src/blockinput.h

   1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
   2    Copyright (C) 1989, 1993, 2001-2012  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 INLINE_HEADER_BEGIN
  23 #ifndef BLOCKINPUT_INLINE
  24 # define BLOCKINPUT_INLINE INLINE
  25 #endif
  26
  27 /* Emacs should avoid doing anything hairy in a signal handler, because
  28    so many system functions are non-reentrant.  For example, malloc
  29    and the Xlib functions aren't usually re-entrant, so if they were
  30    used by the SIGIO handler, we'd lose.
  31
  32    To avoid this, we make the following requirements:
  33
  34    * Everyone must evaluate BLOCK_INPUT before performing actions that
  35    might conflict with a signal handler, and then call UNBLOCK_INPUT
  36    after performing them.  Calls BLOCK_INPUT and UNBLOCK_INPUT may be
  37    nested.
  38
  39    * Any complicated interrupt handling code should test
  40    INPUT_BLOCKED_P, and put off its work until later.
  41
  42    * If the interrupt handling code wishes, it may set
  43    pending_signals to a non-zero value.  If that flag is set
  44    when input becomes unblocked, UNBLOCK_INPUT will then read
  45    input and process timers.
  46
  47    Historically, Emacs signal handlers did much more than they do now,
  48    and this caused many BLOCK_INPUT calls to be sprinkled around the code.
  49    FIXME: Remove calls that aren't needed now.  */
  50
  51 extern volatile int interrupt_input_blocked;
  52
  53 /* Begin critical section. */
  54
  55 BLOCKINPUT_INLINE void
  56 block_input (void)
  57 {
  58   interrupt_input_blocked++;
  59 }
  60
  61 extern void unblock_input (void);
  62 extern void totally_unblock_input (void);
  63 extern void unblock_input_to (int);
  64
  65 /* In critical section ? */
  66
  67 BLOCKINPUT_INLINE bool
  68 input_blocked_p (void)
  69 {
  70   return 0 < interrupt_input_blocked;
  71 }
  72
  73 INLINE_HEADER_END
  74
  75 #endif /* EMACS_BLOCKINPUT_H */