| 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, Inc., 59 Temple Place - Suite 330, |
| 19 | Boston, MA 02111-1307, USA. */ |
| 20 | |
| 21 | |
| 22 | /* When Emacs is using signal-driven input, the processing of those |
| 23 | input signals can get pretty hairy. For example, when Emacs is |
| 24 | running under X windows, handling an input signal can entail |
| 25 | retrieving events from the X event queue, or making other X calls. |
| 26 | |
| 27 | If an input signal occurs while Emacs is in the midst of some |
| 28 | non-reentrant code, and the signal processing invokes that same |
| 29 | code, we lose. For example, malloc and the Xlib functions aren't |
| 30 | usually re-entrant, and both are used by the X input signal handler |
| 31 | - if we try to process an input signal in the midst of executing |
| 32 | any of these functions, we'll lose. |
| 33 | |
| 34 | To avoid this, we make the following requirements: |
| 35 | |
| 36 | * Everyone must evaluate BLOCK_INPUT before entering these functions, |
| 37 | and then call UNBLOCK_INPUT after performing them. Calls |
| 38 | BLOCK_INPUT and UNBLOCK_INPUT may be nested. |
| 39 | |
| 40 | * Any complicated interrupt handling code should test |
| 41 | interrupt_input_blocked, and put off its work until later. |
| 42 | |
| 43 | * If the interrupt handling code wishes, it may set |
| 44 | interrupt_input_pending to a non-zero value. If that flag is set |
| 45 | when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO. */ |
| 46 | |
| 47 | extern int interrupt_input_blocked; |
| 48 | |
| 49 | /* Nonzero means an input interrupt has arrived |
| 50 | during the current critical section. */ |
| 51 | extern int interrupt_input_pending; |
| 52 | |
| 53 | /* Begin critical section. */ |
| 54 | #define BLOCK_INPUT (interrupt_input_blocked++) |
| 55 | |
| 56 | /* End critical section. |
| 57 | |
| 58 | If doing signal-driven input, and a signal came in when input was |
| 59 | blocked, reinvoke the signal handler now to deal with it. |
| 60 | |
| 61 | We used to have two possible definitions of this macro - one for |
| 62 | when SIGIO was #defined, and one for when it wasn't; when SIGIO |
| 63 | wasn't #defined, we wouldn't bother to check if we should re-invoke |
| 64 | the signal handler. But that doesn't work very well; some of the |
| 65 | files which use this macro don't #include the right files to get |
| 66 | SIGIO. |
| 67 | |
| 68 | So, we always test interrupt_input_pending now; that's not too |
| 69 | expensive, and it'll never get set if we don't need to resignal. */ |
| 70 | #define UNBLOCK_INPUT \ |
| 71 | (interrupt_input_blocked--, \ |
| 72 | (interrupt_input_blocked < 0 ? (abort (), 0) : 0), \ |
| 73 | ((interrupt_input_blocked == 0 && interrupt_input_pending != 0) \ |
| 74 | ? (reinvoke_input_signal (), 0) \ |
| 75 | : 0)) |
| 76 | |
| 77 | #define TOTALLY_UNBLOCK_INPUT (interrupt_input_blocked = 0) |
| 78 | #define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT |