src/blockinput.h

   1 /* blockinput.h - interface to blocking complicated interrupt-driven input.
   2    Copyright (C) 1989, 1993 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 2, or (at your option)
   9 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; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20
  21 /* When Emacs is using signal-driven input, the processing of those
  22    input signals can get pretty hairy.  For example, when Emacs is
  23    running under X windows, handling an input signal can entail
  24    retrieving events from the X event queue, or making other X calls.
  25
  26    If an input signal occurs while Emacs is in the midst of some
  27    non-reentrant code, and the signal processing invokes that same
  28    code, we lose.  For example, malloc and the Xlib functions aren't
  29    usually re-entrant, and both are used by the X input signal handler
  30    - if we try to process an input signal in the midst of executing
  31    any of these functions, we'll lose.
  32
  33    To avoid this, we make the following requirements:
  34
  35    * Everyone must evaluate BLOCK_INPUT before entering these functions,
  36    and then call UNBLOCK_INPUT after performing them.  Calls
  37    BLOCK_INPUT and UNBLOCK_INPUT may be nested.
  38
  39    * Any complicated interrupt handling code should test
  40    interrupt_input_blocked, and put off its work until later.
  41
  42    * If the interrupt handling code wishes, it may set
  43    interrupt_input_pending to a non-zero value.  If that flag is set
  44    when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO.  */
  45
  46 extern int interrupt_input_blocked;
  47
  48 /* Nonzero means an input interrupt has arrived
  49    during the current critical section.  */
  50 extern int interrupt_input_pending;
  51
  52 /* Begin critical section. */
  53 #define BLOCK_INPUT (interrupt_input_blocked++)
  54
  55 /* End critical section.
  56
  57    If doing signal-driven input, and a signal came in when input was
  58    blocked, reinvoke the signal handler now to deal with it.
  59
  60    We used to have two possible definitions of this macro - one for
  61    when SIGIO was #defined, and one for when it wasn't; when SIGIO
  62    wasn't #defined, we wouldn't bother to check if we should re-invoke
  63    the signal handler.  But that doesn't work very well; some of the
  64    files which use this macro don't #include the right files to get
  65    SIGIO.
  66
  67    So, we always test interrupt_input_pending now; that's not too
  68    expensive, and it'll never get set if we don't need to resignal.  */
  69 #define UNBLOCK_INPUT \
  70   (interrupt_input_blocked--, \
  71    (interrupt_input_blocked < 0 ? (abort (), 0) : 0), \
  72    ((interrupt_input_blocked == 0 && interrupt_input_pending != 0) \
  73     ? (reinvoke_input_signal (), 0) \
  74     : 0))
  75
  76 #define TOTALLY_UNBLOCK_INPUT (interrupt_input_blocked = 0)
  77 #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT