Concurrency in Daily Life: The Milk Run Saga

Multiple threads of activity unfold as Roommate A and Roommate B experience a series of events involving a lack of milk, store visits, and automated purchasing attempts. The narrative traverses the comical mishaps and coordination challenges faced in everyday tasks, depicted with a touch of humor and threaded with the essence of concurrency. CS 140 lecture notes on concurrency further contextualize the scenarios in a technical light.

• Concurrency
• Everyday Life
• Roommates
• Milk Run
• CS 140

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1. Too Much Milk Roommate A Arrive home: no milk Leave for store Arrive at store Leave store Arrive home, put milk away 3:00 3:05 3:10 3:15 3:20 3:25 3:30 CS 140 Lecture Notes: Concurrency Slide 1

2. Too Much Milk Roommate A Arrive home: no milk Leave for store Arrive at store Leave store Arrive home, put milk away Roommate B 3:00 3:05 3:10 3:15 3:20 3:25 3:30 Arrive home: no milk Leave for store Arrive at store Leave store Arrive home: too much milk! CS 140 Lecture Notes: Concurrency Slide 2

3. Computerized Milk Purchase 1 if (milk == 0) { 2 if (note == 0) { 3 note = 1; 4 buy_milk(); 5 note = 0; 6 } 7 } CS 140 Lecture Notes: Concurrency Slide 3

4. Still Too Much Milk Thread A: 1 if (milk == 0) { 2 if (note == 0) { 3 4 5 6 7 8 9 10 note = 1; 11 buy_milk(); 12 note = 0; 13 } 14 } Thread B: if (milk == 0) { if (note == 0) { note = 1; buy_milk(); note = 0; } } CS 140 Lecture Notes: Concurrency Slide 4

5. Second Attempt Thread A: 1 if (note == 0) { 2 if (milk == 0) { 3 buy_milk(); 4 } 5 note = 1; 6 } Thread B: 1 if (note == 1) { 2 if (milk == 0) { 3 buy_milk(); 4 } 5 note = 0; 6 } CS 140 Lecture Notes: Concurrency Slide 5

6. Third Attempt Thread A: 1 noteA = 1; 2 if (noteB == 0) { 3 if (milk == 0) { 4 buy_milk(); 5 } 6 } 7 noteA = 0; Thread B: 1 noteB = 1; 2 if (noteA == 0) { 3 if (milk == 0) { 4 buy_milk(); 5 } 6 } 7 noteB = 0; CS 140 Lecture Notes: Concurrency Slide 6

7. Fourth Attempt Thread A: 1 noteA = 1; 2 if (noteB == 0) { 3 if (milk == 0) { 4 buy_milk(); 5 } 6 } 7 noteA = 0; Thread B: 1 noteB = 1; 2 while (noteA == 1) { 3 // do nothing 4 } 5 if (milk == 0) { 6 buy_milk(); 7 } 8 noteB = 0; CS 140 Lecture Notes: Concurrency Slide 7

8. CS 140 Lecture Notes: Concurrency Slide 8