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/*
 * garbage-collected memory manager in Rust
 * Copyright (C) 2020  Xie Ruifeng
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

//! Memory allocation primitives.
mod unix;
mod windows;

/// Common errors from `mmap`.
///
/// Error codes on Windows is far more complicated then `errno` on UNIX-like systems. Also, we
/// don't know what error code can be caused by an API call, for they are both not documented
/// and officially-announced as unstable. Therefore on Windows, we try our best to match on
/// the error, but likely some errors would still end up as an `UnknownError`.
///
/// **Note**: items marked as UNIX-specific will not show up on Windows.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum MMapError {
    /// Arguments provided to `mmap` is invalid.
    InvalidArguments,
    /// (UNIX-specific) Too much memory has been locked.
    TryAgain,
    /// (UNIX-specific) Any of the following applies:
    /// - No memory available, or
    /// - Maximum number of mappings exceeded, or
    /// - `RLIMIT_DATA` exceeded
    NoMemory,
    /// Number of pages overflows `unsigned long`.
    /// (32-bit platform only, UNIX-specific)
    LengthOverflow,
    /// Errors not recognized, with the raw error code on the host system.
    UnknownError(u32),
    /// No error at all, NOT EXPECTED.
    /// Whenever received, this should be considered as a bug in the implementation.
    NoError,
}

/// Memory allocation results.
pub type Result<T> = core::result::Result<T, MMapError>;

#[cfg(unix)]
use unix as detail;
#[cfg(windows)]
use windows as detail;

pub use detail::Protection;

pub use detail::get_page_size;
pub use detail::get_minimum_alignment;

pub use detail::aligned_allocate_chunk;
pub use detail::deallocate_chunk;

#[cfg(test)]
mod tests {
    extern crate std;

    use super::Protection;
    use super::get_minimum_alignment;
    use super::aligned_allocate_chunk;
    use super::deallocate_chunk;

    #[test]
    fn test_aligned_allocate_chunk() {
        let page_size = get_minimum_alignment().unwrap();
        let alignment = page_size * 2;
        let size = alignment * 3;
        let addr = unsafe {
            aligned_allocate_chunk(alignment, size, Protection::NONE).unwrap()
        };
        assert_eq!(addr as usize % alignment, 0);
        unsafe { deallocate_chunk(addr, size).unwrap() }
    }
}