juliuszsompolski commented on a change in pull request #25612:
[SPARK-3137][Core]Replace the global TorrentBroadcast lock with fine grained
locks
URL: https://github.com/apache/spark/pull/25612#discussion_r318971022
##########
File path:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala
##########
@@ -290,6 +293,42 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
private object TorrentBroadcast extends Logging {
+ /** Locks to ensure there is only one thread fetching the same
[[TorrentBroadcast]] block. */
+ private val torrentBroadcastLock = new ConcurrentHashMap[BroadcastBlockId,
AnyRef]()
+
+ /** Acquire a lock for fetching a [[TorrentBroadcast]] block. */
+ private def acquireTorrentBroadcastLock(broadcastId: BroadcastBlockId): Unit
= {
+ while (true) {
+ val lock = torrentBroadcastLock.putIfAbsent(broadcastId, new Object)
+ if (lock == null) return
+ lock.synchronized {
+ while (torrentBroadcastLock.get(broadcastId) eq lock) {
+ lock.wait()
Review comment:
Why not just stripe over a fixed number of Reentrant locks? This should
reduce contention enough (and potential collissions can be controlled with
numLocks) is easy to understand and doesn't reimplement its own lock queues.
It's also fully interruptible, while in the current implementation the threads
that are queueing for the lock are not interruptible.
```
private val numLocks = 100
private val locks = (1 to numLocks).map(_ => new
java.util.concurrent.locks.ReentrantLock)
private def withTorrentBroadcastLock[T](broadcastId: BroadcastBlockId)(func:
=> T): T = {
val lock = locks(broadcastId.broadcastId % numLocks)
lock.lockInterruptibly()
try {
func
} finally {
lock.unlock()
}
}
```
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