Provide direct access to the underlying buffer (#91)

This allows zero-copy access to the linear memory.
This commit is contained in:
Sergey Pepyakin 2018-05-31 16:01:15 +02:00 committed by GitHub
parent 6cf0ebc79e
commit 724a32ad60
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1 changed files with 55 additions and 3 deletions

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@ -48,7 +48,7 @@ impl ::std::ops::Deref for MemoryRef {
///
/// [`LINEAR_MEMORY_PAGE_SIZE`]: constant.LINEAR_MEMORY_PAGE_SIZE.html
pub struct MemoryInstance {
/// Memofy limits.
/// Memory limits.
limits: ResizableLimits,
/// Linear memory buffer.
buffer: RefCell<Vec<u8>>,
@ -315,7 +315,7 @@ impl MemoryInstance {
Ok(())
}
/// Fill memory region with a specified value.
/// Fill the memory region with the specified value.
///
/// Semantically equivalent to `memset`.
///
@ -330,7 +330,7 @@ impl MemoryInstance {
Ok(())
}
/// Fill specified memory region with zeroes.
/// Fill the specified memory region with zeroes.
///
/// # Errors
///
@ -338,6 +338,35 @@ impl MemoryInstance {
pub fn zero(&self, offset: usize, len: usize) -> Result<(), Error> {
self.clear(offset, 0, len)
}
/// Provides direct access to the underlying memory buffer.
///
/// # Panics
///
/// Any call that requires write access to memory (such as [`set`], [`clear`], etc) made within
/// the closure will panic. Proceed with caution.
///
/// [`set`]: #method.get
/// [`clear`]: #method.set
pub fn with_direct_access<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
let buf = self.buffer.borrow();
f(&*buf)
}
/// Provides direct mutable access to the underlying memory buffer.
///
/// # Panics
///
/// Any calls that requires either read or write access to memory (such as [`get`], [`set`], [`copy`], etc) made
/// within the closure will panic. Proceed with caution.
///
/// [`get`]: #method.get
/// [`set`]: #method.set
/// [`copy`]: #method.copy
pub fn with_direct_access_mut<R, F: FnOnce(&mut [u8]) -> R>(&self, f: F) -> R {
let mut buf = self.buffer.borrow_mut();
f(&mut *buf)
}
}
pub fn validate_memory(initial: Pages, maximum: Option<Pages>) -> Result<(), String> {
@ -484,4 +513,27 @@ mod tests {
assert_eq!(data, [17, 129]);
}
#[test]
fn zero_copy() {
let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
mem.with_direct_access_mut(|buf| {
assert_eq!(buf.len(), 65536);
buf[..10].copy_from_slice(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
});
mem.with_direct_access(|buf| {
assert_eq!(buf.len(), 65536);
assert_eq!(&buf[..10], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
});
}
#[should_panic]
#[test]
fn zero_copy_panics_on_nested_access() {
let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
let mem_inner = mem.clone();
mem.with_direct_access(move |_| {
let _ = mem_inner.set(0, &[11, 12, 13]);
});
}
}