lib/fatal-signal.h

   1 /* Emergency actions in case of a fatal signal.
   2    Copyright (C) 2003-2004, 2009-2020 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 <https://www.gnu.org/licenses/>.  */
  17
  18
  19 #ifndef _FATAL_SIGNAL_H
  20 #define _FATAL_SIGNAL_H
  21
  22 #include <signal.h>
  23
  24 #ifdef __cplusplus
  25 extern "C" {
  26 #endif
  27
  28
  29 /* It is often useful to do some cleanup action when a usually fatal signal
  30    terminates the process, like removing a temporary file or killing a
  31    subprocess that may be stuck waiting for a device, pipe or network input.
  32    Such signals are SIGHUP, SIGINT, SIGPIPE, SIGTERM, and possibly others.
  33    The limitation of this facility is that it cannot work for SIGKILL.
  34
  35    Signals with a SIG_IGN handler are considered to be non-fatal.  The
  36    functions in this file assume that when a SIG_IGN handler is installed
  37    for a signal, it was installed before any functions in this file were
  38    called and it stays so for the whole lifetime of the process.  */
  39
  40 /* Register a cleanup function to be executed when a catchable fatal signal
  41    occurs.
  42
  43    Restrictions for the cleanup function:
  44      - The cleanup function can do all kinds of system calls.  It may also
  45        modify (clobber) errno.
  46      - It can also access application dependent memory locations and data
  47        structures provided they are in a consistent state. One way to ensure
  48        this is through block_fatal_signals()/unblock_fatal_signals(), see
  49        below.  Another - more tricky - way to ensure this is the careful use
  50        of 'volatile'.
  51    However,
  52      - malloc() and similarly complex facilities are not safe to be called
  53        because they are not guaranteed to be in a consistent state.
  54      - Also, the cleanup function must not block the catchable fatal signals
  55        and leave them blocked upon return.
  56
  57    The cleanup function is executed asynchronously.  It is unspecified
  58    whether during its execution the catchable fatal signals are blocked
  59    or not.  */
  60 extern void at_fatal_signal (_GL_ASYNC_SAFE void (*function) (int sig));
  61
  62
  63 /* Sometimes it is necessary to block the usually fatal signals while the
  64    data structures being accessed by the cleanup action are being built or
  65    reorganized.  This is the case, for example, when a temporary file or
  66    directory is created through mkstemp() or mkdtemp(), because these
  67    functions create the temporary file or directory _before_ returning its
  68    name to the application.  */
  69
  70 /* Temporarily delay the catchable fatal signals.
  71    The signals will be blocked (= delayed) until the next call to
  72    unblock_fatal_signals().  If the signals are already blocked, a further
  73    call to block_fatal_signals() has no effect.  */
  74 extern void block_fatal_signals (void);
  75
  76 /* Stop delaying the catchable fatal signals.  */
  77 extern void unblock_fatal_signals (void);
  78
  79
  80 /* Return the list of signals that block_fatal_signals/unblock_fatal_signals
  81    would block or unblock.
  82    Fills signals[0..count-1] and returns count.  */
  83 extern unsigned int get_fatal_signals (int signals[64]);
  84
  85 /* Return the list of signals that block_fatal_signals/unblock_fatal_signals
  86    would block or unblock.  */
  87 extern const sigset_t * get_fatal_signal_set (void);
  88
  89
  90 #ifdef __cplusplus
  91 }
  92 #endif
  93
  94 #endif /* _FATAL_SIGNAL_H */