Question

我们的应用程序对延迟至关重要。为了减少GC暂停，我们重用了对象。在这个过程的开始，我们分配了许多小对象，然后（几乎）没有分配内存。但是，我仍然看到以下gc：

的日志

namespace X
{
    using System;

    /// <see cref="I1"/>  (or <see cref="X.I1"/> from outside X)
    /// <see cref="T:X.I1"/>
    interface I1
    {
        /// <see cref="I1.M1(int)"/>  (or <see cref="M1(int)"/> from inside I1)
        /// <see cref="M:X.I1.M1(System.Int32)"/>
        void M1(int p);

        /// <see cref="I1.M2{U}(U)"/>
        /// <see cref="M:X.I1.M2``1(``0)"/>
        void M2<U>(U p);

        /// <see cref="I1.M3(Action{string})"/>
        /// <see cref="M:X.I1.M3(System.Action{System.String})"/>
        void M3(Action<string> p);
    }

    /// <see cref="I2{T}"/>
    /// <see cref="T:X.I2`1"/>
    interface I2<T>
    {
        /// <see cref="I2{T}.M1(int)"/>
        /// <see cref="M:X.I2`1.M1(System.Int32)"/>
        void M1(int p);

        /// <see cref="I2{T}.M2(T)"/>
        /// <see cref="M:X.I2`1.M2(`0)"/>
        void M2(T p);

        /// <see cref="I2{T}.M3{U}(U)"/>
        /// <see cref="M:X.I2`1.M3``1(``0)"/>
        void M3<U>(U p);
    }
}

据我所知，JVM会停止进程以遍历所有引用并标记对象。这是对的吗？

此外，我发现此类日志的频率会随着时间而减少。所以我认为GC会调整一些内部参数，我希望在一开始就提供它们。现在我使用以下参数运行进程：

2016-12-18T13:51:48.650+0200: 1.085: Total time for which application threads were stopped: 0.0001411 seconds, Stopping threads took: 0.0000203 seconds
2016-12-18T13:51:48.776+0200: 1.210: Total time for which application threads were stopped: 0.0002027 seconds, Stopping threads took: 0.0000183 seconds
2016-12-18T13:51:48.894+0200: 1.328: Total time for which application threads were stopped: 0.0002559 seconds, Stopping threads took: 0.0000194 seconds
2016-12-18T13:51:48.906+0200: 1.341: Total time for which application threads were stopped: 0.0002159 seconds, Stopping threads took: 0.0000199 seconds
2016-12-18T13:51:49.047+0200: 1.482: Total time for which application threads were stopped: 0.0002842 seconds, Stopping threads took: 0.0000208 seconds

所有其他参数都与详细说明GC有关。我们的机器有足够的内存来完全避免gc。我怎么解释它到java？

OS：Linux，JVM oracle或openJDK。

谢谢。

Answer 1

这些不一定是垃圾收集。

当JVM打印Total time for which application threads were stopped时，还有许多其他情况（与GC无关）。有关详细信息，请参阅the related answer。

由于类加载和重新编译，非GC安全点在应用程序启动时尤其频繁。

如果要跟踪GC暂停，请使用-XX:+PrintGCDetails。

<强>更新

减少非GC安全点数量的一些技巧：

-XX:-UseBiasedLocking完全禁用偏差撤销暂停;
-XX:+UnlockDiagnosticVMOptions -XX:GuaranteedSafepointInterval=0每秒禁用强制性安全点;
-XX:-TieredCompilation禁用多层编译，从而减少了与重新编译相关的安全点的数量。

注意：这只是一个提示，而不是生产用途的建议。以上选项可能会产生性能副作用。

如何避免GC暂停？

1 个答案: