README

Invoke this script like so 
./snow_leopard_garbage_collection.d -p [PID]

where pid is the process id of the app you are trying to trace
you may need to do

chmod +x snow_leopard_garbage_collection.d 

to fix the permissions on the dtrace script so you can invoke it

snow_leopard_garbage_collection.d

#!/usr/sbin/dtrace -s

garbage_collection$target:::collection_begin
{
	self->collectionString = (arg1 == 0 ? "full" : (arg1 == 1 ? "generational" : "local"));
	self->collectionBeginTime = vtimestamp;
}

garbage_collection$target:::collection_end
{
	self->collectionTotalTime = (vtimestamp - self->collectionBeginTime)/1000;

	printf("\nDuration Time (ms) %d",self->collectionTotalTime);
	printf("\n%d Objects Reclaimed (%d bytes) on Thread %x",(int)arg1,(int)arg2,tid);
	printf("\nCollection Type: %s\n",self->collectionString);
	printf("Bytes in use %d",(int)arg4);
	printf(" Number in Use %d",(int)arg3);
	ustack();
}