GTask used a 10-thread thread pool for g_task_run_in_thread() /
g_task_run_in_thread_sync(), but this ran into problems when task
threads blocked waiting for another g_task_run_in_thread_sync()
operation to complete. Previously there was a workaround for this, by
bumping up the thread limit when that case was detected, but deadlocks
could still happen if there were non-GTask threads involved. (Eg, task
A sends a message to thread X and waits for a response, but thread X
needs to complete task B in a thread before returning the response to
task A.)
So, allow GTask's thread pool to be expanded dynamically, by watching
it from the glib worker thread, and growing it (at an
exponentially-decreasing rate) if too much time passes without any
tasks completing. This should solve the deadlocking problems without
causing sudden breakage in apps that assume they can queue huge
numbers of tasks at once without consequences.
https://bugzilla.gnome.org/show_bug.cgi?id=687223
This can be used to query whether the task has completed, in the sense
that it has had a result set on it, and has already – or will soon –
invoke its callback function.
Notifications for this property are emitted immediately after the task’s
main callback, in the same main context as that callback. This allows
for multiple bits of code to listen for completion of the GTask, which
opens the door for blocking on cancellation of the GTask and improved
handling of ‘pending’ behaviour.
https://bugzilla.gnome.org/show_bug.cgi?id=743636
g_thread_pool_push() only returns an error if it fails to spawn a new
thread. However, it unconditionally adds the task to its worker queue,
so:
• if _any_ threads exist in the pool, the task will eventually be
handled; and
• if _no_ threads exist in the pool, the task will be handled if one
is eventually successfully spawned.
If no more threads are ever spawned, the process probably has bigger
problems than a single GTask which is taking forever to complete.
https://bugzilla.gnome.org/show_bug.cgi?id=736806
Since we are no longer using sgml mode, using /* */ to
escape block comments inside examples does not work anymore.
Switch to using line comments with //
If tasks block waiting for other tasks to complete then the system can
end up starved for threads. Avoid this by bumping up max-threads in
that case.
This also reverts 7b1f8c58 and reverts max-threads for GTask's
GThreadPool back to 10.
https://bugzilla.gnome.org/show_bug.cgi?id=687223
GTask is a replacement for GSimpleAsyncResult and GIOScheduler, that
also allows for making cancellable wrappers around non-cancellable
functions (as in GThreadedResolver).
https://bugzilla.gnome.org/show_bug.cgi?id=661767
