Fix over acquiring of tasks in MultiThreadAgent

Fixes #487.

digdag-core/src/main/java/io/digdag/core/agent/MultiThreadAgent.java

@@ -5,6 +5,9 @@
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.BlockingQueue;
 import java.time.Duration;
 import com.google.common.base.Optional;
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
@@ -23,8 +26,11 @@ public class MultiThreadAgent
     private final TaskServerApi taskServer;
     private final OperatorManager runner;
     private final ErrorReporter errorReporter;
-    private final ThreadPoolExecutor executor;
+
     private final Object newTaskLock = new Object();
+    private final BlockingQueue<Runnable> executorQueue;
+    private final ThreadPoolExecutor executor;
+
     private volatile boolean stop = false;
 
     public MultiThreadAgent(
@@ -37,15 +43,28 @@ public MultiThreadAgent(
         this.taskServer = taskServer;
         this.runner = runner;
         this.errorReporter = errorReporter;
+
         ThreadFactory threadFactory = new ThreadFactoryBuilder()
             .setDaemon(false)  // make them non-daemon threads so that shutting down agent doesn't kill operator execution
             .setNameFormat("task-thread-%d")
             .build();
+
         if (config.getMaxThreads() > 0) {
-            this.executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(config.getMaxThreads(), threadFactory);
+            this.executorQueue = new LinkedBlockingQueue<Runnable>();
+            this.executor = new ThreadPoolExecutor(
+                    0, config.getMaxThreads(),
+                    60L, TimeUnit.SECONDS,
+                    executorQueue, threadFactory);
         }
         else {
-            this.executor = (ThreadPoolExecutor) Executors.newCachedThreadPool(threadFactory);
+            // If there're no upper limit on number of threads, queue actually doesn't need to store entries.
+            // Instead, executor.submit() blocks until a thread starts and takes it.
+            // SynchronousQueue.size() always returns 0.
+            this.executorQueue = new SynchronousQueue<Runnable>();
+            this.executor = new ThreadPoolExecutor(
+                    0, Integer.MAX_VALUE,
+                    60L, TimeUnit.SECONDS,
+                    executorQueue, threadFactory);
         }
     }
 
@@ -54,15 +73,15 @@ public void shutdown(Optional<Duration> maximumCompletionWait)
     {
         stop = true;
         taskServer.interruptLocalWait();
-        int activeCount;
+        int maximumPossibleActiveTaskCount;
         synchronized (newTaskLock) {
             // synchronize newTaskLock not to reject task execution after acquiring them from taskServer
             executor.shutdown();
-            activeCount = executor.getActiveCount();
+            maximumPossibleActiveTaskCount = executorQueue.size() + executor.getActiveCount();
             newTaskLock.notifyAll();
         }
-        if (activeCount > 0) {
-            logger.info("Waiting for completion of {} running tasks...", activeCount);
+        if (maximumPossibleActiveTaskCount > 0) {
+            logger.info("Waiting for completion of {} running tasks...", maximumPossibleActiveTaskCount);
         }
         if (maximumCompletionWait.isPresent()) {
             long seconds = maximumCompletionWait.get().getSeconds();
@@ -86,9 +105,11 @@ public void run()
                     if (executor.isShutdown()) {
                         break;
                     }
-                    int max = Math.min(executor.getMaximumPoolSize() - executor.getActiveCount(), 10);
-                    if (max > 0) {
-                        List<TaskRequest> reqs = taskServer.lockSharedAgentTasks(max, agentId, config.getLockRetentionTime(), 1000);
+                    int maximumPossibleActiveTaskCount = executorQueue.size() + executor.getActiveCount();
+                    int guaranteedAvaialbleThreads = executor.getMaximumPoolSize() - maximumPossibleActiveTaskCount;
+                    int maxAcquire = Math.min(guaranteedAvaialbleThreads, 10);
+                    if (maxAcquire > 0) {
+                        List<TaskRequest> reqs = taskServer.lockSharedAgentTasks(maxAcquire, agentId, config.getLockRetentionTime(), 1000);
                         for (TaskRequest req : reqs) {
                             executor.submit(() -> {
                                 try {

digdag-tests/src/test/java/acceptance/AgentOverAcquireIT.java

@@ -0,0 +1,62 @@
+package acceptance;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assume.assumeThat;
+import static utils.TestUtils.copyResource;
+import static utils.TestUtils.main;
+import utils.CommandStatus;
+
+public class AgentOverAcquireIT
+{
+    @Rule
+    public TemporaryFolder folder = new TemporaryFolder();
+
+    private Path projectDir;
+    private Path config;
+    private Path outdir;
+
+    @Before
+    public void setUp()
+            throws Exception
+    {
+        projectDir = folder.getRoot().toPath();
+        config = folder.newFile().toPath();
+
+        outdir = projectDir.resolve("outdir");
+        Files.createDirectories(outdir);
+    }
+
+    @Test
+    public void testOverAcquire()
+            throws Exception
+    {
+        assumeThat(true, is(false));  // disabled by default to avoid too long execution time.
+
+        copyResource("acceptance/over_acquire/over_acquire.dig", projectDir.resolve("over_acquire.dig"));
+
+        CommandStatus runStatus = main("run",
+                "-o", projectDir.toString(),
+                "--config", config.toString(),
+                "--project", projectDir.toString(),
+                "-X", "agent.heartbeat-interval=10",
+                "-X", "agent.lock-retention-time=20",
+                "-X", "agent.max-task-threads=5",
+                "-p", "outdir=" + outdir,
+                "over_acquire.dig");
+        assertThat(runStatus.errUtf8(), runStatus.code(), is(0));
+
+        for (int i = 0; i < 20; i++) {
+            String one = new String(Files.readAllBytes(outdir.resolve(Integer.toString(i))), UTF_8);
+            assertThat(one, is("1"));
+        }
+    }
+}

digdag-tests/src/test/resources/acceptance/over_acquire/over_acquire.dig

@@ -0,0 +1,7 @@
+
++loop:
+  loop>: 20
+  _parallel: true
+  _do:
+    sh>: sleep 30 && /bin/echo -n 1 >> ${outdir}/${i}
+