portable-dlmalloc

Portable Fork of Doug Lea's malloc Implementation for Rust.

Introduction

This code is originally implemented by Doug Lea. The original source code is no longer available from the FTP URL listed in the website, but you can still find it through Wayback Machine.

You may use this crate to help you make a portable global allocator.
You will have to implement the eight C functions as described in Port To Your Platform chapter.

Global Allocator

To use this crate as your global allocator:

use portable_dlmalloc::DLMalloc;
#[global_alloactor] static GLOBAL_ALLOCATOR:DLMalloc=DLMalloc;

Then you will be able to use alloc crate.

extern crate alloc;

The default alignment of dlmalloc is twice the pointer size (e.g.: 16 bytes on 64-bit systems).
If you need to use a different alignment, use dlmemalign function to implement your GlobalAlloc trait.

Alternate Allocator

The Allocator Trait is currently nightly-only.
Currently, this crate does not support this trait.

Raw FFI

The raw module from this crate exports FFI bindings for dlmalloc library.

use portable_dlmalloc::raw::*;

For example, you may use dlmallopt to adjust mmap granularity (default is 2MiB in Rust crate):

dlmallopt(M_GRANULARITY,0x20000);	// Change `mmap` granularity to 128KiB.

You may use dlpvalloc to allocate memory on page-granularity.

let p=dlpvalloc(12345);
assert_eq!(p as usize & 0xfff,0);

Warning: dlpvalloc - as well as other routines that allocate memories with higher granularities - may cause serious memory fragmentation if you overrely on them.

// Assume 4096 is page size.
let p=dlpvalloc(4096) as usize;
let q=dlpvalloc(4096) as usize;
// Consecutive allocations do not guarantee them to be adjacent.
assert_eq!(q-p,8192);

Port to Your Platform

To port dlmalloc to your platform, implement the following procedures:

• custom_mmap/custom_munmap: Allocate and free pages from the system. mmap should return (void*)-1 to indicate failure instead of NULL. munmap should return 0 to indicate success, and -1 to indicate failure.

   #[no_mangle] unsafe extern "C" custom_mmap(length:usize)->*mut c_void;
   #[no_mangle] unsafe extern "C" custom_munmap(ptr:*mut c_void,length:usize)->i32;
  

• custom_direct_mmap: Extend the allocated pages. This is optional. Return (void*)-1 to indicate failure/no-support.

   #[no_mangle] unsafe extern "C" custom_mmap(length:usize)->*mut c_void;
  

• init_lock/final_lock/acquire_lock/release_lock: Implement thread-safety for dlmalloc. The minimal implementation can be a simple spinlock. You can leave the implementations empty for this set of routines if you do not need thread-safety.

   #[no_mangle] unsafe extern "C" init_lock(lock:*mut *mut c_void);	// Initialize the mutex.
   #[no_mangle] unsafe extern "C" final_lock(lock:*mut *mut c_void);	// Finalize the mutex.
   #[no_mangle] unsafe extern "C" acquire_lock(lock:*mut *mut c_void);	// Acquire the mutex.
   #[no_mangle] unsafe extern "C" release_lock(lock:*mut *mut c_void);	// Release the mutex.
  

• custom_abort: Implement abort() routine. dlmalloc calls custom_abort() when internal assertion fails. You may use panic here.

   #[no_mangle] unsafe extern "C" custom_abort()->!;
  

• memcpy/memset: I suppose no explanations are needed for these two. dlmalloc uses these two routines, but they can be easily implemented anyway. You do not need to implement these two routines in Rust if your linker can find libraries that implement these two routines.

License

This crate is under the MIT license.