Durable Call: Durable Local and Remote Function Calls

Durable call is a library for implementing durable functions from fragile functions.

A function is said to be fragile if any of the following conditions are true: a) the function may fail intermittently, b) the function call has side effects, and thus for a given input it should only be run once.

A durable function is a fault tolerant and idempotent version of a fragile function. This fault tolerance and idempotency is implemented by the runtime. When a durable function is called, the runtime system first saves the parameters of the function call onto a file on disk. Next it repeatedly tries to call the function until it is able to execute it. Once the function has been executed, the result is also saved onto a file on disk. If the function is called in the future with the same arguments, the system will just return the saved result from the previous invocation.

Durable function call persists across process invocations. If a durable function call is initiated, and the process dies before it has been completed, the runtime with continue to execute it if the process is restarted.