PeriodicTaskExceptionHandler (LSST CCS

java.lang.Object
- org.lsst.ccs.utilities.scheduler.PeriodicTaskExceptionHandler

```
public class PeriodicTaskExceptionHandler
extends Object
```
Defines behavior of PeriodicTask under abnormal circumstances. Setters provided by this class can be used to establish policies the periodic task should follow when it throws an exception or runs for an unusually long time. Callback methods onXXX(PeriodicTask task, ... can be overridden to execute client code under these circumstances. They should be implemented to finish quickly, any time consuming or potentially blocking operations should be offloaded to other threads. Default implementations provided by this class log messages at the level set through a call to setLevel(...) or inherited from the Scheduler where the task runs.
Sample Usage. The following code sketch creates a fixed rate task that will skip execution if the previous one has not finished, log a message if an execution is taking longer than the task period, and quit after 2 failures.
```
 
 Scheduler scheduler = new Scheduler("tester", 1);
 ...
 PeriodicTaskExceptionHandler exceptionHandler = new PeriodicTaskExceptionHandler() {
     public void onLongExecution(PeriodicTask task) {
         Logger logger = task.getLogger();
         if (logger != null) {
             logger.log(getLevel(), "Task "+ task.getTaskName() +" is taking more than its period.", (Object[])null);
         }
         alertOperator();
     }
 };
 exceptionHandler.setSkipOverdueExecutions(true);
 exceptionHandler.setDetectLongExecutions(true);
 exceptionHandler.setMaxFailures(2);
 exceptionHandler.setResetFailureCountOnSuccess(false);
 scheduler.scheduleAtFixedRate(command, 0, 1, TimeUnit.SECONDS, "Task name", exceptionHandler);
 ...
 
```
Author:

onoprien

Constructor Summary

Constructors
Constructor and Description

PeriodicTaskExceptionHandler()

Constructors
Constructor and Description
`PeriodicTaskExceptionHandler()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Level`	`getLevel()`
`int`	`getMaxFailures()`
`boolean`	`isDetectLongExecutions()`
`boolean`	`isResetFailureCountOnSuccess()`
`boolean`	`isSkipOverdueExecutions()`
`void`	`onException(PeriodicTask task, Throwable exception)` Called when a task throws an exception, but is not going to be terminated.
`void`	`onFinalException(PeriodicTask task, Throwable exception)` Called when a task throws an exception, and is going to be terminated.
`void`	`onLongExecution(PeriodicTask task)` Called when an execution that takes longer than the task period is detected.
`void`	`onSkippedExecutions(PeriodicTask task, int nSkipped)` Called when a fixed rate task executes after skipping one or more previous executions that could not start on time.
`void`	`setDetectLongExecutions(boolean detectLongExecutions)` Sets a policy on whether or not executions that take longer than the task period to complete should be detected and `onLongExecution(...)` called.
`void`	`setLevel(Level level)` Sets logging level.
`void`	`setMaxFailures(int maxFailures)` Sets the number of times the task can throw an exception before it is terminated.
`void`	`setResetFailureCountOnSuccess(boolean resetFailureCountOnSuccess)` Sets a policy on whether or not only consecutive failures should be counted towards the allowed maximum.
`void`	`setSkipOverdueExecutions(boolean skipOverdueExecutions)` Sets a policy on skipping executions that cannot start on time.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - PeriodicTaskExceptionHandler
```
public PeriodicTaskExceptionHandler()
```
- Method Detail
  - setSkipOverdueExecutions
```
public void setSkipOverdueExecutions(boolean skipOverdueExecutions)
```
    Sets a policy on skipping executions that cannot start on time. This flag is only relevant for fixed rate tasks, and can be set to true to prevent executions from piling up when a previous execution takes a long time, and then running in rapid succession when it finally finishes. This option is usually not suitable for task periods less than 100 milliseconds. The default is false.
    
    Parameters:
    
    skipOverdueExecutions - If true, executions that cannot start on time are skipped.
  - setDetectLongExecutions
```
public void setDetectLongExecutions(boolean detectLongExecutions)
```
    Sets a policy on whether or not executions that take longer than the task period to complete should be detected and onLongExecution(...) called. Note that setting this flag to true adds significant overhead, and is usually not suitable for task periods less than 100 milliseconds. The default is false.
    
    Parameters:
    
    detectLongExecutions - true if long executions should be detected.
  - setMaxFailures
```
public void setMaxFailures(int maxFailures)
```
    Sets the number of times the task can throw an exception before it is terminated.
    
    Parameters:
    
    maxFailures - Allowed number of failures.
  - setResetFailureCountOnSuccess
```
public void setResetFailureCountOnSuccess(boolean resetFailureCountOnSuccess)
```
    Sets a policy on whether or not only consecutive failures should be counted towards the allowed maximum. The default is true.
    
    Parameters:
    
    resetFailureCountOnSuccess - If true, only consecutive failures are counted towards the allowed maximum.
  - setLevel
```
public void setLevel(Level level)
```
    Sets logging level.
    
    Parameters:
    
    level - Level.
  - isSkipOverdueExecutions
```
public boolean isSkipOverdueExecutions()
```
  - isDetectLongExecutions
```
public boolean isDetectLongExecutions()
```
  - getMaxFailures
```
public int getMaxFailures()
```
  - isResetFailureCountOnSuccess
```
public boolean isResetFailureCountOnSuccess()
```
  - getLevel
```
public Level getLevel()
```
  - onSkippedExecutions
```
public void onSkippedExecutions(PeriodicTask task,
                                int nSkipped)
```
    Called when a fixed rate task executes after skipping one or more previous executions that could not start on time. The default implementation logs a message.
    
    Parameters:
    
    task - Periodic task.
    
    nSkipped - Number of skipped executions.
  - onLongExecution
```
public void onLongExecution(PeriodicTask task)
```
    Called when an execution that takes longer than the task period is detected. This method is only called if detectLongExecutions property has been set to true. The default implementation logs a message.
    
    Parameters:
    
    task - Periodic task.
  - onException
```
public void onException(PeriodicTask task,
                        Throwable exception)
```
    Called when a task throws an exception, but is not going to be terminated. If this method throws an exception, the task will terminate. The default implementation logs a message.
    
    Parameters:
    
    task - Periodic task.
    
    exception - Thrown exception.
  - onFinalException
```
public void onFinalException(PeriodicTask task,
                             Throwable exception)
```
    Called when a task throws an exception, and is going to be terminated. The default implementation logs a message.
    
    Parameters:
    
    task - Periodic task.
    
    exception - Thrown exception.

Class PeriodicTaskExceptionHandler

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

PeriodicTaskExceptionHandler

Method Detail

setSkipOverdueExecutions

setDetectLongExecutions

setMaxFailures

setResetFailureCountOnSuccess

setLevel

isSkipOverdueExecutions

isDetectLongExecutions

getMaxFailures

isResetFailureCountOnSuccess

getLevel

onSkippedExecutions

onLongExecution

onException

onFinalException