node接收交易的條件
===

# 不收同時指向衝突交易的交易

由[確認的一節](https://hackmd.io/s/HyYil3DYz#%E5%A4%A7%E9%87%8F-tip-%E6%8C%87%E5%90%91%E5%85%A9%E7%AD%86%E8%A1%9D%E7%AA%81%E4%BA%A4%E6%98%93)可以知道要避免收這樣的交易

所以來看IRI的實作

相關的code:

在[UDPReceiver.java的spawnReceiverThread](https://github.com/iotaledger/iri/blob/dev/src/main/java/com/iota/iri/network/UDPReceiver.java#L57)

 byte[] bytes = Arrays.copyOf(receivingPacket.getData(), receivingPacket.getLength());
                        SocketAddress address = receivingPacket.getSocketAddress();

                        processor.submit(() -> node.preProcessReceivedData(bytes, address, "udp"));
                        processed++;

                        Thread.yield();

有node.preProcessReceivedData這個函數

在[Node.java](https://github.com/iotaledger/iri/blob/dev/src/main/java/com/iota/iri/network/Node.java#L223)可以找到preProcessReceivedData的實做

中間的一段

 //if valid - add to receive queue (receivedTransactionViewModel, neighbor)
                        addReceivedDataToReceiveQueue(receivedTransactionViewModel, neighbor);

addReceivedDataToReceiveQueue會把收到的交易放進receiveQueue

  public void addReceivedDataToReceiveQueue(TransactionViewModel receivedTransactionViewModel, Neighbor neighbor) {
        receiveQueue.add(new ImmutablePair<>(receivedTransactionViewModel, neighbor));
        if (receiveQueue.size() > RECV_QUEUE_SIZE) {
            receiveQueue.pollLast();
        }

receiveQueue在processReceivedDataFromQueue調用pollFirst

而 Node.java會開另一個thread:[spawnProcessReceivedThread](https://github.com/iotaledger/iri/blob/dev/src/main/java/com/iota/iri/network/Node.java#L558)

這個thread會調用processReceivedDataFromQueue

while (!shuttingDown.get()) {

                try {
                    processReceivedDataFromQueue();
                    Thread.sleep(1);
                } catch (final Exception e) {
                    log.error("Process Received Data Thread Exception:", e);
                }
            }

[processReceivedDataFromQueue](https://github.com/iotaledger/iri/blob/dev/src/main/java/com/iota/iri/network/Node.java#L364)會調用processReceivedData

 final Pair<TransactionViewModel, Neighbor> receivedData = receiveQueue.pollFirst();
        if (receivedData != null) {
            processReceivedData(receivedData.getLeft(), receivedData.getRight());
        }

[processReceivedData](https://github.com/iotaledger/iri/blob/dev/src/main/java/com/iota/iri/network/Node.java#L378) 這個函數會把收到的交易寫到 $tangle$

        //store new transaction
        try {
            stored = receivedTransactionViewModel.store(tangle);
        } catch (Exception e) {
            log.error("Error accessing persistence store.", e);
            neighbor.incInvalidTransactions();
        }

所以node藉由UDP的鄰居收交易

開兩個thread , 一個收socket的data放進receiveQueue , 另一個從receiveQueue放進 $tangle$

從這段過程來看 , 並沒有檢查交易是否同時指向衝突交易

###### tags: `IOTA`