❣ [HELP WANTED] Obj-C Block Implementation in Java via JNA (rococoa)

[umjammer]

❣ Obj-C Block Implementation

Background

Rococoa is Objective-C bindings over JNA(Java Native Access).
But JNA does NOT support obj-c block.
I've tried to adapt obj-c block to Java.

So far

my test implementation works!

• with a primitive argument
• with an id argument
• with an ObjCObject argument
• with multiple arguments

but a block which is used in a method provided by Apple doesn't work. WHY?
it got error SIGSEGV at objc_retain.

working codes, not working codes and error log, see below.

😀 working codes

objective-c block definitions

typedef int (^MyBlock)(int);
typedef long (^MyBlockI)(id);
typedef id (^MyBlockS)(id);
typedef id (^MyBlockS2)(id, int);

 ︙

@interface TestShunt : NSObject

- (int) testBlock: (int) number operation: (MyBlock) operationBlock {
    int r = operationBlock(number);
    return r;
}

- (long) testBlockI: (id) id operation: (MyBlockI) operationBlock {
    long r = operationBlock(id);
    return r;
}

- (id) testBlockS: (NSString*) s operation: (MyBlockS) operationBlock {
    id r = operationBlock(s);
    return r;
}

- (id) testBlockS2: (id) s times: (int) n operation: (MyBlockS2) operationBlock {
    id r = operationBlock(s, n);
    return r;
}

java implementation for block

    public interface ObjCBlock extends Callback {
    }

    /** utility conversion java closure to obj-c block */
    public static BlockLiteral block(ObjCBlock block) {
        BlockLiteral literal = new BlockLiteral();
        literal.flags = 0;
        literal.invoke = block;
        literal.write();
        return literal;
    }

    /** */
    public static class BlockDescriptor extends Structure {
        public NativeLong reserved;
        public NativeLong block_size;
        public Pointer rest;
        public BlockDescriptor() {}
        @Override
        protected List<String> getFieldOrder() {
            return Arrays.asList("reserved", "block_size", "rest");
        }
    }

    /** */
    public static class BlockLiteral extends Structure {
        public Pointer isa;
        public int flags;
        public int reserved;
        public ObjCBlock invoke;
        public BlockDescriptor descriptor;
        public BlockLiteral() {}
        @Override
        protected List<String> getFieldOrder() {
            return Arrays.asList("isa", "flags", "reserved", "invoke", "descriptor");
        }
    }

test code (works)

    private interface TestShunt extends ObjCObject {

        int testBlock_operation(int number, BlockLiteral operationBlock);

        long testBlockI_operation(ID id, BlockLiteral operationBlock);

        ID testBlockS_operation(String s, BlockLiteral operationBlock);

        ID testBlockS2_times_operation(String s, int n, BlockLiteral operationBlock);
    }

    public interface MyBlock extends ObjCBlock {
        int apply(BlockLiteral literal, int n);
    }

    public interface MyBlockI extends ObjCBlock {
        long apply(BlockLiteral literal, ID id);
    }

    public interface MyBlockS extends ObjCBlock {
        ID apply(BlockLiteral literal, ID s);
    }

    public interface MyBlockS2 extends ObjCBlock {
        ID apply(BlockLiteral literal, ID s, int n);
    }

    static TestShunt shunt;

    @BeforeAll
    static void setup() {
        shunt = Rococoa.create("TestShunt", TestShunt.class);
    }

    @Test
    public void testBlock2() {
        int r = shunt.testBlock_operation(234, block((MyBlock) ((l, n) -> 1000 + n)));
        assertEquals(1234, r);
    }

    @Test
    public void testBlockI() {
        ID id = new ID(314159265358979L);
        long r = shunt.testBlockI_operation(id, block((MyBlockI) ((l, i) -> i.longValue())));
        assertEquals(314159265358979L, r);
    }

    @Test
    public void testBlockS() {
        ID r = shunt.testBlockS_operation("umjammer", block((MyBlockS) ((l, i) -> {
            NSString s = Rococoa.wrap(i, NSString.class);
            return NSString.stringWithString(s.toString() + "++").id();
        })));
        assertEquals("umjammer++", Rococoa.wrap(r, NSString.class).toString());
    }

    @Test
    public void testBlockS2() {
        ID r = shunt.testBlockS2_times_operation("vavi", 3, block((MyBlockS2) ((l, i, n) -> {
            NSString s = Rococoa.wrap(i, NSString.class);
            return NSString.stringWithString(s.toString().repeat(n)).id();
        })));
        assertEquals("vavivavivavi", Rococoa.wrap(r, NSString.class).toString());
    }

🥺 block which is in a method apple provided (doesn't work)

apple framework definition (CoreML)

public abstract class VNCoreMLRequest extends VNImageBasedRequest {

   ︙

    /**
     * Creates a model container to be used with VNCoreMLRequest
     * based on a Core ML model, with an optional completion handler.
     */
    public abstract VNCoreMLRequest initWithModel_completionHandler(VNCoreMLModel model, BlockLiteral /* ^VNRequestCompletionHandler */ completionHandler);

    public interface VNRequestCompletionHandler extends ObjCBlock {
        void callback(BlockLiteral literal, ID id, ID error);
    }

sample using a block which is in a method apple provided

    @Test
    void test2() throws Exception {
        MLModel mlModel = MLModel.fromPath(model2);
        VNCoreMLModel model = VNCoreMLModel.fromMLModel(mlModel);

        VNCoreMLRequest.CLASS.alloc().initWithModel_completionHandler(model,
                block((VNCoreMLRequest.VNRequestCompletionHandler) (literal, requestId, errorRef) -> {
            NSError error = Rococoa.wrap(errorRef, NSError.class);
            if (error != null) {
                throw new IllegalStateException(error.description());
            }
            VNCoreMLRequest request = Rococoa.wrap(requestId, VNCoreMLRequest.class);
        }));
    }

error log

#  SIGSEGV (0xb) at pc=0x000000018d5fb8f8, pid=78669, tid=10243
#
# JRE version: OpenJDK Runtime Environment JBR-17.0.10+1-1087.17-jcef (17.0.10+1) (build 17.0.10+1-b1087.17)
# Java VM: OpenJDK 64-Bit Server VM JBR-17.0.10+1-1087.17-jcef (17.0.10+1-b1087.17, mixed mode, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-aarch64)
# Problematic frame:
# C  [libobjc.A.dylib+0x78f8]  objc_retain+0x10
#
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
#   https://youtrack.jetbrains.com/issues/JBR
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#

---------------  S U M M A R Y ------------

Command Line: -ea -Djava.util.logging.config.file=/Users/nsano/src/java/rococoa/rococoa-contrib/target/test-classes/logging.properties -Didea.test.cyclic.buffer.size=1048576 -javaagent:/Applications/IntelliJ IDEA CE.app/Contents/lib/idea_rt.jar=57480:/Applications/IntelliJ IDEA CE.app/Contents/bin -Djunit.jupiter.conditions.deactivate=org.junit.*Enabled*Condition -Dfile.encoding=UTF-8 com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit5 org.rococoa.cocoa.coreml.CoreMLTest,test2

Host: "Mac14,14" arm64, 24 cores, 192G, Darwin 23.3.0, macOS 14.3.1 (23D60)
Time: Tue Feb 27 01:27:49 2024 JST elapsed time: 0.843533 seconds (0d 0h 0m 0s)

---------------  T H R E A D  ---------------

Current thread (0x000000013a813600):  JavaThread "main" [_thread_in_native, id=10243, stack(0x000000016b824000,0x000000016ba27000)]

Stack: [0x000000016b824000,0x000000016ba27000],  sp=0x000000016ba22a50,  free space=2042k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C  [libobjc.A.dylib+0x78f8]  objc_retain+0x10
C  [Vision+0x225de8]  -[VNCoreMLRequest initWithModel:completionHandler:]+0x50
C  [jna4316463068936839408.tmp+0x1004c]  ffi_prep_closure_loc+0x164c
C  [jna4316463068936839408.tmp+0xe970]  ffi_call+0x57c
C  [jna4316463068936839408.tmp+0x678c]  Java_com_sun_jna_Native_invokePointer+0x96c
C  [jna4316463068936839408.tmp+0x6b74]  Java_com_sun_jna_Native_invokeLong+0x2c
j  com.sun.jna.Native.invokeLong(Lcom/sun/jna/Function;JI[Ljava/lang/Object;)J+0
j  com.sun.jna.Function.invoke([Ljava/lang/Object;Ljava/lang/Class;ZI)Ljava/lang/Object;+245
j  com.sun.jna.Function.invoke(Ljava/lang/reflect/Method;[Ljava/lang/Class;Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+271
j  com.sun.jna.Function.invoke(Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+37
j  org.rococoa.internal.MsgSendHandler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+114
j  com.sun.jna.Library$Handler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+363
j  jdk.proxy2.$Proxy16.syntheticSendMessage(Ljava/lang/Class;Lorg/rococoa/ID;Lorg/rococoa/Selector;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;+34 jdk.proxy2
j  org.rococoa.Foundation.send(Lorg/rococoa/ID;Lorg/rococoa/Selector;Ljava/lang/Class;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+202
j  org.rococoa.Foundation.send(Lorg/rococoa/ID;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+9
j  org.rococoa.Foundation.send(Lorg/rococoa/ID;Ljava/lang/String;Ljava/lang/Class;[Ljava/lang/Object;)Ljava/lang/Object;+5
j  org.rococoa.internal.ObjCObjectInvocationHandler.sendOnThisOrMainThread(Ljava/lang/reflect/Method;Lorg/rococoa/ID;Ljava/lang/String;Ljava/lang/Class;[Ljava/lang/Object;)Ljava/lang/Object;+29
j  org.rococoa.internal.ObjCObjectInvocationHandler.invokeCocoa(Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+78
j  org.rococoa.internal.ObjCObjectInvocationHandler.intercept(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;Ljava/lang/reflect/Method;Ljava/lang/Object;)Ljava/lang/Object;+130
j  org.rococoa.cocoa.vision.VNCoreMLRequest$$ByRococoa.initWithModel_completionHandler(Lorg/rococoa/cocoa/vision/VNCoreMLModel;Lorg/rococoa/ObjCBlocks$BlockLiteral;)Lorg/rococoa/cocoa/vision/VNCoreMLRequest;+21
j  org.rococoa.cocoa.coreml.CoreMLTest.test2()V+34

references

• https://clang.llvm.org/docs/Block-ABI-Apple.html
• https://github.com/ronaldoussoren/pyobjc/blob/77b98382e52818690449111cd2e23cd469b53cf5/pyobjc-core/Modules/objc/block_support.m

[umjammer]

nativelibs4java/BridJ#9 (comment)