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

java.lang.Object
  extended by org.apache.http.impl.client.cache.ExponentialBackOffSchedulingStrategy
All Implemented Interfaces:
Closeable, SchedulingStrategy

@Contract(threading=SAFE)
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)
          Deprecated. Use Args.notNegative(long, String)
protected static
<T> T
checkNotNull(String parameterName, T value)
          Deprecated. Use Args.notNull(Object, String)
 void close()
           
 long getBackOffRate()
           
 long getInitialExpiryInMillis()
           
 long getMaxExpiryInMillis()
           
 void schedule(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(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

@Deprecated
protected static <T> T checkNotNull(String parameterName,
                                               T value)
Deprecated. Use Args.notNull(Object, String)


checkNotNegative

@Deprecated
protected static long checkNotNegative(String parameterName,
                                                  long value)
Deprecated. Use Args.notNegative(long, String)



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