Can't pass exceptions with Java 7 : java.lang.Throwable.suppressedExceptions

With Java 7, Throwables can no longer be sent successfully over CapTP. The 
error is:

=== 2012-05-14T14:44:15.109Z 
(CapTPConnection.whyNoDeliverOnlyOp:CapTPConnection.java:837) WRN
captp: whyNoDeliverOnlyOp(4, run, java.lang.ClassCastException: cannot 
assign instance of org.erights.e.elib.ref.OldFarRef to field 
java.lang.Throwable.suppressedExceptions of type java.util.List in instance 
of java.lang.ClassCastException)
--vvvv--
cannot assign instance of org.erights.e.elib.ref.OldFarRef to field 
java.lang.Throwable.suppressedExceptions of type java.util.List in instance 
of java.lang.ClassCastException


java.lang.ClassCastException: cannot assign instance of 
org.erights.e.elib.ref.OldFarRef to field 
java.lang.Throwable.suppressedExceptions of type java.util.List in instance 
of java.lang.ClassCastException
         at 
java.io.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2063)
         at 
java.io.ObjectStreamClass.setObjFieldValues(ObjectStreamClass.java:1241)
         at 
java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1970)
         at 
java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:498)
         at java.lang.Throwable.readObject(Throwable.java:913)
         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
         at 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
         at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
         at java.lang.reflect.Method.invoke(Method.java:601)
         at 
java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1004)
         at 
java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1866)
         at 
java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)
         at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
         at 
java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1964)
         at 
java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1888)
         at 
java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)
         at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
         at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1685)
         at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1341)
         at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
         at net.captp.jcomm.CapTPConnection.receiveMsg(CapTPConnection.java:741)
         at 
net.captp.jcomm.CapTPConnection.processMessage(CapTPConnection.java:724)
         at 
net.vattp.data.VatTPConnection.newIncomingMsg(VatTPConnection.java:727)
         at net.vattp.data.DataPath.newIncomingMsg(DataPath.java:699)
         at net.vattp.data.DataCommThunk.run(DataCommThunk.java:207)
         at org.erights.e.elib.vat.PendingCall.innerRun(PendingCall.java:75)
         at org.erights.e.elib.vat.PendingEvent.run(PendingEvent.java:74)
         at org.erights.e.elib.vat.HeadlessRunner.run(HeadlessRunner.java:174)
         at java.lang.Thread.run(Thread.java:722)

--^^^^--

The problem seems to be the new list of "suppressed" exceptions attached to 
each Throwable:

http://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#getSuppressed%28%29

CapTPReplacer turns this into a far ref (presumably on the assumption that 
the list may be mutable), but the Throwable created at the destination needs 
a List, not a far ref.

I assume there's some mechanism to handle things like this (since 
getStackTrace(), which also returns an array, works fine).

This hack fixes it, but I'm not sure it's right in general ("unmodifiable" 
seems to mean "read-only" rather than "const"):

(in CapTPReplacer.substitute)

if (ref.getClass().getName().equals("java.util.Collections$UnmodifiableList")) {
	return null;
}

Suggestions?


-- 
Dr Thomas Leonard
IT Innovation Centre
Gamma House, Enterprise Road,
Southampton SO16 7NS, UK


tel: +44 23 8059 8866

mailto:tal-v5nx5w6akNyLE8xUarVfuPLx9OUvmyODWmv/[email protected]
http://www.it-innovation.soton.ac.uk/