forked from M-Labs/libfringe
Make Generator safe in presence of destructors.
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23cf17865d
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@ -18,10 +18,10 @@ use context;
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#[derive(Debug, Clone, Copy)]
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pub enum State {
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/// Generator can be resumed. This is the initial state.
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Suspended,
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Runnable,
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/// Generator cannot be resumed. This is the state of the generator after
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/// the generator function has returned.
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Finished
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/// the generator function has returned or panicked.
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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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@ -38,8 +38,8 @@ pub enum State {
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/// stack 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::Suspended` after creation and suspension, and `State::Finished`
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/// once the generator function returns.
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/// the state is `State::Runnable` after creation and suspension, and `State::Unavailable`
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/// once the generator function returns or panics.
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///
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/// # Example
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///
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@ -93,7 +93,7 @@ impl<Item, Stack> Generator<Item, Stack>
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}
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let mut generator = Generator {
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state: State::Suspended,
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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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};
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@ -113,11 +113,11 @@ impl<Item, Stack> Generator<Item, Stack>
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/// Extracts the stack from a generator when the generator function has returned.
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/// If the generator function has not returned
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/// (i.e. `self.state() == State::Suspended`), panics.
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/// (i.e. `self.state() == State::Runnable`), panics.
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pub fn unwrap(self) -> Stack {
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match self.state {
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State::Suspended => panic!("Argh! Bastard! Don't touch that!"),
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State::Finished => unsafe { self.context.unwrap() }
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State::Runnable => panic!("Argh! Bastard! Don't touch that!"),
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State::Unavailable => unsafe { self.context.unwrap() }
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}
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}
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}
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@ -171,16 +171,26 @@ impl<Item, Stack> Iterator for Generator<Item, Stack>
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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::Suspended => {
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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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if let None = val { self.state = State::Finished }
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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::Finished => None
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State::Unavailable => None
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}
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}
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}
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@ -22,8 +22,6 @@
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//! [Stack](struct.Stack.html);
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//! * a stack allocator based on anonymous memory mappings with guard pages,
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//! [OsStack](struct.OsStack.html).
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//!
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//! **FIXME:** not actually safe yet in presence of unwinding
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#[cfg(test)]
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#[macro_use]
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@ -38,3 +38,25 @@ fn move_after_new() {
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}
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rest(gen);
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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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}
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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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}
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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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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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}
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