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The mode argument in the call to the _locking function specifies the locking action to be performed.
The mode argument must be one of the following manifest constants.
Locks the specified bytes. If the bytes cannot be locked, the function tries again after 1 second. If, after 10 attempts, the bytes cannot be locked, the function returns an error.
Same as _LK_LOCK.
Locks the specified bytes. If bytes cannot be locked, the function returns an error.
Same as _LK_NBLCK.
Unlocks the specified bytes. (The bytes must have been previously locked.)