Task (io.druid:druid 0.12.0 API)

All Known Implementing Classes:

AbstractFixedIntervalTask, AbstractTask, AppendTask, ArchiveTask, CompactionTask, ConvertSegmentBackwardsCompatibleTask, ConvertSegmentBackwardsCompatibleTask.SubTask, ConvertSegmentTask, ConvertSegmentTask.SubTask, HadoopConverterTask, HadoopConverterTask.ConverterSubTask, HadoopIndexTask, HadoopTask, IndexTask, KafkaIndexTask, KillTask, MergeTask, MergeTaskBase, MoveTask, NoopTask, RealtimeIndexTask, RestoreTask, SameIntervalMergeTask, SameIntervalMergeTask.SubTask
```
public interface Task
```
Represents a task that can run on a worker. The general contracts surrounding Tasks are:
- Tasks must operate on a single datasource.
- Tasks should be immutable, since the task ID is used as a proxy for the task in many locations.
- Task IDs must be unique. This can be done by naming them using UUIDs or the current timestamp.
- Tasks are each part of a "task group", which is a set of tasks that can share interval locks. These are useful for producing sharded segments.
- Tasks do not need to explicitly release locks; they are released upon task completion. Tasks may choose to release locks early if they desire.

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`boolean`	`canRestore()` Returns whether or not this task can restore its progress from its on-disk working directory.
`String`	`getClasspathPrefix()` Returns an extra classpath that should be prepended to the default classpath when running this task.
`Map<String,Object>`	`getContext()`
`default <ContextValueType> ContextValueType`	`getContextValue(String key)`
`default <ContextValueType> ContextValueType`	`getContextValue(String key, ContextValueType defaultValue)`
`String`	`getDataSource()` Returns the datasource this task operates on.
`String`	`getGroupId()` Returns group ID of this task.
`String`	`getId()` Returns ID of this task.
`String`	`getNodeType()` Get the nodeType for if/when this task publishes on zookeeper.
`default int`	`getPriority()` Returns task priority.
`<T> QueryRunner<T>`	`getQueryRunner(Query<T> query)` Returns query runners for this task.
`TaskResource`	`getTaskResource()` Returns a `TaskResource` for this task.
`String`	`getType()` Returns a descriptive label for this task type.
`boolean`	`isReady(TaskActionClient taskActionClient)` Execute preflight actions for a task.
`TaskStatus`	`run(TaskToolbox toolbox)` Execute a task.
`void`	`stopGracefully()` Asks a task to arrange for its "run" method to exit promptly.

- Method Detail
  - getId
```
String getId()
```
    Returns ID of this task. Must be unique across all tasks ever created.
    
    Returns:
    
    task ID
  - getGroupId
```
String getGroupId()
```
    Returns group ID of this task. Tasks with the same group ID can share locks. If tasks do not need to share locks, a common convention is to set group ID equal to task ID.
    
    Returns:
    
    task group ID
  - getPriority
```
default int getPriority()
```
    Returns task priority. The task priority is currently used only for prioritized locking, but, in the future, it can be used for task scheduling, cluster resource management, etc.
    
    Returns:
    
    task priority
    
    See Also:
    
    for default task priorities
  - getTaskResource
```
TaskResource getTaskResource()
```
    Returns a TaskResource for this task. Task resources define specific worker requirements a task may require.
    
    Returns:
    
    TaskResource for this task
  - getType
```
String getType()
```
    Returns a descriptive label for this task type. Used for metrics emission and logging.
    
    Returns:
    
    task type label
  - getNodeType
```
String getNodeType()
```
    Get the nodeType for if/when this task publishes on zookeeper.
    
    Returns:
    
    the nodeType to use when publishing the server to zookeeper. null if the task doesn't expect to publish to zookeeper.
  - getDataSource
```
String getDataSource()
```
    Returns the datasource this task operates on. Each task can operate on only one datasource.
  - getQueryRunner
```
<T> QueryRunner<T> getQueryRunner(Query<T> query)
```
    Returns query runners for this task. If this task is not meant to answer queries over its datasource, this method should return null.
    
    Type Parameters:
    
    T - query result type
    
    Returns:
    
    query runners for this task
  - getClasspathPrefix
```
String getClasspathPrefix()
```
    Returns an extra classpath that should be prepended to the default classpath when running this task. If no extra classpath should be prepended, this should return null or the empty string.
  - isReady
```
boolean isReady(TaskActionClient taskActionClient)
         throws Exception
```
    Execute preflight actions for a task. This can be used to acquire locks, check preconditions, and so on. The actions must be idempotent, since this method may be executed multiple times. This typically runs on the coordinator. If this method throws an exception, the task should be considered a failure.
    This method must be idempotent, as it may be run multiple times per task.
    
    Parameters:
    
    taskActionClient - action client for this task (not the full toolbox)
    
    Returns:
    
    true if ready, false if not ready yet
    
    Throws:
    
    Exception - if the task should be considered a failure
  - canRestore
```
boolean canRestore()
```
    Returns whether or not this task can restore its progress from its on-disk working directory. Restorable tasks may be started with a non-empty working directory. Tasks that exit uncleanly may still have a chance to attempt restores, meaning that restorable tasks should be able to deal with potentially partially written on-disk state.
  - stopGracefully
```
void stopGracefully()
```
    Asks a task to arrange for its "run" method to exit promptly. This method will only be called if canRestore() returns true. Tasks that take too long to stop gracefully will be terminated with extreme prejudice.
  - run
```
TaskStatus run(TaskToolbox toolbox)
        throws Exception
```
    Execute a task. This typically runs on a worker as determined by a TaskRunner, and will be run while holding a lock on our dataSource and implicit lock interval (if any). If this method throws an exception, the task should be considered a failure.
    
    Parameters:
    
    toolbox - Toolbox for this task
    
    Returns:
    
    Some kind of finished status (isRunnable must be false).
    
    Throws:
    
    Exception - if this task failed
  - getContext
```
Map<String,Object> getContext()
```
  - getContextValue
```
@Nullable
default <ContextValueType> ContextValueType getContextValue(String key)
```
  - getContextValue
```
default <ContextValueType> ContextValueType getContextValue(String key,
                                                            ContextValueType defaultValue)
```

Interface Task

Method Summary

Method Detail

getId

getGroupId

getPriority

getTaskResource

getType

getNodeType

getDataSource

getQueryRunner

getClasspathPrefix

isReady

canRestore

stopGracefully

run

getContext

getContextValue

getContextValue