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Fix async JNI strict concurrency #730

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f237988
Fix async JNI strict concurrency
nerzh May 2, 2026
e4fd99a
refactor async JNI captures
nerzh May 14, 2026
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131 changes: 94 additions & 37 deletions Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+NativeTranslation.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -230,7 +230,12 @@ extension JNISwift2JavaGenerator {
parameters: [
JavaParameter(name: parameterName, type: .long)
],
conversion: .pointee(.extractSwiftValue(.placeholder, swiftType: type)),
conversion: .pointee(
.asyncTaskCapture(
.extractSwiftValue(.placeholder, swiftType: type),
name: NativeSwiftConversionStep.extractedSwiftValueName(for: parameterName)
)
),
indirectConversion: nil,
conversionCheck: nil
)
Expand Down Expand Up @@ -327,7 +332,10 @@ extension JNISwift2JavaGenerator {
parameters: [
JavaParameter(name: parameterName, type: .long)
],
conversion: .extractMetatypeValue(.placeholder),
conversion: .asyncTaskCapture(
.extractMetatypeValue(.placeholder),
name: NativeSwiftConversionStep.extractedSwiftValueName(for: parameterName)
),
indirectConversion: nil,
conversionCheck: nil
)
Expand Down Expand Up @@ -441,15 +449,18 @@ extension JNISwift2JavaGenerator {
parameters: [
JavaParameter(name: parameterName, type: .javaLangObject)
],
conversion: .interfaceToSwiftObject(
.placeholder,
swiftWrapperClassName: JNISwift2JavaGenerator.protocolParameterWrapperClassName(
methodName: methodName,
parameterName: parameterName,
parentName: parentName
conversion: .asyncTaskCapture(
.interfaceToSwiftObject(
.placeholder,
swiftWrapperClassName: JNISwift2JavaGenerator.protocolParameterWrapperClassName(
methodName: methodName,
parameterName: parameterName,
parentName: parentName
),
protocolTypes: protocolTypes,
allowsJavaImplementations: allowsJavaImplementations
),
protocolTypes: protocolTypes,
allowsJavaImplementations: allowsJavaImplementations
name: NativeSwiftConversionStep.swiftObjectName(for: parameterName)
),
indirectConversion: nil,
conversionCheck: nil
Expand Down Expand Up @@ -521,10 +532,13 @@ extension JNISwift2JavaGenerator {
parameters: [JavaParameter(name: parameterName, type: .long)],
conversion: .pointee(
.optionalChain(
.extractSwiftValue(
.placeholder,
swiftType: swiftType,
allowNil: true
.asyncTaskCapture(
.extractSwiftValue(
.placeholder,
swiftType: swiftType,
allowNil: true
),
name: NativeSwiftConversionStep.extractedSwiftValueName(for: parameterName)
)
)
),
Expand Down Expand Up @@ -1219,6 +1233,18 @@ extension JNISwift2JavaGenerator {
/// Destructures a Swift tuple result and writes each element to an out-parameter.
indirect case tupleDestructure(elements: [(index: Int, label: String?, conversion: NativeSwiftConversionStep, outParamName: String, javaType: JavaType)])

/// Marks a temporary value produced by the inner conversion as captured by
/// the async task body.
indirect case asyncTaskCapture(NativeSwiftConversionStep, name: String)

static func extractedSwiftValueName(for name: String) -> String {
"\(name)$"
}

static func swiftObjectName(for name: String) -> String {
"\(name)swiftObject$"
}

/// Promotes the outermost `.getJNIValue` to `.getJNILocalRefValue`.
/// Used for `@_cdecl` return positions to ensure the local ref survives
/// ARC destruction of temporary `JavaObject`s.
Expand All @@ -1231,6 +1257,22 @@ extension JNISwift2JavaGenerator {
}
}

var asyncTaskCaptureNames: [String] {
switch self {
case .asyncTaskCapture(let inner, let name):
return [name] + inner.asyncTaskCaptureNames

case .pointee(let inner), .optionalChain(let inner):
return inner.asyncTaskCaptureNames

case .tupleConstruct(let elements):
return elements.flatMap { $0.conversion.asyncTaskCaptureNames }

default:
return []
}
}

/// Returns the conversion string applied to the placeholder.
func render(_ printer: inout CodePrinter, _ placeholder: String) -> String {
// NOTE: 'printer' is used if the conversion wants to cause side-effects.
Expand Down Expand Up @@ -1268,7 +1310,7 @@ extension JNISwift2JavaGenerator {
let allowsJavaImplementations
):
let inner = inner.render(&printer, placeholder)
let variableName = "\(inner)swiftObject$"
let variableName = Self.swiftObjectName(for: inner)
let existentialType = SwiftKitPrinting.renderExistentialType(protocolTypes)
printer.print("let \(variableName): \(existentialType)")

Expand Down Expand Up @@ -1344,7 +1386,7 @@ extension JNISwift2JavaGenerator {

case .extractSwiftValue(let inner, let swiftType, let allowNil, let convertLongFromJNI):
let inner = inner.render(&printer, placeholder)
let pointerName = "\(inner)$"
let pointerName = Self.extractedSwiftValueName(for: inner)
if !allowNil {
printer.print(#"assert(\#(inner) != 0, "\#(inner) memory address was null")"#)
}
Expand All @@ -1367,7 +1409,7 @@ extension JNISwift2JavaGenerator {

case .extractMetatypeValue(let inner):
let inner = inner.render(&printer, placeholder)
let pointerName = "\(inner)$"
let pointerName = Self.extractedSwiftValueName(for: inner)
printer.print(
"""
let \(inner)Bits$ = Int(Int64(fromJNI: \(inner), in: environment))
Expand Down Expand Up @@ -1629,36 +1671,52 @@ extension JNISwift2JavaGenerator {
let completeExceptionallyMethodID
):
var globalRefs: [String] = ["globalFuture"]
var asyncTaskCaptureNames: [String] = []

func appendAsyncTaskCaptureNames(_ names: [String]) {
for name in names where !asyncTaskCaptureNames.contains(name) {
asyncTaskCaptureNames.append(name)
}
}

appendAsyncTaskCaptureNames(nativeFunctionSignature.selfParameter?.conversion.asyncTaskCaptureNames ?? [])
appendAsyncTaskCaptureNames(nativeFunctionSignature.selfTypeParameter?.conversion.asyncTaskCaptureNames ?? [])
for parameter in nativeFunctionSignature.parameters {
appendAsyncTaskCaptureNames(parameter.conversion.asyncTaskCaptureNames)
}

printer.print(
"""
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
"""
)

// Global ref all indirect returns
for outParameter in nativeFunctionSignature.result.outParameters {
printer.print(
"nonisolated(unsafe) let \(outParameter.name) = environment.interface.NewGlobalRef(environment, \(outParameter.name))"
"let \(outParameter.name)Sendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, \(outParameter.name)))"
)
globalRefs.append(outParameter.name)
}

// We also need to global ref any objects passed in
for parameter in nativeFunctionSignature.parameters.flatMap(\.parameters) where !parameter.type.isPrimitive {
printer.print("nonisolated(unsafe) let \(parameter.name) = environment.interface.NewGlobalRef(environment, \(parameter.name))")
printer.print(
"let \(parameter.name)Sendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, \(parameter.name)))"
)
globalRefs.append(parameter.name)
}

printer.print(
"""
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
"""
)

if let selfParameter = nativeFunctionSignature.selfParameter {
for parameter in selfParameter.parameters {
printer.print("nonisolated(unsafe) let \(parameter.name)Sendable$ = \(parameter.name)$")
}
}
if let selfTypeParameter = nativeFunctionSignature.selfTypeParameter {
for parameter in selfTypeParameter.parameters {
printer.print("nonisolated(unsafe) let \(parameter.name)Sendable$ = \(parameter.name)$")
}
for name in asyncTaskCaptureNames {
printer.print("let \(name)Sendable$ = _SwiftJavaUncheckedSendable(value: \(name))")
}

func printDo(printer: inout CodePrinter) {
Expand Down Expand Up @@ -1703,15 +1761,11 @@ extension JNISwift2JavaGenerator {
}

func printTaskBody(printer: inout CodePrinter) {
if let selfParameter = nativeFunctionSignature.selfParameter {
for parameter in selfParameter.parameters {
printer.print("let \(parameter.name)$ = \(parameter.name)Sendable$")
}
for globalRef in globalRefs {
printer.print("let \(globalRef) = \(globalRef)Sendable$.value")
}
if let selfTypeParameter = nativeFunctionSignature.selfTypeParameter {
for parameter in selfTypeParameter.parameters {
printer.print("let \(parameter.name)$ = \(parameter.name)Sendable$")
}
for name in asyncTaskCaptureNames {
printer.print("let \(name) = \(name)Sendable$.value")
}
printer.printBraceBlock("defer") { printer in
// Defer might on any thread, so we need to attach environment.
Expand Down Expand Up @@ -1839,6 +1893,9 @@ extension JNISwift2JavaGenerator {
}
}
return ""

case .asyncTaskCapture(let inner, _):
return inner.render(&printer, placeholder)
}
}
}
Expand Down
40 changes: 34 additions & 6 deletions Tests/JExtractSwiftTests/JNI/JNIAsyncTests.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -61,12 +61,16 @@ struct JNIAsyncTests {
"""
@_cdecl("Java_com_example_swift_SwiftModule__00024asyncVoid__Ljava_util_concurrent_CompletableFuture_2")
public func Java_com_example_swift_SwiftModule__00024asyncVoid__Ljava_util_concurrent_CompletableFuture_2(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, result_future: jobject?) {
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
var task: Task<Void, Never>? = nil
#if swift(>=6.2)
if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *) {
task = Task.immediate {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand All @@ -80,6 +84,7 @@ struct JNIAsyncTests {
if task == nil {
task = Task {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand Down Expand Up @@ -137,12 +142,16 @@ struct JNIAsyncTests {
"""
@_cdecl("Java_com_example_swift_SwiftModule__00024async__Ljava_util_concurrent_CompletableFuture_2")
public func Java_com_example_swift_SwiftModule__00024async__Ljava_util_concurrent_CompletableFuture_2(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, result_future: jobject?) {
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
var task: Task<Void, Never>? = nil
#if swift(>=6.2)
if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *) {
task = Task.immediate {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand All @@ -163,6 +172,7 @@ struct JNIAsyncTests {
if task == nil {
task = Task {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand Down Expand Up @@ -227,12 +237,16 @@ struct JNIAsyncTests {
"""
@_cdecl("Java_com_example_swift_SwiftModule__00024async__JLjava_util_concurrent_CompletableFuture_2")
public func Java_com_example_swift_SwiftModule__00024async__JLjava_util_concurrent_CompletableFuture_2(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, i: jlong, result_future: jobject?) {
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
var task: Task<Void, Never>? = nil
#if swift(>=6.2)
if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *) {
task = Task.immediate {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand All @@ -247,6 +261,7 @@ struct JNIAsyncTests {
if task == nil {
task = Task {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand Down Expand Up @@ -320,12 +335,18 @@ struct JNIAsyncTests {
guard let c$ else {
fatalError("c memory address was null in call to \\(#function)!")
}
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
let c$Sendable$ = _SwiftJavaUncheckedSendable(value: c$)
var task: Task<Void, Never>? = nil
#if swift(>=6.2)
if #available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, *) {
task = Task.immediate {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
let c$ = c$Sendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand All @@ -343,6 +364,8 @@ struct JNIAsyncTests {
if task == nil {
task = Task {
var environment = try! JavaVirtualMachine.shared().environment()
let globalFuture = globalFutureSendable$.value
let c$ = c$Sendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand Down Expand Up @@ -403,9 +426,14 @@ struct JNIAsyncTests {
"""
@_cdecl("Java_com_example_swift_SwiftModule__00024async__Ljava_lang_String_2Ljava_util_concurrent_CompletableFuture_2")
public func Java_com_example_swift_SwiftModule__00024async__Ljava_lang_String_2Ljava_util_concurrent_CompletableFuture_2(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, s: jstring?, result_future: jobject?) {
nonisolated(unsafe) let s = environment.interface.NewGlobalRef(environment, s)
nonisolated(unsafe) let globalFuture = environment.interface.NewGlobalRef(environment, result_future)
struct _SwiftJavaUncheckedSendable<T>: @unchecked Sendable {
let value: T
}
let sSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, s))
let globalFutureSendable$ = _SwiftJavaUncheckedSendable(value: environment.interface.NewGlobalRef(environment, result_future))
...
let globalFuture = globalFutureSendable$.value
let s = sSendable$.value
defer {
let deferEnvironment = try! JavaVirtualMachine.shared().environment()
deferEnvironment.interface.DeleteGlobalRef(deferEnvironment, globalFuture)
Expand Down
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