gaogaotiantian opened a new pull request, #54189:
URL: https://github.com/apache/spark/pull/54189
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### What changes were proposed in this pull request?
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Reimplemented the thread pool mechanism for
ExecutePlanResponseReattachableIterator.
* Number of `ExecutePlanResponseReattachableIterator` instances is counted
with `WeakSet` so we know when to release the thread pool
* Instead of relying on thread pool to finish, we collect the futures for
each release task and wait for them in the client
### Why are the changes needed?
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The current implementation is fundamentally wrong. It tries to shutdown a
thread pool for a class from client instances. We could have multiple client
instances in a process and flipping the state of a global class would just
cause racing issues.
For example, the old code can return a thread pool in a thread which could
be shutdown before it is used.
The original reason that we "shutdown" the thread pool is because we need
the client to wait for the release requests to finish. That can't justify
waiting for the whole thread pool (or shut it down) because it can be shared
with other clients. We actually have a deadlock caused by it.
Now we collect futures explicitly for each
`ExecutePlanResponseReattachableIterator` call and when we need to close the
client, just wait for those future to be done.
Notice that we will not keep these futures longer than they should be. We
used `WeakSet` which means if the future has no reference, it will still be
garbage collected properly. We won't use more memory because we keep track of
these. In normal cases the set will probably be empty because all the release
tasks are done.
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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Simple local test passed. Waiting for CI.
### Was this patch authored or co-authored using generative AI tooling?
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No.
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