Just-in-time state machine compiler. Code that is written in a blocking manner typically cannot be stopped and transparently restarted later. The first time a flow’s call method is invoked a bytecode-to-bytecode transformation occurs that rewrites the classes into a form that implements a resumable state machine. These state machines are sometimes called fibers or coroutines, and the transformation engine Corda uses (Quasar) is capable of rewriting code arbitrarily deep in the stack on the fly. The developer may thus break his or her logic into multiple methods and classes, use loops, and generally structure their program as if it were executing in a single blocking thread. There’s only a small list of things they should not do: sleeping, directly accessing the network APIs, or doing other tasks that might block outside of the framework