[Offline Nodes] Adds new library offline tasks

libs/offline-tasks/build.gradle

@@ -0,0 +1,25 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ *
+ * Modifications Copyright OpenSearch Contributors. See
+ * GitHub history for details.
+ */
+
+dependencies {
+  api project(':libs:opensearch-common')
+
+  testImplementation "com.carrotsearch.randomizedtesting:randomizedtesting-runner:${versions.randomizedrunner}"
+  testImplementation "junit:junit:${versions.junit}"
+  testImplementation "org.hamcrest:hamcrest:${versions.hamcrest}"
+  testImplementation(project(":test:framework")) {
+    exclude group: 'org.opensearch', module: 'opensearch-offline-tasks'
+  }
+}
+
+tasks.named('forbiddenApisMain').configure {
+  replaceSignatureFiles 'jdk-signatures'
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/Task.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.offline_tasks;
+
+/**
+ * A Background Task to be run on Offline Node.
+ */
+public class Task {
+
+    /**
+     * Task identifier used to uniquely identify a Task
+     */
+    private TaskId taskId;
+
+    /**
+     * Various params to used for Task execution
+     */
+    private TaskParams params;
+
+    /**
+     * Type/Category of the Task
+     */
+    private TaskType taskType;
+
+    /**
+     * Constructor for Task
+     *
+     * @param taskId Task identifier
+     * @param params Task Params
+     * @param taskType Task Type
+     */
+    public Task(TaskId taskId, TaskParams params, TaskType taskType) {
+        this.taskId = taskId;
+        this.params = params;
+        this.taskType = taskType;
+    }
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/TaskClient.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.offline_tasks;
+
+import org.opensearch.common.annotation.ExperimentalApi;
+
+import java.util.List;
+
+/**
+ * Client used to interact with Task Store/Queue
+ *
+ * @opensearch.experimental
+ */
+@ExperimentalApi
+public interface TaskClient {
+
+    /**
+     * Submit a new task to Task Store/Queue
+     *
+     * @param task
+     */
+    void submitTask(Task task);
+
+    /**
+     * Claim task from Task Store/Queue. This ensure no 2 nodes work on the same task.
+     *
+     * @param taskId
+     */
+    void claimTask(TaskId taskId);
+
+    /**
+     * Get task from Task Store/Queue
+     *
+     * @param taskId
+     * @return
+     */
+    Task getTask(TaskId taskId);
+
+    /**
+     * Update task in Task Store/Queue
+     *
+     * @param task
+     * @return
+     */
+    Task updateTask(Task task);
+
+    /**
+     * Mark task as cancelled
+     *
+     * @param taskId
+     */
+    void cancelTask(TaskId taskId);
+
+    /**
+     * List all unassigned tasks
+     *
+     * @return
+     */
+    List<Task> getUnassignedTasks();
+
+    /**
+     * List all active tasks
+     *
+     * @return
+     */
+    List<Task> getActiveTasks();
+
+    /**
+     * List all completed tasks
+     *
+     * @return
+     */
+    List<Task> getCompletedTasks();
+
+    /**
+     * Sends task heart beat to Task Store/Queue
+     *
+     * @param taskId
+     * @param timestamp
+     */
+    void sendTaskHeartbeat(TaskId taskId, long timestamp);
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/TaskId.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.offline_tasks;
+
+/**
+ * Class encapsulating Task id
+ */
+public class TaskId {
+
+    /**
+     * Id of the Task
+     */
+    String id;
+
+    public TaskId(String id) {
+        this.id = id;
+    }
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/TaskParams.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.offline_tasks;
+
+/**
+ * Base class for all TaskParams implementation of various TaskTypes
+ */
+public abstract class TaskParams {
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/TaskType.java

@@ -0,0 +1,24 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.offline_tasks;
+
+/**
+ * Enum for task type
+ */
+public enum TaskType {
+    /**
+     * For all segment merge related tasks
+     */
+    MERGE,
+
+    /**
+     * For all snapshot related tasks
+     */
+    SNAPSHOT
+}

libs/offline-tasks/src/main/java/org/opensearch/offline_tasks/package-info.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+/**
+ * Contains telemetry related classes
+ */
+package org.opensearch.offline_tasks;