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    // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Scoped thread-local storage
    //!
    //! This module provides the ability to generate *scoped* thread-local
    //! variables. In this sense, scoped indicates that thread local storage
    //! actually stores a reference to a value, and this reference is only placed
    //! in storage for a scoped amount of time.
    //!
    //! There are no restrictions on what types can be placed into a scoped
    //! variable, but all scoped variables are initialized to the equivalent of
    //! null. Scoped thread local storage is useful when a value is present for a known
    //! period of time and it is not required to relinquish ownership of the
    //! contents.
    //!
    //! # Examples
    //!
    //! ```
    //! #![feature(scoped_tls)]
    //!
    //! scoped_thread_local!(static FOO: u32);
    //!
    //! // Initially each scoped slot is empty.
    //! assert!(!FOO.is_set());
    //!
    //! // When inserting a value, the value is only in place for the duration
    //! // of the closure specified.
    //! FOO.set(&1, || {
    //!     FOO.with(|slot| {
    //!         assert_eq!(*slot, 1);
    //!     });
    //! });
    //! ```

    #![unstable(feature = "thread_local_internals", issue = "0")]

    #[doc(hidden)]
    pub use self::imp::KeyInner as __KeyInner;

    /// Type representing a thread local storage key corresponding to a reference
    /// to the type parameter `T`.
    ///
    /// Keys are statically allocated and can contain a reference to an instance of
    /// type `T` scoped to a particular lifetime. Keys provides two methods, `set`
    /// and `with`, both of which currently use closures to control the scope of
    /// their contents.
    #[unstable(feature = "scoped_tls",
               reason = "scoped TLS has yet to have wide enough use to fully consider \
                         stabilizing its interface",
               issue = "27715")]
    pub struct ScopedKey<T:'static> { inner: fn() -> &'static imp::KeyInner<T> }

    /// Declare a new scoped thread local storage key.
    ///
    /// This macro declares a `static` item on which methods are used to get and
    /// set the value stored within.
    ///
    /// See [ScopedKey documentation](thread/struct.ScopedKey.html) for more
    /// information.
    #[unstable(feature = "thread_local_internals",
               reason = "should not be necessary",
               issue = "0")]
    #[macro_export]
    #[allow_internal_unstable]
    macro_rules! scoped_thread_local {
        (static $name:ident: $t:ty) => (
            static $name: $crate::thread::ScopedKey<$t> =
                __scoped_thread_local_inner!($t);
        );
        (pub static $name:ident: $t:ty) => (
            pub static $name: $crate::thread::ScopedKey<$t> =
                __scoped_thread_local_inner!($t);
        );
    }

    #[doc(hidden)]
    #[unstable(feature = "thread_local_internals",
               reason = "should not be necessary",
               issue = "0")]
    #[macro_export]
    #[allow_internal_unstable]
    macro_rules! __scoped_thread_local_inner {
        ($t:ty) => {{
            #[cfg_attr(target_thread_local, thread_local)]
            static _KEY: $crate::thread::__ScopedKeyInner<$t> =
                $crate::thread::__ScopedKeyInner::new();
            fn _getit() -> &'static $crate::thread::__ScopedKeyInner<$t> { &_KEY }
            $crate::thread::ScopedKey::new(_getit)
        }}
    }

    #[unstable(feature = "scoped_tls",
               reason = "scoped TLS has yet to have wide enough use to fully consider \
                         stabilizing its interface",
               issue = "27715")]
    impl<T> ScopedKey<T> {
        #[doc(hidden)]
        pub const fn new(inner: fn() -> &'static imp::KeyInner<T>) -> ScopedKey<T> {
            ScopedKey { inner: inner }
        }

        /// Inserts a value into this scoped thread local storage slot for a
        /// duration of a closure.
        ///
        /// While `cb` is running, the value `t` will be returned by `get` unless
        /// this function is called recursively inside of `cb`.
        ///
        /// Upon return, this function will restore the previous value, if any
        /// was available.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(scoped_tls)]
        ///
        /// scoped_thread_local!(static FOO: u32);
        ///
        /// FOO.set(&100, || {
        ///     let val = FOO.with(|v| *v);
        ///     assert_eq!(val, 100);
        ///
        ///     // set can be called recursively
        ///     FOO.set(&101, || {
        ///         // ...
        ///     });
        ///
        ///     // Recursive calls restore the previous value.
        ///     let val = FOO.with(|v| *v);
        ///     assert_eq!(val, 100);
        /// });
        /// ```
        pub fn set<R, F>(&'static self, t: &T, cb: F) -> R where
            F: FnOnce() -> R,
        {
            struct Reset<'a, T: 'a> {
                key: &'a imp::KeyInner<T>,
                val: *mut T,
            }
                    impl<'a, T> Drop for Reset<'a, T> {
                fn drop(&mut self) {
                    unsafe { self.key.set(self.val) }
                }
            }

            let inner = (self.inner)();
            let prev = unsafe {
                let prev = inner.get();
                inner.set(t as *const T as *mut T);
                prev
            };

            let _reset = Reset { key: inner, val: prev };
            cb()
        }

        /// Gets a value out of this scoped variable.
        ///
        /// This function takes a closure which receives the value of this
        /// variable.
        ///
        /// # Panics
        ///
        /// This function will panic if `set` has not previously been called.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// #![feature(scoped_tls)]
        ///
        /// scoped_thread_local!(static FOO: u32);
        ///
        /// FOO.with(|slot| {
        ///     // work with `slot`
        /// });
        /// ```
        pub fn with<R, F>(&'static self, cb: F) -> R where
            F: FnOnce(&T) -> R
        {
            unsafe {
                let ptr = (self.inner)().get();
                assert!(!ptr.is_null(), "cannot access a scoped thread local \
                                         variable without calling `set` first");
                cb(&*ptr)
            }
        }

        /// Test whether this TLS key has been `set` for the current thread.
        pub fn is_set(&'static self) -> bool {
            unsafe { !(self.inner)().get().is_null() }
        }
    }

    #[cfg(target_thread_local)]
    #[doc(hidden)]
    mod imp {
        use cell::Cell;
        use ptr;

        pub struct KeyInner<T> { inner: Cell<*mut T> }

        unsafe impl<T> ::marker::Sync for KeyInner<T> { }

        impl<T> KeyInner<T> {
            pub const fn new() -> KeyInner<T> {
                KeyInner { inner: Cell::new(ptr::null_mut()) }
            }
            pub unsafe fn set(&self, ptr: *mut T) { self.inner.set(ptr); }
            pub unsafe fn get(&self) -> *mut T { self.inner.get() }
        }
    }

    #[cfg(not(target_thread_local))]
    #[doc(hidden)]
    mod imp {
        use cell::Cell;
        use marker;
        use sys_common::thread_local::StaticKey as OsStaticKey;

        pub struct KeyInner<T> {
            pub inner: OsStaticKey,
            pub marker: marker::PhantomData<Cell<T>>,
        }

        unsafe impl<T> marker::Sync for KeyInner<T> { }

        impl<T> KeyInner<T> {
            pub const fn new() -> KeyInner<T> {
                KeyInner {
                    inner: OsStaticKey::new(None),
                    marker: marker::PhantomData
                }
            }
            pub unsafe fn set(&self, ptr: *mut T) { self.inner.set(ptr as *mut _) }
            pub unsafe fn get(&self) -> *mut T { self.inner.get() as *mut _ }
        }
    }

    #[cfg(test)]
    mod tests {
        use cell::Cell;

        scoped_thread_local!(static FOO: u32);

        #[test]
        fn smoke() {
            scoped_thread_local!(static BAR: u32);

            assert!(!BAR.is_set());
            BAR.set(&1, || {
                assert!(BAR.is_set());
                BAR.with(|slot| {
                    assert_eq!(*slot, 1);
                });
            });
            assert!(!BAR.is_set());
        }

        #[test]
        fn cell_allowed() {
            scoped_thread_local!(static BAR: Cell<u32>);

            BAR.set(&Cell::new(1), || {
                BAR.with(|slot| {
                    assert_eq!(slot.get(), 1);
                });
            });
        }

        #[test]
        fn scope_item_allowed() {
            assert!(!FOO.is_set());
            FOO.set(&1, || {
                assert!(FOO.is_set());
                FOO.with(|slot| {
                    assert_eq!(*slot, 1);
                });
            });
            assert!(!FOO.is_set());
        }
    }

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