代码jit_但这是不可能的，或者无法发现JIT破坏了您的代码。

代码jit

时不时地查看一些代码，并认为它不可能是错误的。一旦排除了简单的程序员搞砸代码/代码中的敌对行为（确保您阅读Java Puzzlers或类似内容）或并发性问题（阅读Java并发性或继续学习Heniz博士的出色课程），您应该坐下来花几天时间然后开始考虑JDK是否确实可以帮助您。在我从事Java程序员的18多年中，我还没有见过如此狂野的家伙，这让我有些惊讶。

如果在大型Swing应用程序中针对JDK 8运行，则最终可能会看到很多次以下异常。（除非您在日志记录代码中忘记了我在上一个博客中获得的教训，在这种情况下，您可能会看到很多ArrayOfOutBoundsException）

Caused by: java.lang.NullPointerException at javax.swing.text.GlyphView.getBreakSpot(GlyphView.java:799) at javax.swing.text.GlyphView.getBreakWeight(GlyphView.java:724) at javax.swing.text.FlowView$LogicalView.getPreferredSpan(FlowView.java:733) at javax.swing.text.FlowView.calculateMinorAxisRequirements(FlowView.java:233) at javax.swing.text.ParagraphView.calculateMinorAxisRequirements(ParagraphView.java:717) at javax.swing.text.BoxView.checkRequests(BoxView.java:935) at javax.swing.text.BoxView.getMinimumSpan(BoxView.java:568) at javax.swing.text.BoxView.calculateMinorAxisRequirements(BoxView.java:903) at javax.swing.text.BoxView.checkRequests(BoxView.java:935) at javax.swing.text.BoxView.setSpanOnAxis(BoxView.java:343) at javax.swing.text.BoxView.layout(BoxView.java:708) at javax.swing.text.BoxView.setSize(BoxView.java:397) ...

此错误特别隐蔽，因为它需要大约十分钟才能显示出来，有时甚至根本不需要。如果您查看该类的代码，则所讨论的行以“ startsFrom = break”开头，仅访问两个局部变量，这两个变量先前已在该方法中进行了引用。

Segment s = getText(pstart, pend); s.first(); BreakIterator breaker = getBreaker(); breaker.setText(s); // Backward search should start from end+1 unless there's NO end+1 int startFrom = end + (pend > end ? 1 : 0); for (;;) { startFrom = breaker.preceding(s.offset + (startFrom - pstart))   + (pstart - s.offset); if (startFrom > start) { // The break spot is within the view bs[ix++] = startFrom; } else { break; } }

排除JIT错误的最直接方法是仅禁用该单一方法的编译，下面是一个示例；但是您可以在命令行Java工具的文档中找到更多信息。

javaThing -XX:CompileCommand=exclude,javax/swing/text/GlyphView,getBreakSpot

添加此参数后，问题就消失了。 –由于我们已通过代码或并发问题排除了敌方行动，因此我们可以确定这是JIT问题。现在，作为此问题的日志记录的一部分，我输出了该单一方法的诊断信息，并发现直到第五次方法被JITted时问题才出现。

javaThing -XX:CompileCommand=print,javax/swing/text/GlyphView,getBreakSpot

这是上面命令显示的一些诊断输出：

Compiled method (c2)  914078 33142       4       javax.swing.text.GlyphView::getBreakSpot (247 bytes)total in heap  [0x00002aaab0749e10,0x00002aaab0750fe0] = 29136relocation     [0x00002aaab0749f38,0x00002aaab074a1e8] = 688constants      [0x00002aaab074a200,0x00002aaab074a2a0] = 160main code      [0x00002aaab074a2a0,0x00002aaab074cde0] = 11072stub code      [0x00002aaab074cde0,0x00002aaab074ce40] = 96oops           [0x00002aaab074ce40,0x00002aaab074ce58] = 24metadata       [0x00002aaab074ce58,0x00002aaab074d058] = 512scopes data    [0x00002aaab074d058,0x00002aaab074ea20] = 6600scopes pcs     [0x00002aaab074ea20,0x00002aaab0750c50] = 8752dependencies   [0x00002aaab0750c50,0x00002aaab0750c80] = 48handler table  [0x00002aaab0750c80,0x00002aaab0750e90] = 528nul chk table  [0x00002aaab0750e90,0x00002aaab0750fe0] = 336
OopMapSet contains 113 OopMaps
#0 
OopMap{[8]=Oop [32]=Oop [40]=Oop off=892}
#1 
OopMap{[32]=Oop [40]=Oop off=960}
#2 
OopMap{[32]=Oop [40]=Oop off=980}
#3 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=1048}
#4 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=1084}
#5 
OopMap{[0]=Oop [24]=Oop [48]=Oop [56]=Oop [80]=Oop off=2500}
#6 
OopMap{rbx=Oop rdi=Oop [32]=Oop [40]=Oop [112]=Oop off=2533}
#7 
OopMap{rbx=Oop rdi=Oop r14=Oop [32]=Oop [112]=Oop off=3081}
#8 
OopMap{rbx=Oop rdi=Oop r14=Oop [32]=Oop [40]=Oop [112]=Oop off=3190}
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OopMap{[8]=Oop [32]=Oop [40]=Oop off=4408}
#10 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=4640}
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OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=5232}
#12 
OopMap{rbp=Oop [0]=NarrowOop [32]=Oop off=5364}
#13 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=5408}
#14 
OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5436}
#15 
OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5468}
#16 
OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5524}
#17 
OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop [88]=Oop off=5552}
#18 
OopMap{[32]=Oop [40]=Oop [48]=Oop [64]=Oop [72]=Derived_oop_[64] [112]=Oop off=5608}
#19 
OopMap{[8]=Oop [32]=Oop off=5680}
#20 
OopMap{rbp=Oop off=5720}
#21 
OopMap{rbp=Oop off=5752}
#22 
OopMap{rbp=Oop [24]=NarrowOop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop [56]=Oop [64]=Oop [88]=Oop off=5812}
#23 
OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop [88]=Oop off=5960}
#24 
OopMap{[0]=Oop [24]=Oop [48]=Oop [56]=Oop [72]=Oop [88]=NarrowOop off=6056}
#25 
OopMap{[40]=Oop off=6088}
#26 
OopMap{[0]=Oop off=6120}
#27 
OopMap{[8]=Oop [24]=Oop [56]=Oop [72]=Oop [112]=Oop off=6216}
#28 
OopMap{[0]=Oop [32]=NarrowOop [40]=Oop off=6284}
#29 
OopMap{rbp=Oop [16]=Oop [40]=Oop [64]=Oop [112]=Oop off=6384}
#30 
OopMap{[0]=Oop off=6412}
#31 
OopMap{[0]=Oop [16]=Oop [32]=NarrowOop [40]=Oop [48]=Oop off=6488}
#32 
OopMap{rbp=Oop [16]=Oop [40]=Oop [48]=Oop off=6560}
#33 
OopMap{[32]=Oop [40]=Oop [48]=Oop [64]=Oop [112]=Oop off=6608}
#34 
OopMap{[8]=Oop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop off=6768}
#35 
OopMap{rbp=NarrowOop [0]=Oop [16]=Oop [32]=Oop [40]=NarrowOop off=6860}
#36 
OopMap{[0]=Oop [16]=Oop [32]=NarrowOop [40]=Oop [48]=Oop off=6988}
#37 
OopMap{rbp=Oop [32]=Oop off=7024}
#38 
OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=7260}
#39 
OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=7344}
#40 
OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [60]=NarrowOop [64]=Oop off=7452}
#41 
OopMap{rbp=NarrowOop [32]=Oop off=7476}
#42 
OopMap{rbp=NarrowOop [0]=Oop off=7524}
#43 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=7588}
#44 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=7616}
#45 
OopMap{[32]=Oop [40]=Oop [48]=Oop off=7632}
#46 
OopMap{rbp=NarrowOop [32]=Oop off=7676}
#47 
OopMap{rbp=NarrowOop [0]=Oop off=7724}
#48 
OopMap{[0]=Oop [16]=Oop [28]=NarrowOop [40]=Oop [48]=Oop [56]=NarrowOop [64]=Oop off=7868}
#49 
OopMap{[8]=Oop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop [56]=Oop off=7916}
#50 
OopMap{rbp=Oop [16]=Oop [24]=NarrowOop off=8016}
#51 
OopMap{rbp=Oop [16]=Oop [28]=NarrowOop off=8080}
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OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=8152}
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OopMap{rbp=Oop [8]=NarrowOop off=8212}
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#55 
OopMap{rbp=Oop [16]=NarrowOop off=8272}
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#57 
OopMap{rbp=Oop [12]=NarrowOop off=8360}
#58 
OopMap{rbp=NarrowOop [32]=Oop off=8400}
#59 
OopMap{rbp=Oop [12]=NarrowOop off=8460}
#60 
OopMap{rbp=NarrowOop [0]=Oop off=8508}
#61 
OopMap{rbp=Oop [24]=NarrowOop [40]=Oop off=8572}
#62 
OopMap{rbp=Oop off=8600}
#63 
OopMap{rbp=Oop [8]=Oop [28]=NarrowOop off=8640}
#64 
OopMap{rbp=Oop [8]=Oop [20]=NarrowOop [112]=Oop off=8704}
#65 
OopMap{rbp=Oop [16]=Oop [24]=Oop [48]=Oop off=8788}
#66 
OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=8912}
#67 
OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9036}
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OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9160}
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OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9284}
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OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9408}
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OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9532}
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OopMap{off=9556}
#73 
OopMap{off=9580}
#74 
OopMap{off=9604}
#75 
OopMap{[112]=Oop off=9628}
#76 
OopMap{rbp=Oop [8]=Oop [24]=Oop [32]=NarrowOop off=9696}
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OopMap{rbp=Oop [8]=Oop [24]=NarrowOop off=9760}
#78 
OopMap{off=9784}
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OopMap{off=9812}
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OopMap{off=10004}
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#89 
OopMap{rbp=Oop [16]=Oop [28]=NarrowOop off=10092}
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OopMap{off=10200}
#92 
OopMap{off=10224}
#93 
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OopMap{off=10368}
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OopMap{off=10416}
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OopMap{off=10440}
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#103 
OopMap{off=10488}
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OopMap{off=10512}
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OopMap{off=10536}
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OopMap{off=10560}
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OopMap{off=10584}
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OopMap{off=10608}
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OopMap{off=10632}
#110 
OopMap{off=10656}
#111 
OopMap{off=10680}
#112 
OopMap{off=11028}
java.lang.NullPointerExceptionat javax.swing.text.GlyphView.getBreakSpot(GlyphView.java:799)at javax.swing.text.GlyphView.getBreakWeight(GlyphView.java:724)at javax.swing.text.html.InlineView.getBreakWeight(InlineView.java:150)at javax.swing.text.FlowView$LogicalView.getPreferredSpan(FlowView.java:733)at javax.swing.text.FlowView.calculateMinorAxisRequirements(FlowView.java:233)at javax.swing.text.ParagraphView.calculateMinorAxisRequirements(ParagraphView.java:717)at javax.swing.text.html.ParagraphView.calculateMinorAxisRequirements(ParagraphView.java:157)at javax.swing.text.BoxView.checkRequests(BoxView.java:935)at javax.swing.text.BoxView.getMinimumSpan(BoxView.java:568)at javax.swing.text.html.ParagraphView.getMinimumSpan(ParagraphView.java:270)at javax.swing.text.BoxView.calculateMinorAxisRequirements(BoxView.java:903)

现在，我仍在与JDK团队合作以解决此问题。但是我确实觉得我已经找到了一套有用的工具，可以提供一些证据来证明JIT编译器正在造成我的麻烦。更重要的是，我有一种解决方法，因此可以运行测试，直到解决为止。