Reimplement Generator to pass both input and output values around.
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308df32ac2
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@ -13,7 +13,7 @@ without relying on kernel services. It can be used in hosted environments
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(using `std`) as well as on bare metal (using `core`).
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It provides the following safe abstractions:
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* an implementation of internal iterators, also known as generators,
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* an implementation of generators,
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[Generator](https://edef1c.github.io/libfringe/fringe/generator/struct.Generator.html).
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It also provides the necessary low-level building blocks:
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@ -10,9 +10,9 @@ use fringe::{OsStack, Generator};
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#[bench]
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fn generate(b: &mut test::Bencher) {
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let stack = OsStack::new(0).unwrap();
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let mut gen = Generator::new(stack, move |yielder| {
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for i in 1.. { yielder.generate(i) }
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let mut identity = Generator::new(stack, move |yielder, mut input| {
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loop { input = yielder.generate(input) }
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});
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b.iter(|| test::black_box(gen.next()));
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b.iter(|| test::black_box(identity.resume(test::black_box(0))));
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}
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185
src/generator.rs
185
src/generator.rs
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@ -9,11 +9,10 @@
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//! afterwards.
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use core::marker::PhantomData;
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use core::iter::Iterator;
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use core::{ptr, mem};
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use stack;
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use context;
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use context::Context;
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#[derive(Debug, Clone, Copy)]
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pub enum State {
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@ -24,18 +23,20 @@ pub enum State {
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Unavailable
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}
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/// Generator wraps a function and allows suspending its execution more than
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/// once, return a value each time.
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/// Generator wraps a function and allows suspending its execution more than once, returning
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/// a value each time.
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///
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/// It implements the Iterator trait. The first time `next()` is called,
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/// the function is called as `f(yielder)`; every time `next()` is called afterwards,
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/// the function is resumed. In either case, it runs until it suspends its execution
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/// through `yielder.generate(val)`), in which case `next()` returns `Some(val)`, or
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/// returns, in which case `next()` returns `None`. `next()` will return `None`
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/// every time after that.
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/// The first time `resume(input0)` is called, the function is called as `f(yielder, input0)`.
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/// It runs until it suspends its execution through `yielder.generate(output0)`, after which
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/// `resume(input0)` returns `output0`. The function can be resumed again using `resume(input1)`,
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/// after which `yielder.generate(output0)` returns `input1`, and so on. Once the function returns,
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/// the `resume()` call will return `None`, and it will return `None` every time it is called
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/// after that.
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///
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/// After the generator function returns, it is safe to reclaim the generator
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/// stack using `unwrap()`.
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/// If the generator function panics, the panic is propagated through the `resume()` call as usual.
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///
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/// After the generator function returns or panics, it is safe to reclaim the generator stack
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/// using `unwrap()`.
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///
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/// `state()` can be used to determine whether the generator function has returned;
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/// the state is `State::Runnable` after creation and suspension, and `State::Unavailable`
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@ -47,28 +48,29 @@ pub enum State {
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/// use fringe::{OsStack, Generator};
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///
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/// let stack = OsStack::new(0).unwrap();
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/// let mut gen = Generator::new(stack, move |yielder| {
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/// for i in 1..4 {
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/// yielder.generate(i);
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/// let mut add_one = Generator::new(stack, move |yielder, mut input| {
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/// loop {
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/// if input == 0 { break }
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/// input = yielder.generate(input + 1)
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/// }
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/// });
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/// println!("{:?}", gen.next()); // prints Some(1)
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/// println!("{:?}", gen.next()); // prints Some(2)
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/// println!("{:?}", gen.next()); // prints Some(3)
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/// println!("{:?}", gen.next()); // prints None
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/// println!("{:?}", add_one.resume(2)); // prints Some(3)
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/// println!("{:?}", add_one.resume(3)); // prints Some(4)
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/// println!("{:?}", add_one.resume(0)); // prints None
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/// ```
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#[derive(Debug)]
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pub struct Generator<Item: Send, Stack: stack::Stack> {
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pub struct Generator<Input: Send, Output: Send, Stack: stack::Stack> {
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state: State,
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context: context::Context<Stack>,
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phantom: PhantomData<*const Item>
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context: Context<Stack>,
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phantom: (PhantomData<*const Input>, PhantomData<*const Output>)
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}
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impl<Item, Stack> Generator<Item, Stack>
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where Item: Send, Stack: stack::Stack {
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impl<Input, Output, Stack> Generator<Input, Output, Stack>
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where Input: Send, Output: Send, Stack: stack::Stack {
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/// Creates a new generator.
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pub fn new<F>(stack: Stack, f: F) -> Generator<Item, Stack>
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where Stack: stack::GuardedStack, F: FnOnce(&mut Yielder<Item, Stack>) + Send {
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pub fn new<F>(stack: Stack, f: F) -> Generator<Input, Output, Stack>
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where Stack: stack::GuardedStack,
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F: FnOnce(&mut Yielder<Input, Output, Stack>, Input) + Send {
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unsafe { Generator::unsafe_new(stack, f) }
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}
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@ -77,36 +79,70 @@ impl<Item, Stack> Generator<Item, Stack>
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/// This function is unsafe because the generator function can easily violate
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/// memory safety by overflowing the stack. It is useful in environments where
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/// guarded stacks do not exist, e.g. in absence of an MMU.
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pub unsafe fn unsafe_new<F>(stack: Stack, f: F) -> Generator<Item, Stack>
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where F: FnOnce(&mut Yielder<Item, Stack>) + Send {
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unsafe extern "C" fn generator_wrapper<Item, Stack, F>(info: usize) -> !
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where Item: Send, Stack: stack::Stack, F: FnOnce(&mut Yielder<Item, Stack>) {
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pub unsafe fn unsafe_new<F>(stack: Stack, f: F) -> Generator<Input, Output, Stack>
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where F: FnOnce(&mut Yielder<Input, Output, Stack>, Input) + Send {
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unsafe extern "C" fn generator_wrapper<Input, Output, Stack, F>(env: usize) -> !
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where Input: Send, Output: Send, Stack: stack::Stack,
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F: FnOnce(&mut Yielder<Input, Output, Stack>, Input) {
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// Retrieve our environment from the callee and return control to it.
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let (mut yielder, f) = ptr::read(info as *mut (Yielder<Item, Stack>, F));
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let new_context = context::Context::swap(yielder.context, yielder.context, 0);
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// See Yielder::return_.
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yielder.context = new_context as *mut context::Context<Stack>;
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let (mut yielder, f) = ptr::read(env as *mut (Yielder<Input, Output, Stack>, F));
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let data = Context::swap(yielder.context, yielder.context, 0);
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// See the second half of Yielder::generate_bare.
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let (new_context, input) = ptr::read(data as *mut (*mut Context<Stack>, Input));
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yielder.context = new_context as *mut Context<Stack>;
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// Run the body of the generator.
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f(&mut yielder);
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f(&mut yielder, input);
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// Past this point, the generator has dropped everything it has held.
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loop { yielder.return_(None) }
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loop { yielder.generate_bare(None); }
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}
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let mut generator = Generator {
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state: State::Runnable,
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context: context::Context::new(stack, generator_wrapper::<Item, Stack, F>),
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phantom: PhantomData
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context: Context::new(stack, generator_wrapper::<Input, Output, Stack, F>),
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phantom: (PhantomData, PhantomData)
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};
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// Transfer environment to the callee.
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let mut data = (Yielder::new(&mut generator.context), f);
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context::Context::swap(&mut generator.context, &generator.context,
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&mut data as *mut (Yielder<Item, Stack>, F) as usize);
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mem::forget(data);
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let mut env = (Yielder::new(&mut generator.context), f);
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Context::swap(&mut generator.context, &generator.context,
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&mut env as *mut (Yielder<Input, Output, Stack>, F) as usize);
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mem::forget(env);
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generator
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}
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/// Resumes the generator and return the next value it yields.
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/// If the generator function has returned, returns `None`.
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#[inline]
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pub fn resume(&mut self, input: Input) -> Option<Output> {
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match self.state {
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State::Runnable => {
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// Set the state to Unavailable. Since we have exclusive access to the generator,
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// the only case where this matters is the generator function panics, after which
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// it must not be invocable again.
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self.state = State::Unavailable;
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// Switch to the generator function, and retrieve the yielded value.
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let val = unsafe {
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let mut data_in = (&mut self.context as *mut Context<Stack>, input);
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let data_out =
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ptr::read(Context::swap(&mut self.context, &self.context,
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&mut data_in as *mut (*mut Context<Stack>, Input) as usize)
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as *mut Option<Output>);
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mem::forget(data_in);
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data_out
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};
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// Unless the generator function has returned, it can be switched to again, so
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// set the state to Runnable.
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if val.is_some() { self.state = State::Runnable }
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val
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}
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State::Unavailable => None
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}
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}
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/// Returns the state of the generator.
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#[inline]
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pub fn state(&self) -> State { self.state }
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/// Yielder is an interface provided to every generator through which it
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/// returns a value.
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#[derive(Debug)]
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pub struct Yielder<Item: Send, Stack: stack::Stack> {
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context: *mut context::Context<Stack>,
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phantom: PhantomData<Item>
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pub struct Yielder<Input: Send, Output: Send, Stack: stack::Stack> {
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context: *mut Context<Stack>,
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phantom: (PhantomData<*const Input>, PhantomData<*const Output>)
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}
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impl<Item, Stack> Yielder<Item, Stack>
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where Item: Send, Stack: stack::Stack {
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fn new(context: *mut context::Context<Stack>) -> Yielder<Item, Stack> {
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impl<Input, Output, Stack> Yielder<Input, Output, Stack>
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where Input: Send, Output: Send, Stack: stack::Stack {
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fn new(context: *mut Context<Stack>) -> Yielder<Input, Output, Stack> {
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Yielder {
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context: context,
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phantom: PhantomData
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phantom: (PhantomData, PhantomData)
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}
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}
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#[inline(always)]
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fn return_(&mut self, mut val: Option<Item>) {
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fn generate_bare(&mut self, mut val: Option<Output>) -> Input {
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unsafe {
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let new_context = context::Context::swap(self.context, self.context,
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&mut val as *mut Option<Item> as usize);
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let data = Context::swap(self.context, self.context,
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&mut val as *mut Option<Output> as usize);
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let (new_context, input) = ptr::read(data as *mut (*mut Context<Stack>, Input));
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// The generator can be moved (and with it, the context).
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// This changes the address of the context.
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// Thus, we update it after each swap.
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self.context = new_context as *mut context::Context<Stack>;
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// However, between this point and the next time we enter return_
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self.context = new_context;
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// However, between this point and the next time we enter generate_bare
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// the generator cannot be moved, as a &mut Generator is necessary
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// to resume the generator function.
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input
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}
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}
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/// Suspends the generator and returns `Some(item)` from the `next()`
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/// Suspends the generator and returns `Some(item)` from the `resume()`
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/// invocation that resumed the generator.
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#[inline(always)]
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pub fn generate(&mut self, item: Item) {
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self.return_(Some(item))
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}
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}
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impl<Item, Stack> Iterator for Generator<Item, Stack>
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where Item: Send, Stack: stack::Stack {
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type Item = Item;
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/// Resumes the generator and return the next value it yields.
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/// If the generator function has returned, returns `None`.
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#[inline]
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fn next(&mut self) -> Option<Self::Item> {
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match self.state {
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State::Runnable => {
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// Set the state to Unavailable. Since we have exclusive access to the generator,
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// the only case where this matters is the generator function panics, after which
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// it must not be invocable again.
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self.state = State::Unavailable;
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// Switch to the generator function.
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let new_context = &mut self.context as *mut context::Context<Stack> as usize;
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let val = unsafe {
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ptr::read(context::Context::swap(&mut self.context, &self.context, new_context)
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as *mut Option<Item>)
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};
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// Unless the generator function has returned, it can be switched to again, so
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// set the state to Runnable.
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if val.is_some() { self.state = State::Runnable }
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val
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}
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State::Unavailable => None
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}
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pub fn generate(&mut self, item: Output) -> Input {
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self.generate_bare(Some(item))
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}
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}
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@ -13,7 +13,7 @@
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//!
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//! It provides the following safe abstractions:
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//!
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//! * an implementation of internal iterators, also known as generators,
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//! * an implementation of generators,
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//! [Generator](generator/struct.Generator.html).
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//!
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//! It also provides the necessary low-level building blocks:
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@ -20,10 +20,10 @@ extern {
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#[ignore]
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fn fpe() {
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let stack = OsStack::new(0).unwrap();
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let mut gen = Generator::new(stack, move |yielder| {
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let mut gen = Generator::new(stack, move |yielder, ()| {
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yielder.generate(1.0 / black_box(0.0));
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});
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unsafe { feenableexcept(FE_DIVBYZERO); }
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println!("{:?}", gen.next());
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println!("{:?}", gen.resume(()));
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}
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@ -6,57 +6,56 @@ extern crate fringe;
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use fringe::OsStack;
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use fringe::generator::Generator;
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fn new_add_one() -> Generator<i32, i32, OsStack> {
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let stack = OsStack::new(0).unwrap();
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Generator::new(stack, move |yielder, mut input| {
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loop {
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if input == 0 { break }
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input = yielder.generate(input + 1)
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}
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})
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}
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#[test]
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fn generator() {
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let stack = OsStack::new(0).unwrap();
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let mut gen = Generator::new(stack, move |yielder| {
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for i in 1..4 {
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yielder.generate(i);
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}
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});
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assert_eq!(gen.next(), Some(1));
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assert_eq!(gen.next(), Some(2));
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assert_eq!(gen.next(), Some(3));
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assert_eq!(gen.next(), None);
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let mut add_one = new_add_one();
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assert_eq!(add_one.resume(1), Some(2));
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assert_eq!(add_one.resume(2), Some(3));
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assert_eq!(add_one.resume(0), None);
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}
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#[test]
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fn move_after_new() {
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let stack = OsStack::new(0).unwrap();
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let mut gen = Generator::new(stack, move |yielder| {
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for i in 1..4 {
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yielder.generate(i);
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}
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});
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assert_eq!(gen.next(), Some(1));
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let mut add_one = new_add_one();
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assert_eq!(add_one.resume(1), Some(2));
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#[inline(never)]
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fn rest(mut gen: Generator<u32, OsStack>) {
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assert_eq!(gen.next(), Some(2));
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assert_eq!(gen.next(), Some(3));
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assert_eq!(gen.next(), None);
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fn run_moved(mut add_one: Generator<i32, i32, OsStack>) {
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assert_eq!(add_one.resume(2), Some(3));
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assert_eq!(add_one.resume(3), Some(4));
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assert_eq!(add_one.resume(0), None);
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}
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rest(gen);
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run_moved(add_one);
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}
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#[test]
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#[should_panic]
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fn panic_safety() {
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struct Wrapper {
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gen: Generator<u32, OsStack>
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gen: Generator<(), (), OsStack>
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}
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impl Drop for Wrapper {
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fn drop(&mut self) {
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self.gen.next();
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self.gen.resume(());
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}
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}
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let stack = OsStack::new(4 << 20).unwrap();
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let gen = Generator::new(stack, move |_yielder| {
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let gen = Generator::new(stack, move |_yielder, ()| {
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panic!("foo")
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});
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let mut wrapper = Wrapper { gen: gen };
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wrapper.gen.next();
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wrapper.gen.resume(());
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}
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