Re: [nslu2-linux] Re: Lockfiles

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On 02/03/12 22:11, rolandkbs wrote:
> Creating a file and checking for its presence is not an atomic operation.

Actually...

There's a long and honoured art of using the filesystem for locking,
using mkdir(2) and rmdir(2), like this:

while (mkdir("/tmp/lockfile", 0700) == -1) // try to take lock
{
// if mkdir failed, the lock is already taken, so wait and try
// again
sleep(1);
}

// lock now taken
... do something ...
rmdir("/tmp/lockfile"); // release lock

You can even do this from shell scripts; see lockfile(1).

Of course, named semaphores (see sem_open(3) for details) are better in
every possible way, but there are still cases (e.g. mailboxes, or doing
things from scripts) where the above approach is suitable.

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