Consider the extended state machine model of Figure 3.8, the garage counter. Suppose that the garage has two distinct entrance and exit points. Construct a side-byside concurrent composition of two counters that share a variable c that keeps track of the number of cars in the garage. Specify whether you are using synchronous or asynchronous composition, and define exactly the semantics of your composition by giving a single machine modeling the composition. If you choose synchronous semantics, explain what happens if the two machines simultaneously modify the shared variable. If you choose asynchronous composition, explain precisely which variant of asynchronous semantics you have chosen and why. Is your composition machine deterministic?

variable: c: {0,-. M} inputs: up, down: pure output: count: {0,... ,M} up ^-down Ac0/0-1 C:=c-1 Figure 3.8: Extended state machine for the garage counter of Figure 3.4. variable: c: {0,-. M} inputs: up, down: pure output: count: {0,... ,M} up ^-down Ac0/0-1 C:=c-1 Figure 3.8: Extended state machine for the garage counter of Figure 3.4