Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/10042#discussion_r46179366
--- Diff:
core/src/main/scala/org/apache/spark/util/ShutdownHookManager.scala ---
@@ -232,22 +232,23 @@ private [util] class SparkShutdownHookManager {
}
}
- def runAll(): Unit = synchronized {
+ def runAll(): Unit = {
shuttingDown = true
- while (!hooks.isEmpty()) {
- Try(Utils.logUncaughtExceptions(hooks.poll().run()))
+ var nextHook: SparkShutdownHook = null
+ while ({nextHook = hooks synchronized { hooks.poll() }; nextHook !=
null}) {
+ Try(Utils.logUncaughtExceptions(nextHook.run()))
}
}
- def add(priority: Int, hook: () => Unit): AnyRef = synchronized {
+ def add(priority: Int, hook: () => Unit): AnyRef = {
checkState()
val hookRef = new SparkShutdownHook(priority, hook)
- hooks.add(hookRef)
+ hooks synchronized { hooks.add(hookRef) }
--- End diff --
So, technically, this is not really thread-safe anymore. You can have this
order of things:
T1: in add(), passes `checkState()` check
T2: in runAll(), sets `shuttingDown` to true
T2: in runAll(), calls `hooks.poll()`, list is empty, stops calling hooks
T1: in add(), adds hook to the list, hook will never be called.
Granted, that's very unlikely. I think if you move the `checkState()` call
inside the lock it should fix things, though. You may end up adding a new hook
when `shuttingDown` is true in that case, but you make sure that `runAll` will
still pick it up.
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