Two nonsharable resources and two processes.
Horizontal Axis: Number of instructions executed by process P1.
Vertical Axis: Number of instructions executed by process P2.
Shaded regions represent impossible situations: both P1 and P2 having a nonsharable resource.
P1 scheduled: goes from p to q,
P2 scheduled: goes from q to r,
P1 scheduled: goes from r to s,
P2 scheduled: goes from s to t.
Figure based on one appearing on page 177 of Operating Systems: Design and Implementation, 2nd Edition by Andrew S. Tanenbaum and Albert S. Woodhull, Prentice Hall, 1997.