How to check whether a file is locked in Cocoa?

Question

Is there any API to check whether a file is a locked? I am not able to find any API in the NSFileManager class.Let me know if there is any API to check the lock of the file.

I found the following link related to file lock

http://lists.apple.com/archives/cocoa-dev/2006/Nov/msg01399.html

I can invoke – isWritableFileAtPath: on file. Is there any other way to find whether a file is locked?

Answer 1

Following Code worked for me.

NSError * error;
NSDictionary *attributes = [[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:&error];
BOOL isLocked = [[attributes objectForKey:NSFileImmutable] boolValue];
            
if (isLocked) {
    NSLog(@"File is locked");
}

Answer 2

I don't really know the answer to this question as I don't know how OS X implements its locking mechanism.

It might use the POSIX advisory locking as documented in the flock() manpage and if I were you I would write a 10 31-line test program in C to show what fcntl() (manpage) thinks about the advisory lock you have made from within Finder.

Something like (untested):

#include <fcntl.h>
#include <errno.h>
#include <stdio.h>

int main(int argc, const char **argv)
{
    for (int i = 1; i < argc; i++)
    {
        const char *filename = argv[i];
        int fd = open(filename, O_RDONLY);
        if (fd >= 0)
        {
            struct flock flock;
            if (fcntl(fd, F_GETLK, &flock) < 0)
            {
                fprintf(stderr, "Failed to get lock info for '%s': %s\n", filename, strerror(errno));
            }
            else
            {
                // Possibly print out other members of flock as well...
                printf("l_type=%d\n", (int)flock.l_type);
            }
            close(fd);
        }
        else
        {
            fprintf(stderr, "Failed to open '%s': %s\n", filename, strerror(errno));
        }
    }
    return 0;
}

Answer 3

If necessary, the immutable flag (OS X 'file locked') can also be determined with POSIX C functions. The immutable property is not a lock in unix terms but a file flag. It can be obtained with the stat function:

struct stat buf;
stat("my/file/path", &buf);
if (0 != (buf.st_flags & UF_IMMUTABLE)) {
     //is immutable
}

For reference see: https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man2/stat.2.html

The immutable flag can be set with the chflags function:

chflags("my/file/path", UF_IMMUTABLE);

For reference see: https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man2/chflags.2.html