Emma is an EMbeddable Memory Allocator. This means:

• Fully no_std compatible.
• No direct or indirect binary dependencies, including on libc: emma uses raw syscalls instead. Note that your rustc target may depend on libc - use the x86_64-unknown-linux-unknown target, with which emma is compatible, if you want to avoid this.
• No usage of any shared resources: Instead of brk/sbrk to modify the shared data segment, emma only ever maps its own segments using mmap.

Multiple emma instances can coexist with other allocators the same process. If its symbols are renamed, emma can even coexist with other copies and/or versions of itself without interference!

Usage

Use emma as you would any other allocator:

#[global_allocator]
static EMMA: emma::DefaultEmma = emma::DefaultEmma::new();

Performance

Emma seems not far behind (other) state-of-the-art allocators.

Target Architecture

At the moment, emma exclusively targets linux on x86_64.

Known Issues

• It is not clear how emma behaves when a process is forked. (Note: child processes of multi-threaded processes may only access async-signal-safe functions until they call execve anyway.)
• Calling fork (or performing an equivalent clone call) is safe as long as no thread is currently de-/allocating memory. However, if the forking process ever allocated memory on more than one thread, memory usage will be suboptimal until the new main thread terminates.
• Embedding multiple emma instancess into one process should work, but unless their symbols are renamed they may share data structures behind the scenes.
• An emma instance does not return all its resources, even if all allocations are returned. This is reasonable for a global allocator, but makes it not as useful as a temporary allocator.
• Emma is not async-signal-safe, i.e., you may not de-/allocate memory in a signal handler. (The same probably holds true for your default memory allocator; POSIX does not list malloc or free as async-signal safe either.)

Features

• tls enabling thread-local-storage requires a nightly compiler. Enabling tls massively increases performance.
• boundary-checks enables assertions at the library boundary. These assertions cost a small amount of performance.

License

Licensed under either of:

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contributions

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.