Every now and then you look at some code and think that it cannot be possibly be wrong. Once you have ruled out a simple programmer screw up / enemy action in code (Make sure you read Java Puzzlers or similar) or a concurrency issue (Read Java Concurrency or go on Dr Heniz excellent course) you should sit back and take a few days and then starting thinking about whether the JDK is indeed out to get you. I haven’t seen one in the wild in my 18 odd years as a Java programmer so it kinda took me by surprise.
If you are running against JDK 8 in a large scale Swing application you might eventually see the following exception, lots of lots of times. (Unless you forgot the lesson learned in my previous blog in your logging code, in which case you might see lots of ArrayOfOutBoundsException)
01 02 03 04 05 06 07 08 09 10 11 12 13 14 | 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) ... |
This error is particularly insidious because it takes around ten minutes to show itself and sometimes not at all. If you look at the code for this class the line in question, starts with “startsFrom = break”, only accesses two local variables both of which have been previously referenced in the method.
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 | 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; } } |
The most direct way to rule out a JIT error is to disable compilation for just this single method, here is an example; but you can fine more in the documentation for the command line java tool.
1 | javaThing -XX:CompileCommand=exclude,javax/swing/text/GlyphView,getBreakSpot |
When this parameter is added, the problem goes away. – since we have ruled out enemy action by code or a concurrency issue we can be more sure this is a JIT issue. Now as part of the bug logging for this I output diagnostics for this single method, and found out that the problem, didn’t occur until the method was JITted for a fifth time.
1 | javaThing -XX:CompileCommand=print,javax/swing/text/GlyphView,getBreakSpot |
Here is some diagnostic output seen with the above command:
001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 | Compiled method (c2) 914078 33142 4 javax.swing.text.GlyphView::getBreakSpot (247 bytes) total in heap [0x00002aaab0749e10,0x00002aaab0750fe0] = 29136 relocation [0x00002aaab0749f38,0x00002aaab074a1e8] = 688 constants [0x00002aaab074a200,0x00002aaab074a2a0] = 160 main code [0x00002aaab074a2a0,0x00002aaab074cde0] = 11072 stub code [0x00002aaab074cde0,0x00002aaab074ce40] = 96 oops [0x00002aaab074ce40,0x00002aaab074ce58] = 24 metadata [0x00002aaab074ce58,0x00002aaab074d058] = 512 scopes data [0x00002aaab074d058,0x00002aaab074ea20] = 6600 scopes pcs [0x00002aaab074ea20,0x00002aaab0750c50] = 8752 dependencies [0x00002aaab0750c50,0x00002aaab0750c80] = 48 handler table [0x00002aaab0750c80,0x00002aaab0750e90] = 528 nul chk table [0x00002aaab0750e90,0x00002aaab0750fe0] = 336OopMapSet contains 113 OopMaps#0OopMap{[8]=Oop [32]=Oop [40]=Oop off=892}#1OopMap{[32]=Oop [40]=Oop off=960}#2OopMap{[32]=Oop [40]=Oop off=980}#3OopMap{[32]=Oop [40]=Oop [48]=Oop off=1048}#4OopMap{[32]=Oop [40]=Oop [48]=Oop off=1084}#5OopMap{[0]=Oop [24]=Oop [48]=Oop [56]=Oop [80]=Oop off=2500}#6OopMap{rbx=Oop rdi=Oop [32]=Oop [40]=Oop [112]=Oop off=2533}#7OopMap{rbx=Oop rdi=Oop r14=Oop [32]=Oop [112]=Oop off=3081}#8OopMap{rbx=Oop rdi=Oop r14=Oop [32]=Oop [40]=Oop [112]=Oop off=3190}#9OopMap{[8]=Oop [32]=Oop [40]=Oop off=4408}#10OopMap{[32]=Oop [40]=Oop [48]=Oop off=4640}#11OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=5232}#12OopMap{rbp=Oop [0]=NarrowOop [32]=Oop off=5364}#13OopMap{[32]=Oop [40]=Oop [48]=Oop off=5408}#14OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5436}#15OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5468}#16OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop off=5524}#17OopMap{rbp=Oop [32]=Oop [40]=Oop [48]=Oop [88]=Oop off=5552}#18OopMap{[32]=Oop [40]=Oop [48]=Oop [64]=Oop [72]=Derived_oop_[64] [112]=Oop off=5608}#19OopMap{[8]=Oop [32]=Oop off=5680}#20OopMap{rbp=Oop off=5720}#21OopMap{rbp=Oop off=5752}#22OopMap{rbp=Oop [24]=NarrowOop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop [56]=Oop [64]=Oop [88]=Oop off=5812}#23OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop [88]=Oop off=5960}#24OopMap{[0]=Oop [24]=Oop [48]=Oop [56]=Oop [72]=Oop [88]=NarrowOop off=6056}#25OopMap{[40]=Oop off=6088}#26OopMap{[0]=Oop off=6120}#27OopMap{[8]=Oop [24]=Oop [56]=Oop [72]=Oop [112]=Oop off=6216}#28OopMap{[0]=Oop [32]=NarrowOop [40]=Oop off=6284}#29OopMap{rbp=Oop [16]=Oop [40]=Oop [64]=Oop [112]=Oop off=6384}#30OopMap{[0]=Oop off=6412}#31OopMap{[0]=Oop [16]=Oop [32]=NarrowOop [40]=Oop [48]=Oop off=6488}#32OopMap{rbp=Oop [16]=Oop [40]=Oop [48]=Oop off=6560}#33OopMap{[32]=Oop [40]=Oop [48]=Oop [64]=Oop [112]=Oop off=6608}#34OopMap{[8]=Oop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop off=6768}#35OopMap{rbp=NarrowOop [0]=Oop [16]=Oop [32]=Oop [40]=NarrowOop off=6860}#36OopMap{[0]=Oop [16]=Oop [32]=NarrowOop [40]=Oop [48]=Oop off=6988}#37OopMap{rbp=Oop [32]=Oop off=7024}#38OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=7260}#39OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=7344}#40OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [60]=NarrowOop [64]=Oop off=7452}#41OopMap{rbp=NarrowOop [32]=Oop off=7476}#42OopMap{rbp=NarrowOop [0]=Oop off=7524}#43OopMap{[32]=Oop [40]=Oop [48]=Oop off=7588}#44OopMap{[32]=Oop [40]=Oop [48]=Oop off=7616}#45OopMap{[32]=Oop [40]=Oop [48]=Oop off=7632}#46OopMap{rbp=NarrowOop [32]=Oop off=7676}#47OopMap{rbp=NarrowOop [0]=Oop off=7724}#48OopMap{[0]=Oop [16]=Oop [28]=NarrowOop [40]=Oop [48]=Oop [56]=NarrowOop [64]=Oop off=7868}#49OopMap{[8]=Oop [28]=NarrowOop [32]=Oop [40]=Oop [48]=Oop [56]=Oop off=7916}#50OopMap{rbp=Oop [16]=Oop [24]=NarrowOop off=8016}#51OopMap{rbp=Oop [16]=Oop [28]=NarrowOop off=8080}#52OopMap{rbp=NarrowOop [0]=Oop [24]=Oop [32]=Oop off=8152}#53OopMap{rbp=Oop [8]=NarrowOop off=8212}#54OopMap{rbp=NarrowOop [32]=Oop off=8236}#55OopMap{rbp=Oop [16]=NarrowOop off=8272}#56OopMap{rbp=NarrowOop [0]=Oop off=8320}#57OopMap{rbp=Oop [12]=NarrowOop off=8360}#58OopMap{rbp=NarrowOop [32]=Oop off=8400}#59OopMap{rbp=Oop [12]=NarrowOop off=8460}#60OopMap{rbp=NarrowOop [0]=Oop off=8508}#61OopMap{rbp=Oop [24]=NarrowOop [40]=Oop off=8572}#62OopMap{rbp=Oop off=8600}#63OopMap{rbp=Oop [8]=Oop [28]=NarrowOop off=8640}#64OopMap{rbp=Oop [8]=Oop [20]=NarrowOop [112]=Oop off=8704}#65OopMap{rbp=Oop [16]=Oop [24]=Oop [48]=Oop off=8788}#66OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=8912}#67OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9036}#68OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9160}#69OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9284}#70OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9408}#71OopMap{rbp=Oop [16]=Oop [24]=Oop [40]=Oop [64]=Oop off=9532}#72OopMap{off=9556}#73OopMap{off=9580}#74OopMap{off=9604}#75OopMap{[112]=Oop off=9628}#76OopMap{rbp=Oop [8]=Oop [24]=Oop [32]=NarrowOop off=9696}#77OopMap{rbp=Oop [8]=Oop [24]=NarrowOop off=9760}#78OopMap{off=9784}#79OopMap{off=9812}#80OopMap{off=9836}#81OopMap{off=9860}#82OopMap{off=9884}#83OopMap{off=9908}#84OopMap{off=9932}#85OopMap{off=9956}#86OopMap{off=9980}#87OopMap{off=10004}#88OopMap{off=10028}#89OopMap{rbp=Oop [16]=Oop [28]=NarrowOop off=10092}#90OopMap{rbp=Oop [16]=Oop [24]=Oop [48]=Oop off=10176}#91OopMap{off=10200}#92OopMap{off=10224}#93OopMap{off=10248}#94OopMap{off=10272}#95OopMap{off=10296}#96OopMap{off=10320}#97OopMap{off=10344}#98OopMap{off=10368}#99OopMap{off=10392}#100OopMap{off=10416}#101OopMap{off=10440}#102OopMap{off=10464}#103OopMap{off=10488}#104OopMap{off=10512}#105OopMap{off=10536}#106OopMap{off=10560}#107OopMap{off=10584}#108OopMap{off=10608}#109OopMap{off=10632}#110OopMap{off=10656}#111OopMap{off=10680}#112OopMap{off=11028}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.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) |
Now I am still working with the JDK team for a fix for this one; but I do feel I have discovered a useful set of tools for providing some evidence that the JIT compiler is causing my bad day. And more importantly I have a workaround so I can run my tests until this is resolved.
| Reference: | But that’s impossible, or finding out that the JIT has broken your code. from our JCG partner Gerard Davison at the Gerard Davison’s blog blog. |
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