bufmgr
Class Clock

java.lang.Object
  global.AbstractBufMgrReplacer
      bufmgr.Replacer
          bufmgr.Clock

All Implemented Interfaces:

GlobalConst

public class Clock

extends Replacer

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.

Field Summary

Fields inherited from class global.AbstractBufMgrReplacer

Available, Pinned, Referenced

Fields inherited from interface global.GlobalConst

INVALID_PAGE, MAX_NAME, MAXATTRNAME, MAXFILENAME, MAXINDEXNAME, MINIBASE_BUFFER_POOL_SIZE, MINIBASE_DB_SIZE, MINIBASE_DEFAULT_SHAREDMEM_SIZE, MINIBASE_MAX_TRANSACTIONS, MINIBASE_MAXARRSIZE, NUMBUF, PAGE_SIZE, PAGESIZE

Constructor Summary

Clock()

Clock(AbstractBufMgr javamgr)
Creates a clock object.

Method Summary

void	info() Displays information from clock replacement algorithm.
java.lang.String	name() Returns the name of the clock algorithm as a string.
int	pick_victim() Picks up the victim frame to be replaced according to the clock algorithm.
void	setBufferManager(AbstractBufMgr mgrArg) Sets the buffer manager to be eqaul to the buffer manager in the argument, gets the total number of buffer frames, and mainstains the head of the clock.

Methods inherited from class bufmgr.Replacer

free, getNumUnpinnedBuffers, pin, unpin

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Clock

public Clock()

Clock

public Clock(AbstractBufMgr javamgr)

Creates a clock object.

Method Detail

setBufferManager

public void setBufferManager(AbstractBufMgr mgrArg)

Description copied from class: AbstractBufMgrReplacer

Sets the buffer manager to be eqaul to the buffer manager in the argument, gets the total number of buffer frames, and mainstains the head of the clock.

Overrides:

setBufferManager in class AbstractBufMgrReplacer

pick_victim

public int pick_victim()
                throws BufferPoolExceededException,
                       PagePinnedException

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.

Specified by:

pick_victim in class AbstractBufMgrReplacer

Returns:

-1 if no frame is available. head of the list otherwise.

Throws:

BufferPoolExceededException.

BufferPoolExceededException

PagePinnedException

name

public final java.lang.String name()

Returns the name of the clock algorithm as a string.

Specified by:

name in class AbstractBufMgrReplacer

Returns:

"Clock", the name of the algorithm.

info

public void info()

Displays information from clock replacement algorithm.

Overrides:

info in class Replacer