How much time to check a semaphore and a file
you still loose me... they are the same thing (to me) so there is no
difference (to me)...
what, exactly, are you calling a "semaphore"? where, exactly, does it
reside? how, exactly, is it created/removed?
Sorry I'll be more specific.
I need to solve a lock of a resource within a system accessed
simultaneously by dozens (and hundreds in a near future) of processes.
More specific, those processes can be either libraries linked to a
program (static and dynamic) or independent programs.
The resource lock has to be as fast as possible.
When the resource is unlocked, one and only one acquiring process can
lock the resource again. I don't care about FIFO, LIFO or whatever.
No other process has to run to guarantee the atomicity of the lock.
I cannot rely on try ... except blocks because FPC versions on Win64 and
Linux64 fail to keep a good control of exceptions flow (read issues
http://62.166.198.202/view.php?id=12974 and
http://62.166.198.202/view.php?id=17280). To be honest I still have to
re-test on Linux64.
Windows:
Events are not applicable: they help to lock on a system wide basis but
fail to make the lock unique because the is no lock
Mutexes appear to do the job. I've made a test with a dozen of processes
on the same machine and only one of them succeeds to gain control of the
mutex when it becomes free. The wait function locks immediately. One
process at the time gains control over the resource an all processes do
their job on the resource without data mix outide the rules.
So, far so good.
Linux ?
I'm still looking for a solution equivalent to the Windows mutexes.
Events seem to be local to a process.
Semaphores could be a solution but with Lazarus 0.9.31 on an OpenSuse
11.4 64 bit, semaphores can only be used unnamed (*sem_init* function is
available) because function *sem_open* is not defined, only on DARWIN OS.
The problem with a file is that I don't know how to use it as a
semaphore with the above constraints.
The problem looks like a token problem.
Antonio.
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