221 lines
6.7 KiB
Diff
221 lines
6.7 KiB
Diff
From 54a700c45c81f1ffff5f3dfcecb3929143e31d48 Mon Sep 17 00:00:00 2001
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From: Nils Philippsen <nils@redhat.com>
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Date: Wed, 19 Mar 2014 13:23:16 +0100
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Subject: [PATCH] patch: signal-handling
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Squashed commit of the following:
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commit 2b629e1d9c60dcf26defe6d05b515611874db270
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Author: Nils Philippsen <nils@redhat.com>
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Date: Thu Mar 13 13:38:12 2014 +0100
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separate signal handlers in top and bottom half
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This is to avoid race-conditions occurring when a signal is received
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while the signal handler is not yet finished. It also avoids calling
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non-reentrant functions from a signal handler. The top half (the real
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signal handler) just writes a character into a pipe which gets picked up
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and serviced by the bottom half from the normal event loop, this
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serializes things and makes use of non-reentrant functions safe.
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---
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src/xsane.c | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++-------
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1 file changed, 131 insertions(+), 15 deletions(-)
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diff --git a/src/xsane.c b/src/xsane.c
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index eee76ff..02b4da4 100644
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--- a/src/xsane.c
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+++ b/src/xsane.c
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@@ -47,6 +47,7 @@
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#endif
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#include <sys/wait.h>
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+#include <glib-unix.h>
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#include <stdarg.h>
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@@ -121,6 +122,7 @@ static const Preferences_medium_t pref_default_medium[]=
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int DBG_LEVEL = 0;
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static guint xsane_resolution_timer = 0;
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+static int xsane_signal_pipe[2];
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/* ---------------------------------------------------------------------------------------------------------------------- */
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@@ -161,8 +163,11 @@ void xsane_pref_save(void);
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static int xsane_pref_restore(void);
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static void xsane_pref_save_media(void);
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static void xsane_pref_restore_media(void);
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-static RETSIGTYPE xsane_quit_handler(int signal);
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-static RETSIGTYPE xsane_sigchld_handler(int signal);
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+static RETSIGTYPE xsane_signal_handler_top_half(int signal);
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+static gboolean xsane_signal_handler_bottom_half(gint fd,
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+ GIOCondition condition,
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+ gpointer user_data);
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+static void xsane_sigchld_handler(void);
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static void xsane_quit(void);
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static void xsane_exit(void);
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static gint xsane_standard_option_win_delete(GtkWidget *widget, gpointer data);
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@@ -2296,16 +2301,119 @@ static void xsane_pref_restore_media(void)
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/* ---------------------------------------------------------------------------------------------------------------------- */
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-static RETSIGTYPE xsane_quit_handler(int signal)
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+static RETSIGTYPE xsane_signal_handler_top_half(int signal)
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{
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- DBG(DBG_proc, "xsane_quit_handler\n");
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+ const char *msg_func = "xsane_signal_handler_top_half(): ";
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+ const char *msg_short_write = "Short write() while processing signal.\n";
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+ const char *msg_err = "Error during write().\n";
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+ char sig_char;
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+ ssize_t written;
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+ int errno_saved = errno;
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- xsane_quit();
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+ switch (signal)
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+ {
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+ case SIGTERM:
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+ sig_char = 't';
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+ break;
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+ case SIGINT:
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+ sig_char = 'i';
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+ break;
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+ case SIGHUP:
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+ sig_char = 'h';
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+ break;
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+ case SIGCHLD:
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+ sig_char = 'c';
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+ break;
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+ default:
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+ sig_char = '?';
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+ break;
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+ }
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+
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+ if ((written = write(xsane_signal_pipe[1], &sig_char, 1)) <= 0)
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+ {
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+ /* At this point, all bets are off. Salvage what we can. */
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+
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+ const char *msg = (written == 0) ? msg_short_write : msg_err;
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+
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+ if ((write(STDERR_FILENO, msg_func, strlen(msg_func)) < 0) ||
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+ (write(STDERR_FILENO, msg, strlen(msg)) < 0))
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+ {
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+ /* This is really a no-op, but at this point it doesn't really matter
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+ * anymore if the writes succeeded or not. */
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+ goto bail_out;
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+ }
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+
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+bail_out:
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+ /* Ignore SIGCHLD errors, zombie processes don't hurt that much. */
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+ if (signal != SIGCHLD)
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+ {
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+ struct SIGACTION act;
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+ memset(&act, 0, sizeof(act));
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+ act.sa_handler = SIG_DFL;
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+ sigaction(signal, &act, NULL);
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+ raise(signal);
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+ }
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+ }
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+
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+ errno = errno_saved;
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+}
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+
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+static gboolean xsane_signal_handler_bottom_half(gint fd,
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+ GIOCondition condition,
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+ gpointer user_data)
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+{
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+ char sig_char;
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+ ssize_t readlen;
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+
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+ DBG(DBG_proc, "xsane_signal_handler_bottom_half\n");
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+
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+ while ((readlen = read(xsane_signal_pipe[0], &sig_char, 1)) != 0)
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+ {
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+ if (readlen < 0)
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+ {
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+ if (errno == EINTR)
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+ {
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+ /* if interrupted by signal, just repeat reading */
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+ continue;
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+ }
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+ else
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+ {
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+ break;
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+ }
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+ }
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+
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+ switch (sig_char)
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+ {
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+ case 't':
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+ case 'i':
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+ case 'h':
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+ xsane_quit();
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+ break;
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+ case 'c':
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+ xsane_sigchld_handler();
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+ break;
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+ default:
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+ DBG(DBG_error,
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+ "Don't know how to cope with character-encoded signal: '%c'\n",
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+ sig_char);
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+ break;
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+ }
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+ }
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+
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+ /* previous invocation might have read more than it should, so ignore
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+ * EGAIN/EWOULDBLOCK */
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+ if (readlen < 0 && errno != EAGAIN && errno != EWOULDBLOCK)
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+ {
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+ DBG(DBG_error, "Error while reading from pipe: %d '%s'\n", errno,
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+ strerror(errno));
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+ }
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+
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+ return TRUE;
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}
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/* ---------------------------------------------------------------------------------------------------------------------- */
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-static RETSIGTYPE xsane_sigchld_handler(int signal)
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+static void xsane_sigchld_handler(void)
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{
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int status;
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XsaneChildprocess **childprocess_listptr = &xsane.childprocess_list;
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@@ -6062,18 +6170,26 @@ void xsane_interface(int argc, char **argv)
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}
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}
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+ if (!g_unix_open_pipe(xsane_signal_pipe, FD_CLOEXEC, NULL) ||
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+ fcntl(xsane_signal_pipe[0], F_SETFL, O_NONBLOCK, 1) ||
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+ fcntl(xsane_signal_pipe[1], F_SETFL, O_NONBLOCK, 1) ||
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+ !g_unix_fd_add(xsane_signal_pipe[0], G_IO_IN | G_IO_PRI,
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+ xsane_signal_handler_bottom_half, NULL))
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+ {
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+ DBG(DBG_error,
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+ "Couldn't create signal handling pipe, set flags on it or install\n"
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+ "bottom half of handler.\n");
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+ exit(1);
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+ }
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+
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/* define SIGTERM, SIGINT, SIGHUP-handler to make sure that e.g. all temporary files are deleted */
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/* when xsane gets such a signal */
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memset(&act, 0, sizeof(act));
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- act.sa_handler = xsane_quit_handler;
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- sigaction(SIGTERM, &act, 0);
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- sigaction(SIGINT, &act, 0);
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- sigaction(SIGHUP, &act, 0);
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-
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- /* add a signal handler that cleans up zombie child processes */
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- memset(&act, 0, sizeof(act));
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- act.sa_handler = xsane_sigchld_handler;
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- sigaction(SIGCHLD, &act, 0);
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+ act.sa_handler = xsane_signal_handler_top_half;
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+ sigaction(SIGTERM, &act, NULL);
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+ sigaction(SIGINT, &act, NULL);
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+ sigaction(SIGHUP, &act, NULL);
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+ sigaction(SIGCHLD, &act, NULL);
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gtk_main();
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sane_exit();
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--
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1.8.5.3
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