General Purpose Atomic Crosschain Transactions

The General Purpose Atomic Crosschain Transaction (GPACT) protocol allows composable programming across multiple 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 protocol operates on existing Ethereum blockchains without modification. It works for both public and consortium blockchains, and is expected to work across heterogeneous blockchains other than Ethereum. The protocol has been analysed in terms of Gas usage and Finalised Block Periods for writing a value from one blockchain to another.