diff --git a/docs/migration_to_3.0.0.md b/docs/migration_to_3.0.0.md index 68e116187..c115578cd 100644 --- a/docs/migration_to_3.0.0.md +++ b/docs/migration_to_3.0.0.md @@ -117,9 +117,62 @@ env_mut.memory = Some(instance.exports.get_memory("memory")); env_mut.alloc_guest_memory = Some(instance.exports.get_typed_function("__alloc")); ``` -### New `MemoryView` API +### New `MemoryView` API (preparation for shared memory) -Adding the new memory view API (and show how people can update from previous usage) +Reading from memory has slightly changed compared to 2.x: + +```rust +// 2.x +let memory = instance.exports.get_memory("mem")?; +println!("Memory size (pages) {:?}", memory.size()); +println!("Memory size (bytes) {:?}", memory.data_size()); + +let load = instance + .exports + .get_native_function::<(), (WasmPtr, i32)>("load")?; + +let (ptr, length) = load.call(&mut store)?; +let str = ptr.get_utf8_string(memory, length as u32).unwrap(); +println!("Memory contents: {:?}", str); +``` + +```rust +// 3.x +let memory = instance.exports.get_memory("mem")?; +let memory_view = memory.view(&store); +println!("Memory size (pages) {:?}", memory_view.size()); +println!("Memory size (bytes) {:?}", memory_view.data_size()); + +let load: TypedFunction<(), (WasmPtr, i32)> = + instance.exports.get_typed_function(&mut store, "load")?; + +let (ptr, length) = load.call(&mut store)?; +let memory_view = memory.view(&store); +let str = ptr.read_utf8_string(&memory_view, length as u32).unwrap(); +println!("Memory contents: {:?}", str); +``` + +The reason for this change is that in the future this will enable +safely sharing memory across threads. The same thing goes for reading slices: + +```rust +// 2.x +let new_str = b"Hello, Wasmer!"; +let values = ptr.deref(memory, 0, new_str.len() as u32).unwrap(); +for i in 0..new_str.len() { + values[i].set(new_str[i]); +} +``` + +```rust +// 3.x +let memory_view = memory.view(&store); // (can be reused) +let new_str = b"Hello, Wasmer!"; +let values = ptr.slice(&memory_view, new_str.len() as u32).unwrap(); +for i in 0..new_str.len() { + values.index(i as u64).write(new_str[i]).unwrap(); +} +``` ### Managing imports