alloc_counter

Alloc counters

A redesign of the Quick and Dirty Allocation Profiling Tool.

Features

• Count allocations, reallocations and deallocations individually with count_alloc.

• Allow, deny, and forbid use of the global allocator with allow_alloc, deny_alloc and forbid_alloc.

• #[no_alloc] function attribute to deny and #[no_alloc(forbid)] to forbid use of the global allocator.

Limitations and known issues

• Methods must either take a reference to self or Self must be a Copy type.

Usage

An AllocCounter<A> wraps an allocator A to individually count the number of calls to alloc, realloc, and dealloc.

use alloc_counter::AllocCounter;

#[global_allocator]
static A: AllocCounter<MyAllocator> = AllocCounter(MyAllocator);

Std-users may prefer to inherit their system's allocator.

use alloc_counter::AllocCounterSystem;

#[global_allocator]
static A: AllocCounterSystem = AllocCounterSystem;

To count the allocations of an expression, use count_alloc.

assert_eq!(
    count_alloc(|| {
        // no alloc
        let mut v = Vec::new();
        // alloc
        v.push(0);
        // realloc
        v.push(1);
        // dealloc
    })
    .0,
    (1, 1, 1)
);

To deny allocations for an expression use deny_alloc.

fn foo(b: Box<i32>) {
    // dropping causes a panic
    deny_alloc(|| drop(b))
}
foo(Box::new(0));

Similar to Rust's lints, you can still allow allocation inside a deny block.

fn foo(b: Box<i32>) {
    deny_alloc(|| allow_alloc(|| drop(b)))
}
foo(Box::new(0));

Forbidding allocations forces a panic even when allow_alloc is used.

fn foo(b: Box<i32>) {
    // panics because of outer `forbid`, even though drop happens in an allow block
    forbid_alloc(|| allow_alloc(|| drop(b)))
}
foo(Box::new(0));

For added sugar you may use the #[no_alloc] attribute on functions, including methods with self-binds. #[no_alloc] expands to calling deny_alloc and forcefully moves the parameters into the checked block. #[no_alloc(forbid)] calls forbid_alloc.

#[no_alloc(forbid)]
fn foo(b: Box<i32>) {
    allow_alloc(|| drop(b))
}
foo(Box::new(0));

License: MIT OR Apache-2.0