ns_mutex

Overview

Manage mutexes

Syntax

ns_mutex create

ns_mutex destroy mutexid

ns_mutex lock mutexid

ns_mutex unlock mutexid

Description

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.

Example

At startup (for example, in your init.tcl procedure), open a shared file and create a lock for it:

    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:

    global 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:

    global Shared
    close $Shared(file)
    ns_mutex destroy $Shared(lock)

See Also

Ns_DestroyMutex

Ns_InitializeMutex

Ns_LockMutex

Ns_UnlockMutex