The sem_init function creates a new counting semaphore with a
    specific value. A semaphore is used to limit access to a critical
    resource. When a process requires access to the resource without
    interference from other processes, it attempts to establish
    a connection with the associated semaphore. If the semaphore
    value is greater than zero, the connection is established and the
    semaphore value is decremented by one. If the semaphore value is
    less than or equal to zero, the process attempting to access the
    resource is blocked and must wait for another process to release
    the semaphore and increment the semaphore value.

    The sem_init function establishes a connection between an
    unnamed semaphore and a process; the sem_wait and sem_trywait
    functions lock the semaphore; and the sem_post function unlocks
    the semaphore. Use the sem_destroy function to deallocate system
    resources allocated to the process for use with the semaphore.
    You can use the sem_getvalue function to obtain the value of a
    semaphore.

    A semaphore created by a call to the sem_init function remains
    valid until the semaphore is removed by a call to the sem_destroy
    function.