CoW

src/lib.rs

@@ -404,7 +404,7 @@ pub use self::func::{FuncInstance, FuncInvocation, FuncRef, ResumableError};
 pub use self::global::{GlobalInstance, GlobalRef};
 pub use self::host::{Externals, HostError, NopExternals, RuntimeArgs};
 pub use self::imports::{ImportResolver, ImportsBuilder, ModuleImportResolver};
-pub use self::memory::{MemoryInstance, MemoryRef, LINEAR_MEMORY_PAGE_SIZE};
+pub use self::memory::{MemoryBackend, MemoryInstance, MemoryRef, LINEAR_MEMORY_PAGE_SIZE};
 pub use self::module::{ExternVal, ModuleInstance, ModuleRef, NotStartedModuleRef};
 pub use self::runner::{StackRecycler, DEFAULT_CALL_STACK_LIMIT, DEFAULT_VALUE_STACK_LIMIT};
 pub use self::table::{TableInstance, TableRef};

src/memory/mmap_bytebuf.rs

@@ -7,6 +7,7 @@
 
 use std::ptr::{self, NonNull};
 use std::slice;
+use super::MemoryBackend;
 
 struct Mmap {
     /// The pointer that points to the start of the mapping.
@@ -111,11 +112,15 @@ impl Drop for Mmap {
     }
 }
 
-pub struct ByteBuf {
+pub struct MmapByteBuf {
     mmap: Option<Mmap>,
 }
 
-impl ByteBuf {
+impl MmapByteBuf {
+    pub fn empty() -> Self {
+        MmapByteBuf { mmap: None }
+    }
+
     pub fn new(len: usize) -> Result<Self, &'static str> {
         let mmap = if len == 0 {
             None
@@ -124,8 +129,14 @@ impl ByteBuf {
         };
         Ok(Self { mmap })
     }
+}
 
-    pub fn realloc(&mut self, new_len: usize) -> Result<(), &'static str> {
+impl MemoryBackend for MmapByteBuf {
+    fn alloc(&mut self, initial: usize, _maximum: usize) -> Result<(), &'static str> {
+        self.realloc(initial)
+    }
+
+    fn realloc(&mut self, new_len: usize) -> Result<(), &'static str> {
         let new_mmap = if new_len == 0 {
             None
         } else {
@@ -143,22 +154,22 @@ impl ByteBuf {
         Ok(())
     }
 
-    pub fn len(&self) -> usize {
+    fn len(&self) -> usize {
         self.mmap.as_ref().map(|m| m.len).unwrap_or(0)
     }
 
-    pub fn as_slice(&self) -> &[u8] {
+    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] {
+    fn as_slice_mut(&mut self) -> &mut [u8] {
         self.mmap
             .as_mut()
             .map(|m| m.as_slice_mut())
             .unwrap_or(&mut [])
     }
 
-    pub fn erase(&mut self) -> Result<(), &'static str> {
+    fn erase(&mut self) -> Result<(), &'static str> {
         let len = self.len();
         if len > 0 {
             // The order is important.
@@ -176,14 +187,14 @@ impl ByteBuf {
 
 #[cfg(test)]
 mod tests {
-    use super::ByteBuf;
+    use super::{MmapByteBuf, MemoryBackend};
 
     const PAGE_SIZE: usize = 4096;
 
     // This is not required since wasm memories can only grow but nice to have.
     #[test]
     fn byte_buf_shrink() {
-        let mut byte_buf = ByteBuf::new(PAGE_SIZE * 3).unwrap();
+        let mut byte_buf = MmapByteBuf::new(PAGE_SIZE * 3).unwrap();
         byte_buf.realloc(PAGE_SIZE * 2).unwrap();
     }
 }

src/memory/mod.rs

@@ -12,13 +12,13 @@ use Error;
 
 #[cfg(all(unix, not(feature = "vec_memory")))]
 #[path="mmap_bytebuf.rs"]
-mod bytebuf;
+mod mmap_bytebuf;
 
-#[cfg(any(not(unix), feature = "vec_memory"))]
-#[path = "vec_bytebuf.rs"]
-mod bytebuf;
+#[cfg(all(unix, not(feature = "vec_memory")))]
+use self::mmap_bytebuf::MmapByteBuf;
 
-use self::bytebuf::ByteBuf;
+// #[cfg(any(not(unix), feature = "vec_memory"))]
+// mod bytebuf;
 
 /// Size of a page of [linear memory][`MemoryInstance`] - 64KiB.
 ///
@@ -43,6 +43,15 @@ impl ::core::ops::Deref for MemoryRef {
     }
 }
 
+pub trait MemoryBackend {
+    fn alloc(&mut self, initial: usize, maximum: usize) -> Result<(), &'static str>;
+    fn realloc(&mut self, new_len: usize) -> Result<(), &'static str>;
+    fn len(&self) -> usize;
+    fn as_slice(&self) -> &[u8];
+    fn as_slice_mut(&mut self) -> &mut [u8];
+    fn erase(&mut self) -> Result<(), &'static str>;
+}
+
 /// Runtime representation of a linear memory (or `memory` for short).
 ///
 /// A memory is a contiguous, mutable array of raw bytes. Wasm code can load and store values
@@ -60,7 +69,7 @@ pub struct MemoryInstance {
     /// Memory limits.
     limits: ResizableLimits,
     /// Linear memory buffer with lazy allocation.
-    buffer: RefCell<ByteBuf>,
+    buffer: RefCell<Box<dyn MemoryBackend>>,
     initial: Pages,
     current_size: Cell<usize>,
     maximum: Option<Pages>,
@@ -142,17 +151,21 @@ impl MemoryInstance {
         let limits = ResizableLimits::new(initial.0 as u32, maximum.map(|p| p.0 as u32));
 
         let initial_size: Bytes = initial.into();
+        let bytebuf = MmapByteBuf::new(initial_size.0).map_err(|err| Error::Memory(err.to_string()))?;
+
         Ok(MemoryInstance {
             limits: limits,
-            buffer: RefCell::new(
-                ByteBuf::new(initial_size.0).map_err(|err| Error::Memory(err.to_string()))?,
-            ),
+            buffer: RefCell::new(Box::new(bytebuf)),
             initial: initial,
             current_size: Cell::new(initial_size.0),
             maximum: maximum,
         })
     }
 
+    pub fn set_backend(&self, backend: Box<dyn MemoryBackend>) {
+        *self.buffer.borrow_mut() = backend;
+    }
+
     /// Return linear memory limits.
     pub(crate) fn limits(&self) -> &ResizableLimits {
         &self.limits
@@ -296,7 +309,7 @@ impl MemoryInstance {
 
     fn checked_region(
         &self,
-        buffer: &mut ByteBuf,
+        buffer: &mut Box<dyn MemoryBackend>,
         offset: usize,
         size: usize,
     ) -> Result<CheckedRegion, Error> {
@@ -324,7 +337,7 @@ impl MemoryInstance {
 
     fn checked_region_pair(
         &self,
-        buffer: &mut ByteBuf,
+        buffer: &mut Box<dyn MemoryBackend>,
         offset1: usize,
         size1: usize,
         offset2: usize,

src/memory/raw_bytebuf.rs

@@ -0,0 +1,71 @@
+//! An implementation of `ByteBuf` based on a plain `Vec`.
+
+use alloc::vec::Vec;
+use std::{
+    slice,
+    mem,
+};
+use super::MemoryBackend;
+
+pub struct RawByteBuf {
+    ptr: *mut u8,
+    len: usize,
+    cap: usize,
+}
+
+impl RawByteBuf {
+    pub fn from_raw_parts(ptr: *mut u8, len: usize, cap: usize) -> Self {
+        Self {
+            ptr,
+            len,
+            cap,
+        }
+    }
+
+    pub fn new(len: usize) -> Result<Self, &'static str> {
+        let mut v = vec![0u8; len];
+        let cap = len;
+        let ptr = v.as_mut_ptr();
+        mem::forget(v);
+
+        Ok(Self {
+            ptr,
+            len,
+            cap,
+        })
+    }
+}
+
+impl MemoryBackend for RawByteBuf {
+
+    pub fn realloc(&mut self, new_len: usize) -> Result<(), &'static str> {
+        if new_len > self.cap {
+            return Err("exceeds cap");
+        }
+        self.len = new_len;
+        Ok(())
+    }
+
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.ptr, self.len)
+        }
+    }
+
+    pub fn as_slice_mut(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self.ptr, self.len)
+        }
+    }
+
+    pub fn erase(&mut self) -> Result<(), &'static str> {
+        for v in self.as_slice_mut() {
+            *v = 0;
+        }
+        Ok(())
+    }
+}