Refactor JSClosure to leverage FinalizationRegistry

Author: j-f1

IntegrationTests/TestSuites/Sources/BenchmarkTests/Benchmark.swift

@@ -15,6 +15,5 @@ class Benchmark {
             return .undefined
         }
         runner("\(title)/\(name)", jsBody)
-        jsBody.release()
     }
 }

IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift

@@ -191,36 +191,36 @@ try test("Closure Lifetime") {
             return arguments[0]
         }
         try expectEqual(evalClosure(c1, JSValue.number(1.0)), .number(1.0))
-        c1.release()
     }
 
     do {
-        let c1 = JSClosure { arguments in
-            return arguments[0]
-        }
+        let c1 = JSClosure { _ in .undefined }
+        c1.release()
         c1.release()
-        // Call a released closure
-        _ = try expectThrow(try evalClosure.throws(c1))
     }
 
     do {
-        let c1 = JSClosure { _ in
-            // JSClosure will be deallocated before `release()`
-            _ = JSClosure { _ in .undefined }
-            return .undefined
-        }
-        _ = try expectThrow(try evalClosure.throws(c1))
-        c1.release()
+        let array = JSObject.global.Array.function!.new()
+        _ = array.push!(JSClosure { _ in .number(3) })
+        try expectEqual(array[0].function!().number, 3.0)
     }
 
+//    do {
+//        let weakRef = { () -> JSObject in
+//            let c1 = JSClosure { _ in .undefined }
+//            return JSObject.global.WeakRef.function!.new(c1)
+//        }()
+//
+//        // unsure if this will actually work since GC may not run immediately
+//        try expectEqual(weakRef.deref!(), .undefined)
+//    }
+
     do {
         let c1 = JSOneshotClosure { _ in
             return .boolean(true)
         }
         try expectEqual(evalClosure(c1), .boolean(true))
-        // second call will cause `fatalError` that can be caught as a JavaScript exception
-        _ = try expectThrow(try evalClosure.throws(c1))
-        // OneshotClosure won't call fatalError even if it's deallocated before `release`
+        try expectEqual(evalClosure(c1), .boolean(true))
     }
 }
 
@@ -253,8 +253,6 @@ try test("Host Function Registration") {
     try expectEqual(call_host_1Func(), .number(1))
     try expectEqual(isHostFunc1Called, true)
 
-    hostFunc1.release()
-
     let hostFunc2 = JSClosure { (arguments) -> JSValue in
         do {
             let input = try expectNumber(arguments[0])
@@ -266,7 +264,6 @@ try test("Host Function Registration") {
 
     try expectEqual(evalClosure(hostFunc2, 3), .number(6))
     _ = try expectString(evalClosure(hostFunc2, true))
-    hostFunc2.release()
 }
 
 try test("New Object Construction") {
@@ -375,19 +372,14 @@ try test("ObjectRef Lifetime") {
     // }
     // ```
 
-    let identity = JSClosure { $0[0] }
     let ref1 = getJSValue(this: .global, name: "globalObject1").object!
-    let ref2 = evalClosure(identity, ref1).object!
+    let ref2 = evalClosure(JSClosure { $0[0] }, ref1).object!
     try expectEqual(ref1.prop_2, .number(2))
     try expectEqual(ref2.prop_2, .number(2))
-    identity.release()
 }
 
 func closureScope() -> ObjectIdentifier {
-    let closure = JSClosure { _ in .undefined }
-    let result = ObjectIdentifier(closure)
-    closure.release()
-    return result
+    ObjectIdentifier(JSClosure { _ in .undefined })
 }
 
 try test("Closure Identifiers") {
@@ -513,7 +505,7 @@ try test("Timer") {
     interval = JSTimer(millisecondsDelay: 5, isRepeating: true) {
         // ensure that JSTimer is living
         try! expectNotNil(interval)
-        // verify that at least `timeoutMilliseconds * count` passed since the `timeout` 
+        // verify that at least `timeoutMilliseconds * count` passed since the `timeout`
         // timer started
         try! expectEqual(start + timeoutMilliseconds * count <= JSDate().valueOf(), true)
 
@@ -549,7 +541,8 @@ try test("Promise") {
         exp1.fulfill()
         return JSValue.undefined
     }
-    .catch { _ -> JSValue in
+    .catch { err -> JSValue in
+        print(err.object!.stack.string!)
         fatalError("Not fired due to no throw")
     }
     .finally { exp1.fulfill() }

Runtime/src/index.ts

@@ -29,6 +29,8 @@ interface SwiftRuntimeExportedFunctions {
         argc: number,
         callback_func_ref: ref
     ): void;
+
+    swjs_free_host_function(host_func_id: number): void;
 }
 
 enum JavaScriptValueKind {
@@ -118,11 +120,22 @@ class SwiftRuntimeHeap {
 export class SwiftRuntime {
     private instance: WebAssembly.Instance | null;
     private heap: SwiftRuntimeHeap;
+    private functionRegistry: FinalizationRegistry;
     private version: number = 701;
 
     constructor() {
         this.instance = null;
         this.heap = new SwiftRuntimeHeap();
+        this.functionRegistry = new FinalizationRegistry(
+            this.handleFree.bind(this)
+        );
+    }
+
+    handleFree(id: unknown) {
+        if (!this.instance || typeof id !== "number") return;
+        const exports = (this.instance
+            .exports as any) as SwiftRuntimeExportedFunctions;
+        exports.swjs_free_host_function(id);
     }
 
     setInstance(instance: WebAssembly.Instance) {
@@ -452,12 +465,14 @@ export class SwiftRuntime {
                 host_func_id: number,
                 func_ref_ptr: pointer
             ) => {
-                const func_ref = this.heap.retain(function () {
+                const func = function () {
                     return callHostFunction(
                         host_func_id,
                         Array.prototype.slice.call(arguments)
                     );
-                });
+                };
+                const func_ref = this.heap.retain(func);
+                this.functionRegistry.register(func, func_ref);
                 writeUint32(func_ref_ptr, func_ref);
             },
             swjs_call_throwing_new: (

Runtime/tsconfig.json

@@ -7,6 +7,7 @@
         "rootDir": "src",
         "strict": true,
         "target": "es2017",
+        "lib": ["es2017", "DOM", "ESNext.WeakRef"],
         "skipLibCheck": true
     },
     "include": ["src/**/*"],

Sources/JavaScriptKit/Deprecated.swift

@@ -15,3 +15,6 @@ public typealias JSValueConstructible = ConstructibleFromJSValue
 
 @available(*, deprecated, renamed: "JSValueCompatible")
 public typealias JSValueCodable = JSValueCompatible
+
+@available(*, deprecated, renamed: "JSClosure")
+public typealias JSOneshotClosure = JSClosure

Sources/JavaScriptKit/FundamentalObjects/JSClosure.swift

@@ -1,5 +1,6 @@
 import _CJavaScriptKit
 
+fileprivate var closureRef: JavaScriptHostFuncRef = 0
 fileprivate var sharedClosures: [JavaScriptHostFuncRef: ([JSValue]) -> JSValue] = [:]
 
 /// JSClosureProtocol abstracts closure object in JavaScript, whose lifetime is manualy managed
@@ -10,40 +11,9 @@ public protocol JSClosureProtocol: JSValueCompatible {
     func release()
 }
 
-/// `JSOneshotClosure` is a JavaScript function that can be called only once.
-public class JSOneshotClosure: JSObject, JSClosureProtocol {
-    private var hostFuncRef: JavaScriptHostFuncRef = 0
-
-    public init(_ body: @escaping ([JSValue]) -> JSValue) {
-        // 1. Fill `id` as zero at first to access `self` to get `ObjectIdentifier`.
-        super.init(id: 0)
-        let objectId = ObjectIdentifier(self)
-        let funcRef = JavaScriptHostFuncRef(bitPattern: Int32(objectId.hashValue))
-        // 2. Retain the given body in static storage by `funcRef`.
-        sharedClosures[funcRef] = {
-            defer { self.release() }
-            return body($0)
-        }
-        // 3. Create a new JavaScript function which calls the given Swift function.
-        var objectRef: JavaScriptObjectRef = 0
-        _create_function(funcRef, &objectRef)
-
-        hostFuncRef = funcRef
-        id = objectRef
-    }
-
-    /// Release this function resource.
-    /// After calling `release`, calling this function from JavaScript will fail.
-    public func release() {
-        sharedClosures[hostFuncRef] = nil
-    }
-}
 
 /// `JSClosure` represents a JavaScript function the body of which is written in Swift.
 /// This type can be passed as a callback handler to JavaScript functions.
-/// Note that the lifetime of `JSClosure` should be managed by users manually
-/// due to GC boundary between Swift and JavaScript.
-/// For further discussion, see also [swiftwasm/JavaScriptKit #33](https://github.com/swiftwasm/JavaScriptKit/pull/33)
 ///
 /// e.g.
 /// ```swift
@@ -55,12 +25,10 @@ public class JSOneshotClosure: JSObject, JSClosureProtocol {
 /// button.addEventListener!("click", JSValue.function(eventListenter))
 /// ...
 /// button.removeEventListener!("click", JSValue.function(eventListenter))
-/// eventListenter.release()
 /// ```
 ///
 public class JSClosure: JSObject, JSClosureProtocol {
     private var hostFuncRef: JavaScriptHostFuncRef = 0
-    var isReleased: Bool = false
 
     @available(*, deprecated, message: "This initializer will be removed in the next minor version update. Please use `init(_ body: @escaping ([JSValue]) -> JSValue)` and add `return .undefined` to the end of your closure")
     @_disfavoredOverload
@@ -72,33 +40,29 @@ public class JSClosure: JSObject, JSClosureProtocol {
     }
 
     public init(_ body: @escaping ([JSValue]) -> JSValue) {
-        // 1. Fill `id` as zero at first to access `self` to get `ObjectIdentifier`.
-        super.init(id: 0)
-        let objectId = ObjectIdentifier(self)
-        let funcRef = JavaScriptHostFuncRef(bitPattern: Int32(objectId.hashValue))
-        // 2. Retain the given body in static storage by `funcRef`.
-        sharedClosures[funcRef] = body
-        // 3. Create a new JavaScript function which calls the given Swift function.
+        self.hostFuncRef = closureRef
+        closureRef += 1
+
+        // Retain the given body in static storage by `closureRef`.
+        sharedClosures[self.hostFuncRef] = body
+
+        // Create a new JavaScript function which calls the given Swift function.
         var objectRef: JavaScriptObjectRef = 0
-        _create_function(funcRef, &objectRef)
+        _create_function(self.hostFuncRef, &objectRef)
 
-        hostFuncRef = funcRef
-        id = objectRef
+        super.init(id: objectRef)
     }
 
-    public func release() {
-        isReleased = true
-        sharedClosures[hostFuncRef] = nil
-    }
+    @available(*, deprecated, message: "JSClosure.release() is no longer necessary")
+    public func release() {}
+}
 
-    deinit {
-        guard isReleased else {
-            // Safari doesn't support `FinalizationRegistry`, so we cannot automatically manage the lifetime of Swift objects
-            fatalError("release() must be called on JSClosure objects manually before they are deallocated")
-        }
-    }
+@_cdecl("_free_host_function_impl")
+func _free_host_function_impl(_ hostFuncRef: JavaScriptHostFuncRef) {
+    sharedClosures[hostFuncRef] = nil
 }
 
+
 // MARK: - `JSClosure` mechanism note
 //
 // 1. Create a thunk in the JavaScript world, which has a reference

Sources/_CJavaScriptKit/_CJavaScriptKit.c

@@ -14,6 +14,13 @@ void swjs_call_host_function(const JavaScriptHostFuncRef host_func_ref,
     _call_host_function_impl(host_func_ref, argv, argc, callback_func);
 }
 
+void _free_host_function_impl(const JavaScriptHostFuncRef host_func_ref);
+
+__attribute__((export_name("swjs_free_host_function")))
+void swjs_free_host_function(const JavaScriptHostFuncRef host_func_ref) {
+    _free_host_function_impl(host_func_ref);
+}
+
 __attribute__((export_name("swjs_prepare_host_function_call")))
 void *swjs_prepare_host_function_call(const int argc) {
     return malloc(argc * sizeof(RawJSValue));

package-lock.json

@@ -32,6 +32,6 @@
   "license": "MIT",
   "devDependencies": {
     "prettier": "2.1.2",
-    "typescript": "^4.0.2"
+    "typescript": "^4.2.4"
   }
 }