《Java 并发编程·性能诊断与事故》14.2 内存限制、线程栈与容器 OOM

-XX:MaxRAM=512m -XX:MaxRAMPercentage=75   -> MaxHeapSize=384 MiB
-XX:MaxRAM=1g   -XX:MaxRAMPercentage=75   -> MaxHeapSize=768 MiB
-XX:MaxRAM=4g   -XX:MaxRAMPercentage=75   -> MaxHeapSize=3 GiB
-XX:MaxRAMPercentage=50（宿主 32 GiB）    -> MaxHeapSize=16 GiB

宿主 macOS aarch64：ThreadStackSize = 2048 KB（默认），最小可运行 208k
容器 Linux aarch64：ThreadStackSize = 2040 KB（默认），最小可运行 168k

The Java thread stack size specified is too small. Specify at least 208k
Error: Could not create the Java Virtual Machine.

import java.util.ArrayList;
import java.util.List;

public class HeapOom2 {
    public static void main(String[] args) {
        List<byte[]> keep = new ArrayList<>();
        int mib = 0;
        try {
            while (true) {
                keep.add(new byte[1024 * 1024]);
                mib++;
            }
        } catch (OutOfMemoryError first) {
            keep.clear();                       // 先释放，给错误处理留出空间
            System.out.println("allocatedMiB=" + mib + " message=" + first.getMessage());
        }
    }
}

-Xmx32m  -> allocatedMiB=15 message=Java heap space
-Xmx64m  -> allocatedMiB=31 message=Java heap space
容器 --memory=512m -Xmx512m -> allocatedMiB=386 message=Java heap space
容器 --memory=512m 默认25%   -> allocatedMiB=118 message=Java heap space

import java.io.ByteArrayOutputStream;
import java.nio.charset.StandardCharsets;

/** 固定字节码模板，只改类名，反复 defineClass，直到 Metaspace 耗尽。 */
public class MetaOom2 {
    private static final int NAME_OFF = 13;
    private static final int NAME_LEN = 10;

    static byte[] template() {
        byte[] n = "Gen0000000".getBytes(StandardCharsets.US_ASCII);
        byte[] sup = "java/lang/Object".getBytes(StandardCharsets.US_ASCII);
        ByteArrayOutputStream out = new ByteArrayOutputStream(64);
        out.write(0xCA); out.write(0xFE); out.write(0xBA); out.write(0xBE);
        out.write(0); out.write(0); out.write(0); out.write(69);      // Java 25 -> major 69
        out.write(0); out.write(5);                                    // cp_count
        out.write(1); out.write(0); out.write(n.length); out.writeBytes(n);
        out.write(7); out.write(0); out.write(1);
        out.write(1); out.write(0); out.write(sup.length); out.writeBytes(sup);
        out.write(7); out.write(0); out.write(3);
        out.write(0); out.write(0x21);                                 // public super
        out.write(0); out.write(2); out.write(0); out.write(4);
        out.write(0); out.write(0); out.write(0); out.write(0);
        out.write(0); out.write(0); out.write(0); out.write(0);
        return out.toByteArray();
    }

    static final class GenLoader extends ClassLoader {
        Class<?> define(String name, byte[] bytes) {
            return defineClass(name, bytes, 0, bytes.length);
        }
    }

    public static void main(String[] args) {
        byte[] base = template();
        byte[] nb = new byte[NAME_LEN];
        nb[0] = 'G'; nb[1] = 'e'; nb[2] = 'n';
        GenLoader loader = new GenLoader();
        int n = 0;
        try {
            for (; n < 500_000; n++) {
                int v = n;
                for (int p = NAME_LEN - 1; p >= 3; p--) {
                    nb[p] = (byte) ('0' + v % 10);
                    v /= 10;
                }
                byte[] bytes = base.clone();
                System.arraycopy(nb, 0, bytes, NAME_OFF, NAME_LEN);
                loader.define(new String(nb, StandardCharsets.US_ASCII), bytes);
            }
        } catch (OutOfMemoryError e) {
            System.out.print("defined="); System.out.print(n);
            System.out.print(" message="); System.out.println(e.getMessage());
        }
    }
}

-XX:MaxMetaspaceSize=32m -> defined=46745 message=Metaspace
不加限制，加载 25264 个 JDK 类 -> Metaspace used=125MiB, Compressed Class Space used=16MiB

--pids-limit=200, cap 1000 threads
created=100
[warning][os,thread] Failed to start thread "Unknown thread" - pthread_create failed (EAGAIN)
[warning][os,thread] Failed to start the native thread for java.lang.Thread "burn-182"
FAILED_AT created=182
type=java.lang.OutOfMemoryError
message=unable to create native thread: possibly out of memory or process/resource limits reached

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;

public class DirectOom {
    public static void main(String[] args) {
        List<ByteBuffer> keep = new ArrayList<>();
        int mib = 0;
        try {
            while (true) {
                ByteBuffer buf = ByteBuffer.allocateDirect(1024 * 1024);
                for (int i = 0; i < buf.capacity(); i += 4096) {
                    buf.put(i, (byte) 1);          // 触碰每一页，强制提交物理内存
                }
                keep.add(buf);
                mib++;
            }
        } catch (OutOfMemoryError e) {
            System.out.print("directMiB="); System.out.print(mib);
            System.out.print(" message="); System.out.println(e.getMessage());
        }
    }
}

--memory=256m --memory-swap=256m, -Xmx128m -XX:MaxDirectMemorySize=1024m
Killed
java_exit=137
docker inspect: ExitCode=0 OOMKilled=true Status=exited

package com.plume.conc.ops;

/** 容器内存预算：堆 + 线程栈 + 堆外固定开销 必须落在 limit 内。 */
public record ContainerMemoryPlan(long limitBytes, double heapRatio,
                                  int platformThreads, int xssKb, long offHeapMiB) {

    public ContainerMemoryPlan {
        if (limitBytes <= 0 || heapRatio <= 0 || heapRatio >= 1) {
            throw new IllegalArgumentException("limitBytes > 0 且 0 < heapRatio < 1");
        }
        if (platformThreads < 0 || xssKb <= 0) {
            throw new IllegalArgumentException("线程数不能为负，xssKb 必须为正");
        }
    }

    public long heapBytes() {
        return (long) (limitBytes * heapRatio);
    }

    /** 只算已提交部分：每线程约 64 KiB 栈页 + 16 KiB 内核结构，是保守估计。 */
    public long threadBytes() {
        return (long) platformThreads * 80 * 1024;
    }

    public long offHeapBytes() {
        return offHeapMiB * 1024 * 1024;
    }

    public long headroomBytes() {
        return limitBytes - heapBytes() - threadBytes() - offHeapBytes();
    }

    public boolean plausible() {
        return headroomBytes() > 128L * 1024 * 1024;   // 至少留 128 MiB 给 Metaspace/代码缓存
    }

    public static void main(String[] args) {
        long limit = 512L * 1024 * 1024;
        ContainerMemoryPlan plan = new ContainerMemoryPlan(limit, 0.70, 200, 1024, 64);
        System.out.printf("heap=%dMiB threads=%dMiB offHeap=%dMiB headroom=%dMiB plausible=%b%n",
                plan.heapBytes() >> 20, plan.threadBytes() >> 20,
                plan.offHeapBytes() >> 20, plan.headroomBytes() >> 20, plan.plausible());
    }
}