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ns_mutex create initializes a mutual exclusion lock and returns an ID for it.
ns_mutex destroy frees the resources associated with the specified mutual exclusion lock. The mutexid argument is the mutex ID returned by ns_mutex create when the mutex was created.
ns_mutex lock acquires the specified mutual exclusion lock. The mutexid argument is the mutex ID returned by ns_mutex create when the mutex was created.
ns_mutex unlock unlocks the specified mutual exclusion lock. The mutexid argument is the mutex ID returned by ns_mutex create when the mutex was created.
At startup (for example, in your init.tcl procedure), open a shared file and create a lock for it:
ns_share Shared
set Shared(file) [open myfile.data]
set Shared(lock) [ns_mutex create]
detach $Shared(file)
Later (for example, in a request procedure), access the data file:
ns_share Shared
ns_mutex lock $Shared(lock)
catch {
... access $Shared(file) ...
}
ns_mutex unlock $Shared(lock)
Note: The "catch" is important so the lock isn't held if Tcl unwinds due to an error accessing the file.
At shutdown (for example, in your shutdown procedure registered with ns_atshutdown), close the file and destroy the lock:
ns_share Shared
close $Shared(file)
ns_mutex destroy $Shared(lock)