netty堆外内存监控

直接new DirectMemReporter().startReport();调用就可以了

netty4.1x默认使用池化的bytebuf，每个池子初始16mb，使用直接内存的最大池子数默认16，由jvm启动参数决定-Dio.netty.allocator.numDirectArenas。默认最大堆外内存默认3817865216 bytes，由-Dio.netty.maxDirectMemory决定

@Slf4j
public class DirectMemReporter {
    private AtomicLong directMem = new AtomicLong();
    private ScheduledExecutorService executor = MoreExecutors.getExitingScheduledExecutorService(
            new ScheduledThreadPoolExecutor(1), 10, TimeUnit.SECONDS);

    public DirectMemReporter() {
        Field field = ReflectionUtils.findField(PlatformDependent.class, "DIRECT_MEMORY_COUNTER");
        field.setAccessible(true);
        try {
            directMem = (AtomicLong) field.get(PlatformDependent.class);
        } catch (IllegalAccessException e) {}
    }

    public void startReport() {
        executor.scheduleAtFixedRate(() -> {
            log.info("netty direct memory size:{}b, max:{}", directMem.get(), PlatformDependent.maxDirectMemory());
        }, 0, 1, TimeUnit.SECONDS);
    }
}