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//! 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. Libraries, however, //! like `cdylib`s and `staticlib`s are guaranteed to use the [`System`] by //! default. //! //! [`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 core::ptr::NonNull; use crate::sys_common::util::dumb_print; #[stable(feature = "alloc_module", since = "1.28.0")] #[doc(inline)] pub use alloc_crate::alloc::*; /// The default memory allocator provided by the operating system. /// /// This is based on `malloc` on Unix platforms and `HeapAlloc` on Windows, /// plus related functions. /// /// This type implements the `GlobalAlloc` trait and Rust programs by default /// work as if they had this definition: /// /// ```rust /// use std::alloc::System; /// /// #[global_allocator] /// static A: System = System; /// /// fn main() { /// let a = Box::new(4); // Allocates from the system allocator. /// println!("{}", a); /// } /// ``` /// /// You can also define your own wrapper around `System` if you'd like, such as /// keeping track of the number of all bytes allocated: /// /// ```rust /// use std::alloc::{System, GlobalAlloc, Layout}; /// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; /// /// struct Counter; /// /// static ALLOCATED: AtomicUsize = AtomicUsize::new(0); /// /// unsafe impl GlobalAlloc for Counter { /// unsafe fn alloc(&self, layout: Layout) -> *mut u8 { /// let ret = System.alloc(layout); /// if !ret.is_null() { /// ALLOCATED.fetch_add(layout.size(), SeqCst); /// } /// return ret /// } /// /// unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) { /// System.dealloc(ptr, layout); /// ALLOCATED.fetch_sub(layout.size(), SeqCst); /// } /// } /// /// #[global_allocator] /// static A: Counter = Counter; /// /// fn main() { /// println!("allocated bytes before main: {}", ALLOCATED.load(SeqCst)); /// } /// ``` /// /// It can also be used directly to allocate memory independently of whatever /// global allocator has been selected for a Rust program. For example if a Rust /// program opts in to using jemalloc as the global allocator, `System` will /// still allocate memory using `malloc` and `HeapAlloc`. #[stable(feature = "alloc_system_type", since = "1.28.0")] #[derive(Debug, Default, Copy, Clone)] pub struct System; // The Alloc impl just forwards to the GlobalAlloc impl, which is in `std::sys::*::alloc`. #[unstable(feature = "allocator_api", issue = "32838")] unsafe impl Alloc for System { #[inline] unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> { NonNull::new(GlobalAlloc::alloc(self, layout)).ok_or(AllocErr) } #[inline] unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> { NonNull::new(GlobalAlloc::alloc_zeroed(self, layout)).ok_or(AllocErr) } #[inline] unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) { GlobalAlloc::dealloc(self, ptr.as_ptr(), layout) } #[inline] unsafe fn realloc(&mut self, ptr: NonNull<u8>, layout: Layout, new_size: usize) -> Result<NonNull<u8>, AllocErr> { NonNull::new(GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size)).ok_or(AllocErr) } } 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. /// /// [`set_alloc_error_hook`]: fn.set_alloc_error_hook.html /// [`take_alloc_error_hook`]: fn.take_alloc_error_hook.html #[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. /// /// [`set_alloc_error_hook`]: fn.set_alloc_error_hook.html #[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 { crate::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}; // These magic symbol names are used as a fallback for implementing the // `__rust_alloc` etc symbols (see `src/liballoc/alloc.rs) when there is // no `#[global_allocator]` attribute. // 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) } }