ExponentialTimer (Alluxio Core - Common Utilities 294 API)

java.lang.Object
- alluxio.time.ExponentialTimer

```
public class ExponentialTimer
extends java.lang.Object
```
The ExponentialTimer can be used for generating a sequence of events that are exponentially distributed in time. The intended usage is to associate the timer with an operation that should to be re-attempted if it fails using exponential back-off. For instance, an event loop iterates over scheduled operations each of which is associated with a timer and the event loop can use the timer to check if the operation is ready to be attempted and whether it should be re-attempted again in the future in case it fails.
```
 while (true) {
   Operation op = operations.pop();
   switch (op.getTimer().tick()) {
   case EXPIRED:
     // operation will not be re-attempted
     break;
   case NOT_READY:
     // operation is not ready to be re-attempted
     operations.push(op);
     break;
   case READY:
     boolean success = op.run();
     if (!success) {
       operations.push(op);
     }
   }
   Thread.sleep(10);
 }
 
```
Note that in the above scenario, the ExponentialBackoffRetry policy cannot be used because the RetryPolicy#attemptRetry() is blocking.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static class ExponentialTimer.Result
Represents the result of tick().

Constructor Summary

Constructors
Constructor	Description
`ExponentialTimer(long initialIntervalMs, long maxIntervalMs, long initialWaitTimeMs, long maxTotalWaitTimeMs)`	Creates a new instance of `ExponentialTimer`.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type Method Description

long getNumEvents()

ExponentialTimer.Result tick()
Attempts to perform a timer tick.
- Methods inherited from class java.lang.Object
  clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - ExponentialTimer
```
public ExponentialTimer(long initialIntervalMs,
                        long maxIntervalMs,
                        long initialWaitTimeMs,
                        long maxTotalWaitTimeMs)
```
    Creates a new instance of ExponentialTimer.
    
    Parameters:
    
    initialIntervalMs - the initial interval between events (in milliseconds)
    
    maxIntervalMs - the maximum interval between events (in milliseconds)
    
    initialWaitTimeMs - the initial wait time before first event (in milliseconds)
    
    maxTotalWaitTimeMs - the maximum total wait time (in milliseconds)
- Method Detail
  - getNumEvents
```
public long getNumEvents()
```
    Returns:
    
    the number of generated events so far
  - tick
```
public ExponentialTimer.Result tick()
```
    Attempts to perform a timer tick. One of three scenarios can be encountered: 1. the timer has expired 2. the next event is not ready 3. the next event is generated The last option has the side-effect of updating the internal state of the timer to reflect the generation of the event.
    
    Returns:
    
    the ExponentialTimer.Result that indicates which scenario was encountered