RedBear-OS/src/platform/allocator/sys.rs

use crate::{
    header::{
        pthread::pthread_atfork,
        sys_mman::{self, MREMAP_MAYMOVE},
    },
    platform::{Pal, Sys},
    sync::Mutex,
};
use core::ptr;

use dlmalloc::Allocator;

/// System setting for Redox/Linux
pub struct System {
    _priv: (),
}

impl System {
    pub const fn new() -> System {
        System { _priv: () }
    }
}

static LOCK: Mutex<()> = Mutex::new(());

unsafe impl Allocator for System {
    fn alloc(&self, size: usize) -> (*mut u8, usize, u32) {
        let Ok(addr) = (unsafe {
            Sys::mmap(
                ptr::null_mut(),
                size,
                sys_mman::PROT_WRITE | sys_mman::PROT_READ,
                sys_mman::MAP_ANON | sys_mman::MAP_PRIVATE,
                -1,
                0,
            )
        }) else {
            return (ptr::null_mut(), 0, 0);
        };
        (addr.cast::<u8>(), size, 0)
    }

    fn remap(&self, ptr: *mut u8, oldsize: usize, newsize: usize, can_move: bool) -> *mut u8 {
        let flags = if can_move { MREMAP_MAYMOVE } else { 0 };
        let Ok(ptr) =
            (unsafe { Sys::mremap(ptr.cast(), oldsize, newsize, flags, ptr::null_mut()) })
        else {
            return ptr::null_mut();
        };
        ptr.cast::<u8>()
    }

    fn free_part(&self, ptr: *mut u8, oldsize: usize, newsize: usize) -> bool {
        unsafe {
            if Sys::mremap(ptr.cast(), oldsize, newsize, 0, ptr::null_mut()).is_ok() {
                return true;
            }
            Sys::munmap(ptr.add(newsize).cast(), oldsize - newsize).is_ok()
        }
    }

    fn free(&self, ptr: *mut u8, size: usize) -> bool {
        unsafe { Sys::munmap(ptr.cast(), size).is_ok() }
    }

    fn can_release_part(&self, _flags: u32) -> bool {
        true
    }

    fn allocates_zeros(&self) -> bool {
        true
    }

    fn page_size(&self) -> usize {
        4096
    }
}

pub fn acquire_global_lock() {
    unsafe {
        // SAFETY: No data inside
        LOCK.manual_lock();
    }
}

pub(super) fn release_global_lock() {
    unsafe {
        // SAFETY: No data inside
        LOCK.manual_unlock();
    }
}

/// Allows the allocator to remain unsable in the child process,
/// after a call to `fork(2)`
///
/// # Safety
///
/// if used, this function must be called,
/// before any allocations are made with the global allocator.
pub unsafe fn enable_alloc_after_fork() {
    // atfork must only be called once, to avoid a deadlock,
    // where the handler attempts to acquire the global lock twice
    static mut FORK_PROTECTED: bool = false;

    extern "C" fn _acquire_global_lock() {
        acquire_global_lock()
    }

    extern "C" fn _release_global_lock() {
        release_global_lock()
    }

    acquire_global_lock();
    // if a process forks,
    // it will acquire the lock before any other thread,
    // protecting it from deadlock,
    // due to the child being created with only the calling thread.
    unsafe {
        if !FORK_PROTECTED {
            pthread_atfork(
                Some(_acquire_global_lock),
                Some(_release_global_lock),
                Some(_release_global_lock),
            );
            FORK_PROTECTED = true;
        }
    }
    release_global_lock();
}