src/blockinput.h

   1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
   2    Copyright (C) 1989, 1993, 2001-2016 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 (at
   9 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
  24 /* Emacs should avoid doing anything hairy in a signal handler, because
  25    so many system functions are non-reentrant.  For example, malloc
  26    and the Xlib functions aren't usually re-entrant, so if they were
  27    used by the SIGIO handler, we'd lose.
  28
  29    To avoid this, we make the following requirements:
  30
  31    * Everyone must evaluate BLOCK_INPUT before performing actions that
  32    might conflict with a signal handler, and then call UNBLOCK_INPUT
  33    after performing them.  Calls BLOCK_INPUT and UNBLOCK_INPUT may be
  34    nested.
  35
  36    * Any complicated interrupt handling code should test
  37    INPUT_BLOCKED_P, and put off its work until later.
  38
  39    * If the interrupt handling code wishes, it may set
  40    pending_signals to a non-zero value.  If that flag is set
  41    when input becomes unblocked, UNBLOCK_INPUT will then read
  42    input and process timers.
  43
  44    Historically, Emacs signal handlers did much more than they do now,
  45    and this caused many BLOCK_INPUT calls to be sprinkled around the code.
  46    FIXME: Remove calls that aren't needed now.  */
  47
  48 extern volatile int interrupt_input_blocked;
  49
  50 /* Begin critical section. */
  51
  52 INLINE void
  53 block_input (void)
  54 {
  55   interrupt_input_blocked++;
  56 }
  57
  58 extern void unblock_input (void);
  59 extern void totally_unblock_input (void);
  60 extern void unblock_input_to (int);
  61
  62 /* In critical section?  */
  63
  64 INLINE bool
  65 input_blocked_p (void)
  66 {
  67   return interrupt_input_blocked > 0;
  68 }
  69
  70 INLINE_HEADER_END
  71
  72 #endif /* EMACS_BLOCKINPUT_H */