clock.java

minibase diskmanger buffermanger

/* File Clock.java */

package bufmgr;

/**
 * A clock algorithm for buffer pool replacement policy. It picks up the frame
 * in the buffer pool to be replaced. This is the default replacement policy.
 */
class Clock extends Replacer {

	/**
	 * Creates a clock object.
	 *
	 * @param javamgr
	 *            the buffer manage to be assigned to.
	 */
	public Clock(BufMgr javamgr) {
		super(javamgr);

	}

	/**
	 * Picks up the victim frame to be replaced according to the clock
	 * algorithm. Pin the victim so that other process can not pick it as a
	 * victim.
	 *
	 * @return -1 if no frame is available, head of the list otherwise.
	 * @throws BufferPoolExceededException
	 * @throws PagePinnedException
	 */
	public int pick_victim() throws BufferPoolExceededException,
			PagePinnedException {

		// type your code here
		// Note: readability of your code will be considered during marking

		return 0; // replace it by your code
	}

	/**
	 * Returns the name of the clock algorithm as a string.
	 *
	 * @return "Clock", the name of the algorithm.
	 */
	public final String name() {
		return "Clock";
	}

	/** Displays information from clock replacement algorithm. */
	public void info() {
		super.info();
		System.out.println("Clock hand:\t" + head);
		System.out.println("\n\n");
	}

} // end of Clock