Complete a transaction outside of Solidity

Question

Example for my e-commerce site:

uint public PO;

function () {
    emit Purchase(PO++, msg.sender, msg.value, msg.data); // first param is indexed
}

The code above is for illustrative purpose only.

I have code listening to the Purchase event. May I know if the following possible?

1. the Indexed PO value skipped some numbers because some of the transaction are rejected by the block chain?

2. After receiving Purchase event at my listener, the transaction was rejected by blockchain?

3. The PO+ was received out of order because some transactions were outgassed

Thanks dude

Answer 1

the Indexed PO value skipped some numbers because some of the transaction are rejected by the block chain?

If a transaction is rejected, it will not be mined at all, and thus won't increment PO to begin with. You should still receive them in order.

After receiving Purchase event at my listener, the transaction was rejected by blockchain?

This is possible if the block you were originally mined into is dropped. You can watch for this by looking for the removed: true field on the log events you receive. Note that if this does happen, the transaction will usually be mined into another block fairly soon, and your PO will still be in serial order.

The PO+ was received out of order because some transactions were outgassed

If the actual transaction's logic is identical to this, then you will still receive them in order, since the PO variable is only incremented on successful completion of a transaction.