How does one efficiently implement file region locking using grand central dispatch?

For my project, I am reading from and writing to a file from multiple threads, so I need to implement file locking. I have tried fcntl(), however it seems that function only works with locking between processes, not between threads. As such, I am looking for another solution. The solu开发者_如何学编程tion which I came up with (which is probably not the best) is to have a byte in each record in my file to indicate whether the record is locked, and I could then use a busy loop to read and check the byte.

So, I have two questions. First, what is the most efficient way to implement file region locking? Second, if I go with the busy loop approach, how can I optimize that with grand central dispatch? I was thinking that I could make all of the busy loops occur in blocks sent to dispatch_sync(). But I don't know whether or not that would even work efficiently.

Thanks.

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How about Dispatch Semaphore? You can use Dispatch Semaphore to access exclusively resources. For instance, create Dispatch Semaphores for your file regions.

for (int i = 0; i < regions; ++i)
    sema_[i] = dispatch_semaphore_create(1);

And then, access resources with wait and signal.

dispatch_semaphore_wait(sema_[region], DISPATCH_TIME_FOREVER);
/* access the region */
dispatch_semaphore_signal(sema_[region]);