allocation and memory release for native functions - android-ndk

Question

I try to work with android-ndk use. Faced such problem:
It is necessary to allocate the buffer for use on jni part, and then to release it.
I found here such realization:
functions on jni part:
jobject Java_com_domain_applicationname_FFMpegWrapper_allocNative(JNIEnv* env, jobject thiz, jlong size)
{
void* buffer = malloc(size);
jobject directBuffer = (*env)->NewDirectByteBuffer(env, buffer, size);
jobject globalRef = (*env)->NewGlobalRef(env, directBuffer);
return globalRef;
}
void Java_com_domain_applicationname_FFMpegWrapper_freeNative(JNIEnv* env, jobject thiz, jobject globalRef)
{
void *buffer = (*env)->GetDirectBufferAddress(env, globalRef);
free(buffer);
(*env)->DeleteGlobalRef(env, globalRef);
}
On the Java part I do so:
public class FFMpegWrapper {
.........
/** allocate buffer*/
public static native ByteBuffer allocNative(long bufferSize);
/** free buffer*/
public static native void freeNative(ByteBuffer buffer);
}
onCreate in MainActivity:
long bufferSize = 1024;
ByteBuffer my_buffer = FFMpegWrapper.allocNative(bufferSize);
FFMpegWrapper.logFileInfo("/storage/sdcard0/movies/126_3_17.avi");//this function I won't describe it business doesn't treat but it works it is visible from logs below
//to here everything works well
FFMpegWrapper.freeNative(my_buffer);//and here we receive a departure from the program and even the window of an exception isn't shown simply is closed activity.
LogCat:
01-14 17:53:06.924: I/com.domain.tag(22249): initialize_passed
01-14 17:53:06.964: I/com.domain.tag(22249): openened
01-14 17:53:06.964: I/ttag(22249): 3270391527096277528
01-14 17:53:06.984: I/com.domain.tag(22249): File was opened
01-14 17:53:06.984: I/com.domain.tag(22249): File '/storage/sdcard0/Movies/126_3_17.avi', Codec avi
01-14 17:53:06.984: W/dalvikvm(22249): JNI WARNING: DeleteGlobalRef on non-global 0x4780001d (type=1)
01-14 17:53:06.984: I/dalvikvm(22249): "main" prio=5 tid=1 NATIVE
01-14 17:53:06.984: I/dalvikvm(22249): | group="main" sCount=0 dsCount=0 obj=0x41065568 self=0x40ebe9a0
01-14 17:53:06.984: I/dalvikvm(22249): | sysTid=22249 nice=0 sched=0/0 cgrp=apps handle=1074450224
01-14 17:53:06.984: I/dalvikvm(22249): | schedstat=( 74908625 168640538 138 ) utm=4 stm=2 core=0
01-14 17:53:06.999: I/dalvikvm(22249): #00 pc 00001260 /system/lib/libcorkscrew.so (unwind_backtrace_thread+27)
01-14 17:53:06.999: I/dalvikvm(22249): #01 pc 0005f904 /system/lib/libdvm.so (dvmDumpNativeStack(DebugOutputTarget const*, int)+35)
01-14 17:53:06.999: I/dalvikvm(22249): #02 pc 000537ac /system/lib/libdvm.so (dvmDumpThreadEx(DebugOutputTarget const*, Thread*, bool)+303)
01-14 17:53:06.999: I/dalvikvm(22249): #03 pc 00053846 /system/lib/libdvm.so (dvmDumpThread(Thread*, bool)+25)
01-14 17:53:06.999: I/dalvikvm(22249): #04 pc 00038e02 /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #05 pc 000414da /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #06 pc 0002f728 /data/data/ru.dzakhov.ffmpeg.test/lib/libmylib.so (Java_ru_dzakhov_ffmpeg_test_FFMpegWrapper_freeNative+25)
01-14 17:53:06.999: I/dalvikvm(22249): #07 pc 0001de70 /system/lib/libdvm.so (dvmPlatformInvoke+112)
01-14 17:53:06.999: I/dalvikvm(22249): #08 pc 0004d0c2 /system/lib/libdvm.so (dvmCallJNIMethod(unsigned int const*, JValue*, Method const*, Thread*)+393)
01-14 17:53:06.999: I/dalvikvm(22249): #09 pc 0004f1dc /system/lib/libdvm.so (dvmResolveNativeMethod(unsigned int const*, JValue*, Method const*, Thread*)+171)
01-14 17:53:06.999: I/dalvikvm(22249): #10 pc 000272a0 /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #11 pc 0002bba8 /system/lib/libdvm.so (dvmInterpret(Thread*, Method const*, JValue*)+180)
01-14 17:53:06.999: I/dalvikvm(22249): #12 pc 0005faf6 /system/lib/libdvm.so (dvmInvokeMethod(Object*, Method const*, ArrayObject*, ArrayObject*, ClassObject*, bool)+373)
01-14 17:53:06.999: I/dalvikvm(22249): #13 pc 0006709c /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #14 pc 000272a0 /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #15 pc 0002bba8 /system/lib/libdvm.so (dvmInterpret(Thread*, Method const*, JValue*)+180)
01-14 17:53:06.999: I/dalvikvm(22249): #16 pc 0005f830 /system/lib/libdvm.so (dvmCallMethodV(Thread*, Method const*, Object*, bool, JValue*, std::__va_list)+271)
01-14 17:53:06.999: I/dalvikvm(22249): #17 pc 000496b2 /system/lib/libdvm.so
01-14 17:53:06.999: I/dalvikvm(22249): #18 pc 0004c44e /system/lib/libandroid_runtime.so
01-14 17:53:06.999: I/dalvikvm(22249): #19 pc 0004d556 /system/lib/libandroid_runtime.so (android::AndroidRuntime::start(char const*, char const*)+389)
01-14 17:53:07.004: I/dalvikvm(22249): #20 pc 00000dce /system/bin/app_process
01-14 17:53:07.004: I/dalvikvm(22249): #21 pc 00017120 /system/lib/libc.so (__libc_init+35)
01-14 17:53:07.004: I/dalvikvm(22249): at ru.dzakhov.ffmpeg.test.FFMpegWrapper.freeNative(Native Method)
01-14 17:53:07.004: I/dalvikvm(22249): at ru.dzakhov.ffmpeg.test.MainActivity.onCreate(MainActivity.java:39)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.Activity.performCreate(Activity.java:5184)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1083)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.ActivityThread.access$600(ActivityThread.java:140)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
01-14 17:53:07.004: I/dalvikvm(22249): at android.os.Handler.dispatchMessage(Handler.java:99)
01-14 17:53:07.004: I/dalvikvm(22249): at android.os.Looper.loop(Looper.java:137)
01-14 17:53:07.004: I/dalvikvm(22249): at android.app.ActivityThread.main(ActivityThread.java:4898)
01-14 17:53:07.004: I/dalvikvm(22249): at java.lang.reflect.Method.invokeNative(Native Method)
01-14 17:53:07.004: I/dalvikvm(22249): at java.lang.reflect.Method.invoke(Method.java:511)
01-14 17:53:07.004: I/dalvikvm(22249): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
01-14 17:53:07.004: I/dalvikvm(22249): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
01-14 17:53:07.004: I/dalvikvm(22249): at dalvik.system.NativeStart.main(Native Method)
01-14 17:53:07.004: E/dalvikvm(22249): VM aborting
01-14 17:53:07.004: A/libc(22249): Fatal signal 11 (SIGSEGV) at 0xdeadd00d (code=1), thread 22249 (hov.ffmpeg.test)
What I do incorrectly?

Answer 1

About JNI: http://docs.oracle.com/javase/6/docs/technotes/guides/jni/spec/design.html#wp16785
Objects are passed to native methods as local references. This means that you must store global ref on native side, if you pass global ref back to java it will be wrapped as local object. So when you try to free it later this local object passed to you code.
When you create global ref from local - free local ref if you don't need it anymore.
So you can maintain some sort of map for allocated global objects ( or for allocated buffers ) and return local reference to jobject returned by NewDirectByteBuffer.