1 /*
2 * Copyright 2019-2022 The OSHI Project Contributors
3 * SPDX-License-Identifier: MIT
4 */
5 package oshi.util;
6
7 import java.util.concurrent.TimeUnit;
8 import java.util.function.Supplier;
9
10 import oshi.annotation.concurrent.ThreadSafe;
11
12 /**
13 * A memoized function stores the output corresponding to some set of specific inputs. Subsequent calls with remembered
14 * inputs return the remembered result rather than recalculating it.
15 */
16 @ThreadSafe
17 public final class Memoizer {
18
19 private static final Supplier<Long> DEFAULT_EXPIRATION_NANOS = memoize(Memoizer::queryExpirationConfig,
20 TimeUnit.MINUTES.toNanos(1));
21
22 private Memoizer() {
23 }
24
25 private static long queryExpirationConfig() {
26 return TimeUnit.MILLISECONDS.toNanos(GlobalConfig.get(GlobalConfig.OSHI_UTIL_MEMOIZER_EXPIRATION, 300));
27 }
28
29 /**
30 * Default exipiration of memoized values in nanoseconds, which will refresh after this time elapses. Update by
31 * setting {@link GlobalConfig} property <code>oshi.util.memoizer.expiration</code> to a value in milliseconds.
32 *
33 * @return The number of nanoseconds to keep memoized values before refreshing
34 */
35 public static long defaultExpiration() {
36 return DEFAULT_EXPIRATION_NANOS.get();
37 }
38
39 /**
40 * Store a supplier in a delegate function to be computed once, and only again after time to live (ttl) has expired.
41 *
42 * @param <T> The type of object supplied
43 * @param original The {@link java.util.function.Supplier} to memoize
44 * @param ttlNanos Time in nanoseconds to retain calculation. If negative, retain indefinitely.
45 * @return A memoized version of the supplier
46 */
47 public static <T> Supplier<T> memoize(Supplier<T> original, long ttlNanos) {
48 // Adapted from Guava's ExpiringMemoizingSupplier
49 return new Supplier<T>() {
50 private final Supplier<T> delegate = original;
51 private volatile T value; // NOSONAR squid:S3077
52 private volatile long expirationNanos;
53
54 @Override
55 public T get() {
56 long nanos = expirationNanos;
57 long now = System.nanoTime();
58 if (nanos == 0 || (ttlNanos >= 0 && now - nanos >= 0)) {
59 synchronized (this) {
60 if (nanos == expirationNanos) { // recheck for lost race
61 T t = delegate.get();
62 value = t;
63 nanos = now + ttlNanos;
64 expirationNanos = (nanos == 0) ? 1 : nanos;
65 return t;
66 }
67 }
68 }
69 return value;
70 }
71 };
72 }
73
74 /**
75 * Store a supplier in a delegate function to be computed only once.
76 *
77 * @param <T> The type of object supplied
78 * @param original The {@link java.util.function.Supplier} to memoize
79 * @return A memoized version of the supplier
80 */
81 public static <T> Supplier<T> memoize(Supplier<T> original) {
82 return memoize(original, -1L);
83 }
84 }