Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/5907#discussion_r29689099
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala ---
@@ -607,8 +614,27 @@ class StreamingContext private[streaming] (
*/
object StreamingContext extends Logging {
+ /**
+ * Lock that guards access to global variables that track active
StreamingContext.
+ */
+ private val ACTIVATION_LOCK = new Object()
- private[streaming] val DEFAULT_CLEANER_TTL = 3600
+ private var activeContext: AtomicReference[StreamingContext] =
+ new AtomicReference[StreamingContext](null)
+
+ private def assertNoOtherContextIsActive(): Unit = {
+ ACTIVATION_LOCK.synchronized {
+ if (activeContext.get() != null) {
+ throw new SparkException("Only one StreamingContext may be started
in this JVM")
--- End diff --
To clarify, we're allowed to start multiple StreamingContexts provided that
only one context is running at a time, right? Since that's the case, what do
you think about rewording this to something like "Only one StreamingContext may
be running in this JVM"? I just worry that "started" might be misinterpreted
as saying that you can only _create_ one SparkContext per JVM.
We don't need to add an explicit test for starting a new StreamingContext
after stopping the old one since this case is implicitly handled by all of our
other test suites.
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