GDHP g Distributed Hanoi Protocol NIIBE Yutaka - - PowerPoint PPT Presentation

GDHP — ‘g’ Distributed Hanoi Protocol

NIIBE Yutaka

<gniibe@fsij.org>

The Free Software Initiative of Japan

2005-11-08 IWFST 2005 – p. 1

Towers of Hanoi

• In 1893, invented by Édouard Lucas (Professor N. CLAUS).
• Good example to explain RECURSION.
• With N disks, it requires 2N − 1 steps.

⇓ 127 ⇒ 128 ⇓ 255

2005-11-08 IWFST 2005 – p. 2

GDHP — ‘g’ Distributed Hanoi Protocol (1)

• Three tasks correspond to three towers

(Source, Destination, and Auxiliary), respectively.

• Each task has a state: one of two directions (Left or Right).
• Initially, all disks are on Source.
• Initial direction of each towers:
• Destination faces to Source
• Auxiliary faces to Source
• Depending numbers of disks, Source faces to

Destination (odd), or Auxiliary (even).

2005-11-08 IWFST 2005 – p. 3

GDHP — ‘g’ Distributed Hanoi Protocol (2)

Main Routine:

• Two tasks which face each other exchange a disk.
• Compare top of disks (No disk means ∞).
• The one with bigger disk wins, receives a disk from

loser, and puts it onto the top.

• Two tasks change directions.

Terminate condition:

• Both of two tasks which face each other have no disk.

2005-11-08 IWFST 2005 – p. 4

GDHP in fugures

2005-11-08 IWFST 2005 – p. 5

Implementations of GDHP

• POSIX Thread version with TTY
• http://www.gniibe.org/code/towers-of-hanoi.c
• TCP/IP version with GTK+
• http://www.gniibe.org/code/gtk-toh.scm
• Friendly Game by Human Being
• Hanoi (March 2004)
• Tokyo (November 2004)
• Seoul (December 2004)
• Beijin (March 2005)
• Shanghai (November 2005)

2005-11-08 IWFST 2005 – p. 6