Use mmap

Cargo.toml

@@ -17,6 +17,7 @@ memory_units = "0.3.0"
 libm = { version = "0.1.2", optional = true }
 num-rational = "0.2.2"
 num-traits = "0.2.8"
+libc = "0.2.58"
 
 [dev-dependencies]
 assert_matches = "1.1"

src/memory/mmap.rs

@@ -0,0 +1,94 @@
+//! An implementation of a `ByteBuf` based on virtual memory.
+//!
+//! This implementation uses `mmap` on POSIX systems (and should use `VirtualAlloc` on windows).
+
+use std::ptr::{self, NonNull};
+use std::slice;
+
+struct Mmap {
+    ptr: NonNull<u8>,
+    len: usize,
+}
+
+impl Mmap {
+    fn new(len: usize) -> Self {
+        assert!(len > 0);
+        unsafe {
+            let ptr = libc::mmap(
+                ptr::null_mut(),
+                len,
+                libc::PROT_READ | libc::PROT_WRITE,
+                libc::MAP_PRIVATE | libc::MAP_ANON,
+                -1,
+                0,
+            );;
+            assert!(ptr as isize != -1);
+            Self {
+                ptr: NonNull::new(ptr as *mut u8).unwrap(),
+                len,
+            }
+        }
+    }
+
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
+    }
+
+    pub fn as_slice_mut(&mut self) -> &mut [u8] {
+        unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
+    }
+}
+
+impl Drop for Mmap {
+    fn drop(&mut self) {
+        let r = unsafe { libc::munmap(self.ptr.as_ptr() as *mut libc::c_void, self.len) };
+        assert_eq!(r, 0, "munmap failed");
+    }
+}
+
+pub struct ByteBuf {
+    mmap: Option<Mmap>,
+}
+
+impl ByteBuf {
+    pub fn new(len: usize) -> Self {
+        let mmap = if len == 0 { None } else { Some(Mmap::new(len)) };
+
+        Self { mmap }
+    }
+
+    pub fn realloc(&mut self, new_len: usize) {
+        let new_mmap = if new_len == 0 {
+            None
+        } else {
+            if self.len() == 0 {
+                Some(Mmap::new(new_len))
+            } else {
+                let mut new_mmap = Mmap::new(new_len);
+
+                unsafe {
+                    let src = self.mmap.as_ref().unwrap().as_slice();
+                    let dst = new_mmap.as_slice_mut();
+
+                    ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), src.len());
+                }
+
+                Some(new_mmap)
+            }
+        };
+
+        self.mmap = new_mmap;
+    }
+
+    pub fn len(&self) -> usize {
+        self.mmap.as_ref().map(|m| m.len).unwrap_or(0)
+    }
+
+    pub fn as_slice(&self) -> &[u8] {
+        self.mmap.as_ref().map(|m| m.as_slice()).unwrap_or(&[])
+    }
+
+    pub fn as_slice_mut(&mut self) -> &mut [u8] {
+        self.mmap.as_mut().map(|m| m.as_slice_mut()).unwrap_or(&mut [])
+    }
+}

src/memory/mod.rs

@@ -69,13 +69,15 @@ impl fmt::Debug for MemoryInstance {
     }
 }
 
-mod rust_alloc as byte_buf;
-use self::rust_alloc::ByteBuf;
+mod mmap;
+use self::mmap::ByteBuf;
+
+// mod rust_alloc as byte_buf;
+// use self::rust_alloc::ByteBuf;
 
 // mod vec_backed;
 // use self::vec_backed::ByteBuf;
 
-
 struct CheckedRegion {
     offset: usize,
     size: usize,
@@ -196,7 +198,10 @@ impl MemoryInstance {
         let mut buffer = self.buffer.borrow_mut();
         let region =
             self.checked_region(&mut buffer, offset as usize, ::core::mem::size_of::<T>())?;
-        Ok(T::from_little_endian(&buffer.as_slice_mut()[region.range()]).expect("Slice size is checked"))
+        Ok(
+            T::from_little_endian(&buffer.as_slice_mut()[region.range()])
+                .expect("Slice size is checked"),
+        )
     }
 
     /// Copy data from memory at given offset.
@@ -289,8 +294,7 @@ impl MemoryInstance {
         buffer: &mut ByteBuf,
         offset: usize,
         size: usize,
-    ) -> Result<CheckedRegion, Error>
-    {
+    ) -> Result<CheckedRegion, Error> {
         let end = offset.checked_add(size).ok_or_else(|| {
             Error::Memory(format!(
                 "trying to access memory block of size {} from offset {}",