we have a C function in one of the libraries which are loaded in java, which accepts a function pointer
function defination as below
typedef char int8 typedef unsigned short uint16 uint32 poll_broadcasts(void *(pfn)(int8*,uint16)); In C it is used as below
void handle_broadcasts( int8 *broadcast, uint16 length ) uint32 a = poll_broadcasts( (void*(*)(int8*,uint16)) handle_broadcasts ) But when you use Swig to generate JNI wrapper it creates following definition for poll_broadcast
public static long poll_broadcasts(SWIGTYPE_p_f_p_char_unsigned_short__p_void pfn) { return TestJNI.poll_broadcasts(SWIGTYPE_p_f_p_char_unsigned_short__p_void.getCPtr(pfn)); } As per answer for
How should I write the .i file to wrap callbacks in Java or C#
Tried below
test.h
void * data; typedef void* (*callback_handle_broadcast_t)(int8*, uint16); static callback_handle_broadcast_t handle_broadcast; static void set_handle_broadcast(callback_handle_broadcast_t cb, void *userdata) { handle_broadcast = cb; data = userdata; } Swig interface file Test.i
%module Test %include "cpointer.i" %include "carrays.i" %include "various.i" %include "arrays_java.i" %pointer_functions(int, intp); %pointer_functions(char, charp); %include "arrays_java.i" %include "typemaps.i" %{ #include <assert.h> #include "test.h" struct callback_data { JNIEnv *env; jobject obj; }; void java_callback(int8* arg1, uint16 arg2, void *ptr) { struct callback_data *data = ptr; const jclass callbackInterfaceClass = (*data->env)->FindClass(data->env, "BroadcastCallback"); assert(callbackInterfaceClass); const jmethodID meth = (*data->env)->GetMethodID(data->env, callbackInterfaceClass, "handle", "([C)V"); assert(meth); jcharArray charArr = (*data->env)->NewCharArray(data->env, arg2); (*data->env)->CallVoidMethod(data->env, data->obj, meth, (jcharArray)charArr); } %} %typemap(jstype) callback_handle_broadcast_t cb "BroadcastCallback"; %typemap(jtype) callback_handle_broadcast_t cb "BroadcastCallback"; %typemap(jni) callback_handle_broadcast_t cb "jobject"; %typemap(javain) callback_handle_broadcast_t cb "$javainput"; %typemap(in,numinputs=1) (callback_handle_broadcast_t cb, void *userdata) { struct callback_data *data = malloc(sizeof *data); data->env = jenv; data->obj = JCALL1(NewGlobalRef, jenv, $input); JCALL1(DeleteLocalRef, jenv, $input); $1 = java_callback; $2 = data; } %include "test.h" Java Interface BrodcastCallback.java
public interface BroadcastCallback { //public void handle(String broadcast); public void handle(char[] broadcast); } Implement the interface
class BtCallback implements BroadcastCallback { @Override public void handle(char[] broadcast) { LOG.debug("Broadcast callback handled: " + broadcast.length); } } Finally when used
BroadcastCallback cb = new BtCallback(); Test.set_handle_broadcast(cb, null); Test.poll_broadcasts(Test.getHandle_broadcast()); There is no compilation error, but when program is run and and poll_broadcasts calls the handle broadcast function pointer (within C) passed from java, it crashes with EXCEPTION_ACCESS_VIOLATION.
Looks like it has to do something with int8* arg of the function, but can't figure out
somebody please help.