lib/fatal-signal.h

   1 /* Emergency actions in case of a fatal signal.
   2    Copyright (C) 2003-2004, 2009-2024 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser 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 /* This file uses _GL_ASYNC_SAFE.  */
  23 #if !_GL_CONFIG_H_INCLUDED
  24  #error "Please include config.h first."
  25 #endif
  26
  27 #include <signal.h>
  28
  29 #ifdef __cplusplus
  30 extern "C" {
  31 #endif
  32
  33
  34 /* It is often useful to do some cleanup action when a usually fatal signal
  35    terminates the process, like removing a temporary file or killing a
  36    subprocess that may be stuck waiting for a device, pipe or network input.
  37    Such signals are SIGHUP, SIGINT, SIGPIPE, SIGTERM, and possibly others.
  38    The limitation of this facility is that it cannot work for SIGKILL.
  39
  40    Signals with a SIG_IGN handler are considered to be non-fatal.  The
  41    functions in this file assume that when a SIG_IGN handler is installed
  42    for a signal, it was installed before any functions in this file were
  43    called and it stays so for the whole lifetime of the process.  */
  44
  45 /* Register a cleanup function to be executed when a catchable fatal signal
  46    occurs.
  47
  48    Restrictions for the cleanup function:
  49      - The cleanup function can do all kinds of system calls.  It may also
  50        modify (clobber) errno.
  51      - It can also access application dependent memory locations and data
  52        structures provided they are in a consistent state. One way to ensure
  53        this is through block_fatal_signals()/unblock_fatal_signals(), see
  54        below.  Another - more tricky - way to ensure this is the careful use
  55        of 'volatile'.
  56    However,
  57      - malloc() and similarly complex facilities are not safe to be called
  58        because they are not guaranteed to be in a consistent state.
  59      - Also, the cleanup function must not block the catchable fatal signals
  60        and leave them blocked upon return.
  61
  62    The cleanup function is executed asynchronously.  It is unspecified
  63    whether during its execution the catchable fatal signals are blocked
  64    or not.
  65
  66    Return 0 upon success, or -1 if there was a memory allocation problem.  */
  67 extern int at_fatal_signal (_GL_ASYNC_SAFE void (*function) (int sig));
  68
  69
  70 /* Sometimes it is necessary to block the usually fatal signals while the
  71    data structures being accessed by the cleanup action are being built or
  72    reorganized.  This is the case, for example, when a temporary file or
  73    directory is created through mkstemp() or mkdtemp(), because these
  74    functions create the temporary file or directory _before_ returning its
  75    name to the application.  */
  76
  77 /* Temporarily delay the catchable fatal signals.
  78    The signals will be blocked (= delayed) until the next call to
  79    unblock_fatal_signals().  If the signals are already blocked, a further
  80    call to block_fatal_signals() has no effect.  */
  81 extern void block_fatal_signals (void);
  82
  83 /* Stop delaying the catchable fatal signals.  */
  84 extern void unblock_fatal_signals (void);
  85
  86
  87 /* Return the list of signals that block_fatal_signals/unblock_fatal_signals
  88    would block or unblock.
  89    Fills signals[0..count-1] and returns count.  */
  90 extern unsigned int get_fatal_signals (int signals[64]);
  91
  92 /* Return the list of signals that block_fatal_signals/unblock_fatal_signals
  93    would block or unblock.  */
  94 extern const sigset_t * get_fatal_signal_set (void);
  95
  96
  97 #ifdef __cplusplus
  98 }
  99 #endif
 100
 101 #endif /* _FATAL_SIGNAL_H */