java PrintCompilation 输出 : what's the meaning of "made not entrant" and "made zombie"

Question

在运行 Java 1.6 (1.6.0_03-b05) 应用程序时，我添加了 -XX:+PrintCompilation 标志。在某些方法的输出中，尤其是我知道的一些方法被调用了很多，我看到文本 made not entrant 和 madezombie。

这些是什么意思？最好的猜测是，在重新编译该方法或具有更大优化的依赖项之前，这是一个反编译步骤。真的吗？为什么是“僵尸”和“进入者”？

例如，其中一些行之间有相当长的时间:

[... near the beginning]
42       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... much later]
42    made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
---   n   sun.misc.Unsafe::compareAndSwapObject
170       jsr166y.LinkedTransferQueue::xfer (294 bytes)
170   made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
  4%      jsr166y.LinkedTransferQueue::xfer @ 29 (294 bytes)
171       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... even later]
42    made zombie  jsr166y.LinkedTransferQueue::xfer (294 bytes)
170   made zombie  jsr166y.LinkedTransferQueue::xfer (294 bytes)
171   made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
172       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... no further logs]

Answer 1

我在 my blog 上收集了一些关于此的信息.我发现的一条 Cliff Click 评论说:

Zombie methods are methods whose code has been made invalid by class loading. Generally the server compiler makes aggressive inlining decisions of non-final methods. As long as the inlined method is never overridden the code is correct. When a subclass is loaded and the method overridden, the compiled code is broken for all future calls to it. The code gets declared "not entrant" (no future callers to the broken code), but sometimes existing callers can keep using the code. In the case of inlining, that's not good enough; existing callers' stack frames are "deoptimized" when they return to the code from nested calls (or just if they are running in the code). When no more stack frames hold PC's into the broken code it's declared a "zombie" - ready for removal once the GC gets around to it.