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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.

    //! Thread local storage

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

    use cell::UnsafeCell;
    use mem;

    /// A thread local storage key which owns its contents.
    ///
    /// This key uses the fastest possible implementation available to it for the
    /// target platform. It is instantiated with the `thread_local!` macro and the
    /// primary method is the `with` method.
    ///
    /// The `with` method yields a reference to the contained value which cannot be
    /// sent across threads or escape the given closure.
    ///
    /// # Initialization and Destruction
    ///
    /// Initialization is dynamically performed on the first call to `with()`
    /// within a thread, and values support destructors which will be run when a
    /// thread exits.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::cell::RefCell;
    /// use std::thread;
    ///
    /// thread_local!(static FOO: RefCell<u32> = RefCell::new(1));
    ///
    /// FOO.with(|f| {
    ///     assert_eq!(*f.borrow(), 1);
    ///     *f.borrow_mut() = 2;
    /// });
    ///
    /// // each thread starts out with the initial value of 1
    /// thread::spawn(move|| {
    ///     FOO.with(|f| {
    ///         assert_eq!(*f.borrow(), 1);
    ///         *f.borrow_mut() = 3;
    ///     });
    /// });
    ///
    /// // we retain our original value of 2 despite the child thread
    /// FOO.with(|f| {
    ///     assert_eq!(*f.borrow(), 2);
    /// });
    /// ```
    ///
    /// # Platform-specific behavior
    ///
    /// Note that a "best effort" is made to ensure that destructors for types
    /// stored in thread local storage are run, but not all platforms can guarantee
    /// that destructors will be run for all types in thread local storage. For
    /// example, there are a number of known caveats where destructors are not run:
    ///
    /// 1. On Unix systems when pthread-based TLS is being used, destructors will
    ///    not be run for TLS values on the main thread when it exits. Note that the
    ///    application will exit immediately after the main thread exits as well.
    /// 2. On all platforms it's possible for TLS to re-initialize other TLS slots
    ///    during destruction. Some platforms ensure that this cannot happen
    ///    infinitely by preventing re-initialization of any slot that has been
    ///    destroyed, but not all platforms have this guard. Those platforms that do
    ///    not guard typically have a synthetic limit after which point no more
    ///    destructors are run.
    /// 3. On OSX, initializing TLS during destruction of other TLS slots can
    ///    sometimes cancel *all* destructors for the current thread, whether or not
    ///    the slots have already had their destructors run or not.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct LocalKey<T: 'static> {
        // This outer `LocalKey<T>` type is what's going to be stored in statics,
        // but actual data inside will sometimes be tagged with #[thread_local].
        // It's not valid for a true static to reference a #[thread_local] static,
        // so we get around that by exposing an accessor through a layer of function
        // indirection (this thunk).
        //
        // Note that the thunk is itself unsafe because the returned lifetime of the
        // slot where data lives, `'static`, is not actually valid. The lifetime
        // here is actually `'thread`!
        //
        // Although this is an extra layer of indirection, it should in theory be
        // trivially devirtualizable by LLVM because the value of `inner` never
        // changes and the constant should be readonly within a crate. This mainly
        // only runs into problems when TLS statics are exported across crates.
        inner: fn() -> Option<&'static UnsafeCell<Option<T>>>,

        // initialization routine to invoke to create a value
        init: fn() -> T,
    }

    /// Declare a new thread local storage key of type `std::thread::LocalKey`.
    ///
    /// See [LocalKey documentation](thread/struct.LocalKey.html) for more
    /// information.
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow_internal_unstable]
    macro_rules! thread_local {
        (static $name:ident: $t:ty = $init:expr) => (
            static $name: $crate::thread::LocalKey<$t> =
                __thread_local_inner!($t, $init);
        );
        (pub static $name:ident: $t:ty = $init:expr) => (
            pub static $name: $crate::thread::LocalKey<$t> =
                __thread_local_inner!($t, $init);
        );
    }

    #[doc(hidden)]
    #[unstable(feature = "thread_local_internals",
               reason = "should not be necessary",
               issue = "0")]
    #[macro_export]
    #[allow_internal_unstable]
    macro_rules! __thread_local_inner {
        ($t:ty, $init:expr) => {{
            fn __init() -> $t { $init }

            fn __getit() -> $crate::option::Option<
                &'static $crate::cell::UnsafeCell<
                    $crate::option::Option<$t>>>
            {
                #[thread_local]
                #[cfg(target_thread_local)]
                static __KEY: $crate::thread::__ElfLocalKeyInner<$t> =
                    $crate::thread::__ElfLocalKeyInner::new();

                #[cfg(not(target_thread_local))]
                static __KEY: $crate::thread::__OsLocalKeyInner<$t> =
                    $crate::thread::__OsLocalKeyInner::new();

                __KEY.get()
            }

            $crate::thread::LocalKey::new(__getit, __init)
        }}
    }

    /// Indicator of the state of a thread local storage key.
    #[unstable(feature = "thread_local_state",
               reason = "state querying was recently added",
               issue = "27716")]
    #[derive(Eq, PartialEq, Copy, Clone)]
    pub enum LocalKeyState {
        /// All keys are in this state whenever a thread starts. Keys will
        /// transition to the `Valid` state once the first call to `with` happens
        /// and the initialization expression succeeds.
        ///
        /// Keys in the `Uninitialized` state will yield a reference to the closure
        /// passed to `with` so long as the initialization routine does not panic.
        Uninitialized,

        /// Once a key has been accessed successfully, it will enter the `Valid`
        /// state. Keys in the `Valid` state will remain so until the thread exits,
        /// at which point the destructor will be run and the key will enter the
        /// `Destroyed` state.
        ///
        /// Keys in the `Valid` state will be guaranteed to yield a reference to the
        /// closure passed to `with`.
        Valid,

        /// When a thread exits, the destructors for keys will be run (if
        /// necessary). While a destructor is running, and possibly after a
        /// destructor has run, a key is in the `Destroyed` state.
        ///
        /// Keys in the `Destroyed` states will trigger a panic when accessed via
        /// `with`.
        Destroyed,
    }

    impl<T: 'static> LocalKey<T> {
        #[doc(hidden)]
        #[unstable(feature = "thread_local_internals",
                   reason = "recently added to create a key",
                   issue = "0")]
        pub const fn new(inner: fn() -> Option<&'static UnsafeCell<Option<T>>>,
                         init: fn() -> T) -> LocalKey<T> {
            LocalKey {
                inner: inner,
                init: init,
            }
        }

        /// Acquires a reference to the value in this TLS key.
        ///
        /// This will lazily initialize the value if this thread has not referenced
        /// this key yet.
        ///
        /// # Panics
        ///
        /// This function will `panic!()` if the key currently has its
        /// destructor running, and it **may** panic if the destructor has
        /// previously been run for this thread.
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn with<F, R>(&'static self, f: F) -> R
                          where F: FnOnce(&T) -> R {
            unsafe {
                let slot = (self.inner)();
                let slot = slot.expect("cannot access a TLS value during or \
                                        after it is destroyed");
                f(match *slot.get() {
                    Some(ref inner) => inner,
                    None => self.init(slot),
                })
            }
        }

        unsafe fn init(&self, slot: &UnsafeCell<Option<T>>) -> &T {
            // Execute the initialization up front, *then* move it into our slot,
            // just in case initialization fails.
            let value = (self.init)();
            let ptr = slot.get();

            // note that this can in theory just be `*ptr = Some(value)`, but due to
            // the compiler will currently codegen that pattern with something like:
            //
            //      ptr::drop_in_place(ptr)
            //      ptr::write(ptr, Some(value))
            //
            // Due to this pattern it's possible for the destructor of the value in
            // `ptr` (e.g. if this is being recursively initialized) to re-access
            // TLS, in which case there will be a `&` and `&mut` pointer to the same
            // value (an aliasing violation). To avoid setting the "I'm running a
            // destructor" flag we just use `mem::replace` which should sequence the
            // operations a little differently and make this safe to call.
            mem::replace(&mut *ptr, Some(value));

            (*ptr).as_ref().unwrap()
        }

        /// Query the current state of this key.
        ///
        /// A key is initially in the `Uninitialized` state whenever a thread
        /// starts. It will remain in this state up until the first call to `with`
        /// within a thread has run the initialization expression successfully.
        ///
        /// Once the initialization expression succeeds, the key transitions to the
        /// `Valid` state which will guarantee that future calls to `with` will
        /// succeed within the thread.
        ///
        /// When a thread exits, each key will be destroyed in turn, and as keys are
        /// destroyed they will enter the `Destroyed` state just before the
        /// destructor starts to run. Keys may remain in the `Destroyed` state after
        /// destruction has completed. Keys without destructors (e.g. with types
        /// that are `Copy`), may never enter the `Destroyed` state.
        ///
        /// Keys in the `Uninitialized` state can be accessed so long as the
        /// initialization does not panic. Keys in the `Valid` state are guaranteed
        /// to be able to be accessed. Keys in the `Destroyed` state will panic on
        /// any call to `with`.
        #[unstable(feature = "thread_local_state",
                   reason = "state querying was recently added",
                   issue = "27716")]
        pub fn state(&'static self) -> LocalKeyState {
            unsafe {
                match (self.inner)() {
                    Some(cell) => {
                        match *cell.get() {
                            Some(..) => LocalKeyState::Valid,
                            None => LocalKeyState::Uninitialized,
                        }
                    }
                    None => LocalKeyState::Destroyed,
                }
            }
        }
    }

    #[cfg(target_thread_local)]
    #[doc(hidden)]
    pub mod elf {
        use cell::{Cell, UnsafeCell};
        use intrinsics;
        use ptr;

        pub struct Key<T> {
            inner: UnsafeCell<Option<T>>,

            // Metadata to keep track of the state of the destructor. Remember that
            // these variables are thread-local, not global.
            dtor_registered: Cell<bool>,
            dtor_running: Cell<bool>,
        }

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

        impl<T> Key<T> {
            pub const fn new() -> Key<T> {
                Key {
                    inner: UnsafeCell::new(None),
                    dtor_registered: Cell::new(false),
                    dtor_running: Cell::new(false)
                }
            }

            pub fn get(&'static self) -> Option<&'static UnsafeCell<Option<T>>> {
                unsafe {
                    if intrinsics::needs_drop::<T>() && self.dtor_running.get() {
                        return None
                    }
                    self.register_dtor();
                }
                Some(&self.inner)
            }

            unsafe fn register_dtor(&self) {
                if !intrinsics::needs_drop::<T>() || self.dtor_registered.get() {
                    return
                }

                register_dtor(self as *const _ as *mut u8,
                              destroy_value::<T>);
                self.dtor_registered.set(true);
            }
        }

        // Since what appears to be glibc 2.18 this symbol has been shipped which
        // GCC and clang both use to invoke destructors in thread_local globals, so
        // let's do the same!
        //
        // Note, however, that we run on lots older linuxes, as well as cross
        // compiling from a newer linux to an older linux, so we also have a
        // fallback implementation to use as well.
        //
        // Due to rust-lang/rust#18804, make sure this is not generic!
        #[cfg(target_os = "linux")]
        unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
            use prelude::v1::*;
            use mem;
            use libc;
            use sys_common::thread_local as os;

            extern {
                #[linkage = "extern_weak"]
                static __dso_handle: *mut u8;
                #[linkage = "extern_weak"]
                static __cxa_thread_atexit_impl: *const libc::c_void;
            }
            if !__cxa_thread_atexit_impl.is_null() {
                type F = unsafe extern fn(dtor: unsafe extern fn(*mut u8),
                                          arg: *mut u8,
                                          dso_handle: *mut u8) -> libc::c_int;
                mem::transmute::<*const libc::c_void, F>(__cxa_thread_atexit_impl)
                (dtor, t, &__dso_handle as *const _ as *mut _);
                return
            }

            // The fallback implementation uses a vanilla OS-based TLS key to track
            // the list of destructors that need to be run for this thread. The key
            // then has its own destructor which runs all the other destructors.
            //
            // The destructor for DTORS is a little special in that it has a `while`
            // loop to continuously drain the list of registered destructors. It
            // *should* be the case that this loop always terminates because we
            // provide the guarantee that a TLS key cannot be set after it is
            // flagged for destruction.
            static DTORS: os::StaticKey = os::StaticKey::new(Some(run_dtors));
            type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
            if DTORS.get().is_null() {
                let v: Box<List> = box Vec::new();
                DTORS.set(Box::into_raw(v) as *mut u8);
            }
            let list: &mut List = &mut *(DTORS.get() as *mut List);
            list.push((t, dtor));

            unsafe extern fn run_dtors(mut ptr: *mut u8) {
                while !ptr.is_null() {
                    let list: Box<List> = Box::from_raw(ptr as *mut List);
                    for &(ptr, dtor) in list.iter() {
                        dtor(ptr);
                    }
                    ptr = DTORS.get();
                    DTORS.set(ptr::null_mut());
                }
            }
        }

        // OSX's analog of the above linux function is this _tlv_atexit function.
        // The disassembly of thread_local globals in C++ (at least produced by
        // clang) will have this show up in the output.
        #[cfg(target_os = "macos")]
        unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
            extern {
                fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
                               arg: *mut u8);
            }
            _tlv_atexit(dtor, t);
        }

        pub unsafe extern fn destroy_value<T>(ptr: *mut u8) {
            let ptr = ptr as *mut Key<T>;
            // Right before we run the user destructor be sure to flag the
            // destructor as running for this thread so calls to `get` will return
            // `None`.
            (*ptr).dtor_running.set(true);

            // The OSX implementation of TLS apparently had an odd aspect to it
            // where the pointer we have may be overwritten while this destructor
            // is running. Specifically if a TLS destructor re-accesses TLS it may
            // trigger a re-initialization of all TLS variables, paving over at
            // least some destroyed ones with initial values.
            //
            // This means that if we drop a TLS value in place on OSX that we could
            // revert the value to its original state halfway through the
            // destructor, which would be bad!
            //
            // Hence, we use `ptr::read` on OSX (to move to a "safe" location)
            // instead of drop_in_place.
            if cfg!(target_os = "macos") {
                ptr::read((*ptr).inner.get());
            } else {
                ptr::drop_in_place((*ptr).inner.get());
            }
        }
    }

    #[doc(hidden)]
    pub mod os {
        use prelude::v1::*;

        use cell::{Cell, UnsafeCell};
        use marker;
        use ptr;
        use sys_common::thread_local::StaticKey as OsStaticKey;

        pub struct Key<T> {
            // OS-TLS key that we'll use to key off.
            os: OsStaticKey,
            marker: marker::PhantomData<Cell<T>>,
        }

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

        struct Value<T: 'static> {
            key: &'static Key<T>,
            value: UnsafeCell<Option<T>>,
        }

        impl<T: 'static> Key<T> {
            pub const fn new() -> Key<T> {
                Key {
                    os: OsStaticKey::new(Some(destroy_value::<T>)),
                    marker: marker::PhantomData
                }
            }

            pub fn get(&'static self) -> Option<&'static UnsafeCell<Option<T>>> {
                unsafe {
                    let ptr = self.os.get() as *mut Value<T>;
                    if !ptr.is_null() {
                        if ptr as usize == 1 {
                            return None
                        }
                        return Some(&(*ptr).value);
                    }

                    // If the lookup returned null, we haven't initialized our own local
                    // copy, so do that now.
                    let ptr: Box<Value<T>> = box Value {
                        key: self,
                        value: UnsafeCell::new(None),
                    };
                    let ptr = Box::into_raw(ptr);
                    self.os.set(ptr as *mut u8);
                    Some(&(*ptr).value)
                }
            }
        }

        pub unsafe extern fn destroy_value<T: 'static>(ptr: *mut u8) {
            // The OS TLS ensures that this key contains a NULL value when this
            // destructor starts to run. We set it back to a sentinel value of 1 to
            // ensure that any future calls to `get` for this thread will return
            // `None`.
            //
            // Note that to prevent an infinite loop we reset it back to null right
            // before we return from the destructor ourselves.
            let ptr = Box::from_raw(ptr as *mut Value<T>);
            let key = ptr.key;
            key.os.set(1 as *mut u8);
            drop(ptr);
            key.os.set(ptr::null_mut());
        }
    }

    #[cfg(test)]
    mod tests {
        use prelude::v1::*;

        use sync::mpsc::{channel, Sender};
        use cell::{Cell, UnsafeCell};
        use super::LocalKeyState;
        use thread;

        struct Foo(Sender<()>);

        impl Drop for Foo {
            fn drop(&mut self) {
                let Foo(ref s) = *self;
                s.send(()).unwrap();
            }
        }

        #[test]
        fn smoke_no_dtor() {
            thread_local!(static FOO: Cell<i32> = Cell::new(1));

            FOO.with(|f| {
                assert_eq!(f.get(), 1);
                f.set(2);
            });
            let (tx, rx) = channel();
            let _t = thread::spawn(move|| {
                FOO.with(|f| {
                    assert_eq!(f.get(), 1);
                });
                tx.send(()).unwrap();
            });
            rx.recv().unwrap();

            FOO.with(|f| {
                assert_eq!(f.get(), 2);
            });
        }

        #[test]
        fn states() {
            struct Foo;
            impl Drop for Foo {
                fn drop(&mut self) {
                    assert!(FOO.state() == LocalKeyState::Destroyed);
                }
            }
            fn foo() -> Foo {
                assert!(FOO.state() == LocalKeyState::Uninitialized);
                Foo
            }
            thread_local!(static FOO: Foo = foo());

            thread::spawn(|| {
                assert!(FOO.state() == LocalKeyState::Uninitialized);
                FOO.with(|_| {
                    assert!(FOO.state() == LocalKeyState::Valid);
                });
                assert!(FOO.state() == LocalKeyState::Valid);
            }).join().ok().unwrap();
        }

        #[test]
        fn smoke_dtor() {
            thread_local!(static FOO: UnsafeCell<Option<Foo>> = UnsafeCell::new(None));

            let (tx, rx) = channel();
            let _t = thread::spawn(move|| unsafe {
                let mut tx = Some(tx);
                FOO.with(|f| {
                    *f.get() = Some(Foo(tx.take().unwrap()));
                });
            });
            rx.recv().unwrap();
        }

        #[test]
        fn circular() {
            struct S1;
            struct S2;
            thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
            thread_local!(static K2: UnsafeCell<Option<S2>> = UnsafeCell::new(None));
            static mut HITS: u32 = 0;

            impl Drop for S1 {
                fn drop(&mut self) {
                    unsafe {
                        HITS += 1;
                        if K2.state() == LocalKeyState::Destroyed {
                            assert_eq!(HITS, 3);
                        } else {
                            if HITS == 1 {
                                K2.with(|s| *s.get() = Some(S2));
                            } else {
                                assert_eq!(HITS, 3);
                            }
                        }
                    }
                }
            }
            impl Drop for S2 {
                fn drop(&mut self) {
                    unsafe {
                        HITS += 1;
                        assert!(K1.state() != LocalKeyState::Destroyed);
                        assert_eq!(HITS, 2);
                        K1.with(|s| *s.get() = Some(S1));
                    }
                }
            }

            thread::spawn(move|| {
                drop(S1);
            }).join().ok().unwrap();
        }

        #[test]
        fn self_referential() {
            struct S1;
            thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));

            impl Drop for S1 {
                fn drop(&mut self) {
                    assert!(K1.state() == LocalKeyState::Destroyed);
                }
            }

            thread::spawn(move|| unsafe {
                K1.with(|s| *s.get() = Some(S1));
            }).join().ok().unwrap();
        }

        // Note that this test will deadlock if TLS destructors aren't run (this
        // requires the destructor to be run to pass the test). OSX has a known bug
        // where dtors-in-dtors may cancel other destructors, so we just ignore this
        // test on OSX.
        #[test]
        #[cfg_attr(target_os = "macos", ignore)]
        fn dtors_in_dtors_in_dtors() {
            struct S1(Sender<()>);
            thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
            thread_local!(static K2: UnsafeCell<Option<Foo>> = UnsafeCell::new(None));

            impl Drop for S1 {
                fn drop(&mut self) {
                    let S1(ref tx) = *self;
                    unsafe {
                        if K2.state() != LocalKeyState::Destroyed {
                            K2.with(|s| *s.get() = Some(Foo(tx.clone())));
                        }
                    }
                }
            }

            let (tx, rx) = channel();
            let _t = thread::spawn(move|| unsafe {
                let mut tx = Some(tx);
                K1.with(|s| *s.get() = Some(S1(tx.take().unwrap())));
            });
            rx.recv().unwrap();
        }
    }

    #[cfg(test)]
    mod dynamic_tests {
        use prelude::v1::*;

        use cell::RefCell;
        use collections::HashMap;

        #[test]
        fn smoke() {
            fn square(i: i32) -> i32 { i * i }
            thread_local!(static FOO: i32 = square(3));

            FOO.with(|f| {
                assert_eq!(*f, 9);
            });
        }

        #[test]
        fn hashmap() {
            fn map() -> RefCell<HashMap<i32, i32>> {
                let mut m = HashMap::new();
                m.insert(1, 2);
                RefCell::new(m)
            }
            thread_local!(static FOO: RefCell<HashMap<i32, i32>> = map());

            FOO.with(|map| {
                assert_eq!(map.borrow()[&1], 2);
            });
        }

        #[test]
        fn refcell_vec() {
            thread_local!(static FOO: RefCell<Vec<u32>> = RefCell::new(vec![1, 2, 3]));

            FOO.with(|vec| {
                assert_eq!(vec.borrow().len(), 3);
                vec.borrow_mut().push(4);
                assert_eq!(vec.borrow()[3], 4);
            });
        }
    }

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