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gthreadedresolver: Switch to using a separate thread pool and support timeouts

Philip Withnall requested to merge pwithnall/glib:resolver-thread-pool into main

Rather than running lookups in the global shared thread pool belonging to GTask, run them in a private thread pool.

This is needed because the global shared thread pool is constrained to only 14 threads. If there are 14 ongoing calls to g_task_run_in_thread() from any library/code in the process, and then one of them asks to do a DNS lookup, the lookup will block forever.

Under certain circumstances, particularly where there are a couple of deep chains of dependent tasks running with g_task_run_in_thread(), this can livelock the program.

Since GResolver is likely to be called as a frequent leaf call in certain workloads, and in particular there are likely to be several lookups requested at the same time, it makes sense to move resolver lookups to a private thread pool.

At the same time, add timeout support as GResolver:timeout.

Without a timeout, some lookup requests can go on forever, typically due to bugs in underlying systems.

This can have particularly significant effects on the Happy Eyeballs algorithm in GSocketClient, which relies on multiple name lookups as its first step.

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

Edited by Philip Withnall

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