生成随机UUID非阻塞

Question

通过使用Blockhound io.projectreactor.tools块-junit-平台，我发现UUID.randomUUID是一个阻塞调用，这对我们来说是一个问题，因为我们使用的是SpringBootWeb通量版本2.2.2.RELEASE。

是否有其他方法可以以非阻塞的方式获得随机uuid，或者是否有任何其他java库推荐用于非阻塞生成随机字符串。

从封锁犬的堆栈跟踪：

java.lang.Error: Blocking call! java.io.FileInputStream#readBytes
at reactor.blockhound.BlockHound$Builder.lambda$new$0(BlockHound.java:196) ~[blockhound-1.0.1.RELEASE.jar:na]
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain][ExceptionHandlingWebHandler]
Stack trace:
    at reactor.blockhound.BlockHound$Builder.lambda$new$0(BlockHound.java:196) ~[blockhound-1.0.1.RELEASE.jar:na]
    at reactor.blockhound.BlockHound$Builder.lambda$install$6(BlockHound.java:318) ~[blockhound-1.0.1.RELEASE.jar:na]
    at reactor.blockhound.BlockHoundRuntime.checkBlocking(BlockHoundRuntime.java:46) ~[na:na]
    at java.base/java.io.FileInputStream.readBytes(FileInputStream.java) ~[na:na]
    at java.base/java.io.FileInputStream.read(FileInputStream.java:279) ~[na:na]
    at java.base/java.io.FilterInputStream.read(FilterInputStream.java:133) ~[na:na]
    at java.base/sun.security.provider.NativePRNG$RandomIO.readFully(NativePRNG.java:424) ~[na:na]
    at java.base/sun.security.provider.NativePRNG$RandomIO.ensureBufferValid(NativePRNG.java:526) ~[na:na]
    at java.base/sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:545) ~[na:na]
    at java.base/sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:220) ~[na:na]
    at java.base/java.security.SecureRandom.nextBytes(SecureRandom.java:741) ~[na:na]
    at java.base/java.util.UUID.randomUUID(UUID.java:150) ~[na:na]

Answer 1

这是关于如何使用uuid-创造者来减少Linux上线程争用的三个示例的列表。

另一个示例使用乌利德-创造者生成单调性ULID，然后将它们转换为RFC-4122UUID(标准)。单调的ULID生成非常快。

基准代码可在GitHub吉斯特上使用。

示例1:使用UuidCreator和SHA1PRNG

如何设置SHA1PRNG算法供UuidCreator使用

# Append to /etc/environment or ~/.profile
# Use the the algorithm SHA1PRNG for SecureRandom
export UUIDCREATOR_SECURERANDOM="SHA1PRNG"

// generate a random-based UUID
UUID uuid = UuidCreator.getRandomBased();

UuidCreator使用固定的SecureRandom池。变量UUIDCREATOR_SECURERANDOM告诉UuidCreator使用另一个SecureRandom算法，而不是在Linux上使用NativePRNG。UuidCreator和SHA1PRNG算法生成的UUID比UUID.randomUUID()具有更少的线程争用(更少阻塞)。

请参见使用4个线程的基准测试：

----------------------------------------------------------------------
Benchmark                      Mode  Cnt      Score     Error   Units
----------------------------------------------------------------------
UUID.randomUUID()             thrpt    5   1423,060 ±  30,125  ops/ms
UuidCreator.getRandomBased()  thrpt    5  10616,016 ± 281,486  ops/ms
----------------------------------------------------------------------

示例2:使用ThreadLocalRandom

如何使用ThreadLocalRandom实现UUID生成器

public class UuidGenerator {

    private static final RandomBasedFactory UUID_FACTORY;

    static {
        UUID_FACTORY = new RandomBasedFactory((int length) -> {
            final byte[] bytes = new byte[length];
            ThreadLocalRandom.current().nextBytes(bytes);
            return bytes;
        });
    }

    public static UUID generate() {
        return UUID_FACTORY.create();
    }
}

ThreadLocalRandom是一个快速(且不安全)的随机生成器，没有线程争用(非阻塞)。

请参见使用4个线程的基准测试：

----------------------------------------------------------------------
Benchmark                     Mode  Cnt      Score      Error   Units
----------------------------------------------------------------------
UUID.randomUUID()            thrpt    5   1423,060 ±   30,125  ops/ms
UuidGenerator.generate()     thrpt    5  85390,979 ± 1564,589  ops/ms
----------------------------------------------------------------------

示例3:使用RandomBasedFactory[]和SHA1PRNG

如何使用RandomBasedFactory和SHA1PRNG算法的ana数组实现UUID生成器：

    public static class UuidGenerator {

        private static final int SIZE = 8; // you choose
        private static final RandomBasedFactory[] FACTORIES;

        static {
            FACTORIES = new RandomBasedFactory[SIZE];
            try {
                for (int i = 0; i < FACTORIES.length; i++) {
                    // SHA1PRNG or DRBG can be used to reduce thread contention.
                    SecureRandom argument = SecureRandom.getInstance("SHA1PRNG");
                    FACTORIES[i] = new RandomBasedFactory(argument);
                }
            } catch (NoSuchAlgorithmException e) {
                // oops!
            }
        }

        public static UUID generate() {
            // calculate the factory index given the current thread ID
            final int index = (int) Thread.currentThread().getId() % SIZE;
            return FACTORIES[index].create();
        }
    }

RandomBasedFactory with和SHA1PRNG算法的数组可以生成线程争用较少(阻塞较少)的UUID。

请参见使用4个线程的基准测试：

----------------------------------------------------------------------
Benchmark                     Mode  Cnt      Score      Error   Units
----------------------------------------------------------------------
UUID.randomUUID()            thrpt    5   1423,060 ±   30,125  ops/ms
UuidGenerator.generate()     thrpt    5  10048,747 ±  195,209  ops/ms
----------------------------------------------------------------------

示例4:使用UlidCreator和Monotonic ULIDs

如何使用乌利德-创造者从单调性ULID生成RFC-4122 UUID

// create a Monotonic ULID and convert it to RFC-4122 UUID v4
UUID uuid = UlidCreator.getMonotonicUlid().toRfc4122().toUuid();

请参见使用4个线程的基准测试：

-----------------------------------------------------------------------
Benchmark                       Mode  Cnt     Score      Error   Units
-----------------------------------------------------------------------
UUID.randomUUID()              thrpt    5  1423,060 ±   30,125  ops/ms
UlidCreator.getMonotonicUlid() thrpt    5  7391,917 ±  871,799  ops/ms
-----------------------------------------------------------------------

编辑：添加了第四个使用单调ULID的示例。