? the space 20480K,? 99% used [0x04610000, 0x05a052b8, 0x05a05400,0x05a10000)

?

4、可扩展的JAVA虚拟机空间

使用源代码中对应的outOfMemoryByExpansionSize方法和配套的参数。

运行结果如下：

[GC [ParNew: 1990K->132K(2112K),0.0007742 secs] 24112K->24110K(30528K), 0.0007964 secs] [Times: user=0.00sys=0.00, real=0.00 secs]

[GC [ParNew: 1990K->130K(2112K),0.0008112 secs] 25969K->25965K(30528K), 0.0008477 secs] [Times: user=0.00sys=0.00, real=0.00 secs]

[GC [ParNew: 1988K->130K(2112K),0.0009319 secs] 27823K->27821K(30528K), 0.0009553 secs] [Times: user=0.00sys=0.00, real=0.00 secs]

[GC [ParNew: 1991K->134K(2112K),0.0008219 secs][Tenured: 29548K->29551K(29568K), 0.0031503 secs] 29682K->29679K(31680K),[Perm : 2086K->2086K(12288K)], 0.0040531 secs] [Times: user=0.01 sys=0.00,real=0.00 secs]

[GC [ParNew: 2562K->194K(2880K),0.0024877 secs] 32113K->32113K(40704K), 0.0025124 secs] [Times: user=0.00sys=0.00, real=0.00 secs]

[GC [ParNew: 2756K->196K(2880K),0.0010854 secs] 34676K->34680K(40704K), 0.0011096 secs] [Times: user=0.00sys=0.00, real=0.00 secs]

[GC [ParNew: 2758K->196K(2880K),0.0011059 secs] 37243K->37241K(40704K), 0.0011285 secs] [Times: user=0.03sys=0.00, real=0.00 secs]

[GC [ParNew: 2758K->2758K(2880K),0.0000123 secs][Tenured: 37045K->37813K(37824K), 0.0037394 secs]39803K->39798K(40704K), [Perm : 2086K->2086K(12288K)], 0.0037977 secs][Times: user=0.00 sys=0.00, real=0.00 secs]

[Full GC [Tenured:37813K->37813K(37824K), 0.0034278 secs] 40569K->40567K(40704K), [Perm :2086K->2086K(12288K)], 0.0034685 secs] [Times: user=0.00 sys=0.00, real=0.00secs]

[Full GC [Tenured:37813K->37792K(37824K), 0.0107084 secs] 40567K->40546K(40704K), [Perm :2086K->2084K(12288K)], 0.0107696 secs] [Times: user=0.01 sys=0.00, real=0.01secs]

Exception in thread "main"java.lang.OutOfMemoryError: Java heap space

? ? atcom.gc.EasyParNew.(EasyParNew.java:12)

? ? atcom.gc.EasyParNew.outOfMemoryByExpansionSize(EasyParNew.java:39)

? ? atcom.gc.EasyParNew.main(EasyParNew.java:14)

Heap

?par new generation? total 2880K, used 2810K [0x03bf0000,0x03f00000, 0x03f00000)

?eden space 2624K,? 99% used[0x03bf0000, 0x03e7e8e8, 0x03e80000)

?from space 256K,? 75% used[0x03ec0000, 0x03ef0030, 0x03f00000)

?to? space 256K,? 0% used [0x03e80000, 0x03e80000, 0x03ec0000)

?tenured generation? total 37824K, used 37792K [0x03f00000,0x063f0000, 0x063f0000)

? the space 37824K,? 99% used[0x03f00000, 0x063e82e0, 0x063e8400, 0x063f0000)

?compacting perm gen? total 12288K, used 2105K [0x063f0000,0x06ff0000, 0x0a3f0000)

? the space 12288K,? 17% used [0x063f0000, 0x065fe4a8, 0x065fe600,0x06ff0000)

?

5、ParNew收集器和Serial收集器的差异

ParNew收集器在单CPU的环境中绝对不会有比Serial收集器更好的效果，甚至由于存在线程交互的开销，该收集器在通过超线程技术实现的两个CPU的环境中都不能百分之百地保证能超越Serial收集器。当然，随着可以使用的CPU的数量的增加，它对于GC时系统资源的利用还是很有好处的。它默认开启的收集线程数与CPU的数量相同，在CPU非常多（譬如32个，现在CPU动辄就4核加超线程，服务器超过32个逻辑CPU的情况越来越多了）的环境下，可以使用-XX:ParallelGCThreads参数来限制垃圾收集的线程数。

?

并行（Parallel）：指多条垃圾收集线程并行工作，但此时用户线程仍然处于等待状态。

并发（Concurrent）：指用户线程与垃圾收集线程同时执行（但不一定是并行的，可能会交替执行），用户程序继续运行，而垃圾收集程序运行于另一个CPU上。

[GC [DefNew:1986K->128K(2112K), 0.0011191 secs] 27809K->27808K(30528K), 0.0011425secs] [Times: user=0.00 sys=0.01, real=0.00 secs]

和

[GC [ParNew:1990K->132K(2112K), 0.0007742 secs] 24112K->24110K(30528K), 0.0007964secs] [Times: user=0.00 sys=0.00, real=0.00 secs]

其中的GC [ParNew 表示使用的是parNew收集器。