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Too Much Milk

Too Much Milk. Roommate A 3:00 Arrive home: no milk 3:05 Leave for store 3:10 Arrive at store 3:15 Leave store 3:20 Arrive home, put milk away. Too Much Milk. Roommate A Roommate B 3:00 Arrive home: no milk 3:05 Leave for store 3:10 Arrive at store Arrive home: no milk

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Too Much Milk

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

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

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

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

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

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

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

  8. CS 140 Lecture Notes: Concurrency

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