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+/* Interface to blocking complicated interrupt-driven input.
+   Copyright (C) 1989, 1993 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs; see the file COPYING.  If not, write to
+the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+
+/* When Emacs is using signal-driven input, the processing of those
+   input signals can get pretty hairy.  For example, when Emacs is
+   running under X windows, handling an input signal can entail
+   retrieving events from the X event queue, or making other X calls.
+
+   If an input signal occurs while Emacs is in the midst of some
+   non-reentrant code, and the signal processing invokes that same
+   code, we lose.  For example, malloc and the Xlib functions aren't
+   usually re-entrant, and both are used by the X input signal handler
+   - if we try to process an input signal in the midst of executing
+   any of these functions, we'll lose.
+
+   To avoid this, we make the following requirements:
+
+   * Everyone must evaluate BLOCK_INPUT before entering these functions,
+   and then call UNBLOCK_INPUT after performing them.  Calls
+   BLOCK_INPUT and UNBLOCK_INPUT may be nested.
+
+   * Any complicated interrupt handling code should test
+   interrupt_input_blocked, and put off its work until later.  
+
+   * If the interrupt handling code wishes, it may set
+   interrupt_input_pending to a non-zero value.  If that flag is set
+   when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO.  */
+
+extern unsigned int interrupt_input_blocked;
+
+/* Nonzero means an input interrupt has arrived
+   during the current critical section.  */
+extern int interrupt_input_pending;
+
+/* Begin critical section. */
+#define BLOCK_INPUT (interrupt_input_blocked++)
+
+/* End critical section. */
+#ifdef SIGIO
+/* If doing interrupt input, and an interrupt came in when input was blocked,
+   reinvoke the interrupt handler now to deal with it.  */
+#define UNBLOCK_INPUT \
+  (interrupt_input_blocked--, \
+   (interrupt_input_blocked < 0 ? (abort (), 0) : 0), \
+   ((interrupt_input_blocked == 0 && interupt_input_pending != 0) \
+    ? (kill (0, SIGIO), 0) \
+    : 0))
+#else
+#define UNBLOCK_INPUT \
+  (interrupt_input_blocked--, \
+   (interrupt_input_blocked < 0 ? (abort (), 0) : 0))
+#endif
+
+#define TOTALLY_UNBLOCK_INPUT (interrupt_input_blocked = 0)
+#define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT