gimpsignal.c 3.69 KB
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/* LIBGIMP - The GIMP Library
 * Copyright (C) 1995-1997 Peter Mattis and Spencer Kimball
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 *
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 * This library is free software: you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
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 * version 3 of the License, or (at your option) any later version.
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 *
 * This library 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
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 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
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 * License along with this library.  If not, see
 * <http://www.gnu.org/licenses/>.
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 *
 * $Revision$
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 */
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#include "config.h"

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#define _GNU_SOURCE  /* for the sigaction stuff */
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#include <glib.h>

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#include "gimpsignal.h"

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/**
 * SECTION: gimpsignal
 * @title: gimpsignal
 * @short_description: Portable signal handling.
 * @see_also: signal(2), signal(5 or 7), sigaction(2).
 *
 * Portable signal handling.
 **/


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/* Courtesy of Austin Donnelly 06-04-2000 to address bug #2742 */

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/**
 * gimp_signal_private:
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 * @signum: Selects signal to be handled see man 5 signal (or man 7 signal)
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 * @handler: Handler that maps to signum. Invoked by O/S.
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 *           Handler gets signal that caused invocation. Corresponds
 *           to the @sa_handler field of the @sigaction struct.
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 * @flags: Preferences. OR'ed SA_&lt;xxx&gt;. See man sigaction. Corresponds
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 *         to the @sa_flags field of the @sigaction struct.
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 *
 * This function furnishes a workalike for signal(2) but
 * which internally invokes sigaction(2) after certain
 * sa_flags are set; these primarily to ensure restarting
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 * of interrupted system calls. See sigaction(2)  It is a
 * aid to transition and not new development: that effort
 * should employ sigaction directly. [gosgood 18.04.2000]
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 *
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 * Cause @handler to be run when @signum is delivered.  We
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 * use sigaction(2) rather than signal(2) so that we can control the
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 * signal handler's environment completely via @flags: some signal(2)
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 * implementations differ in their sematics, so we need to nail down
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 * exactly what we want. [austin 06.04.2000]
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 *
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 * Returns: A reference to the signal handling function which was
 *          active before the call to gimp_signal_private().
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 */
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GimpSignalHandlerFunc
gimp_signal_private (gint                   signum,
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                     GimpSignalHandlerFunc  handler,
                     gint                   flags)
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{
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#ifndef G_OS_WIN32
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  gint ret;
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  struct sigaction sa;
  struct sigaction osa;

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  /*  The sa_handler (mandated by POSIX.1) and sa_sigaction (a
   *  common extension) are often implemented by the OS as members
   *  of a union.  This means you CAN NOT set both, you set one or
   *  the other.  Caveat programmer!
   */
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  /*  Passing gimp_signal_private a gimp_sighandler of NULL is not
   *  an error, and generally results in the action for that signal
   *  being set to SIG_DFL (default behavior).  Many OSes define
   *  SIG_DFL as (void (*)()0, so setting sa_handler to NULL is
   *  the same thing as passing SIG_DFL to it.
   */
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  sa.sa_handler = handler;
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  /*  Mask all signals while handler runs to avoid re-entrancy
   *  problems.
   */
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  sigfillset (&sa.sa_mask);

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  sa.sa_flags = flags;
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  ret = sigaction (signum, &sa, &osa);
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  if (ret < 0)
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    g_error ("unable to set handler for signal %d\n", signum);
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  return (GimpSignalHandlerFunc) osa.sa_handler;
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#else
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  return NULL;                  /* Or g_error()? Should all calls to
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                                 * this function really be inside
                                 * #ifdef G_OS_UNIX?
                                 */
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#endif
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}