Implement RFC 11: Redesigning Wasmtime's APIs (#2897)

Implement Wasmtime's new API as designed by RFC 11. This is quite a large commit which has had lots of discussion externally, so for more information it's best to read the RFC thread and the PR thread.

crates/wasi-common/src/table.rs

@@ -1,6 +1,5 @@
 use crate::{Error, ErrorExt};
 use std::any::Any;
-use std::cell::{Ref, RefCell, RefMut};
 use std::collections::HashMap;
 
 /// The `Table` type is designed to map u32 handles to resources. The table is now part of the
@@ -11,7 +10,7 @@ use std::collections::HashMap;
 /// The `Table` type is intended to model how the Interface Types concept of Resources is shaping
 /// up. Right now it is just an approximation.
 pub struct Table {
-    map: HashMap<u32, RefCell<Box<dyn Any>>>,
+    map: HashMap<u32, Box<dyn Any + Send + Sync>>,
     next_key: u32,
 }
 
@@ -25,12 +24,12 @@ impl Table {
     }
 
     /// Insert a resource at a certain index.
-    pub fn insert_at(&mut self, key: u32, a: Box<dyn Any>) {
-        self.map.insert(key, RefCell::new(a));
+    pub fn insert_at(&mut self, key: u32, a: Box<dyn Any + Send + Sync>) {
+        self.map.insert(key, a);
     }
 
     /// Insert a resource at the next available index.
-    pub fn push(&mut self, a: Box<dyn Any>) -> Result<u32, Error> {
+    pub fn push(&mut self, a: Box<dyn Any + Send + Sync>) -> Result<u32, Error> {
         // NOTE: The performance of this new key calculation could be very bad once keys wrap
         // around.
         if self.map.len() == u32::MAX as usize {
@@ -42,7 +41,7 @@ impl Table {
             if self.map.contains_key(&key) {
                 continue;
             }
-            self.map.insert(key, RefCell::new(a));
+            self.map.insert(key, a);
             return Ok(key);
         }
     }
@@ -55,12 +54,8 @@ impl Table {
     /// Check if the resource at a given index can be downcast to a given type.
     /// Note: this will always fail if the resource is already borrowed.
     pub fn is<T: Any + Sized>(&self, key: u32) -> bool {
-        if let Some(refcell) = self.map.get(&key) {
-            if let Ok(refmut) = refcell.try_borrow_mut() {
-                refmut.is::<T>()
-            } else {
-                false
-            }
+        if let Some(r) = self.map.get(&key) {
+            r.is::<T>()
         } else {
             false
         }
@@ -69,17 +64,10 @@ impl Table {
     /// Get an immutable reference to a resource of a given type at a given index. Multiple
     /// immutable references can be borrowed at any given time. Borrow failure
     /// results in a trapping error.
-    pub fn get<T: Any + Sized>(&self, key: u32) -> Result<Ref<T>, Error> {
-        if let Some(refcell) = self.map.get(&key) {
-            if let Ok(r) = refcell.try_borrow() {
-                if r.is::<T>() {
-                    Ok(Ref::map(r, |r| r.downcast_ref::<T>().unwrap()))
-                } else {
-                    Err(Error::badf().context("element is a different type"))
-                }
-            } else {
-                Err(Error::trap("table get of mutably borrowed element"))
-            }
+    pub fn get<T: Any + Sized>(&self, key: u32) -> Result<&T, Error> {
+        if let Some(r) = self.map.get(&key) {
+            r.downcast_ref::<T>()
+                .ok_or_else(|| Error::badf().context("element is a different type"))
         } else {
             Err(Error::badf().context("key not in table"))
         }
@@ -87,17 +75,10 @@ impl Table {
 
     /// Get a mutable reference to a resource of a given type at a given index. Only one mutable
     /// reference can be borrowed at any given time. Borrow failure results in a trapping error.
-    pub fn get_mut<T: Any + Sized>(&self, key: u32) -> Result<RefMut<T>, Error> {
-        if let Some(refcell) = self.map.get(&key) {
-            if let Ok(r) = refcell.try_borrow_mut() {
-                if r.is::<T>() {
-                    Ok(RefMut::map(r, |r| r.downcast_mut::<T>().unwrap()))
-                } else {
-                    Err(Error::badf().context("element is a different type"))
-                }
-            } else {
-                Err(Error::trap("table get_mut of borrowed element"))
-            }
+    pub fn get_mut<T: Any + Sized>(&mut self, key: u32) -> Result<&mut T, Error> {
+        if let Some(r) = self.map.get_mut(&key) {
+            r.downcast_mut::<T>()
+                .ok_or_else(|| Error::badf().context("element is a different type"))
         } else {
             Err(Error::badf().context("key not in table"))
         }
@@ -105,7 +86,7 @@ impl Table {
 
     /// Remove a resource at a given index from the table. Returns the resource
     /// if it was present.
-    pub fn delete(&mut self, key: u32) -> Option<Box<dyn Any>> {
-        self.map.remove(&key).map(|rc| RefCell::into_inner(rc))
+    pub fn delete(&mut self, key: u32) -> Option<Box<dyn Any + Send + Sync>> {
+        self.map.remove(&key)
     }
 }