Created
October 20, 2011 08:20
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request throttler based on http://1-800-magic.blogspot.com/2008/02/throttling-requests-java.html
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/** | |
* Class that throttles requests. Ensures that the StartRequest cannot be called | |
* more than a given amount of time in any given interval. | |
* | |
* StartRequest blocks until this requirement is satisfied. | |
* | |
* TryStartRequest returns 0 if the request was cleared, or a non-0 number of | |
* millisecond to sleep before the next attempt. | |
* | |
* Simple usage, 10 requests per second: | |
* | |
* Throttler t = new Throttler(10, 1000); ... ServiceRequest(Throtter t, ...) { | |
* t.StartRequest(); .. do work .. | |
* | |
* @author sergey@solyanik.com (Sergey Solyanik) | |
* http://1-800-magic.blogspot.com/2008/02/throttling-requests-java.html | |
* | |
*/ | |
public class RequestThrottler { | |
/** | |
* The interval within we're ensuring max number of calls. | |
*/ | |
private final long _interval; | |
/** | |
* The maximum number of calls that can be made within the interval. | |
*/ | |
private final int _maxCalls; | |
/** | |
* Previous calls within the interval. | |
*/ | |
private final long[] _ticks; | |
/** | |
* Available element at the insertion point (back of the queue). | |
*/ | |
private int _tickNext; | |
/** | |
* Element at the removal point (front of the queue). | |
*/ | |
private int _tickLast; | |
/** | |
* the time when the last expired request occured. might be used to auto | |
* disable some services all together | |
*/ | |
private long _lastExpiredMaxWait = 0; | |
/** | |
* Constructor. | |
* | |
* @param maxCalls | |
* Max number of calls that can be made within the interval. | |
* @param interval | |
* The interval. | |
*/ | |
public RequestThrottler(final int maxCalls, final long interval) { | |
if (maxCalls < 1) { | |
throw new IllegalArgumentException("maxCalls must be >=1, was " + maxCalls); | |
} | |
if (interval < 1) { | |
throw new IllegalArgumentException("interval must be >=1, was " + interval); | |
} | |
_interval = interval; | |
_maxCalls = maxCalls + 1; | |
_ticks = new long[_maxCalls]; | |
_tickLast = _tickNext = 0; | |
} | |
/** | |
* Returns the next element in the queue. | |
* | |
* @param index | |
* The element for which to compute the next. | |
* @return | |
*/ | |
private int next(int index) { | |
index += 1; | |
return index < _maxCalls ? index : 0; | |
} | |
/** | |
* Attempts to clear the request. | |
* | |
* @return Returns 0 if successful, or a time hint (ms) in which we should | |
* attempt to clear it again. | |
*/ | |
public synchronized long tryStartRequest() { | |
long result = 0; | |
final long now = System.currentTimeMillis(); | |
while (_tickLast != _tickNext) { | |
if (now - _ticks[_tickLast] < _interval) { | |
break; | |
} | |
_tickLast = next(_tickLast); | |
} | |
final int next = next(_tickNext); | |
if (next != _tickLast) { | |
_ticks[_tickNext] = now; | |
_tickNext = next; | |
} else { | |
result = _interval - (now - _ticks[_tickLast]); | |
} | |
return result; | |
} | |
/** | |
* Clears the request. Blocks until the request can execute. | |
*/ | |
public void startRequest() { | |
startRequest(Integer.MAX_VALUE); | |
} | |
/** | |
* Clears the request. Blocks until the request can execute or until waxWait | |
* would be exceeded. | |
* | |
* @return true if successful or false if request should not execute | |
*/ | |
public boolean startRequest(final int maxWait) { | |
long sleep; | |
long total = 0; | |
while ((sleep = tryStartRequest()) > 0) { | |
if (maxWait > 0 && (total += sleep) > maxWait) { | |
_lastExpiredMaxWait = System.currentTimeMillis(); | |
return false; | |
} else { | |
try { | |
Thread.sleep(sleep); | |
} catch (final InterruptedException ex) { | |
ex.printStackTrace(); | |
} | |
} | |
} | |
return true; | |
} | |
public long getLastExpiredMaxWait() { | |
return _lastExpiredMaxWait; | |
} | |
} |
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