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wasm: rm static mut #142727

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Merged
merged 1 commit into from
Aug 28, 2025
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wasm: rm static mut #142727

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17 changes: 10 additions & 7 deletions library/std/src/sys/alloc/wasm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,12 +16,15 @@
//! The crate itself provides a global allocator which on wasm has no
//! synchronization as there are no threads!

// FIXME(static_mut_refs): Do not allow `static_mut_refs` lint
#![allow(static_mut_refs)]
use core::cell::SyncUnsafeCell;

use crate::alloc::{GlobalAlloc, Layout, System};

static mut DLMALLOC: dlmalloc::Dlmalloc = dlmalloc::Dlmalloc::new();
struct SyncDlmalloc(dlmalloc::Dlmalloc);
unsafe impl Sync for SyncDlmalloc {}
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@juntyr juntyr Jun 19, 2025

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This is only safe if we're in WASM without threads, is this file already gated for that?

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@hkBst hkBst Jun 20, 2025

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The same file also contains a Lock impl for the case there are threads, which is used to guard the Allocator impl against unsynchronized accesses.


static DLMALLOC: SyncUnsafeCell<SyncDlmalloc> =
SyncUnsafeCell::new(SyncDlmalloc(dlmalloc::Dlmalloc::new()));

#[stable(feature = "alloc_system_type", since = "1.28.0")]
unsafe impl GlobalAlloc for System {
Expand All @@ -30,31 +33,31 @@ unsafe impl GlobalAlloc for System {
// SAFETY: DLMALLOC access is guaranteed to be safe because the lock gives us unique and non-reentrant access.
// Calling malloc() is safe because preconditions on this function match the trait method preconditions.
let _lock = lock::lock();
unsafe { DLMALLOC.malloc(layout.size(), layout.align()) }
unsafe { (*DLMALLOC.get()).0.malloc(layout.size(), layout.align()) }
}

#[inline]
unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
// SAFETY: DLMALLOC access is guaranteed to be safe because the lock gives us unique and non-reentrant access.
// Calling calloc() is safe because preconditions on this function match the trait method preconditions.
let _lock = lock::lock();
unsafe { DLMALLOC.calloc(layout.size(), layout.align()) }
unsafe { (*DLMALLOC.get()).0.calloc(layout.size(), layout.align()) }
}

#[inline]
unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
// SAFETY: DLMALLOC access is guaranteed to be safe because the lock gives us unique and non-reentrant access.
// Calling free() is safe because preconditions on this function match the trait method preconditions.
let _lock = lock::lock();
unsafe { DLMALLOC.free(ptr, layout.size(), layout.align()) }
unsafe { (*DLMALLOC.get()).0.free(ptr, layout.size(), layout.align()) }
}

#[inline]
unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
// SAFETY: DLMALLOC access is guaranteed to be safe because the lock gives us unique and non-reentrant access.
// Calling realloc() is safe because preconditions on this function match the trait method preconditions.
let _lock = lock::lock();
unsafe { DLMALLOC.realloc(ptr, layout.size(), layout.align(), new_size) }
unsafe { (*DLMALLOC.get()).0.realloc(ptr, layout.size(), layout.align(), new_size) }
}
}

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