Long description

In all three parts, the horizontal axis represents time. An arrow labeled Time is placed below all three parts. Part (a): A vertical rectangular block is labeled Barrier. There are four processes labeled A, B, C, and D placed from top to bottom on the left of the block and connected to the barrier with dotted lines. Process "A" has the most dotted lines, C has lesser dotted lines than A, B has lesser dotted lines than C, and D has the least dotted lines. Part (b): A vertical rectangular block is labeled Barrier. There are four processes labeled A, B, C, and D placed from top to bottom on the left of the block. "A", B, and D are placed on the left edge of the block but the C process is connected with the Barrier with the dotted line. Part (c): A vertical rectangular block is labeled Barrier and Time with a forward arrow at the bottom. There are four processes labeled A, B, C, and D placed on the right edge of the block from top to bottom.