Previously, when a ReadPortal or a WritePortal was returned from an
ArrayHandle, it had wrapped in it a Token that was attached to the
ArrayHandle. This Token would prevent other reads and writes from the
ArrayHandle.
This added safety in the form of making sure that the ArrayPortal was
always valid. Unfortunately, it also made deadlocks very easy. They
happened when an ArrayPortal did not leave scope immediately after use
(which is not all that uncommon).
Now, the ArrayPortal no longer locks up the ArrayHandle. Instead, when
an access happens on the ArrayPortal, it checks to make sure that
nothing has happened to the data being accessed. If it has, a fatal
error is reported to the log.
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