Here are a couple of synchronization problems for practice. Solve each using a semaphore solution. Solve using a monitor solution. Solutions will be discussed Monday, July 14th, after class.

1. Larry, Moe, and Curly are planting seeds. Larry digs the holes. Moe then places a seed in each hole. Curly then fills the hole up.

There are several synchronization constraints:

• Moe cannot plant a seed unless at least one empty hole exists, but Moe does not care how far Larry gets ahead of Moe.
• Curly cannot fill a hole unless at least one hole exists in which Moe has planted a seed, but the hole has not yet been filled. Curly does not care how far Moe gets ahead of Curly.
• Curly does care that Larry does not get more than MAX holes ahead of Curly. Thus, if there are MAX unfilled holes, Larry has to wait.
• There is only one shovel with which both Larry and Curly need to dig and fill the holes, respectively.

Sketch out the pseudocode for the 3 processes which represent Larry, Curly, and Moe using semaphores as the synchronization mechanism.

2. A student majoring in anthropology and minoring in computer science has embarked on a research project to see if African baboons can be taught about deadlocks. He locates a deep canyon and fastens a rope across it, so the baboons can cross hand-over-hand. Several baboons can cross at the same time, provided that they are all going in the same direction. If eastward moving and westward moving baboons ever get onto the rope at the same time, a deadlock will result (the baboons will get stuck in the middle) because it is impossible for one baboon to climb over another one while suspended over the canyon. If a baboon wants to cross the canyon, it must check to see that no other baboon is currently crossing in the opposite direction. Write a program that avoids deadlock. Do not worry about a series of eastward moving baboons holding up the westward moving baboons indefinitely (starvation).