gtask: Track pending GTasks if G_ENABLE_DEBUG is defined

Track the GTasks which are still alive (not finalised) in a shared list, and provide a secret debugging function for printing that list.

Too often when debugging apps, I have found that a ‘leaked’ object is actually still (validly) referenced by an ongoing GTask which hasn’t completed for whatever reason. Or I have found that an operation has obviously stalled, but there are no pointers available to the GTask which is stalled, because it’s being tracked as a collection of closure pointers from some GSource which is hard to get to in the debugger.

It will be very useful for debugging apps, if there’s a list of all the still alive GTasks somewhere. This is that list.

The code is disabled if G_ENABLE_DEBUG is not defined, to avoid every GTask construction/finalisation imposing a global locking penalty.

To use the new list, break in gdb while running your app, and call g_task_print_alive_tasks(), or inspect the task_list manually:

(gdb) print g_task_print_alive_tasks()
16:44:17:788 GLib-GIO 5 GTasks still alive:
 • GTask 0x6100000ac740, gs_plugin_appstream_setup_async, ref count: 1, ever_returned: 0, completed: 0
 • GTask 0x6100000bf940, [gio] D-Bus read, ref count: 2, ever_returned: 0, completed: 0
 • GTask 0x6100000aac40, gs_plugin_loader_setup_async, ref count: 1, ever_returned: 0, completed: 0
 • GTask 0x61000006d940, gs_plugin_loader_job_process_async GsPluginJobRefine, ref count: 1, ever_returned: 0, completed: 0
 • GTask 0x610000118c40, [gio] D-Bus read, ref count: 2, ever_returned: 0, completed: 0

Signed-off-by: Philip Withnall pwithnall@endlessos.org