Vendor things

third-party/vendor/scoped-tls/src/lib.rs

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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
+//!
+//! ```
+//! #[macro_use]
+//! extern crate scoped_tls;
+//!
+//! scoped_thread_local!(static FOO: u32);
+//!
+//! # fn main() {
+//! // 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);
+//!     });
+//! });
+//! # }
+//! ```
+
+#![deny(missing_docs, warnings)]
+
+use std::cell::Cell;
+use std::marker;
+use std::thread::LocalKey;
+
+/// The macro. See the module level documentation for the description and examples.
+#[macro_export]
+macro_rules! scoped_thread_local {
+    ($(#[$attrs:meta])* $vis:vis static $name:ident: $ty:ty) => (
+        $(#[$attrs])*
+        $vis static $name: $crate::ScopedKey<$ty> = $crate::ScopedKey {
+            inner: {
+                ::std::thread_local!(static FOO: ::std::cell::Cell<*const ()> = const {
+                    ::std::cell::Cell::new(::std::ptr::null())
+                });
+                &FOO
+            },
+            _marker: ::std::marker::PhantomData,
+        };
+    )
+}
+
+/// 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.
+pub struct ScopedKey<T> {
+    #[doc(hidden)]
+    pub inner: &'static LocalKey<Cell<*const ()>>,
+    #[doc(hidden)]
+    pub _marker: marker::PhantomData<T>,
+}
+
+unsafe impl<T> Sync for ScopedKey<T> {}
+
+impl<T> ScopedKey<T> {
+    /// Inserts a value into this scoped thread local storage slot for a
+    /// duration of a closure.
+    ///
+    /// While `f` is running, the value `t` will be returned by `get` unless
+    /// this function is called recursively inside of `f`.
+    ///
+    /// Upon return, this function will restore the previous value, if any
+    /// was available.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #[macro_use]
+    /// extern crate scoped_tls;
+    ///
+    /// scoped_thread_local!(static FOO: u32);
+    ///
+    /// # fn main() {
+    /// 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<F, R>(&'static self, t: &T, f: F) -> R
+        where F: FnOnce() -> R
+    {
+        struct Reset {
+            key: &'static LocalKey<Cell<*const ()>>,
+            val: *const (),
+        }
+        impl Drop for Reset {
+            fn drop(&mut self) {
+                self.key.with(|c| c.set(self.val));
+            }
+        }
+        let prev = self.inner.with(|c| {
+            let prev = c.get();
+            c.set(t as *const T as *const ());
+            prev
+        });
+        let _reset = Reset { key: self.inner, val: prev };
+        f()
+    }
+
+    /// 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
+    /// #[macro_use]
+    /// extern crate scoped_tls;
+    ///
+    /// scoped_thread_local!(static FOO: u32);
+    ///
+    /// # fn main() {
+    /// FOO.with(|slot| {
+    ///     // work with `slot`
+    /// # drop(slot);
+    /// });
+    /// # }
+    /// ```
+    pub fn with<F, R>(&'static self, f: F) -> R
+        where F: FnOnce(&T) -> R
+    {
+        let val = self.inner.with(|c| c.get());
+        assert!(!val.is_null(), "cannot access a scoped thread local \
+                                 variable without calling `set` first");
+        unsafe {
+            f(&*(val as *const T))
+        }
+    }
+
+    /// Test whether this TLS key has been `set` for the current thread.
+    pub fn is_set(&'static self) -> bool {
+        self.inner.with(|c| !c.get().is_null())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::Cell;
+    use std::sync::mpsc::{channel, Sender};
+    use std::thread;
+
+    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());
+    }
+
+    #[test]
+    fn panic_resets() {
+        struct Check(Sender<u32>);
+        impl Drop for Check {
+            fn drop(&mut self) {
+                FOO.with(|r| {
+                    self.0.send(*r).unwrap();
+                })
+            }
+        }
+
+        let (tx, rx) = channel();
+        let t = thread::spawn(|| {
+            FOO.set(&1, || {
+                let _r = Check(tx);
+
+                FOO.set(&2, || {
+                    panic!()
+                });
+            });
+        });
+
+        assert_eq!(rx.recv().unwrap(), 1);
+        assert!(t.join().is_err());
+    }
+
+    #[test]
+    fn attrs_allowed() {
+        scoped_thread_local!(
+            /// Docs
+            static BAZ: u32
+        );
+
+        scoped_thread_local!(
+            #[allow(non_upper_case_globals)]
+            static quux: u32
+        );
+
+        let _ = BAZ;
+        let _ = quux;
+    }
+}