/** Gets the median timestamp of the last 11 blocks */
private static long getMedianTimestampOfRecentBlocks(StoredBlock storedBlock, BlockStore store)
throws BlockStoreException {
long[] timestamps = new long[11];
int unused = 9;
timestamps[10] = storedBlock.getHeader().getTimeSeconds();
while (unused >= 0 && (storedBlock = storedBlock.getPrev(store)) != null)
timestamps[unused--] = storedBlock.getHeader().getTimeSeconds();
Arrays.sort(timestamps, unused + 1, 11);
return timestamps[unused + (11 - unused) / 2];
}
/**
* Returns the set of contiguous blocks between 'higher' and 'lower'. Higher is included, lower is
* not.
*/
private static LinkedList<StoredBlock> getPartialChain(
StoredBlock higher, StoredBlock lower, BlockStore store) throws BlockStoreException {
checkArgument(higher.getHeight() > lower.getHeight(), "higher and lower are reversed");
LinkedList<StoredBlock> results = new LinkedList<StoredBlock>();
StoredBlock cursor = higher;
while (true) {
results.add(cursor);
cursor = checkNotNull(cursor.getPrev(store), "Ran off the end of the chain");
if (cursor.equals(lower)) break;
}
return results;
}
/**
* Locates the point in the chain at which newStoredBlock and chainHead diverge. Returns null if
* no split point was found (ie they are part of the same chain).
*/
private StoredBlock findSplit(StoredBlock newChainHead, StoredBlock chainHead)
throws BlockStoreException {
StoredBlock currentChainCursor = chainHead;
StoredBlock newChainCursor = newChainHead;
// Loop until we find the block both chains have in common. Example:
//
// A -> B -> C -> D
// \--> E -> F -> G
//
// findSplit will return block B. chainHead = D and newChainHead = G.
while (!currentChainCursor.equals(newChainCursor)) {
if (currentChainCursor.getHeight() > newChainCursor.getHeight()) {
currentChainCursor = currentChainCursor.getPrev(blockStore);
assert currentChainCursor != null : "Attempt to follow an orphan chain";
} else {
newChainCursor = newChainCursor.getPrev(blockStore);
assert newChainCursor != null : "Attempt to follow an orphan chain";
}
}
return currentChainCursor;
}
/**
* Locates the point in the chain at which newStoredBlock and chainHead diverge. Returns null if
* no split point was found (ie they are not part of the same chain). Returns newChainHead or
* chainHead if they don't actually diverge but are part of the same chain.
*/
private static StoredBlock findSplit(
StoredBlock newChainHead, StoredBlock oldChainHead, BlockStore store)
throws BlockStoreException {
StoredBlock currentChainCursor = oldChainHead;
StoredBlock newChainCursor = newChainHead;
// Loop until we find the block both chains have in common. Example:
//
// A -> B -> C -> D
// \--> E -> F -> G
//
// findSplit will return block B. oldChainHead = D and newChainHead = G.
while (!currentChainCursor.equals(newChainCursor)) {
if (currentChainCursor.getHeight() > newChainCursor.getHeight()) {
currentChainCursor = currentChainCursor.getPrev(store);
checkNotNull(currentChainCursor, "Attempt to follow an orphan chain");
} else {
newChainCursor = newChainCursor.getPrev(store);
checkNotNull(newChainCursor, "Attempt to follow an orphan chain");
}
}
return currentChainCursor;
}
/**
* Returns the set of contiguous blocks between 'higher' and 'lower'. Higher is included, lower is
* not.
*/
private List<StoredBlock> getPartialChain(StoredBlock higher, StoredBlock lower)
throws BlockStoreException {
assert higher.getHeight() > lower.getHeight();
LinkedList<StoredBlock> results = new LinkedList<StoredBlock>();
StoredBlock cursor = higher;
while (true) {
results.add(cursor);
cursor = cursor.getPrev(blockStore);
assert cursor != null : "Ran off the end of the chain";
if (cursor.equals(lower)) break;
}
return results;
}
/**
* Called as part of connecting a block when the new block results in a different chain having
* higher total work.
*
* <p>if (shouldVerifyTransactions) Either newChainHead needs to be in the block store as a
* FullStoredBlock, or (block != null && block.transactions != null)
*/
private void handleNewBestChain(
StoredBlock storedPrev, StoredBlock newChainHead, Block block, boolean expensiveChecks)
throws BlockStoreException, VerificationException, PrunedException {
checkState(lock.isHeldByCurrentThread());
// This chain has overtaken the one we currently believe is best. Reorganize is required.
//
// Firstly, calculate the block at which the chain diverged. We only need to examine the
// chain from beyond this block to find differences.
StoredBlock head = getChainHead();
final StoredBlock splitPoint = findSplit(newChainHead, head, blockStore);
log.info("Re-organize after split at height {}", splitPoint.getHeight());
log.info("Old chain head: {}", head.getHeader().getHashAsString());
log.info("New chain head: {}", newChainHead.getHeader().getHashAsString());
log.info("Split at block: {}", splitPoint.getHeader().getHashAsString());
// Then build a list of all blocks in the old part of the chain and the new part.
final LinkedList<StoredBlock> oldBlocks = getPartialChain(head, splitPoint, blockStore);
final LinkedList<StoredBlock> newBlocks = getPartialChain(newChainHead, splitPoint, blockStore);
// Disconnect each transaction in the previous main chain that is no longer in the new main
// chain
StoredBlock storedNewHead = splitPoint;
if (shouldVerifyTransactions()) {
for (StoredBlock oldBlock : oldBlocks) {
try {
disconnectTransactions(oldBlock);
} catch (PrunedException e) {
// We threw away the data we need to re-org this deep! We need to go back to a peer with
// full
// block contents and ask them for the relevant data then rebuild the indexs. Or we could
// just
// give up and ask the human operator to help get us unstuck (eg, rescan from the genesis
// block).
// TODO: Retry adding this block when we get a block with hash e.getHash()
throw e;
}
}
StoredBlock cursor;
// Walk in ascending chronological order.
for (Iterator<StoredBlock> it = newBlocks.descendingIterator(); it.hasNext(); ) {
cursor = it.next();
Block cursorBlock = cursor.getHeader();
if (expensiveChecks
&& cursorBlock.getTimeSeconds()
<= getMedianTimestampOfRecentBlocks(cursor.getPrev(blockStore), blockStore))
throw new VerificationException("Block's timestamp is too early during reorg");
TransactionOutputChanges txOutChanges;
if (cursor != newChainHead || block == null) txOutChanges = connectTransactions(cursor);
else txOutChanges = connectTransactions(newChainHead.getHeight(), block);
storedNewHead = addToBlockStore(storedNewHead, cursorBlock.cloneAsHeader(), txOutChanges);
}
} else {
// (Finally) write block to block store
storedNewHead = addToBlockStore(storedPrev, newChainHead.getHeader());
}
// Now inform the listeners. This is necessary so the set of currently active transactions (that
// we can spend)
// can be updated to take into account the re-organize. We might also have received new coins we
// didn't have
// before and our previous spends might have been undone.
for (final ListenerRegistration<BlockChainListener> registration : listeners) {
if (registration.executor == Threading.SAME_THREAD) {
// Short circuit the executor so we can propagate any exceptions.
// TODO: Do we really need to do this or should it be irrelevant?
registration.listener.reorganize(splitPoint, oldBlocks, newBlocks);
} else {
registration.executor.execute(
new Runnable() {
@Override
public void run() {
try {
registration.listener.reorganize(splitPoint, oldBlocks, newBlocks);
} catch (VerificationException e) {
log.error("Block chain listener threw exception during reorg", e);
}
}
});
}
}
// Update the pointer to the best known block.
setChainHead(storedNewHead);
}