Allocate JavaScriptEventLoop per thread in multi-threaded environment

.github/workflows/test.yml

@@ -17,11 +17,11 @@ jobs:
           - { os: ubuntu-22.04, toolchain: wasm-5.10.0-RELEASE, wasi-backend: Node }
 
           # Ensure that test succeeds with all toolchains and wasi backend combinations
-          - { os: ubuntu-20.04, toolchain: wasm-5.7.3-RELEASE, wasi-backend: Node }
           - { os: ubuntu-20.04, toolchain: wasm-5.8.0-RELEASE, wasi-backend: Node }
-          - { os: ubuntu-20.04, toolchain: wasm-5.7.3-RELEASE, wasi-backend: MicroWASI }
+          - { os: ubuntu-20.04, toolchain: wasm-5.10.0-RELEASE, wasi-backend: Node }
           - { os: ubuntu-20.04, toolchain: wasm-5.8.0-RELEASE, wasi-backend: MicroWASI }
           - { os: ubuntu-20.04, toolchain: wasm-5.9.1-RELEASE, wasi-backend: MicroWASI }
+          - { os: ubuntu-20.04, toolchain: wasm-5.10.0-RELEASE, wasi-backend: MicroWASI }
           - os: ubuntu-22.04
             toolchain: DEVELOPMENT-SNAPSHOT-2024-05-01-a
             swift-sdk:
@@ -76,8 +76,6 @@ jobs:
     strategy:
       matrix:
         include:
-          - os: macos-12
-            xcode: Xcode_14.0
           - os: macos-13
             xcode: Xcode_14.3
           - os: macos-14

Sources/JavaScriptEventLoop/JavaScriptEventLoop.swift

@@ -57,7 +57,28 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
     }
 
     /// A singleton instance of the Executor
-    public static let shared: JavaScriptEventLoop = {
+    public static var shared: JavaScriptEventLoop {
+        return _shared
+    }
+
+    #if compiler(>=6.0) && _runtime(_multithreaded)
+    // In multi-threaded environment, we have an event loop executor per
+    // thread (per Web Worker). A job enqueued in one thread should be
+    // executed in the same thread under this global executor.
+    private static var _shared: JavaScriptEventLoop {
+        if let tls = swjs_thread_local_event_loop {
+            let eventLoop = Unmanaged<JavaScriptEventLoop>.fromOpaque(tls).takeUnretainedValue()
+            return eventLoop
+        }
+        let eventLoop = create()
+        swjs_thread_local_event_loop = Unmanaged.passRetained(eventLoop).toOpaque()
+        return eventLoop
+    }
+    #else
+    private static let _shared: JavaScriptEventLoop = create()
+    #endif
+
+    private static func create() -> JavaScriptEventLoop {
         let promise = JSPromise(resolver: { resolver -> Void in
             resolver(.success(.undefined))
         })
@@ -79,7 +100,7 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
             }
         )
         return eventLoop
-    }()
+    }
 
     private static var didInstallGlobalExecutor = false
 
@@ -124,7 +145,7 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
             JavaScriptEventLoop.shared.unsafeEnqueue(job)
         }
         swift_task_enqueueMainExecutor_hook = unsafeBitCast(swift_task_enqueueMainExecutor_hook_impl, to: UnsafeMutableRawPointer?.self)
-        
+
         didInstallGlobalExecutor = true
     }
 

Sources/JavaScriptKit/FundamentalObjects/JSObject.swift

@@ -137,7 +137,16 @@ public class JSObject: Equatable {
 
     /// A `JSObject` of the global scope object.
     /// This allows access to the global properties and global names by accessing the `JSObject` returned.
-    public static let global = JSObject(id: _JS_Predef_Value_Global)
+    public static var global: JSObject { return _global }
+
+    // `JSObject` storage itself is immutable, and use of `JSObject.global` from other
+    // threads maintains the same semantics as `globalThis` in JavaScript.
+    #if compiler(>=5.10)
+    nonisolated(unsafe)
+    static let _global = JSObject(id: _JS_Predef_Value_Global)
+    #else
+    static let _global = JSObject(id: _JS_Predef_Value_Global)
+    #endif
 
     deinit { swjs_release(id) }
 

Sources/_CJavaScriptEventLoop/_CJavaScriptEventLoop.c

@@ -0,0 +1,3 @@
+#include "_CJavaScriptEventLoop.h"
+
+_Thread_local void *swjs_thread_local_event_loop;

Sources/_CJavaScriptEventLoop/include/_CJavaScriptEventLoop.h

@@ -61,4 +61,9 @@ typedef SWIFT_CC(swift) void (*swift_task_asyncMainDrainQueue_override)(
 SWIFT_EXPORT_FROM(swift_Concurrency)
 extern void *_Nullable swift_task_asyncMainDrainQueue_hook;
 
+
+/// MARK: - thread local storage
+
+extern _Thread_local void * _Nullable swjs_thread_local_event_loop;
+
 #endif