// synch.ii

/**
 * A semaphore is a synchronization object.  It
 * has the standard atomic wait (P) and signal (V)
 * operations.
 */
interface Semaphore {

    /**
     * Wait on the semaphore.
     */
    wait()

    /**
     * Signal the semaphore.
     */
    signal()
}

/**
 * Creates a counting semaphore.  It can count from
 * 0 to max, and begins at init.  The wait operation
 * causes the calling thread to block until the count is > 0,
 * then decrements the count and unblocks the thread.
 * The signal operation causes the count to increment up to 
 * a maximum of max.
 * A standard binary semaphore can be created by passing
 * 1 for max.
 * Precondition: max > 0, 0 <= init <= max
 * Postcondition: A semaphore, as just described, is returned.
 *   null is returned if no more semaphores can be allocated.
 */
createSemaphore(init:int, max:int):Semaphore