) reinvoke any pending signal.  */
 109
 110 #define UNBLOCK_INPUT_TO(LEVEL)                         \
 111   do                                                    \
 112     {                                                   \
 113       interrupt_input_blocked = (LEVEL) + 1;            \
 114       UNBLOCK_INPUT;                                    \
 115     }                                                   \
 116   while (0)
 117
 118 #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT
 119
 120 /* In critical section ? */
 121 #define INPUT_BLOCKED_P (interrupt_input_blocked > 0)
 122
 123 /* Defined in keyboard.c */
 124 extern void reinvoke_input_signal (void);
 125
 126 #endif /* EMACS_BLOCKINPUT_H */
 127