protocol wrappers emit a frame

Author: madsodgaard

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -171,6 +171,19 @@ extension JNISwift2JavaGenerator {
     }
 
     printer.printBraceBlock(function.swiftDecl.signatureString) { printer in
+      // Push a local JNI frame so refs created during this upcall are freed on exit.
+      // When called from a Swift async context (e.g. cooperative thread pool) there is
+      // no enclosing JNI frame, so refs would otherwise accumulate indefinitely. When
+      // called from a Java-initiated native call there is already a frame, but pushing
+      // a sub-frame still frees refs earlier and prevents overflow within a single call.
+      let paramCount = function.originalFunctionSignature.parameters.count
+      printer.print(
+        """
+        let environment$ = try! JavaVirtualMachine.shared().environment()
+        environment$.interface.PushLocalFrame(environment$, \(paramCount * 2 + 4))
+        defer { environment$.interface.PopLocalFrame(environment$, nil) }
+        """
+      )
       var upcallArguments = zip(
         function.originalFunctionSignature.parameters,
         function.parameterConversions

Tests/JExtractSwiftTests/JNI/JNIProtocolTests.swift

@@ -315,9 +315,15 @@ struct JNIProtocolTests {
         """
         extension SwiftJavaSomeProtocolWrapper {
           public func method() {
+            let environment$ = try! JavaVirtualMachine.shared().environment()
+            environment$.interface.PushLocalFrame(environment$, 4)
+            defer { environment$.interface.PopLocalFrame(environment$, nil) }
             _javaSomeProtocolInterface.method()
           }
           public func withObject(c: SomeClass) -> SomeClass {
+            let environment$ = try! JavaVirtualMachine.shared().environment()
+            environment$.interface.PushLocalFrame(environment$, 6)
+            defer { environment$.interface.PopLocalFrame(environment$, nil) }
             let cClass = try! JavaClass<JavaSomeClass>(environment: JavaVirtualMachine.shared().environment())
             let cPointer = UnsafeMutablePointer<SomeClass>.allocate(capacity: 1)
             cPointer.initialize(to: c)