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//! Example of limiting a WebAssembly function's runtime using "fuel consumption".
// You can execute this example with `cargo run --example fuel`
use wasmtime::*;
fn main() -> Result<()> {
let mut config = Config::new();
config.consume_fuel(true);
let engine = Engine::new(&config)?;
let mut store = Store::new(&engine, ());
store.set_fuel(10_000)?;
let module = Module::from_file(store.engine(), "examples/fuel.wat")?;
let instance = Instance::new(&mut store, &module, &[])?;
// Invoke `fibonacci` export with higher and higher numbers until we exhaust our fuel.
let fibonacci = instance.get_typed_func::<i32, i32>(&mut store, "fibonacci")?;
for n in 1.. {
let fuel_before = store.get_fuel().unwrap();
let output = match fibonacci.call(&mut store, n) {
Ok(v) => v,
Err(e) => {
assert_eq!(e.downcast::<Trap>()?, Trap::OutOfFuel);
println!("Exhausted fuel computing fib({n})");
break;
}
};
let fuel_consumed = fuel_before - store.get_fuel().unwrap();
println!("fib({n}) = {output} [consumed {fuel_consumed} fuel]");
store.set_fuel(10_000)?;
}
Ok(())
}
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