When polling in Java, use Thread.sleep or yield.

[Nathan D]

In Java, I'm developing a blocking file lock, and while attempting to acquire a lock, I have a code block that looks like this:

while(!fileLockIsAcquired())
{
    Thread.sleep(100); //is this cool?
    tryAcquireFileLock();
}

That figure of 100 milliseconds seems very stiff to me, and I'm wondering if the scheduler couldn't be more clever if I used Thread.sleep(0) or Thread.yield() instead. Yield appears to express purpose more effectively, although I'm not sure I really understand how the JVM interprets it. Also, I tried reading similar online articles but they didn't assist me well. Is one choice plainly superior to the other?

Because the file is a remote file accessible via a web service that lacks a blocking lock mechanism, I must implement the blocking myself.

[wolle]

Because the file is a remote file

Maybe the idea is not to hog the remote connection with frequent lock requests. A compromise would be to send a couple of quick requests and, if unsuccessful, wait a little longer, like

int yield_count = 0;
while (true) {
    tryAcquireFileLock();
    if (fileLockIsAcquired()) break;
    if (yield_count++ < 5  {
       Thread.yield();
    } else {
       Thread.sleep(100);
       yield_count = 0;
    }
}

I would also put in another counter to ensure the lock-acquiring process does not go on forever. It will hang your code.