proto_faaslets.md

Proto-Faaslets

Proto-Faaslets are a way to restore the execution state of a function without rerunning the code that got it to that state.

Proto-Faaslets mean we can snapshot a function when it's running, then restore it later, resuming its execution. The same proto-function can be restored multiple times and across different hosts.

Reducing cold starts

Proto-Faaslets can be used to reduce function cold starts by:

• Running initialisation code once when the function is uploaded
• Creating a proto-function after this function has been run
• Restoring all subsequent function calls from this snapshot

Any slow or resource-intensive initialisation that would otherwise be performed on every call can be captured in this proto-function snapshot, thus repeatedly saving on overheads.

Defining a proto-function

Proto-Faaslets can be defined in C/C++ with the FAASM_ZYGOTE macro:

#include "faasm/faasm.h"

int myGlobal;

FAASM_ZYGOTE() {
    // Run once
    myGlobal = 5;

    return 0;
}

FAASM_MAIN_FUNC() {
    // Context available to all subsequent function calls
    printf("My global = %i\n", myGlobal);

    return 0;
}

Cross-host migration

Proto-Faaslets are also used in Faasm to migrate functions across hosts.