src/blockinput.h

   1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
   2    Copyright (C) 1989, 1993, 2001, 2002, 2003, 2004,
   3                  2005, 2006, 2007, 2008  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, or (at your option)
  10 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; see the file COPYING.  If not, write to
  19 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  20 Boston, MA 02110-1301, USA.  */
  21
  22 #ifndef EMACS_BLOCKINPUT_H
  23 #define EMACS_BLOCKINPUT_H
  24
  25 #include "atimer.h"
  26
  27 /* When Emacs is using signal-driven input, the processing of those
  28    input signals can get pretty hairy.  For example, when Emacs is
  29    running under X windows, handling an input signal can entail
  30    retrieving events from the X event queue, or making other X calls.
  31
  32    If an input signal occurs while Emacs is in the midst of some
  33    non-reentrant code, and the signal processing invokes that same
  34    code, we lose.  For example, malloc and the Xlib functions aren't
  35    usually re-entrant, and both are used by the X input signal handler
  36    - if we try to process an input signal in the midst of executing
  37    any of these functions, we'll lose.
  38
  39    To avoid this, we make the following requirements:
  40
  41    * Everyone must evaluate BLOCK_INPUT before entering these functions,
  42    and then call UNBLOCK_INPUT after performing them.  Calls
  43    BLOCK_INPUT and UNBLOCK_INPUT may be nested.
  44
  45    * Any complicated interrupt handling code should test
  46    interrupt_input_blocked, and put off its work until later.
  47
  48    * If the interrupt handling code wishes, it may set
  49    interrupt_input_pending to a non-zero value.  If that flag is set
  50    when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO.  */
  51
  52 extern volatile int interrupt_input_blocked;
  53
  54 /* Nonzero means an input interrupt has arrived
  55    during the current critical section.  */
  56 extern int interrupt_input_pending;
  57
  58
  59 /* Non-zero means asynchronous timers should be run when input is
  60    unblocked.  */
  61
  62 extern int pending_atimers;
  63
  64 /* Begin critical section. */
  65 #define BLOCK_INPUT (interrupt_input_blocked++)
  66
  67 /* End critical section.
  68
  69    If doing signal-driven input, and a signal came in when input was
  70    blocked, reinvoke the signal handler now to deal with it.
  71
  72    We used to have two possible definitions of this macro - one for
  73    when SIGIO was #defined, and one for when it wasn't; when SIGIO
  74    wasn't #defined, we wouldn't bother to check if we should re-invoke
  75    the signal handler.  But that doesn't work very well; some of the
  76    files which use this macro don't #include the right files to get
  77    SIGIO.
  78
  79    So, we always test interrupt_input_pending now; that's not too
  80    expensive, and it'll never get set if we don't need to resignal.  */
  81
  82 #define UNBLOCK_INPUT                           \
  83   do                                            \
  84     {                                           \
  85       --interrupt_input_blocked;                \
  86       if (interrupt_input_blocked == 0)         \
  87         {                                       \
  88           if (interrupt_input_pending)          \
  89             reinvoke_input_signal ();           \
  90           if (pending_atimers)                  \
  91             do_pending_atimers ();              \
  92         }                                       \
  93       else if (interrupt_input_blocked < 0)     \
  94         abort ();                               \
  95     }                                           \
  96   while (0)
  97
  98 /* Undo any number of BLOCK_INPUT calls,
  99    and also reinvoke any pending signal.  */
 100
 101 #define TOTALLY_UNBLOCK_INPUT                   \
 102   do if (interrupt_input_blocked != 0)          \
 103     {                                           \
 104       interrupt_input_blocked = 1;              \
 105       UNBLOCK_INPUT;                            \
 106     }                                           \
 107   while (0)
 108
 109 /* Undo any number of BLOCK_INPUT calls down to level LEVEL,
 110    and also (if the level is now 0) reinvoke any pending signal.  */
 111
 112 #define UNBLOCK_INPUT_TO(LEVEL)                         \
 113   do                                                    \
 114     {                                                   \
 115       interrupt_input_blocked = (LEVEL) + 1;            \
 116       UNBLOCK_INPUT;                                    \
 117     }                                                   \
 118   while (0)
 119
 120 #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT
 121
 122 /* In critical section ? */
 123 #define INPUT_BLOCKED_P (interrupt_input_blocked > 0)
 124
 125 /* Defined in keyboard.c */
 126 /* Don't use a prototype here; it causes trouble in some files.  */
 127 extern void reinvoke_input_signal ();
 128
 129 #endif /* EMACS_BLOCKINPUT_H */
 130
 131 /* arch-tag: 51a9ec86-945a-4966-8f04-2d1341250e03
 132    (do not change this comment) */