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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 final long backOffRate;
65 private final TimeValue initialExpiry;
66 private final TimeValue maxExpiry;
67
68 public ExponentialBackOffSchedulingStrategy(
69 final long backOffRate,
70 final TimeValue initialExpiry,
71 final TimeValue maxExpiry) {
72 this.backOffRate = Args.notNegative(backOffRate, "BackOff rate");
73 this.initialExpiry = Args.notNull(initialExpiry, "Initial expiry");
74 this.maxExpiry = Args.notNull(maxExpiry, "Max expiry");
75 }
76
77 public ExponentialBackOffSchedulingStrategy(final long backOffRate, final TimeValue initialExpiry) {
78 this(backOffRate, initialExpiry, DEFAULT_MAX_EXPIRY);
79 }
80
81 public ExponentialBackOffSchedulingStrategy(final long backOffRate) {
82 this(backOffRate, DEFAULT_INITIAL_EXPIRY, DEFAULT_MAX_EXPIRY);
83 }
84
85 public ExponentialBackOffSchedulingStrategy() {
86 this(DEFAULT_BACK_OFF_RATE, DEFAULT_INITIAL_EXPIRY, DEFAULT_MAX_EXPIRY);
87 }
88
89 @Override
90 public TimeValue schedule(final int attemptNumber) {
91 return calculateDelay(attemptNumber);
92 }
93
94 public long getBackOffRate() {
95 return backOffRate;
96 }
97
98 public TimeValue getInitialExpiry() {
99 return initialExpiry;
100 }
101
102 public TimeValue getMaxExpiry() {
103 return maxExpiry;
104 }
105
106 protected TimeValue calculateDelay(final int consecutiveFailedAttempts) {
107 if (consecutiveFailedAttempts > 0) {
108 final long delay = (long) (initialExpiry.toMilliseconds() * Math.pow(backOffRate, consecutiveFailedAttempts - 1));
109 return TimeValue.ofMilliseconds(Math.min(delay, maxExpiry.toMilliseconds()));
110 }
111 return TimeValue.ZERO_MILLISECONDS;
112 }
113
114 }