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_r331048980
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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:
Does `@transient` work here? or will it not be reinitialized when the object
is deserialized? `@transient lazy` probably works but may be overkill. Rather
than define a class (which isn't a big deal), just use some random serializable
object like `new Integer(0)`?
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