BackOff

JVM 在申请 Direct Memory 时使用了指数退避算法，源码位于 jdk8u/Bits.java at jdk8u332-b04 · openjdk/jdk8u · GitHub:

// max. number of sleeps during try-reserving with exponentially
// increasing delay before throwing OutOfMemoryError:
// 1, 2, 4, 8, 16, 32, 64, 128, 256 (total 511 ms ~ 0.5 s)
// which means that OOME will be thrown after 0.5 s of trying
private static final int MAX_SLEEPS = 9;

// These methods should be called whenever direct memory is allocated or
// freed.  They allow the user to control the amount of direct memory
// which a process may access.  All sizes are specified in bytes.
static void reserveMemory(long size, int cap) {

    if (!memoryLimitSet && VM.isBooted()) {
        maxMemory = VM.maxDirectMemory();
        memoryLimitSet = true;
    }

    // optimist!
    if (tryReserveMemory(size, cap)) {
        return;
    }

    final JavaLangRefAccess jlra = SharedSecrets.getJavaLangRefAccess();

    // retry while helping enqueue pending Reference objects
    // which includes executing pending Cleaner(s) which includes
    // Cleaner(s) that free direct buffer memory
    while (jlra.tryHandlePendingReference()) {
        if (tryReserveMemory(size, cap)) {
            return;
        }
    }

    // trigger VM's Reference processing
    System.gc();

    // a retry loop with exponential back-off delays
    // (this gives VM some time to do it's job)
    boolean interrupted = false;
    try {
        long sleepTime = 1;
        int sleeps = 0;
        while (true) {
            if (tryReserveMemory(size, cap)) {
                return;
            }
            if (sleeps >= MAX_SLEEPS) {
                break;
            }
            if (!jlra.tryHandlePendingReference()) {
                try {
                    Thread.sleep(sleepTime);
                    sleepTime <<= 1;
                    sleeps++;
                } catch (InterruptedException e) {
                    interrupted = true;
                }
            }
        }

        // no luck
        throw new OutOfMemoryError("Direct buffer memory");

    } finally {
        if (interrupted) {
            // don't swallow interrupts
            Thread.currentThread().interrupt();
        }
    }
}

类似地，退避相关算法在 Spring 中也有使用，可参考文末链接。

References

Exponential backoff - Wikipedia
FixedBackOff (Spring Framework 5.3.16 API)
ExponentialBackOff (Spring Framework 5.3.16 API)