File Locking using java.nio package

Question

I am trying to lock a file using FileChannel's lock method on a CIFS file system. My application is on windows and the CIFS is accessed using UNC format ( \\1.2.3.4\blah.. ). I get the following error
     java.io.IOException: The network request is not supported
     at sun.nio.ch.FileChannelImpl.lock0(Native Method)
     at sun.nio.ch.FileChannelImpl.lock(FileChannelImpl.java:750)
     at java.nio.channels.FileChannel.lock(FileChannel.java:865)
From the same machine using the same UNC formatm, when I lock the file using windows C API, I can successfull lock.
Anyone has any idea why JVM can not lock even using nio package. Shouldnt it use the same ( or similar ) API under the hood as its clear by the package name java.nio
The C program I am using is
#include <io.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/locking.h>
#include <share.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void main( int argc, char **argv )
int fh,numread;
char buffer[40];
char filename[500];
/* Quit if can't open file or system doesn't
* support sharing.
if ( argc > 1 )
          strcpy(filename,argv[1]);
else
          strcpy(filename,"locking.c");
fh = sopen(filename , O_RDWR, SHDENYNO, //_SH_DENYRW,
SIREAD | SIWRITE );
if( fh == -1 )
exit( 1 );
/* Lock some bytes and read them. Then unlock. */
if( locking( fh, LKNBLCK, 30L ) != -1 )
printf( "No one can change these bytes while I'm reading them\n" );
numread = _read( fh, buffer, 30 );
printf( "%d bytes read: %.30s\n", numread, buffer );
lseek( fh, 0L, SEEK_SET );
     printf( "Press a key to unlock the file.....\n" );
     getchar();
     locking( fh, LKUNLCK, 30L );
printf( "Now I'm done. Do what you will with them\n" );
else
perror( "Locking failed\n" );
_close( fh );
}

Answer 1

It uses LockFile and LockFileEx. Please check in the MSDN documentation the peculiarities of such APIs.
JNIEXPORT jint JNICALL
Java_sun_nio_ch_FileChannelImpl_lock0(JNIEnv *env, jobject this, jobject fdo,
                                      jboolean block, jlong pos, jlong size,
                                      jboolean shared)
    jint fd = fdval(env, fdo);
    HANDLE h = (HANDLE)_get_osfhandle(fd);
    DWORD lowPos = (DWORD)pos;
    long highPos = (long)(pos >> 32);
    DWORD lowNumBytes = (DWORD)size;
    DWORD highNumBytes = (DWORD)(size >> 32);
    jint result = 0;
    if (onNT) {
        DWORD flags = 0;
        OVERLAPPED o;
        o.hEvent = 0;
        o.Offset = lowPos;
        o.OffsetHigh = highPos;
        if (block == JNI_FALSE) {
            flags |= LOCKFILE_FAIL_IMMEDIATELY;
        if (shared == JNI_FALSE) {
            flags |= LOCKFILE_EXCLUSIVE_LOCK;
        result = LockFileEx(h, flags, 0, lowNumBytes, highNumBytes, &o);
        if (result == 0) {
            int error = GetLastError();
            if (error != ERROR_LOCK_VIOLATION) {
                JNU_ThrowIOExceptionWithLastError(env, "Lock failed");
                return sun_nio_ch_FileChannelImpl_NO_LOCK;
            if (flags & LOCKFILE_FAIL_IMMEDIATELY) {
                return sun_nio_ch_FileChannelImpl_NO_LOCK;
            JNU_ThrowIOExceptionWithLastError(env, "Lock failed");
            return sun_nio_ch_FileChannelImpl_NO_LOCK;
        return sun_nio_ch_FileChannelImpl_LOCKED;
    } else {
        for(;;) {
            if (size > 0x7fffffff) {
                size = 0x7fffffff;
            lowNumBytes = (DWORD)size;
            highNumBytes = 0;
            result = LockFile(h, lowPos, highPos, lowNumBytes, highNumBytes);
            if (result != 0) {
                if (shared == JNI_TRUE) {
                    return sun_nio_ch_FileChannelImpl_RET_EX_LOCK;
                } else {
                    return sun_nio_ch_FileChannelImpl_LOCKED;
            } else {
                int error = GetLastError();
                if (error != ERROR_LOCK_VIOLATION) {
                    JNU_ThrowIOExceptionWithLastError(env, "Lock failed");
                    return sun_nio_ch_FileChannelImpl_NO_LOCK;
                if (block == JNI_FALSE) {
                    return sun_nio_ch_FileChannelImpl_NO_LOCK;
            Sleep(100);
    return sun_nio_ch_FileChannelImpl_NO_LOCK;
}