jni jnienv ReleaseByteArrayElements example c c++ java

Release<PrimitiveType>ArrayElements Routines - ReleaseByteArrayElements

void Release<PrimitiveType>ArrayElements(JNIEnv *env,ArrayType array, NativeType *elems, jint mode);

A family of functions that informs the VM that the native code no longer needs access to elems. The elems argument is a pointer derived from array using the corresponding Get<PrimitiveType>ArrayElements() function. If necessary, this function copies back all changes made to elems to the original array. (ReleaseByteArrayElements)

The mode argument provides information on how the array buffer should be released. mode has no effect if elems is not a copy of the elements in array. Otherwise, mode has the following impact, as shown in the following table:

Table 4-10 Primitive Array Release Modes (ReleaseByteArrayElements)

mode	actions
0	copy back the content and free the elems buffer
JNI_COMMIT	copy back the content but do not free the elems buffer
JNI_ABORT	free the buffer without copying back the possible changes

In most cases, programmers pass “0” to the mode argument to ensure consistent behavior for both pinned and copied arrays. The other options give the programmer more control over memory management and should be used with extreme care. (ReleaseByteArrayElements)

The next table describes the specific routines that comprise the family of primitive array disposers. You should make the following substitutions:

• Replace Release<PrimitiveType>ArrayElements with one of the actual primitive array disposer routine names from Table 4-11.

• Replace ArrayType with the corresponding array type.

• Replace NativeType with the corresponding native type for that routine.

Table 4-11a Release<PrimitiveType>ArrayElements Family of Array Routines

Release<PrimitiveType>ArrayElements Routines	Array Type	Native Type
ReleaseBooleanArrayElements()	jbooleanArray	jboolean
ReleaseByteArrayElements()	jbyteArray	jbyte
ReleaseCharArrayElements()	jcharArray	jchar
ReleaseShortArrayElements()	jshortArray	jshort
ReleaseIntArrayElements()	jintArray	jint
ReleaseLongArrayElements()	jlongArray	jlong
ReleaseFloatArrayElements()	jfloatArray	jfloat
ReleaseDoubleArrayElements()	jdoubleArray	jdouble

LINKAGE:

Indices in the JNIEnv interface function table.

Table 4-11b Release<PrimitiveType>ArrayElements Family of Array Routines

Release<PrimitiveType>ArrayElements Routines	Index
ReleaseBooleanArrayElements()	191
ReleaseByteArrayElements()	192
ReleaseCharArrayElements()	193
ReleaseShortArrayElements()	194
ReleaseIntArrayElements()	195
ReleaseLongArrayElements()	196
ReleaseFloatArrayElements()	197
ReleaseDoubleArrayElements()	198

PARAMETERS of ReleaseByteArrayElements

env: the JNI interface pointer.

array: a Java array object.

elems: a pointer to array elements.

mode: the release mode.

Example of ReleaseByteArrayElements

JNIEXPORT jboolean JNICALL Java_com_mycompany_jni400_UserQueue_jniResolve(JNIEnv *jep,jobject thsObj,                
jbyteArray queueLibrary,jbyteArray queueName) {                                                                             
    jbyte            *lib,*nam;                                                                                             
    bool             rtn;                                                                                                   

    thsObj=thsObj;                                                                                                          
    lib=(*jep)->GetByteArrayElements(jep,queueLibrary,0);                                                                   
    nam=(*jep)->GetByteArrayElements(jep,queueName,0);                                                                      
    rtn=(usrq_resolve((byte*)lib,(byte*)nam)!=NULL);                                                                        
    (*jep)->ReleaseByteArrayElements(jep,queueLibrary,lib,JNI_ABORT); /* abort to not copy back contents */                 
    (*jep)->ReleaseByteArrayElements(jep,queueName   ,nam,JNI_ABORT); /* abort to not copy back contents */                 
    if(rtn) { return JNI_TRUE;  }                                                                                           
    else    { return JNI_FALSE; }                                                                                           
    }