# Execution Order

# Overview

Root Actions - Actions submitted by a user as part of a transaction.

Inline Actions - Actions generated from inside a smart contract (as opposed to user-generated).

Notifications - Incoming alerts from other smart contracts.

Proton's architecture helps mitigate re-entrancy attacks by scheduling inline actions instead of executing them immediately:

If we have 3 root actions, all notifications and inline actions inside root action 1 must execute before root action 2, and so on.
However, the order of the notifications and inline actions inside each of the root actions is dependant on the execution order,

There are 2 queues per root action, Notifications queue (RootN) and Inline actions queue (RootIA)

New notifications (NewN) and new inline actions (NewIA) are added at the end of the every notification or action as:

RootN = [...RootN, ...NewN]
Is current context a notification?
- Yes: RootIA = [...RootIA, ...NewIA]
- No: RootIA = [...NewIA, ...RootIA]

Note that Proton will only process the inline actions queue when the notifications queue is empty.