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gmain: Guarantee handler dispatch after receiving UNIX signal

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Guarantee that user signal callback is dispatched _after_ receiving a
signal as long as the handler expresses continued interest in receiving
such a notification.

Previously if a signal has been received during user callback dispatch
but before pending flag had been cleared then the signal would be
irrevocably lost.

This is a very useful guarantee to have in cases where signals are used
to signify a need for synchronization with external resources. For
example: reloading configuration file after SIGUSR1 or retrieving a
terminal size after SIGWINCH.
This commit is contained in:
Tomasz Miąsko
2018-11-02 00:00:00 +00:00
parent 9e652f94d2
commit 969b0e00b3
2 changed files with 53 additions and 2 deletions
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4
glib/gmain.c
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@@ -5214,10 +5214,10 @@ g_unix_signal_watch_dispatch (GSource *source,
return FALSE;
}
again = (callback) (user_data);
g_atomic_int_set (&unix_signal_source->pending, FALSE);
again = (callback) (user_data);
return again;
}

51
glib/tests/unix.c
View File

@@ -245,6 +245,56 @@ test_sighup_nested (void)
g_main_loop_unref (mainloop);
}
static gboolean
on_sigwinch_received (gpointer data)
{
GMainLoop *loop = (GMainLoop *) data;
sig_counter ++;
if (sig_counter == 1)
kill (getpid (), SIGWINCH);
else if (sig_counter == 2)
g_main_loop_quit (loop);
else if (sig_counter > 2)
g_assert_not_reached ();
/* Increase the time window in which an issue could happen. */
g_usleep (G_USEC_PER_SEC);
return G_SOURCE_CONTINUE;
}
static void
test_callback_after_signal (void)
{
/* Checks that user signal callback is invoked *after* receiving a signal.
* In other words a new signal is never merged with the one being currently
* dispatched or whose dispatch had already finished. */
GMainLoop *mainloop;
GMainContext *context;
GSource *source;
sig_counter = 0;
context = g_main_context_new ();
mainloop = g_main_loop_new (context, FALSE);
source = g_unix_signal_source_new (SIGWINCH);
g_source_set_callback (source, on_sigwinch_received, mainloop, NULL);
g_source_attach (source, context);
g_source_unref (source);
g_assert_cmpint (sig_counter, ==, 0);
kill (getpid (), SIGWINCH);
g_main_loop_run (mainloop);
g_assert_cmpint (sig_counter, ==, 2);
g_main_loop_unref (mainloop);
g_main_context_unref (context);
}
int
main (int argc,
char *argv[])
@@ -259,6 +309,7 @@ main (int argc,
g_test_add_func ("/glib-unix/sighup_again", test_sighup);
g_test_add_func ("/glib-unix/sighup_add_remove", test_sighup_add_remove);
g_test_add_func ("/glib-unix/sighup_nested", test_sighup_nested);
g_test_add_func ("/glib-unix/callback_after_signal", test_callback_after_signal);
return g_test_run();
}