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JDK6u25里添加的按线程统计分配内存量: JMX
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轉(zhuǎn)載自?http://rednaxelafx.iteye.com/blog/1021619
Oracle幾天前發(fā)布的JDK 6 update 25里添加的一個新功能非常有趣，可以按照線程來跟蹤（GC堆）內(nèi)存的分配量。這個功能在VM核心、解釋器、C1編譯器、C2編譯器以及GC中都有代碼支持，并且通過JMX API暴露出來。?
不過新加的這功能不是加在java.開頭的包里，而是加在com.sun.management.ThreadMXBean這個接口上，要用的話還得cast一下。?
當(dāng)然，這么底層的功能不可能沒有代價。添加這個功能后，在GC堆上分配空間的slow-path會比以前稍微慢一些。但希望對整體性能的影響并不大吧。?
Fast-path是在TLAB上分配空間的，而TLAB的分配數(shù)據(jù)是在TLAB refill的時候才批量更新，所以這個功能對fast-path的執(zhí)行效率基本上沒影響，以稍微放寬數(shù)據(jù)精準(zhǔn)性為代價。?
相關(guān)鏈接：?
Bug ID 7003271: Hotspot should track cumulative Java heap bytes allocated on a per-thread basis?
changeset?
JMX中，該功能由ThreadMXBean上新增的幾個方法提供。詳情可見下面例子。?
ThreadMXBean.getThreadAllocatedBytes(long threadId)的用法基本上可以看成跟System.currentTimeMillis()用于計時的用法一樣，在兩點上記錄并且求差即可。?
不知道為什么JVMTI沒得到這個更新，或許是因為更新JVMTI spec涉及committee stuff？?
==============================================================?
直接拿一段Groovy腳本來演示吧：?
先看JDK 6 update 24的情況?
Groovysh代碼?
?
D:\sdk\groovy-1.7.2\bin>groovysh??Groovy?Shell?(1.7.2,?JVM:?1.6.0_24)??Type?'help'?or?'\h'?for?help.??-------------------------------------------------------------------------------??groovy:000>?import?java.lang.management.*??===>?[import?java.lang.management.*]??groovy:000>?tb?=?ManagementFactory.threadMXBean??===>?sun.management.ThreadImpl@8b677f??groovy:000>?tb.class.methods.name.unique().sort()??===>?[dumpAllThreads,?equals,?findDeadlockedThreads,?findMonitorDeadlockedThreads,?getAllThreadIds,?getClass,?getCurrentThreadCpuTime,?getCurrentThreadUserTime,?getDaemonThreadCount,?getPeakThreadCount,?getThreadCount,?getThreadCpuTime,?getThreadInfo,?getThreadUserTime,?getTotalStartedThreadCount,?hashCode,?isCurrentThreadCpuTimeSupported,?isObjectMonitorUsageSupported,?isSynchronizerUsageSupported,?isThreadContentionMonitoringEnabled,?isThreadContentionMonitoringSupported,?isThreadCpuTimeEnabled,?isThreadCpuTimeSupported,?notify,?notifyAll,?resetPeakThreadCount,?setThreadContentionMonitoringEnabled,?setThreadCpuTimeEnabled,?toString,?wait]??groovy:000>?tb.class.methods.findAll?{?it.name?=~?/Alloc/}.each?{?println?it?};?null??===>?null??
這個時候ThreadMXBean上還沒有跟alloc相關(guān)的方法。?
?
Groovysh代碼?
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D:\sdk\groovy-1.7.2\bin>groovysh??Groovy?Shell?(1.7.2,?JVM:?1.6.0_25)??Type?'help'?or?'\h'?for?help.??-------------------------------------------------------------------------------??groovy:000>?import?java.lang.management.*??===>?[import?java.lang.management.*]??groovy:000>?tb?=?ManagementFactory.threadMXBean??===>?sun.management.ThreadImpl@9b1670??groovy:000>?tb.class.methods.name.unique().sort()??===>?[dumpAllThreads,?equals,?findDeadlockedThreads,?findMonitorDeadlockedThreads,?getAllThreadIds,?getClass,?getCurrentThreadCpuTime,?getCurrentThreadUserTime,?getDaemonThreadCount,?getPeakThreadCount,?getThreadAllocatedBytes,?getThreadCount,?getThreadCpuTime,?getThreadInfo,?getThreadUserTime,?getTotalStartedThreadCount,?hashCode,?isCurrentThreadCpuTimeSupported,?isObjectMonitorUsageSupported,?isSynchronizerUsageSupported,?isThreadAllocatedMemoryEnabled,?isThreadAllocatedMemorySupported,?isThreadContentionMonitoringEnabled,?isThreadContentionMonitoringSupported,?isThreadCpuTimeEnabled,?isThreadCpuTimeSupported,?notify,?notifyAll,?resetPeakThreadCount,?setThreadAllocatedMemoryEnabled,?setThreadContentionMonitoringEnabled,?setThreadCpuTimeEnabled,?toString,?wait]??groovy:000>?tb.class.methods.findAll?{?it.name?=~?/Alloc/}.each?{?println?it?};??null??public?boolean?sun.management.ThreadImpl.isThreadAllocatedMemoryEnabled()??public?boolean?sun.management.ThreadImpl.isThreadAllocatedMemorySupported()??public?long[]?sun.management.ThreadImpl.getThreadAllocatedBytes(long[])??public?long?sun.management.ThreadImpl.getThreadAllocatedBytes(long)??public?void?sun.management.ThreadImpl.setThreadAllocatedMemoryEnabled(boolean)??===>?null??groovy:000>?tb.threadAllocatedMemoryEnabled??===>?true??groovy:000>?tid?=?Thread.currentThread().id??===>?1??groovy:000>?tb.getThreadAllocatedBytes(tid)??===>?48106672??groovy:000>?tb.getThreadAllocatedBytes(tid)??===>?48751520??groovy:000>?tb.getThreadAllocatedBytes(tid)??===>?49384752??groovy:000>?tb.getThreadAllocatedBytes(tid)??===>?50086240??groovy:000>?quit??
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