alloc_counter

Alloc counters

A redesign of the Quick and Dirty Allocation Profiling Tool.

Features

• Although #[no_std] is intended, it isn't currently supported due to the lack of portable thread_local implementation. This may be "fixed" with a feature flag to use a global atomic under the contract that the program is single threaded.

• 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.

• #[count_alloc] function attribute to print the counts to stderr. Alternatively use #[count_alloc(func = "my_function")] where my_function accepts a triple of usizes and returns () to redirect the output.

Limitations and known issues

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

• Ordinary and async functions must be treated differently. Use count_alloc for functions and count_alloc_future for futures.

Usage

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

use alloc_counter::AllocCounter;

type MyAllocator = std::alloc::System;
const MyAllocator: MyAllocator = std::alloc::System;

#[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.

# use alloc_counter::{count_alloc, AllocCounterSystem};
# #[global_allocator]
# static A: AllocCounterSystem = AllocCounterSystem;
let (counts, v) = count_alloc(|| {
    // no alloc
    let mut v = Vec::new();
    // alloc
    v.push(0);
    // realloc
    v.push(1);
    // return the vector without deallocating
    v
});
assert_eq!(counts, (1, 1, 0));

To deny allocations for an expression use deny_alloc.

# use alloc_counter::{deny_alloc, AllocCounterSystem};
# #[global_allocator]
# static A: AllocCounterSystem = AllocCounterSystem;
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.

# use alloc_counter::{allow_alloc, deny_alloc, AllocCounterSystem};
# #[global_allocator]
# static A: AllocCounterSystem = AllocCounterSystem;
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.

# use alloc_counter::{allow_alloc, forbid_alloc, AllocCounterSystem};
# #[global_allocator]
# static A: AllocCounterSystem = AllocCounterSystem;
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.

# #[cfg(not(feature = "macros"))]
# panic!("macros feature disabled");
# #[cfg(feature = "macros")] {
# use alloc_counter::{allow_alloc, no_alloc, AllocCounterSystem};
# #[global_allocator]
# static A: AllocCounterSystem = AllocCounterSystem;
#[no_alloc(forbid)]
fn foo(b: Box<i32>) {
    allow_alloc(|| drop(b))
}
foo(Box::new(0));
# }

License: MIT OR Apache-2.0