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27 package org.apache.hc.client5.http.impl.schedule;
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29 import org.apache.hc.client5.http.schedule.SchedulingStrategy;
30 import org.apache.hc.core5.annotation.Contract;
31 import org.apache.hc.core5.annotation.ThreadingBehavior;
32 import org.apache.hc.core5.util.Args;
33 import org.apache.hc.core5.util.TimeValue;
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57 @Contract(threading = ThreadingBehavior.STATELESS)
58 public class ExponentialBackOffSchedulingStrategy implements SchedulingStrategy {
59
60 public static final long DEFAULT_BACK_OFF_RATE = 10;
61 public static final TimeValue DEFAULT_INITIAL_EXPIRY = TimeValue.ofSeconds(6);
62 public static final TimeValue DEFAULT_MAX_EXPIRY = TimeValue.ofSeconds(86400);
63
64 private static final ExponentialBackOffSchedulingStrategylBackOffSchedulingStrategy.html#ExponentialBackOffSchedulingStrategy">ExponentialBackOffSchedulingStrategy INSTANCE = new ExponentialBackOffSchedulingStrategy(
65 DEFAULT_BACK_OFF_RATE, DEFAULT_INITIAL_EXPIRY, DEFAULT_MAX_EXPIRY);
66
67 private final long backOffRate;
68 private final TimeValue initialExpiry;
69 private final TimeValue maxExpiry;
70
71 public ExponentialBackOffSchedulingStrategy(
72 final long backOffRate,
73 final TimeValue initialExpiry,
74 final TimeValue maxExpiry) {
75 this.backOffRate = Args.notNegative(backOffRate, "BackOff rate");
76 this.initialExpiry = Args.notNull(initialExpiry, "Initial expiry");
77 this.maxExpiry = Args.notNull(maxExpiry, "Max expiry");
78 }
79
80 public ExponentialBackOffSchedulingStrategy(final long backOffRate, final TimeValue initialExpiry) {
81 this(backOffRate, initialExpiry, DEFAULT_MAX_EXPIRY);
82 }
83
84 public ExponentialBackOffSchedulingStrategy(final long backOffRate) {
85 this(backOffRate, DEFAULT_INITIAL_EXPIRY, DEFAULT_MAX_EXPIRY);
86 }
87
88 public ExponentialBackOffSchedulingStrategy() {
89 this(DEFAULT_BACK_OFF_RATE, DEFAULT_INITIAL_EXPIRY, DEFAULT_MAX_EXPIRY);
90 }
91
92 @Override
93 public TimeValue schedule(final int attemptNumber) {
94 return calculateDelay(attemptNumber);
95 }
96
97 public long getBackOffRate() {
98 return backOffRate;
99 }
100
101 public TimeValue getInitialExpiry() {
102 return initialExpiry;
103 }
104
105 public TimeValue getMaxExpiry() {
106 return maxExpiry;
107 }
108
109 protected TimeValue calculateDelay(final int consecutiveFailedAttempts) {
110 if (consecutiveFailedAttempts > 0) {
111 final long delay = (long) (initialExpiry.toMilliseconds() * Math.pow(backOffRate, consecutiveFailedAttempts - 1));
112 return TimeValue.ofMilliseconds(Math.min(delay, maxExpiry.toMilliseconds()));
113 }
114 return TimeValue.ZERO_MILLISECONDS;
115 }
116
117 }