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    // Copyright 2017 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.

    //! Memory allocation APIs
    //!
    //! In a given program, the standard library has one “global” memory allocator
    //! that is used for example by `Box<T>` and `Vec<T>`.
    //!
    //! Currently the default global allocator is unspecified.
    //! The compiler may link to a version of [jemalloc] on some platforms,
    //! but this is not guaranteed.
    //! Libraries, however, like `cdylib`s and `staticlib`s are guaranteed
    //! to use the [`System`] by default.
    //!
    //! [jemalloc]: https://github.com/jemalloc/jemalloc
    //! [`System`]: struct.System.html
    //!
    //! # The `#[global_allocator]` attribute
    //!
    //! This attribute allows configuring the choice of global allocator.
    //! You can use this to implement a completely custom global allocator
    //! to route all default allocation requests to a custom object.
    //!
    //! ```rust
    //! use std::alloc::{GlobalAlloc, System, Layout};
    //!
    //! struct MyAllocator;
    //!
    //! unsafe impl GlobalAlloc for MyAllocator {
    //!     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
    //!         System.alloc(layout)
    //!     }
    //!
    //!     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
    //!         System.dealloc(ptr, layout)
    //!     }
    //! }
    //!
    //! #[global_allocator]
    //! static GLOBAL: MyAllocator = MyAllocator;
    //!
    //! fn main() {
    //!     // This `Vec` will allocate memory through `GLOBAL` above
    //!     let mut v = Vec::new();
    //!     v.push(1);
    //! }
    //! ```
    //!
    //! The attribute is used on a `static` item whose type implements the
    //! [`GlobalAlloc`] trait. This type can be provided by an external library:
    //!
    //! [`GlobalAlloc`]: ../../core/alloc/trait.GlobalAlloc.html
    //!
    //! ```rust,ignore (demonstrates crates.io usage)
    //! extern crate jemallocator;
    //!
    //! use jemallocator::Jemalloc;
    //!
    //! #[global_allocator]
    //! static GLOBAL: Jemalloc = Jemalloc;
    //!
    //! fn main() {}
    //! ```
    //!
    //! The `#[global_allocator]` can only be used once in a crate
    //! or its recursive dependencies.

    #![stable(feature = "alloc_module", since = "1.28.0")]

    use core::sync::atomic::{AtomicPtr, Ordering};
    use core::{mem, ptr};
    use sys_common::util::dumb_print;

    #[stable(feature = "alloc_module", since = "1.28.0")]
    #[doc(inline)]
    pub use alloc_crate::alloc::*;

    #[stable(feature = "alloc_system_type", since = "1.28.0")]
    #[doc(inline)]
    pub use alloc_system::System;

    static HOOK: AtomicPtr<()> = AtomicPtr::new(ptr::null_mut());

    /// Registers a custom allocation error hook, replacing any that was previously registered.
    ///
    /// The allocation error hook is invoked when an infallible memory allocation fails, before
    /// the runtime aborts. The default hook prints a message to standard error,
    /// but this behavior can be customized with the [`set_alloc_error_hook`] and
    /// [`take_alloc_error_hook`] functions.
    ///
    /// The hook is provided with a `Layout` struct which contains information
    /// about the allocation that failed.
    ///
    /// The allocation error hook is a global resource.
    #[unstable(feature = "alloc_error_hook", issue = "51245")]
    pub fn set_alloc_error_hook(hook: fn(Layout)) {
        HOOK.store(hook as *mut (), Ordering::SeqCst);
    }

    /// Unregisters the current allocation error hook, returning it.
    ///
    /// *See also the function [`set_alloc_error_hook`].*
    ///
    /// If no custom hook is registered, the default hook will be returned.
    #[unstable(feature = "alloc_error_hook", issue = "51245")]
    pub fn take_alloc_error_hook() -> fn(Layout) {
        let hook = HOOK.swap(ptr::null_mut(), Ordering::SeqCst);
        if hook.is_null() {
            default_alloc_error_hook
        } else {
            unsafe { mem::transmute(hook) }
        }
    }

    fn default_alloc_error_hook(layout: Layout) {
        dumb_print(format_args!("memory allocation of {} bytes failed", layout.size()));
    }

    #[cfg(not(test))]
    #[doc(hidden)]
    #[alloc_error_handler]
    #[unstable(feature = "alloc_internals", issue = "0")]
    pub fn rust_oom(layout: Layout) -> ! {
        let hook = HOOK.load(Ordering::SeqCst);
        let hook: fn(Layout) = if hook.is_null() {
            default_alloc_error_hook
        } else {
            unsafe { mem::transmute(hook) }
        };
        hook(layout);
        unsafe { ::sys::abort_internal(); }
    }

    #[cfg(not(test))]
    #[doc(hidden)]
    #[allow(unused_attributes)]
    #[unstable(feature = "alloc_internals", issue = "0")]
    pub mod __default_lib_allocator {
        use super::{System, Layout, GlobalAlloc};
        // for symbol names src/librustc/middle/allocator.rs
        // for signatures src/librustc_allocator/lib.rs

        // linkage directives are provided as part of the current compiler allocator
        // ABI

        #[rustc_std_internal_symbol]
        pub unsafe extern fn __rdl_alloc(size: usize, align: usize) -> *mut u8 {
            let layout = Layout::from_size_align_unchecked(size, align);
            System.alloc(layout)
        }

        #[rustc_std_internal_symbol]
        pub unsafe extern fn __rdl_dealloc(ptr: *mut u8,
                                           size: usize,
                                           align: usize) {
            System.dealloc(ptr, Layout::from_size_align_unchecked(size, align))
        }

        #[rustc_std_internal_symbol]
        pub unsafe extern fn __rdl_realloc(ptr: *mut u8,
                                           old_size: usize,
                                           align: usize,
                                           new_size: usize) -> *mut u8 {
            let old_layout = Layout::from_size_align_unchecked(old_size, align);
            System.realloc(ptr, old_layout, new_size)
        }

        #[rustc_std_internal_symbol]
        pub unsafe extern fn __rdl_alloc_zeroed(size: usize, align: usize) -> *mut u8 {
            let layout = Layout::from_size_align_unchecked(size, align);
            System.alloc_zeroed(layout)
        }
    }

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