Using libgcj with different memory management library.

abhishek desai
Mon Jun 8 09:43:00 GMT 2009

> I don't understand how this can work.  The gc is a memory manager; how
> can it use some other memory manager to do its own work?  You'll have
> to explain a little more.

From what I understand GC uses GC_unix_get_mem to allocate memory
which calls mmap on /dev/zero on my system. This memory is managed by
GC for object allocation and also for GC internal working. I hope this
is correct. What I want to do is replace the mmap with my_malloc call
which will return a pointer to the allocated memory. my_malloc will
allocate memory from an internal fixed memory pool.

On Mon, Jun 8, 2009 at 2:39 PM, Andrew Haley<> wrote:
> abhishek desai wrote:
>> 1. As per my understanding libgcj uses boehm garbage collector for
>> memory allocations. Are there any allocations in libgcj which are
>> not routed to the garbage collector ? specially the parts of the
>> library written in C++. From what I understand is that the memory
>> allocated with the 'new' operator are routed to the gc .
> Not exactly.  If you have a Java class, i.e. one which inherits from
> java.lang.Object, then its new uses the GC.
>> Is it necessary that the class of object being allocated should be
>> derived from the 'object' class for it to be allocated on the gc ?
>> or all the allocations with new get routed to gc ?
> Yes, it is.  Of course, you can always overload new in your own classes
> to use the Boehm gc, evernif they don't derive from Object.  You'll
> have to make sure they're marked correctly, though.
>> 2. I have a memory manager which allocates memory from a specific
>> memory pool. I want to port boehm gc to use this memory manager for
>> its allocations.
> I don't understand how this can work.  The gc is a memory manager; how
> can it use some other memory manager to do its own work?  You'll have
> to explain a little more.
>> Can someone give me some pointers as to where I can make the
>> necessary modifications ? I can see the gcconfig.h and os_dep.c is
>> the file containing the final system memory allocation calls.  Is
>> there some other place I need to look at ? Are there any tricky
>> issues I need to look at while doing the porting ?
> You'll need to the gc just to scan your memory pool, or also manage
> it?  Doing the latter will be hard, the former easy.
> Andrew.

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