solve the shuffle problem for HashSet

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -482,26 +482,25 @@ private[spark] class Master(
 
     // First schedule drivers, they take strict precedence over applications
     // Randomization helps balance drivers
-    val shuffledWorkers = Random.shuffle(workers).toArray
-    val workerNum = shuffledWorkers.size
+    val shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state == WorkerState.ALIVE))
+    val aliveWorkerNum = shuffledAliveWorkers.size
     var curPos = 0
     for (driver <- List(waitingDrivers: _*)) { // iterate over a copy of waitingDrivers
       // For each waiting driver we pick a worker that has enough resources to launch it.
       // The picking does in a round-robin fashion, starting from position behind last
       // worker on which driver was just launched and ending with driver being launched
       // or we have iterated over all workers.
       val startPos = curPos
-      curPos = (curPos + 1) % workerNum
+      curPos = (curPos + 1) % aliveWorkerNum
       var launched = false
       while (curPos - 1 != startPos && !launched) {
-        val worker = shuffledWorkers(curPos)
-        if (worker.state == WorkerState.ALIVE
-          && worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {
+        val worker = shuffledAliveWorkers(curPos)
+        if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {
           launchDriver(worker, driver)
           waitingDrivers -= driver
           launched = true
         }
-        curPos = (curPos + 1) % workerNum
+        curPos = (curPos + 1) % aliveWorkerNum
       }
     }