Now all accesses to quark_notify_queue are guarded by the GData lock.
Several non-trivial operations are implemented via
g_datalist_id_update_atomic().
The OPTIONAL_BIT_LOCK_NOTIFY lock is thus unnecessary and can be dropped.
Note that with the move to g_datalist_id_update_atomic(), we now
potentially do more work while holding the GData lock (e.g. some code
paths allocation additional memory). But note that
g_datalist_id_set_data() already has code paths where it must allocate
memory to track the GDataElt. Also, most objects are not used in
parallel, so holding the per-object (per-GData) lock longer does not
affect them. Also, many operations also require a object_bit_lock(), so
it seems very unlikely that you really could achieve higher parallelism
by taking more locks (and minimizing the time to hold the GData lock).
On the contrary, taking one lock less and doing all the work there is
beneficial.
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