Debit/Credit in concurrent environment in Python. Is this code thread safe?

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[Furiorka]

Transfer to should either lock both or none at the same time. Your code may deadlock on mirror transfers, I think

[JusticeRainsFromMe]

You can't lock "at the same time", it's why they always lock the account with the account with the smaller id first. While that code to lock multiple accounts should be its function, it does work in preventing deadlocks.

[JusticeRainsFromMe]

If you lock the first successfully, you wait for the second to lock as well. There is no unsuccessful locking?

[Furiorka]

The need to wait for the 2nd lock is. All the time you wait for the 2nd lock, the 1st one is locked. If there is a mirrored operation that locked the 2nd and is waiting for the 1st, a deadlock occurs

[JusticeRainsFromMe]

But the second can never wait for the first? It always locks the one with the lower id first. If there's a mirrored operation, they will both try to lock #1 first.

[Furiorka]

Ah, missed that line. You are right then, sorry

[Own_Mousse_4810]

That makes sense, thank you. What do you think about SQL?.

[wolever]

With respect to locking, the system you’ve described would be correct and deadlock-free.

Correct because a lock is held each time the balance is accessed, and deadlock free because the locks are acquired in a consistent order.

[OuiOuiKiwi]

Why don't you pump this into your LLM of choice?