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Use the Semaphore VIs to limit the number of tasks that can simultaneously operate on a shared (protected) resource. A protected resource or critical section of code might include writing to global variables or communicating with external instruments.

You can use the Semaphore VIs to synchronize two or more separate, parallel tasks so that only one task at a time executes a critical section of code protected by a common semaphore. In particular, use these VIs when you want certain VIs or parts of a block diagram to wait until another VI or part of a block diagram is finished with the execution of a critical section.

Palette Object	Description
Acquire Semaphore	Acquires access to a semaphore.
Create Semaphore	Looks up an existing semaphore or creates a new semaphore and returns a refnum.
Destroy Semaphore	Destroys the specified semaphore.
Get Semaphore Status	Returns current status information of a semaphore.
Not A Semaphore	Returns TRUE if semaphore is not a valid semaphore refnum.
Release Semaphore	Releases access to a semaphore.