Sharing Files Between Interpreters

To share a file between the interpreters in a group, use the Tcl detach command. A shared file is left open after an interpreter is deallocated when the AutoClose parameter is on (it is on by default). For example:

    #init time:
    set sharedFile [open myfile.dat]
    detach $sharedFile

You must manually close the shared file (by performing a close) when it is no longer needed or when the server is shut down.

Note that there is no implicit locking between interpreters. This means that one interpreter can be performing a gets command on the shared file at the same time another interpreter performs a close on the same file. The results are unpredictable, and could potentially cause a core dump. To avoid this situation, use a mutex to protect access to the file whenever it is accessed.

For example:, at initialization time (for example, in your init.tcl script), open a shared file and create a mutex:

    set sharedLock [ns_mutex create]
    set sharedFile [open myfile.dat]
    detach $sharedFile

At run time, use the mutex to protect any actions you perform on the shared file:

    ns_share sharedLock
    ns_share sharedFile
    ns_mutex lock $sharedLock
    puts $sharedFile ...
    gets $sharedFile ...
    ns_mutex unlock $sharedLock

At shutdown (for example, in your shutdown procedure registered with ns_atshutdown), close the file and destroy the lock:

    ns_share sharedLock
    ns_share sharedFile
    close $SharedFile
    ns_mutex destroy $SharedLock

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