Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/11436#discussion_r54646125
--- Diff: core/src/main/scala/org/apache/spark/storage/BlockManager.scala
---
@@ -648,8 +647,38 @@ private[spark] class BlockManager(
}
/**
- * @return true if the block was stored or false if the block was
already stored or an
- * error occurred.
+ * Retrieve the given block if it exists, otherwise call the provided
`makeIterator` method
+ * to compute the block, persist it, and return its values.
+ *
+ * @return either a BlockResult if the block was successfully cached, or
an iterator if the block
+ * could not be cached.
+ */
+ def getOrElseUpdate(
+ blockId: BlockId,
+ level: StorageLevel,
+ makeIterator: () => Iterator[Any]): Either[BlockResult,
Iterator[Any]] = {
+ // Initially we hold no locks on this block.
+ doPut(blockId, IteratorValues(makeIterator), level,
downgradeToReadLock = true) match {
--- End diff --
I think we can simplify this by moving the acquiring lock logic outside of
`doPut`. If we fail to acquire a write lock for the new block we used to return
`None` in `doPut` anyway, so it would make sense to instead call `doPut` only
if we're able to acquire the write lock. Then you don't need the complicated
return type in `doPut`.
(If you don't want to change all the *other* places where `doPut` is
called, we can just make an overloaded `doPut` method that takes in a
`blockInfo` and assumes the write lock is already held.)
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