95 lines
2.3 KiB
Rust
95 lines
2.3 KiB
Rust
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//! An implementation of a `ByteBuf` based on virtual memory.
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//!
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//! This implementation uses `mmap` on POSIX systems (and should use `VirtualAlloc` on windows).
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use std::ptr::{self, NonNull};
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use std::slice;
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struct Mmap {
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ptr: NonNull<u8>,
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len: usize,
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}
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impl Mmap {
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fn new(len: usize) -> Self {
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assert!(len > 0);
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unsafe {
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let ptr = libc::mmap(
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ptr::null_mut(),
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len,
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libc::PROT_READ | libc::PROT_WRITE,
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libc::MAP_PRIVATE | libc::MAP_ANON,
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-1,
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0,
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);;
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assert!(ptr as isize != -1);
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Self {
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ptr: NonNull::new(ptr as *mut u8).unwrap(),
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len,
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}
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}
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}
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pub fn as_slice(&self) -> &[u8] {
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unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
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}
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pub fn as_slice_mut(&mut self) -> &mut [u8] {
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unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
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}
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}
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impl Drop for Mmap {
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fn drop(&mut self) {
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let r = unsafe { libc::munmap(self.ptr.as_ptr() as *mut libc::c_void, self.len) };
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assert_eq!(r, 0, "munmap failed");
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}
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}
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pub struct ByteBuf {
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mmap: Option<Mmap>,
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}
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impl ByteBuf {
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pub fn new(len: usize) -> Self {
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let mmap = if len == 0 { None } else { Some(Mmap::new(len)) };
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Self { mmap }
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}
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pub fn realloc(&mut self, new_len: usize) {
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let new_mmap = if new_len == 0 {
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None
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} else {
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if self.len() == 0 {
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Some(Mmap::new(new_len))
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} else {
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let mut new_mmap = Mmap::new(new_len);
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unsafe {
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let src = self.mmap.as_ref().unwrap().as_slice();
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let dst = new_mmap.as_slice_mut();
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ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), src.len());
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}
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Some(new_mmap)
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}
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};
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self.mmap = new_mmap;
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}
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pub fn len(&self) -> usize {
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self.mmap.as_ref().map(|m| m.len).unwrap_or(0)
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}
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pub fn as_slice(&self) -> &[u8] {
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self.mmap.as_ref().map(|m| m.as_slice()).unwrap_or(&[])
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}
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pub fn as_slice_mut(&mut self) -> &mut [u8] {
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self.mmap.as_mut().map(|m| m.as_slice_mut()).unwrap_or(&mut [])
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}
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}
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