Java 代码监控 JVM 运行状态 —— 记一次 JVM 调优的毛招

public class GCUtil {
 
    /**
     * 调用 System.gc
     */
    public static void systemGC() {
        long startTime = System.currentTimeMillis();
        LOGGER.info("Call for system gc start...");
        System.gc();
        LOGGER.info("Call for system gc end, spend {}ms", System.currentTimeMillis() - startTime);
    }
 
    /**
     * 保证当前年轻代进入老年代的 gc，用于模型更新以及刚上线期间
     */
    public static void youngPromoteGC() {
        try {
            long startTime = System.currentTimeMillis();
            LOGGER.info("Call for young promote gc start...");
 
            RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
            List<String> args = runtimeMXBean.getInputArguments();
 
            // 获取 eden 区大小
            long edenMSize = 0;
            for (String arg : args) {
                LOGGER.info("--------------- Jvm param: {}", arg);
                if (arg.startsWith(JVM_XMN)) {
                    String edenSizeStr = arg.substring(JVM_XMN.length());
                    if (edenSizeStr.toLowerCase().endsWith("g")) {
                        long edenGSize = Long.valueOf(edenSizeStr.substring(0, edenSizeStr.length() - 1));
                        edenMSize = edenGSize * 1024;
                    } else if (edenSizeStr.toLowerCase().endsWith("m")) {
                        edenMSize = Long.valueOf(edenSizeStr.substring(0, edenSizeStr.length() - 1));
                    } else {
                        LOGGER.warn("Cannot recognize -Xmn argument: " + JVM_XMN);
                    }
                }
            }
 
            if (edenMSize == 0) {
                edenMSize = getEdenMemorySize();
            }
 
            if (edenMSize <= 0) {
                LOGGER.warn("Extract jvm -Xmn failed");
                return;
            }
 
            // 获取 晋升老年代最大次数
            int tenuringThreshold = DEFAULT_TENURING_THRESHOLD;
            for (String arg : args) {
                if (arg.startsWith(MAX_TENURING_THRESHOLD)) {
                    String tenuringThresholdStr = arg.substring(MAX_TENURING_THRESHOLD.length() + 1);
                    tenuringThreshold = Integer.valueOf(tenuringThresholdStr);
                    if (tenuringThreshold > DEFAULT_TENURING_THRESHOLD) {
                        tenuringThreshold = DEFAULT_TENURING_THRESHOLD;
                    }
                }
            }
 
            LOGGER.info("Start to young gc, -Xmn={}m, -XX:MaxTenuringThreshold={}", edenMSize, tenuringThreshold);
 
            // 手动触发 Young GC
            for (int i = 0; i < edenMSize * tenuringThreshold; ++i) {
                allocate_1M();
            }
 
            // System GC，清理老年代
            System.gc();
 
            LOGGER.info("Call for young promote gc end, spend {}ms", System.currentTimeMillis() - startTime);
        } catch (Exception e) {
            LOGGER.error("Trigger young promote gc failed: ", e);
        }
    }
 
    /**
     * 获取新生代大小，单位 M
     */
    private static long getEdenMemorySize() {
        List<MemoryPoolMXBean> poolMXBeanList = ManagementFactory.getMemoryPoolMXBeans();
        for (MemoryPoolMXBean memoryPoolMXBean : poolMXBeanList) {
            if (memoryPoolMXBean.getName().toLowerCase().contains("eden")) {
                long maxUsage = memoryPoolMXBean.getUsage().getMax();
                return maxUsage >> 20;
            }
        }
        return -1;
    }
 
    /**
     * 生成个 1M 对象
     */
    private static void allocate_1M() {
        byte[] _1M = new byte[1024 * 1024];
    }
 
    private GCUtil() {
    }
 
    private static final String MAX_TENURING_THRESHOLD = "-XX:MaxTenuringThreshold";
 
    private static final int DEFAULT_TENURING_THRESHOLD = 15;
 
    private static final String JVM_XMN = "-Xmn";
 
    private static final Logger LOGGER = LoggerFactory.getLogger(GCUtil.class);
 
}