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Add fn for splitting borrow of memory & data in Ctx, use in WASI #1069

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Dec 17, 2019
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Add fn for splitting borrow of memory & data in Ctx, use in WASI #1069

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bb344c1
Add fn for splitting borrow of memory & data in Ctx, use in WASI
Dec 16, 2019
15c52fd
Update doc comment on borrow splitting ctx fn
Dec 16, 2019
2819821
Fix typo in doc comment
MarkMcCaskey Dec 17, 2019
3a2881e
Add split borrow memory/data from Ctx to changelog
Dec 17, 2019
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15 changes: 15 additions & 0 deletions lib/runtime-core/src/vm.rs
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Expand Up @@ -401,6 +401,21 @@ impl Ctx {
}
}

/// Splits the borrow, getting both Memory and a mutable reference to
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"Splits the borrow" sounds like a function that takes a borrow and splits it. Instead, this is a variation on memory that returns a Memory and a mutable reference to the Ctx.data.

Also, I'd replace "a hostcall" with simply "the host".

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It's required by the Rust borrow checker; it's a split borrow in that one borrow comes in and 2 come out that otherwise is not possible with safe Rust. There's a function for splitting borrows over slices I believe &mut [u8] -> (&mut [u8], &mut [u8]) which is where I got the terminology from

/// the data type provided.
///
/// This method is required to access both at the same time.
/// This is useful if the data stores information about locations in Wasm
/// memory that a hostcall needs to access.
///
/// # Safety
///
/// This function must be called with the same type, `T`, that the `data`
/// was set to.
pub unsafe fn memory_and_data_mut<T>(&mut self, mem_index: u32) -> (&Memory, &mut T) {
(self.memory(mem_index), &mut *(self.data as *mut T))
}

/// Gives access to the emscripten symbol map, used for debugging
pub unsafe fn borrow_symbol_map(&self) -> &Option<HashMap<u32, String>> {
&(*self.module).info.em_symbol_map
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