[PATCH] Deadlock in PropertyCache class

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 ??