Minor improvements (#177)

* Add task batch size in order to dynamically increase/reduce scheduling iteration time
* Name the fenzo threads

fenzo-core/src/main/java/com/netflix/fenzo/TaskScheduler.java

@@ -16,6 +16,7 @@
 
 package com.netflix.fenzo;
 
+import com.netflix.fenzo.common.ThreadFactoryBuilder;
 import com.netflix.fenzo.plugins.NoOpScaleDownOrderEvaluator;
 import com.netflix.fenzo.queues.Assignable;
 import com.netflix.fenzo.queues.QueuableTask;
@@ -34,8 +35,10 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 /**
@@ -103,6 +106,7 @@ public Boolean call(Double f) {
         private boolean singleOfferMode=false;
         private final List<SchedulingEventListener> schedulingEventListeners = new ArrayList<>();
         private int maxConcurrent = Runtime.getRuntime().availableProcessors();
+        private Supplier<Long> taskBatchSizeSupplier = () -> Long.MAX_VALUE;
 
         /**
          * (Required) Call this method to establish a method that your task scheduler will call to notify you
@@ -442,6 +446,20 @@ public Builder withMaxConcurrent(int maxConcurrent) {
             return this;
         }
 
+        /**
+         * Use the given supplier to determine how many successful tasks should be evaluated in the next scheduling iteration. This
+         * can be used to dynamically change how many successful task evaluations are done in order to increase/reduce the scheduling iteration
+         * duration. The default supplier implementation will return {@link Long#MAX_VALUE} such that all tasks will be
+         * evaluated.
+         *
+         * @param taskBatchSizeSupplier the supplier that returns the task batch size for the next scheduling iteration.
+         * @return this same {@code Builder}, suitable for further chaining or to build the {@link TaskSchedulingService}.
+         */
+        public Builder withTaskBatchSizeSupplier(Supplier<Long> taskBatchSizeSupplier) {
+            this.taskBatchSizeSupplier = taskBatchSizeSupplier;
+            return this;
+        }
+
         /**
          * Creates a {@link TaskScheduler} based on the various builder methods you have chained.
          *
@@ -497,7 +515,8 @@ private TaskScheduler(Builder builder) {
             throw new IllegalArgumentException("Lease reject action must be non-null");
         this.builder = builder;
         this.maxConcurrent = builder.maxConcurrent;
-        this.executorService = Executors.newFixedThreadPool(maxConcurrent);
+        ThreadFactory threadFactory = ThreadFactoryBuilder.newBuilder().withNameFormat("fenzo-worker-%d").build();
+        this.executorService = Executors.newFixedThreadPool(maxConcurrent, threadFactory);
         this.stateMonitor = new StateMonitor();
         this.schedulingEventListener = CompositeSchedulingEventListener.of(builder.schedulingEventListeners);
         taskTracker = new TaskTracker();
@@ -795,6 +814,8 @@ private SchedulingResult doSchedule(
         Set<TaskRequest> failedTasksForAutoScaler = new HashSet<>();
         Map<String, VMAssignmentResult> resultMap = new HashMap<>(avms.size());
         final SchedulingResult schedulingResult = new SchedulingResult(resultMap);
+        long taskBatchSize = builder.taskBatchSizeSupplier.get();
+        long tasksIterationCount = 0;
         if(avms.isEmpty()) {
             while (true) {
                 final Assignable<? extends TaskRequest> taskOrFailure = taskIterator.next();
@@ -806,6 +827,9 @@ private SchedulingResult doSchedule(
             schedulingEventListener.onScheduleStart();
             try {
                 while (true) {
+                    if (tasksIterationCount >= taskBatchSize) {
+                        break;
+                    }
                     final Assignable<? extends TaskRequest> taskOrFailure = taskIterator.next();
                     if(logger.isDebugEnabled())
                         logger.debug("TaskSched: task=" + (taskOrFailure == null? "null" : taskOrFailure.getTask().getId()));
@@ -904,6 +928,7 @@ public EvalResult call() throws Exception {
                             logger.debug("Task {}: found successful assignment on host {}", task.getId(),
                                     successfulResult.getHostname());
                         successfulResult.assignResult();
+                        tasksIterationCount++;
                         failedTasksForAutoScaler.remove(task);
                         schedulingEventListener.onAssignment(successfulResult);
                     }

fenzo-core/src/main/java/com/netflix/fenzo/TaskSchedulingService.java

@@ -16,6 +16,7 @@
 
 package com.netflix.fenzo;
 
+import com.netflix.fenzo.common.ThreadFactoryBuilder;
 import com.netflix.fenzo.functions.Action0;
 import com.netflix.fenzo.functions.Action1;
 import com.netflix.fenzo.functions.Func1;
@@ -39,6 +40,7 @@
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 
@@ -495,7 +497,8 @@ public final static class Builder {
         private boolean optimizingShortfallEvaluator = false;
 
         public Builder() {
-            executorService = new ScheduledThreadPoolExecutor(1);
+            ThreadFactory threadFactory = ThreadFactoryBuilder.newBuilder().withNameFormat("fenzo-main").build();
+            executorService = new ScheduledThreadPoolExecutor(1, threadFactory);
         }
 
         /**

fenzo-core/src/main/java/com/netflix/fenzo/common/ThreadFactoryBuilder.java

@@ -0,0 +1,74 @@
+package com.netflix.fenzo.common;
+
+import java.util.Locale;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * A ThreadFactory builder based on <a href="https://github.com/google/guava">Guava's</a> ThreadFactoryBuilder.
+ */
+public final class ThreadFactoryBuilder {
+    private String nameFormat = null;
+    private Boolean daemon = null;
+
+    private ThreadFactoryBuilder() {
+    }
+
+    /**
+     * Creates a new {@link ThreadFactoryBuilder} builder.
+     */
+    public static ThreadFactoryBuilder newBuilder() {
+        return new ThreadFactoryBuilder();
+    }
+
+    /**
+     * Sets the naming format to use when naming threads ({@link Thread#setName}) which are created
+     * with this ThreadFactory.
+     *
+     * @param nameFormat a {@link String#format(String, Object...)}-compatible format String, to which
+     *                   a unique integer (0, 1, etc.) will be supplied as the single parameter. This integer will
+     *                   be unique to the built instance of the ThreadFactory and will be assigned sequentially. For
+     *                   example, {@code "rpc-pool-%d"} will generate thread names like {@code "rpc-pool-0"},
+     *                   {@code "rpc-pool-1"}, {@code "rpc-pool-2"}, etc.
+     * @return this for the builder pattern
+     */
+    public ThreadFactoryBuilder withNameFormat(String nameFormat) {
+        this.nameFormat = nameFormat;
+        return this;
+    }
+
+    /**
+     * Sets whether or not the created thread will be a daemon thread.
+     *
+     * @param daemon whether or not new Threads created with this ThreadFactory will be daemon threads
+     * @return this for the builder pattern
+     */
+    public ThreadFactoryBuilder withDaemon(boolean daemon) {
+        this.daemon = daemon;
+        return this;
+    }
+
+    public ThreadFactory build() {
+        return build(this);
+    }
+
+    private static ThreadFactory build(ThreadFactoryBuilder builder) {
+        final String nameFormat = builder.nameFormat;
+        final Boolean daemon = builder.daemon;
+        final AtomicLong count = (nameFormat != null) ? new AtomicLong(0) : null;
+        return runnable -> {
+            Thread thread = new Thread(runnable);
+            if (nameFormat != null) {
+                thread.setName(format(nameFormat, count.getAndIncrement()));
+            }
+            if (daemon != null) {
+                thread.setDaemon(daemon);
+            }
+            return thread;
+        };
+    }
+
+    private static String format(String format, Object... args) {
+        return String.format(Locale.ROOT, format, args);
+    }
+}

fenzo-core/src/test/java/com/netflix/fenzo/BasicSchedulerTests.java

@@ -552,4 +552,29 @@ public Result evaluate(TaskRequest taskRequest, VirtualMachineCurrentState targe
         Assert.assertNotNull(ref.get());
         Assert.assertEquals(2, ref.get().size());
     }
+
+    @Test
+    public void testTaskBatchSize() {
+        TaskScheduler taskScheduler = new TaskScheduler.Builder()
+                .withLeaseOfferExpirySecs(1000000)
+                .withLeaseRejectAction(virtualMachineLease -> System.out.println("Rejecting offer on host " + virtualMachineLease.hostname()))
+                .withTaskBatchSizeSupplier(() -> 2L)
+                .build();
+        List<VirtualMachineLease> leases = LeaseProvider.getLeases(1, 5, 50, 1, 10);
+        List<TaskRequest> taskRequests = new ArrayList<>();
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        SchedulingResult schedulingResult = taskScheduler.scheduleOnce(taskRequests, leases);
+        Assert.assertEquals(2, schedulingResult.getResultMap().values().iterator().next().getTasksAssigned().size());
+        taskRequests = new ArrayList<>();
+        taskRequests.add(TaskRequestProvider.getTaskRequest(1, 10, 0));
+        schedulingResult = taskScheduler.scheduleOnce(taskRequests, leases);
+        Assert.assertEquals(1, schedulingResult.getResultMap().values().iterator().next().getTasksAssigned().size());
+        taskRequests = new ArrayList<>();
+        schedulingResult = taskScheduler.scheduleOnce(taskRequests, leases);
+        Assert.assertEquals(0, schedulingResult.getResultMap().size());
+    }
 }