Layer 2 Atomic Cross-Blockchain Function Calls

The Layer 2 Atomic Cross-Blockchain Function Calls protocol allows composable programming across Ethereum blockchains. It allows for inter-contract and inter-blockchain function calls that are both synchronous and atomic: if one part fails, the whole call graph of function calls is rolled back. The only existing atomic cross-blockchain function call protocol is a Blockchain Layer 1 protocol, which requires changes to the blockchain client software to operate. Blockchain Layer 2 technologies such as the one described in this paper require no such changes. They operate on top of the infrastructure provided by the blockchain client software. This paper introduces the protocol, provides an initial safety and liveness analysis, and presents the expected overhead of using this technology when compared to using non-atomic single blockchain transactions. The protocol's atomic behaviour comes at the cost of additional transactions. On the Root Blockchain, three transactions plus one transaction for each Segment Blockchain where there are no state updates and two transactions for each Segment Blockchain where there are state updates is required.