Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/10835#discussion_r50781374
--- Diff: core/src/main/scala/org/apache/spark/Accumulator.scala ---
@@ -75,43 +84,65 @@ private[spark] object Accumulators extends Logging {
* This global map holds the original accumulator objects that are
created on the driver.
* It keeps weak references to these objects so that accumulators can be
garbage-collected
* once the RDDs and user-code that reference them are cleaned up.
+ * TODO: Don't use a global map; these should be tied to a SparkContext
at the very least.
*/
+ @GuardedBy("Accumulators")
val originals = mutable.Map[Long, WeakReference[Accumulable[_, _]]]()
- private var lastId: Long = 0
+ private val nextId = new AtomicLong(0L)
- def newId(): Long = synchronized {
- lastId += 1
- lastId
- }
+ /**
+ * Return a globally unique ID for a new [[Accumulable]].
+ * Note: Once you copy the [[Accumulable]] the ID is no longer unique.
+ */
+ def newId(): Long = nextId.getAndIncrement
+ /**
+ * Register an [[Accumulable]] created on the driver such that it can be
used on the executors.
+ *
+ * All accumulators registered here can later be used as a container for
accumulating partial
+ * values across multiple tasks. This is what
[[org.apache.spark.scheduler.DAGScheduler]] does.
+ * Note: if an accumulator is registered here, it should also be
registered with the active
+ * context cleaner for cleanup so as to avoid memory leaks.
+ *
+ * If an [[Accumulable]] with the same ID was already registered, do
nothing instead of
--- End diff --
"this does nothing instead of..." ?
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