https://issues.apache.org/bugzilla/show_bug.cgi?id=46962

           Summary: Deadlock in PropertyCache class
           Product: Fop
           Version: 0.95
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: general
        AssignedTo: fop-dev@xmlgraphics.apache.org
        ReportedBy: ro...@devexperts.com


I have a multithreaded rendering application. Shortly after we had migrated to
some nice smooth and very fast hardware, we started getting Java deadlocks in
FOP code. Stack traces always looked like this one:

"T4-CFD_MR accId=3065" prio=10 tid=0x00002aab37aa1400 nid=0x6123 waiting for
monitor entry [0x000000004193e000..0x0000000041941ac0]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at
org.apache.fop.fo.properties.PropertyCache.get(PropertyCache.java:204)
        - waiting to lock <0x00002aaab388a3f8> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:283)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:301)
        at
org.apache.fop.fo.properties.NumberProperty.getInstance(NumberProperty.java:120)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:262)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)
        at
org.apache.fop.fo.expr.PropertyParser.parseAdditiveExpr(PropertyParser.java:151)
        at
org.apache.fop.fo.expr.PropertyParser.parseArgs(PropertyParser.java:378)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:343)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)
        at
org.apache.fop.fo.expr.PropertyParser.parseAdditiveExpr(PropertyParser.java:151)
        at
org.apache.fop.fo.expr.PropertyParser.parseProperty(PropertyParser.java:125)

================================

"T3-CFD_MR accId=3031" prio=10 tid=0x00002aab37a68800 nid=0x6122 waiting for
monitor entry [0x000000004183c000..0x0000000041840c40]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:226)
        - waiting to lock <0x00002aaab388a650> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b200> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b228> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b250> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b278> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b2a0> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)
        - locked <0x00002aaab388b368> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.rehash(PropertyCache.java:228)

================================

"T2-CFD_MR accId=2823" prio=10 tid=0x00002aab37a66c00 nid=0x6121 waiting for
monitor entry [0x000000004173c000..0x000000004173fbc0]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at
org.apache.fop.fo.properties.PropertyCache.cleanSegment(PropertyCache.java:114)
        - waiting to lock <0x00002aaab38a33b8> (a [Z)
        at
org.apache.fop.fo.properties.PropertyCache.put(PropertyCache.java:176)
        - locked <0x00002aaab388a650> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:287)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:301)
        at
org.apache.fop.fo.properties.NumberProperty.getInstance(NumberProperty.java:120)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:262)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)
        at
org.apache.fop.fo.expr.PropertyParser.parseAdditiveExpr(PropertyParser.java:151)
        at
org.apache.fop.fo.expr.PropertyParser.parseArgs(PropertyParser.java:378)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:343)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)

================================

"T1-CFD_MR accId=3070" prio=10 tid=0x00002aab37a5a000 nid=0x6120 waiting for
monitor entry [0x000000004163c000..0x000000004163ed40]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at
org.apache.fop.fo.properties.PropertyCache.cleanSegment(PropertyCache.java:114)
        - waiting to lock <0x00002aaab38a33b8> (a [Z)
        at
org.apache.fop.fo.properties.PropertyCache.put(PropertyCache.java:176)
        - locked <0x00002aaab388a330> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:287)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:301)
        at
org.apache.fop.fo.properties.NumberProperty.getInstance(NumberProperty.java:109)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:258)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)
        at
org.apache.fop.fo.expr.PropertyParser.parseAdditiveExpr(PropertyParser.java:151)
        at
org.apache.fop.fo.expr.PropertyParser.parseProperty(PropertyParser.java:125)
        at org.apache.fop.fo.expr.PropertyParser.parse(PropertyParser.java:91)
        at
org.apache.fop.fo.properties.PropertyMaker.make(PropertyMaker.java:436)
        at
org.apache.fop.fo.properties.CompoundPropertyMaker.make(CompoundPropertyMaker.java:207)

================================

"T0-CFD_MR accId=2852" prio=10 tid=0x00002aab37a59800 nid=0x611f waiting for
monitor entry [0x000000004153a000..0x000000004153dcc0]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at
org.apache.fop.fo.properties.PropertyCache.cleanSegment(PropertyCache.java:114)
        - waiting to lock <0x00002aaab38a33b8> (a [Z)
        at
org.apache.fop.fo.properties.PropertyCache.put(PropertyCache.java:176)
        - locked <0x00002aaab388a3f8> (a
org.apache.fop.fo.properties.PropertyCache$CacheSegment)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:287)
        at
org.apache.fop.fo.properties.PropertyCache.fetch(PropertyCache.java:301)
        at
org.apache.fop.fo.properties.NumberProperty.getInstance(NumberProperty.java:120)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:262)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)
        at
org.apache.fop.fo.expr.PropertyParser.parseAdditiveExpr(PropertyParser.java:151)
        at
org.apache.fop.fo.expr.PropertyParser.parseArgs(PropertyParser.java:378)
        at
org.apache.fop.fo.expr.PropertyParser.parsePrimaryExpr(PropertyParser.java:343)
        at
org.apache.fop.fo.expr.PropertyParser.parseUnaryExpr(PropertyParser.java:212)
        at
org.apache.fop.fo.expr.PropertyParser.parseMultiplicativeExpr(PropertyParser.java:177)

================================
END OF STACKS


with some combination of get(), put(), cleanSegment() and rehash() methods.

Can you provide any kind of workaround for this that can be done quickly ?? We
are in production and suffer from these nasty deadlocks badly, since this
application is mostly launched by schedule and we can't monitor it all the
time. Is there something that can be done ??

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