srowen commented on a change in pull request #25951: [SPARK-28917][CORE]
Synchronize access to RDD mutable state.
URL: https://github.com/apache/spark/pull/25951#discussion_r331225818
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File path: core/src/main/scala/org/apache/spark/rdd/RDD.scala
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@@ -103,6 +103,17 @@ abstract class RDD[T: ClassTag](
_sc
}
+ /**
+ * Lock for all mutable state of this RDD (persistence, partitions,
dependencies, etc.). We do
+ * not use `this` because RDDs are user-visible, so users might have added
their own locking on
+ * RDDs; sharing that could lead to a deadlock.
+ *
+ * One thread might hold the lock on many of these, for a chain of RDD
dependencies; but
+ * because DAGs are acyclic, and we only ever hold locks for one path in
that DAG, there is no
+ * chance of deadlock.
+ */
+ private val stateLock = new SerializableObject()
Review comment:
Yeah I recall the RDDs get serialized as a side effect, but that is mostly
accidental? you can't perform operations on it. At least, I'd say that one
shouldn't assume anything about an RDD works once it's on the executors. I
doubt that just making it transient (thus null on the executors) breaks
anything that happened to work now?
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