Re: g_main_context_push_thread_default() & g_io_*()

["A. Walton" <awalton gnome org>]

On Mon, Mar 29, 2010 at 6:58 PM, Thomas Stover <thomas wsinnovations com> wrote:
> In the documentation for g_main_context_push_thread_default(), the
> following sentence appears:
>
> "This will cause certain asynchronous operations (such as most gio-based
> I/O) which are started in this thread to run under context and deliver
> their results to its main loop, rather than running under the global
> default context in the main thread."
>
> This makes me think my experiment program below would work, yet on ubuntu
> 9.10 at least, it does not. Perhaps g_io_channel_unix_new() is not in the
> "most" group referred to above? Or maybe I'm doing this wrong. Thanks for
> any input.

GIO refers to the GIO library
(http://library.gnome.org/devel/gio/stable/), not to the g_io_* family
of functions. Probably worth filing a bug to make this clearer in the
documentation.

-A. Walton

> ====
> #include <glib.h>
> #include <unistd.h>
> #include <sys/syscall.h>
>
> GMainContext *thread1_context, *thread2_context;
> GMainLoop *main_loop1, *main_loop2;
>
> gboolean idle_callback(gpointer data)
> {
> Âg_print("idle_callback() %d\n", (pid_t) syscall (SYS_gettid));
> Âreturn FALSE;
> }
>
> gboolean input_callback(GIOChannel *source,
> Â Â Â Â Â Â Â Â Â Â Â ÂGIOCondition condition,
> Â Â Â Â Â Â Â Â Â Â Â Âgpointer data)
> {
> ÂGSource *idle_source;
> Âunsigned char buffer[16];
> Âg_print("input_callback() %d\n", (pid_t) syscall (SYS_gettid));
>
> Âif(read(0, buffer, 16) < 1)
> Âreturn FALSE;
>
> Âidle_source = g_idle_source_new();
> Âg_source_set_callback(idle_source, idle_callback, NULL, NULL);
> Âg_source_attach(idle_source, thread1_context);
>
> Âreturn TRUE;
> }
>
> gpointer thread2_entry(gpointer data)
> {
> ÂGIOChannel *channel;
> Âg_print("thread2_entry() %d\n", (pid_t) syscall (SYS_gettid));
>
> Âmain_loop2 = g_main_loop_new(thread2_context, FALSE);
>
> Âg_main_context_push_thread_default(thread2_context);
>
> Âchannel = g_io_channel_unix_new(0);
> Âg_io_add_watch(channel, G_IO_IN, input_callback, NULL);
>
> Âg_main_loop_run(main_loop2);
> }
>
> int main(int argc, char **argv)
> {
> Âg_thread_init(NULL);
>
> Âthread1_context = g_main_context_default();
> Âthread2_context = g_main_context_new();
>
> Âmain_loop1 = g_main_loop_new(thread1_context, FALSE);
>
> Âg_thread_create(thread2_entry, NULL, FALSE, NULL);
>
> Âg_main_loop_run(main_loop1);
> Âreturn 0;
> }
> ====
>
> Here is an example session:
>
> $ ./a.out
> thread2_entry() 24928
> f
> input_callback() 24927
> idle_callback() 24927
> e
> input_callback() 24927
> idle_callback() 24927
> k
> input_callback() 24927
> idle_callback() 24927
> ^C
>
> What I was expecting is for input_callback() to run in thread 24928
> instead of 24927.
>
> --
> www.thomasstover.com
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