/**
* Resize an existing block to new capacity by slicing the <code>Pointer</code> pointed to by
* existing pointer. The new <code>Pointer</code> is a slice present before the existing.
*
* @param existing points to existing Pointer(referring existing block).
* @param capacity to be resized to.
* @return Pointer to resized block.
*/
private Pointer slice(Pointer existing, int capacity) {
if ((existing.getEnd() - existing.getStart()) == capacity + 1 && existing.isFree()) {
return existing;
}
Pointer fresh = new Pointer();
fresh.setBlockNumber(existing.getBlockNumber());
fresh.setStart(existing.getStart());
fresh.setEnd(fresh.getStart() + capacity);
fresh.setFree(true);
fresh.setPrev(existing.getPrev());
existing.setPrev(fresh);
fresh.setNext(existing);
existing.setStart(existing.getStart() + (capacity + 1));
return fresh;
}
/*
* (non-Javadoc)
*
* @see com.prashant.memory.MemoryBuffer#store(byte[], int)
*/
public synchronized Pointer store(byte[] payload, int capacity) throws DMBufferOverFlowException {
// First good match is page that has capacity equal or greater than
// payload.
Pointer goodOne = firstMatch(capacity);
if (goodOne == null) {
RuntimeException e = new NullPointerException();
// logger.error("Did not find a suitable buffer");
throw new DMBufferOverFlowException("did not find a suitable buffer", e.getCause());
}
Pointer fresh = slice(goodOne, capacity);
fresh.setFree(false);
used.addAndGet(payload.length);
ByteBuffer buf = buffer.slice();
buf.position(fresh.getStart());
try {
buf.put(payload);
} catch (BufferOverflowException e) {
goodOne.setStart(fresh.getStart());
goodOne.setEnd(buffer.limit());
// return null; //Uncomment incase we want to ignore this exception.
throw new DMBufferOverFlowException(
"An attempt to store more than the configured capacity", e.getCause());
}
pointers.add(fresh);
return fresh;
}
/**
* It is synchronized as it does merging of adjacent blocks. An easiest way to somewhat address
* fragmentation problem.
*
* @param pointer2free
*/
private void freeAndMerge(Pointer pointer2free) {
synchronized (pointers) {
pointers.remove(pointer2free);
// merge adjacent blocks
if (null != pointer2free.getPrev() && pointer2free.getPrev().isFree()) {
// Merge previous
pointers.remove(pointer2free.getPrev());
pointer2free.setStart(pointer2free.getPrev().getStart());
pointer2free.setPrev(pointer2free.getPrev().getPrev());
// Recursive call
freeAndMerge(pointer2free);
}
if (null != pointer2free.getNext() && pointer2free.getNext().isFree()) {
// Merge Next
pointers.remove(pointer2free.getNext());
pointer2free.setEnd(pointer2free.getNext().getEnd());
pointer2free.setNext(pointer2free.getNext().getNext());
// Recursive call
freeAndMerge(pointer2free);
}
if (!pointer2free.isFree()) {
pointer2free.setFree(true);
pointer2free.setClazz(null);
pointers.add(pointer2free);
}
}
}
private Pointer createAndAddFirstPointer() {
Pointer first = new Pointer();
first.setBlockNumber(0);
first.setStart(0);
first.setFree(true);
first.setEnd(buffer.capacity() - 1);
first.setNext(null);
first.setPrev(null);
pointers.add(first);
return first;
}
