org.apache.http.impl.client.cache
Class ExponentialBackOffSchedulingStrategy

java.lang.Object
  org.apache.http.impl.client.cache.ExponentialBackOffSchedulingStrategy

All Implemented Interfaces:

Closeable, SchedulingStrategy

@ThreadSafe
public class ExponentialBackOffSchedulingStrategy
extends Object
implements SchedulingStrategy

An implementation that backs off exponentially based on the number of consecutive failed attempts stored in the AsynchronousValidationRequest. It uses the following defaults:

         no delay in case it was never tried or didn't fail so far
     6 secs delay for one failed attempt (= getInitialExpiryInMillis())
    60 secs delay for two failed attempts
    10 mins delay for three failed attempts
   100 mins delay for four failed attempts
  ~16 hours delay for five failed attempts
   24 hours delay for six or more failed attempts (= getMaxExpiryInMillis())
 

The following equation is used to calculate the delay for a specific revalidation request:

     delay = getInitialExpiryInMillis() * Math.pow(getBackOffRate(), AsynchronousValidationRequest#getConsecutiveFailedAttempts() - 1))
 

The resulting delay won't exceed getMaxExpiryInMillis().

Since:

4.3

Field Summary

static long	DEFAULT_BACK_OFF_RATE
static long	DEFAULT_INITIAL_EXPIRY_IN_MILLIS
static long	DEFAULT_MAX_EXPIRY_IN_MILLIS

Constructor Summary

ExponentialBackOffSchedulingStrategy(CacheConfig cacheConfig)
Create a new scheduling strategy using a fixed pool of worker threads.

ExponentialBackOffSchedulingStrategy(CacheConfig cacheConfig, long backOffRate, long initialExpiryInMillis, long maxExpiryInMillis)
Create a new scheduling strategy by using a fixed pool of worker threads and the given parameters to calculated the delay.

Method Summary

protected long	calculateDelayInMillis(int consecutiveFailedAttempts)
protected static long	checkNotNegative(String parameterName, long value)
protected static <T> T	checkNotNull(String parameterName, T value)
void	close()
long	getBackOffRate()
long	getInitialExpiryInMillis()
long	getMaxExpiryInMillis()
void	schedule(org.apache.http.impl.client.cache.AsynchronousValidationRequest revalidationRequest) Schedule an AsynchronousValidationRequest to be executed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_BACK_OFF_RATE

public static final long DEFAULT_BACK_OFF_RATE

See Also:

Constant Field Values

DEFAULT_INITIAL_EXPIRY_IN_MILLIS

public static final long DEFAULT_INITIAL_EXPIRY_IN_MILLIS

DEFAULT_MAX_EXPIRY_IN_MILLIS

public static final long DEFAULT_MAX_EXPIRY_IN_MILLIS

Constructor Detail

ExponentialBackOffSchedulingStrategy

public ExponentialBackOffSchedulingStrategy(CacheConfig cacheConfig)

Create a new scheduling strategy using a fixed pool of worker threads.

Parameters:

cacheConfig - the thread pool configuration to be used; not null

See Also:

CacheConfig.getAsynchronousWorkersMax(), DEFAULT_BACK_OFF_RATE, DEFAULT_INITIAL_EXPIRY_IN_MILLIS, DEFAULT_MAX_EXPIRY_IN_MILLIS

ExponentialBackOffSchedulingStrategy

public ExponentialBackOffSchedulingStrategy(CacheConfig cacheConfig,
                                            long backOffRate,
                                            long initialExpiryInMillis,
                                            long maxExpiryInMillis)

Create a new scheduling strategy by using a fixed pool of worker threads and the given parameters to calculated the delay.

Parameters:

cacheConfig - the thread pool configuration to be used; not null

backOffRate - the back off rate to be used; not negative

initialExpiryInMillis - the initial expiry in milli seconds; not negative

maxExpiryInMillis - the upper limit of the delay in milli seconds; not negative

See Also:

CacheConfig.getAsynchronousWorkersMax(), ExponentialBackOffSchedulingStrategy

Method Detail

schedule

public void schedule(org.apache.http.impl.client.cache.AsynchronousValidationRequest revalidationRequest)

Description copied from interface: SchedulingStrategy

Schedule an AsynchronousValidationRequest to be executed.

Specified by:

schedule in interface SchedulingStrategy

Parameters:

revalidationRequest - the request to be executed; not null

close

public void close()

Specified by:

close in interface Closeable

getBackOffRate

public long getBackOffRate()

getInitialExpiryInMillis

public long getInitialExpiryInMillis()

getMaxExpiryInMillis

public long getMaxExpiryInMillis()

calculateDelayInMillis

protected long calculateDelayInMillis(int consecutiveFailedAttempts)

checkNotNull

protected static <T> T checkNotNull(String parameterName,
                                    T value)

checkNotNegative

protected static long checkNotNegative(String parameterName,
                                       long value)