Modified Master to prevent from 0 divide

Author: sarutak

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

@@ -490,24 +490,28 @@ private[spark] class Master(
     // Randomization helps balance drivers
     val shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state == WorkerState.ALIVE))
     val aliveWorkerNum = shuffledAliveWorkers.size
-    var curPos = 0
-    var stopPos = aliveWorkerNum
-    for (driver <- waitingDrivers.toList) { // iterate over a copy of waitingDrivers
-      // We assign workers to each waiting driver in a round-robin fashion. For each driver, we
-      // start from the last worker that was assigned a driver, and continue onwards until we have
-      // explored all alive workers.
-      var launched = false
-      while (curPos != stopPos && !launched) {
-        val worker = shuffledAliveWorkers(curPos)
-        if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {
-          launchDriver(worker, driver)
-          waitingDrivers -= driver
-          launched = true
+
+    if (aliveWorkerNum > 0) {
+      var curPos = 0
+      var stopPos = aliveWorkerNum
+      for (driver <- waitingDrivers.toList) {
+        // iterate over a copy of waitingDrivers
+        // We assign workers to each waiting driver in a round-robin fashion. For each driver, we
+        // start from the last worker that was assigned a driver, and continue onwards until we have
+        // explored all alive workers.
+        var launched = false
+        while (curPos != stopPos && !launched) {
+          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) % aliveWorkerNum
         }
-        curPos = (curPos + 1) % aliveWorkerNum
+        curPos = (stopPos + 1) % aliveWorkerNum
+        stopPos = curPos + aliveWorkerNum
       }
-      curPos = (stopPos + 1) % aliveWorkerNum
-      stopPos = curPos + aliveWorkerNum
     }
 
     // Right now this is a very simple FIFO scheduler. We keep trying to fit in the first app