Having Trouble understanding CNI string allocation

Mon Sep 27 19:19:00 GMT 2004

Where are you keeping the pointers to the java::lang::Strings? They must 
be kept in something that can be seen by the garbage collector - either 
on the stack or in a java array. As Andrew pointed out, you can't keep 
Java object references in C arrays or any structure alocated by malloc 
or C++ "new" because the garbage collector won't see them.
Bryce
Sebastian Kloska wrote:
> Thank you very much --
>> How's about these random errors when doing all String
> allocation dynamically (i.e. java::lang::String * is
> only used for one call and then forgotten). Is this
> explainable from within CNI or should I try to find
> the misbehaviour in the JDBC driver ?
>> BTW I'm sing gcj-3.3.3 as shipped with Fedora Core 2
>> Thanks
>> Sebastian
>>> Andrew Haley wrote:
>>> Sebastian Kloska writes:
>> > > In an attempt to reduce the calls to JvNewStringUTF I was trying
>> > to store the colum names I like it access in an array of
>> > 'java::lang::String *', but after initializatons (as a none static
>> > class array) and befor using these pointers in another class method
>> > the strings seem to be gone. So it seems I do not realy understand
>> > the concept of how long I'm alowed to hold a (valid ?) reference
>> > to an JAVA object (e.g. String) and that somehow the garbage
>> > collector is 'stealing' these from me....
>>>> The gcj garbage collector will recycle memory when it determines that
>> there are no live references to it. The gc won't look inside
>> structures allocated by malloc() or the C++ runtime library's new().
>>>> If you want to make an array of 'java::lang::String *' you had better
>> make it a JArray<jstring>, not a C++ array, and you'd better make sure
>> that a pointer to that jarray is live in a Java object somewhere, or
>> the strings will be deallocated.
>>>> Andrew.
>>>