lib/fatal-signal.h

   1 /* Emergency actions in case of a fatal signal.
   2    Copyright (C) 2003-2004, 2009-2017 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18
  19 #ifdef __cplusplus
  20 extern "C" {
  21 #endif
  22
  23
  24 /* It is often useful to do some cleanup action when a usually fatal signal
  25    terminates the process, like removing a temporary file or killing a
  26    subprocess that may be stuck waiting for a device, pipe or network input.
  27    Such signals are SIGHUP, SIGINT, SIGPIPE, SIGTERM, and possibly others.
  28    The limitation of this facility is that it cannot work for SIGKILL.
  29
  30    Signals with a SIG_IGN handler are considered to be non-fatal.  The
  31    functions in this file assume that when a SIG_IGN handler is installed
  32    for a signal, it was installed before any functions in this file were
  33    called and it stays so for the whole lifetime of the process.  */
  34
  35 /* Register a cleanup function to be executed when a catchable fatal signal
  36    occurs.
  37
  38    Restrictions for the cleanup function:
  39      - The cleanup function can do all kinds of system calls.
  40      - It can also access application dependent memory locations and data
  41        structures provided they are in a consistent state. One way to ensure
  42        this is through block_fatal_signals()/unblock_fatal_signals(), see
  43        below.  Another - more tricky - way to ensure this is the careful use
  44        of 'volatile'.
  45    However,
  46      - malloc() and similarly complex facilities are not safe to be called
  47        because they are not guaranteed to be in a consistent state.
  48      - Also, the cleanup function must not block the catchable fatal signals
  49        and leave them blocked upon return.
  50
  51    The cleanup function is executed asynchronously.  It is unspecified
  52    whether during its execution the catchable fatal signals are blocked
  53    or not.  */
  54 extern void at_fatal_signal (void (*function) (void));
  55
  56
  57 /* Sometimes it is necessary to block the usually fatal signals while the
  58    data structures being accessed by the cleanup action are being built or
  59    reorganized.  This is the case, for example, when a temporary file or
  60    directory is created through mkstemp() or mkdtemp(), because these
  61    functions create the temporary file or directory _before_ returning its
  62    name to the application.  */
  63
  64 /* Temporarily delay the catchable fatal signals.
  65    The signals will be blocked (= delayed) until the next call to
  66    unblock_fatal_signals().  If the signals are already blocked, a further
  67    call to block_fatal_signals() has no effect.  */
  68 extern void block_fatal_signals (void);
  69
  70 /* Stop delaying the catchable fatal signals.  */
  71 extern void unblock_fatal_signals (void);
  72
  73
  74 #ifdef __cplusplus
  75 }
  76 #endif