alluxio.time

Class ExponentialTimer

java.lang.Object

alluxio.time.ExponentialTimer

public class ExponentialTimer
extends 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 and Description
static class	ExponentialTimer.Result Represents the result of tick().

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method and 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