[Disco] Allow allocation that only exists on worker0 #16993
Merged
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The
disco.Session.scatter_from_worker0
function expects aDRef
which anNDArray
on worker 0, andNullOpt
on all other workers. Prior to this commit, there was no method in thedisco.Session
that could be used to make such aDRef
. As a result, every use ofscatter_from_worker0
generated an error, stating that non-zero workers should haveNullOpt
as theirsend
argument.This commit adds a
worker0_only: bool
argument todisco.Session.empty
. This can be used to generate an allocation that only exists on worker zero, suitable for use inscatter_from_worker0
.