[JExtract/JNI] Add support for async Swift methods

Package.swift

@@ -170,10 +170,15 @@ let package = Package(
     // Support library written in Swift for SwiftKit "Java"
     .library(
       name: "SwiftJavaRuntimeSupport",
-      type: .dynamic,
       targets: ["SwiftJavaRuntimeSupport"]
     ),
 
+    .library(
+      name: "SwiftRuntimeFunctions",
+      type: .dynamic,
+      targets: ["SwiftRuntimeFunctions"]
+    ),
+
     .library(
       name: "JExtractSwiftLib",
       targets: ["JExtractSwiftLib"]
@@ -214,6 +219,7 @@ let package = Package(
       dependencies: [
         "SwiftJava",
         "SwiftJavaRuntimeSupport",
+        "SwiftRuntimeFunctions",
       ]
     ),
 
@@ -362,6 +368,18 @@ let package = Package(
       ]
     ),
 
+    .target(
+      name: "SwiftRuntimeFunctions",
+      dependencies: [
+        "CSwiftJavaJNI",
+        "SwiftJava"
+      ],
+      swiftSettings: [
+        .swiftLanguageMode(.v5),
+        .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
+      ]
+    ),
+
     .target(
       name: "CSwiftJavaJNI",
       swiftSettings: [

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/Async.swift

@@ -33,6 +33,10 @@ public func asyncOptional(i: Int64) async throws -> Int64? {
   return i
 }
 
+public func asyncThrows() async throws {
+  throw MySwiftError.swiftError
+}
+
 public func asyncRunningSum() async -> Int64 {
     let totalSum = await withTaskGroup(of: Int64.self) { group in
         // 1. Add child tasks to the group

Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/AsyncTest.java

@@ -56,4 +56,22 @@ void asyncCopy() {
             assertEquals(5, result.getY());
         }
     }
+
+    @Test
+    void asyncThrows() {
+        CompletableFuture<Void> future = MySwiftLibrary.asyncThrows();
+
+        ExecutionException ex = assertThrows(ExecutionException.class, future::get);
+
+        Throwable cause = ex.getCause();
+        assertNotNull(cause);
+        assertEquals(Exception.class, cause.getClass());
+        assertEquals("swiftError", cause.getMessage());
+    }
+
+    @Test
+    void asyncOptional() {
+        CompletableFuture<OptionalLong> future = MySwiftLibrary.asyncOptional(42);
+        assertEquals(OptionalLong.of(42), future.join());
+    }
 }

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -108,7 +108,7 @@ extension FFMSwift2JavaGenerator {
       """
       // Generated by swift-java
 
-      import SwiftJavaRuntimeSupport
+      import SwiftRuntimeFunctions
 
       """)
 
@@ -136,7 +136,7 @@ extension FFMSwift2JavaGenerator {
       """
       // Generated by swift-java
 
-      import SwiftJavaRuntimeSupport
+      import SwiftRuntimeFunctions
 
       """
     )

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift

@@ -528,7 +528,8 @@ extension JNISwift2JavaGenerator {
           nativeFunctionSignature.result.conversion,
           swiftFunctionResultType: originalFunctionSignature.result.type,
           nativeReturnType: nativeFunctionSignature.result.javaType,
-          outParameters: nativeFunctionSignature.result.outParameters
+          outParameters: nativeFunctionSignature.result.outParameters,
+          isThrowing: originalFunctionSignature.isThrowing
         )
         nativeFunctionSignature.result.outParameters.append(.init(name: "result_future", type: nativeFutureType))
 

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+NativeTranslation.swift

@@ -573,7 +573,8 @@ extension JNISwift2JavaGenerator {
       NativeSwiftConversionStep,
       swiftFunctionResultType: SwiftType,
       nativeReturnType: JavaType,
-      outParameters: [JavaParameter]
+      outParameters: [JavaParameter],
+      isThrowing: Bool
     )
 
     /// Returns the conversion string applied to the placeholder.
@@ -808,7 +809,8 @@ extension JNISwift2JavaGenerator {
         let inner,
         let swiftFunctionResultType,
         let nativeReturnType,
-        let outParameters
+        let outParameters,
+        let isThrowing
       ):
         // Global ref all indirect returns
         for outParameter in outParameters {
@@ -818,71 +820,66 @@ extension JNISwift2JavaGenerator {
         printer.print(
           """
           let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
-          let completableFutureClazz$ = environment.interface.FindClass(environment, "java/util/concurrent/CompletableFuture")!
-          let completeMethodID = environment.interface.GetMethodID(environment, completableFutureClazz$, "complete", "(Ljava/lang/Object;)Z")!
           """
         )
 
-        printer.printBraceBlock("Task") { printer in
+        func printDo(printer: inout CodePrinter) {
           printer.print("let swiftResult$ = await \(placeholder)")
-          printer.print(
-            """
-            let environment = try JavaVirtualMachine.shared().environment()
-            """
-          )
-          printer.printBraceBlock("defer") { printer in
-            printer.print("environment.interface.DeleteGlobalRef(environment, globalFuture)")
-            for outParameter in outParameters {
-              printer.print("environment.interface.DeleteGlobalRef(environment, \(outParameter.name))")
-            }
-          }
+          printer.print("environment = try JavaVirtualMachine.shared().environment()")
           let inner = inner.render(&printer, "swiftResult$")
           if swiftFunctionResultType.isVoid {
-            printer.print(inner)
+            printer.print("environment.interface.CallBooleanMethodA(environment, globalFuture, _JNIMethodIDCache.CompletableFuture.complete, [jvalue(l: nil)])")
           } else {
             printer.printBraceBlock("withVaList([SwiftJavaRuntimeSupport._JNIBoxedConversions.box(\(inner), in: environment)])") { printer in
-              printer.print("environment.interface.CallBooleanMethodV(environment, globalFuture, completeMethodID, $0)")
+              printer.print("environment.interface.CallBooleanMethodV(environment, globalFuture, _JNIMethodIDCache.CompletableFuture.complete, $0)")
             }
           }
         }
 
-        return ""
+        func printTask(printer: inout CodePrinter) {
+          printer.printBraceBlock("defer") { printer in
+            // Defer might on any thread, so we need to attach environment.
+            printer.print("let deferEnvironment = try! JavaVirtualMachine.shared().environment()")
+            printer.print("environment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)")
+            for outParameter in outParameters {
+              printer.print("environment.interface.DeleteGlobalRef(deferEnvironment, \(outParameter.name))")
+            }
+          }
+          if isThrowing {
+            printer.printBraceBlock("do") { printer in
+              printDo(printer: &printer)
+            }
+            printer.printBraceBlock("catch") { printer in
+              // We might not be on the same thread after the suspension, so we need to attach the thread again.
+              printer.print(
+              """
+              let catchEnvironment = try! JavaVirtualMachine.shared().environment()
+              let exception = catchEnvironment.interface.NewObjectA(catchEnvironment, _JNIMethodIDCache.Exception.class, _JNIMethodIDCache.Exception.constructWithMessage, [String(describing: error).getJValue(in: catchEnvironment)])
+              catchEnvironment.interface.CallBooleanMethodA(catchEnvironment, globalFuture, _JNIMethodIDCache.CompletableFuture.completeExceptionally, [jvalue(l: exception)])
+              """
+              )
+            }
+          } else {
+            printDo(printer: &printer)
+          }
+        }
 
-//        printer.print("let _semaphore$ = _Semaphore(value: 0)")
-//        let resultType = isThrowing ? "Result<\(swiftFunctionResultType), any Error>" : swiftFunctionResultType.description
-//        printer.print("var swiftResult$: \(resultType)!")
-//
-//        func printInner(printer: inout CodePrinter) {
-//          if isThrowing {
-//            printer.printBraceBlock("do") { printer in
-//              printer.print("swiftResult$ = await Result.success(\(placeholder))")
-//            }
-//            printer.printBraceBlock("catch") { printer in
-//              printer.print("swiftResult$ = Result.failure(error)")
-//            }
-//          } else {
-//            printer.print("swiftResult$ = await \(placeholder)")
-//          }
-//          printer.print("_semaphore$.signal()")
-//        }
-//
-//        printer.printBraceBlock("if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *)") { printer in
-//          printer.printBraceBlock("Task.immediate") { printer in
-//            printInner(printer: &printer)
-//          }
-//        }
-//        printer.printBraceBlock("else") { printer in
-//          printer.printBraceBlock("Task") { printer in
-//            printInner(printer: &printer)
-//          }
-//        }
-//        printer.print(
-//          """
-//          _semaphore$.wait() 
-//          """
-//        )
-//        let inner = inner.render(&printer, isThrowing ? "try swiftResult$.get()" : "swiftResult$")
-//        return inner
+        printer.printBraceBlock("if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *)") { printer in
+          printer.printBraceBlock("Task.immediate") { printer in
+            // Immediate runs on the caller thread, so we don't need to attach the environment again.
+            printer.print("var environment = environment!") // this is to ensure we always use the same environment name, even though we are rebinding it.
+            printTask(printer: &printer)
+          }
+        }
+        printer.printBraceBlock("else") { printer in
+          printer.printBraceBlock("Task") { printer in
+            // We can be on any thread, so we need to attach the thread.
+            printer.print("var environment = try! JavaVirtualMachine.shared().environment()")
+            printTask(printer: &printer)
+          }
+        }
+
+        return ""
       }
     }
   }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -363,7 +363,7 @@ extension JNISwift2JavaGenerator {
       }
     }
 
-    if decl.isThrowing {
+    if decl.isThrowing, !decl.isAsync {
       let dummyReturn: String
 
       if nativeSignature.result.javaType.isVoid {

Sources/JExtractSwiftLib/SwiftTypes/SwiftFunctionSignature.swift

@@ -34,6 +34,10 @@ public struct SwiftFunctionSignature: Equatable {
     effectSpecifiers.contains(.async)
   }
 
+  var isThrowing: Bool {
+    effectSpecifiers.contains(.throws)
+  }
+
   init(
     selfParameter: SwiftSelfParameter? = nil,
     parameters: [SwiftParameter],

Sources/SwiftJavaRuntimeSupport/DefaultCaches.swift

@@ -0,0 +1,53 @@
+import SwiftJava
+
+extension _JNIMethodIDCache {
+  public enum CompletableFuture {
+    private static let completeMethod = Method(
+      name: "complete",
+      signature: "(Ljava/lang/Object;)Z"
+    )
+
+    private static let completeExceptionallyMethod = Method(
+      name: "completeExceptionally",
+      signature: "(Ljava/lang/Throwable;)Z"
+    )
+
+    private static let cache = _JNIMethodIDCache(
+      environment: try! JavaVirtualMachine.shared().environment(),
+      className: "java/util/concurrent/CompletableFuture",
+      methods: [completeMethod, completeExceptionallyMethod]
+    )
+
+    public static var `class`: jclass {
+      cache.javaClass
+    }
+
+    /// CompletableFuture<T>.complete(T)
+    public static var complete: jmethodID {
+      cache.methods[completeMethod]!
+    }
+
+    /// CompletableFuture<T>.completeExceptionally(Throwable)
+    public static var completeExceptionally: jmethodID {
+      cache.methods[completeExceptionallyMethod]!
+    }
+  }
+
+  public enum Exception {
+    private static let messageConstructor = Method(name: "<init>", signature: "(Ljava/lang/String;)V")
+
+    private static let cache = _JNIMethodIDCache(
+      environment: try! JavaVirtualMachine.shared().environment(),
+      className: "java/lang/Exception",
+      methods: [messageConstructor]
+    )
+
+    public static var `class`: jclass {
+      cache.javaClass
+    }
+
+    public static var constructWithMessage: jmethodID {
+      cache.methods[messageConstructor]!
+    }
+  }
+}