dispatch_source_get_data does not return correct flag when monitoring a directory - objective-c

Question

Can someone please tell me what is this code not working ? it always return a DISPATH_VNODE_WRITE while monitoring application documents directory in iOS 6.0. (iPad) Below is my code. It returns 0x2 always no matter a file is deleted or renamed or added :(. Is this because it is a directory that I am monitoring ? not a file !!! is there any way I can find out what caused the directory to send notification ?
int directoryFileDescripter = open([documentDirectory UTF8String], O_EVTONLY);
if (directoryFileDescripter < 0) {
NSLog(#"Couldn't obtain file descripter from the system.");
return;
}
dispatch_queue_t mainQueue = /*dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);*/dispatch_get_main_queue();
if (mainQueue == NULL) {
NSLog(#"Couldn't obtain mainQueue from the system.");
close(directoryFileDescripter);
return;
}
dispSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE, directoryFileDescripter, DISPATCH_VNODE_WRITE | DISPATCH_VNODE_DELETE | DISPATCH_VNODE_RENAME, mainQueue);
if (dispSource == NULL) {
NSLog(#"Couldn't obtain dispatch source for directory from the system.");
close(directoryFileDescripter);
return;
}
dispatch_source_set_event_handler(dispSource, ^{
NSLog(#"directory notification received.");
int fileDes = dispatch_source_get_handle(dispSource);
unsigned long mask = dispatch_source_get_data(dispSource);
char path[PATH_MAX] = {0};
int nRes = fcntl(fileDes, F_GETPATH, &path);
if (nRes < 0) {
return;
}
if (mask & DISPATCH_VNODE_WRITE) {
NSLog(#"A file has been written.");
}
if (mask & DISPATCH_VNODE_DELETE) {
NSLog(#"A file has been deleted.");
}
if (mask & DISPATCH_VNODE_RENAME) {
NSLog(#"A file has been renamed.");
}
});
dispatch_source_set_cancel_handler(dispSource, ^{
close(directoryFileDescripter);
});
dispatch_resume(dispSource);

Answer 1

You are correct about the "why." When files are created, renamed, or deleted, the directory is modified. You are watching the directory, so you get a "WRITE" event.
I would typically deal with this by re-scanning the directory each time it is marked as written, and noting the changes yourself. If you're not worried about the directory itself moving or being deleted, you can just watch for WRITE events.
You can of course also watch each file's VNODE, but I expect this would be much more complicated to implement well for this kind of problem.