Question

What is the largest value y can contain after the code runs?

Hint: Since x is relatively small (loop count is small), try writing out the different y values for each thread as they execute. If you want to maximize the value of y, how can two threads 'force' more iterations to happen?
If x was initialized to 2 instead of 3, the largest possible value for y would be 5. Think about how to get this.

Answer 1

The largest value of y in concurrent programming depends on threads extending a loop's execution through synchronization. Without specific code, the largest y is achieved by thread interleaving that results in additional iterations beyond the initial value of the controlling variable x.

• The question pertains to a scenario involving concurrent programming where multiple threads are modifying the value of a shared variable y.
• The aim is to determine the largest possible value y can hold after the execution of a code fragment, given that the initial value of x determines the number of iterations a loop will perform.
• Not knowing the specific code, it is assumed that threads are competing to increase the value of y within a loop controlled by the variable x.
• To maximize y, threads would have to be synchronized in a way that they extend the loop's execution as much as possible.
• In the example provided, if x is initialized to 2, the largest y can become is 5, through potential thread interleaving that result in additional iterations.
• To generalize a strategy without specific code, when a thread reads the current value of x and then yields (due to a context switch), another thread can decrement x and increase y.
• If the first thread then resumes, it still believes x is higher than it is and proceeds to modify y.
• This interleaving can lead to a higher y through extra iterations of the loop.