Disconnects Store state fields from Compiler (#1761)

*  Moves CodeMemory, VMInterrupts and SignatureRegistry from Compiler
*  CompiledModule holds CodeMemory and GdbJitImageRegistration
*  Store keeps track of its JIT code
*  Makes "jit_int.rs" stuff Send+Sync
*  Adds the threads example.

crates/runtime/src/sig_registry.rs

@@ -3,27 +3,16 @@
 
 use crate::vmcontext::VMSharedSignatureIndex;
 use more_asserts::assert_lt;
-use std::collections::HashMap;
+use std::collections::{hash_map, HashMap};
 use std::convert::TryFrom;
-use std::sync::RwLock;
 use wasmtime_environ::{ir, wasm::WasmFuncType};
 
 /// WebAssembly requires that the caller and callee signatures in an indirect
 /// call must match. To implement this efficiently, keep a registry of all
 /// signatures, shared by all instances, so that call sites can just do an
 /// index comparison.
-#[derive(Debug)]
-pub struct SignatureRegistry {
-    // This structure is stored in a `Compiler` and is intended to be shared
-    // across many instances. Ideally instances can themselves be sent across
-    // threads, and ideally we can compile across many threads. As a result we
-    // use interior mutability here with a lock to avoid having callers to
-    // externally synchronize calls to compilation.
-    inner: RwLock<Inner>,
-}
-
 #[derive(Debug, Default)]
-struct Inner {
+pub struct SignatureRegistry {
     wasm2index: HashMap<WasmFuncType, VMSharedSignatureIndex>,
 
     // Maps the index to the original Wasm signature.
@@ -34,35 +23,31 @@ struct Inner {
 }
 
 impl SignatureRegistry {
-    /// Create a new `SignatureRegistry`.
-    pub fn new() -> Self {
-        Self {
-            inner: Default::default(),
-        }
-    }
-
     /// Register a signature and return its unique index.
-    pub fn register(&self, wasm: WasmFuncType, native: ir::Signature) -> VMSharedSignatureIndex {
-        let Inner {
-            wasm2index,
-            index2wasm,
-            index2native,
-        } = &mut *self.inner.write().unwrap();
-        let len = wasm2index.len();
+    pub fn register(
+        &mut self,
+        wasm: WasmFuncType,
+        native: ir::Signature,
+    ) -> VMSharedSignatureIndex {
+        let len = self.wasm2index.len();
 
-        *wasm2index.entry(wasm.clone()).or_insert_with(|| {
-            // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(std::u32::MAX)
-            // is reserved for VMSharedSignatureIndex::default().
-            assert_lt!(
-                len,
-                std::u32::MAX as usize,
-                "Invariant check: signature_hash.len() < std::u32::MAX"
-            );
-            let index = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
-            index2wasm.insert(index, wasm);
-            index2native.insert(index, native);
-            index
-        })
+        match self.wasm2index.entry(wasm.clone()) {
+            hash_map::Entry::Occupied(entry) => *entry.get(),
+            hash_map::Entry::Vacant(entry) => {
+                // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(std::u32::MAX)
+                // is reserved for VMSharedSignatureIndex::default().
+                assert_lt!(
+                    len,
+                    std::u32::MAX as usize,
+                    "Invariant check: signature_hash.len() < std::u32::MAX"
+                );
+                let index = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
+                entry.insert(index);
+                self.index2wasm.insert(index, wasm);
+                self.index2native.insert(index, native);
+                index
+            }
+        }
     }
 
     /// Looks up a shared native signature within this registry.
@@ -70,7 +55,7 @@ impl SignatureRegistry {
     /// Note that for this operation to be semantically correct the `idx` must
     /// have previously come from a call to `register` of this same object.
     pub fn lookup_native(&self, idx: VMSharedSignatureIndex) -> Option<ir::Signature> {
-        self.inner.read().unwrap().index2native.get(&idx).cloned()
+        self.index2native.get(&idx).cloned()
     }
 
     /// Looks up a shared Wasm signature within this registry.
@@ -78,6 +63,6 @@ impl SignatureRegistry {
     /// Note that for this operation to be semantically correct the `idx` must
     /// have previously come from a call to `register` of this same object.
     pub fn lookup_wasm(&self, idx: VMSharedSignatureIndex) -> Option<WasmFuncType> {
-        self.inner.read().unwrap().index2wasm.get(&idx).cloned()
+        self.index2wasm.get(&idx).cloned()
     }
 }