[GitHub] [samza] Sanil15 commented on a change in pull request #1227: SAMZA-2404: Container Placement Handler for dispatching container placement messages between metastore and JobCoordinator

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Sanil15 commented on a change in pull request #1227: SAMZA-2404: Container Placement Handler for dispatching container placement messages between metastore and JobCoordinator
URL: https://github.com/apache/samza/pull/1227#discussion_r353470304
 
 

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 File path: samza-core/src/main/java/org/apache/samza/clustermanager/container/placement/ContainerPlacementHandler.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.samza.clustermanager.container.placement;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import org.apache.commons.lang3.ArrayUtils;
+import org.apache.samza.SamzaException;
+import org.apache.samza.clustermanager.ContainerProcessManager;
+import org.apache.samza.container.placement.ContainerPlacementMessage;
+import org.apache.samza.container.placement.ContainerPlacementRequestMessage;
+import org.apache.samza.container.placement.ContainerPlacementResponseMessage;
+import org.apache.samza.coordinator.metadatastore.NamespaceAwareCoordinatorStreamStore;
+import org.apache.samza.metadatastore.MetadataStore;
+import org.codehaus.jackson.map.ObjectMapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Stateless handler that dispatches {@link ContainerPlacementRequestMessage} read from {@link MetadataStore} to Job Coordinator
+ * and writes responses {@link org.apache.samza.container.placement.ContainerPlacementResponseMessage} from Job Coordinator
+ * to Metastore.
+ *
+ * {@link ContainerPlacementRequestMessage} are written under namespace {@code REQUEST_STORE_NAMESPACE}
+ * {@link ContainerPlacementResponseMessage} are written under namespace {@code RESPONSE_STORE_NAMESPACE}
+ */
+public class ContainerPlacementHandler implements Runnable {
+
+  private static final Logger LOG = LoggerFactory.getLogger(ContainerPlacementHandler.class);
+
+  private static final Integer VERSION = 1;
+  public static final String REQUEST_STORE_NAMESPACE = "samza-request-place-container-v" + VERSION;
+  public static final String RESPONSE_STORE_NAMESPACE = "samza-response-place-container-v" + VERSION;
+
+  private final NamespaceAwareCoordinatorStreamStore requestStore;
+  private final NamespaceAwareCoordinatorStreamStore responseStore;
+  /**
+   * {@link ContainerProcessManager} needs to intercept container placement actions between ContainerPlacementHandler and
+   * {@link org.apache.samza.clustermanager.ContainerManager} to avoid cyclic dependency between
+   * {@link org.apache.samza.clustermanager.ContainerManager} and {@link org.apache.samza.clustermanager.ContainerAllocator}
+   */
+  private final Optional<ContainerProcessManager> containerProcessManager;
+  private final Optional<Integer> containerPlacementHandlerSleepMs;
+
+  private final ObjectMapper objectMapper = ContainerPlacementMessageObjectMapper.getObjectMapper();
+
+  /**
+   * State that controls the lifecycle of the ContainerPlacementHandler thread
+   */
+  private volatile boolean isRunning;
+
+  private ContainerPlacementHandler(MetadataStore metadataStore, Optional<ContainerProcessManager> manager,
+      Optional<Integer> containerPlacementHandlerSleepMs) {
+    Preconditions.checkNotNull(metadataStore, "MetadataStore cannot be null");
+    if (manager.isPresent()) {
+      Preconditions.checkNotNull(manager.get(), "ContainerProcessManager cannot be null");
+      Preconditions.checkState(containerPlacementHandlerSleepMs.isPresent());
+    }
+    this.containerProcessManager = manager;
+    this.requestStore = new NamespaceAwareCoordinatorStreamStore(metadataStore, REQUEST_STORE_NAMESPACE);
+    this.responseStore = new NamespaceAwareCoordinatorStreamStore(metadataStore, RESPONSE_STORE_NAMESPACE);
+    this.requestStore.init();
+    this.responseStore.init();
+    this.containerPlacementHandlerSleepMs = containerPlacementHandlerSleepMs;
+    this.isRunning = true;
+  }
+
+  public ContainerPlacementHandler(MetadataStore metadataStore) {
+    this(metadataStore, Optional.empty(), Optional.empty());
+  }
+
+  public ContainerPlacementHandler(MetadataStore metadataStore, ContainerProcessManager manager, Integer containerPlacementHandlerSleepMs) {
+    this(metadataStore, Optional.of(manager), Optional.of(containerPlacementHandlerSleepMs));
+  }
+
+  @Override
+  public void run() {
+    while (isRunning && containerProcessManager.isPresent()) {
+      try {
+        for (ContainerPlacementRequestMessage message : readAllContainerPlacementRequestMessages()) {
+          // We do not need to dispatch ContainerPlacementResponseMessage because they are written from JobCoordinator
+          // in response to a Container Placement Action
+          LOG.info("Received a container placement message {}", message);
+          containerProcessManager.get().registerContainerPlacementAction(message);
+        }
+        Thread.sleep(containerPlacementHandlerSleepMs.get());
+      } catch (InterruptedException e) {
+        LOG.warn("Got InterruptedException in ContainerPlacementHandler thread.", e);
+        Thread.currentThread().interrupt();
+      } catch (Exception e) {
+        LOG.error(
+            "Got unknown Exception while registering ContainerPlacement actions in ContainerPlacementHandler thread.",
+            e);
+      }
+    }
+  }
+
+  /**
+   * Writes a {@link ContainerPlacementRequestMessage} to the underlying metastore. This method should be used by external controllers
+   * to issue a request to JobCoordinator
+   * @param message container placement request
+   */
+  public void writeContainerPlacementRequestMessage(ContainerPlacementRequestMessage message) {
+    Preconditions.checkState(isRunning, "Underlying metadata store not available");
+    Preconditions.checkNotNull(message);
+    try {
+      requestStore.put(message.getProcessorId(), objectMapper.writeValueAsBytes(message));
+    } catch (Exception ex) {
+      throw new SamzaException(
+          String.format("ContainerPlacementRequestMessage might have been not written to metastore %s", message), ex);
+    }
+  }
+
+  /**
+   * Writes a {@link ContainerPlacementResponseMessage} to the underlying metastore. This method should be used by external controllers
+   * to issue a request to JobCoordinator
+   * @param message
+   */
+  public void writeContainerPlacementResponseMessage(ContainerPlacementResponseMessage message) {
 
 Review comment:
   Good catch, I will change the visibility to default!

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