Slide 1 Too Much Milk Roomate A 300 Arrive home no milk 305 Leave for store 310 Arrive at store 315 Leave store 320 Arrive home put milk away CS 140 Lecture Notes Concurrency ID: 795344
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Slide1
CS 140 Lecture Notes: Concurrency
Slide 1
Too Much Milk
Roomate
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
Slide2CS 140 Lecture Notes: Concurrency
Slide 2
Too Much Milk
Roomate
A
Roomate
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!
Slide3CS 140 Lecture Notes: Concurrency
Slide 3
Computerized Milk Purchase
1
if
(milk == 0)
{
2
if
(note == 0)
{
3
note = 1;
4
buy_milk
();
5
note = 0;
6
}
7
}
Slide4CS 140 Lecture Notes: Concurrency
Slide 4
Still Too Much Milk
Thread A:
Thread B:
if
(milk == 0)
{
if
(note == 0)
{
if
(milk == 0)
{
if
(note == 0)
{
note = 1;
buy_milk
();
note = 0;
}
}
note = 1;
buy_milk
();
note = 0;
}
}
Slide5CS 140 Lecture Notes: Concurrency
Slide 5
Second Attempt
Thread A:
if
(note == 0)
{
if
(milk == 0)
{
buy_milk
();
}
note = 1;
}
Thread B:
if
(note == 1)
{
if
(milk == 0)
{
buy_milk
();
}
note = 0;
}
Slide6CS 140 Lecture Notes: Concurrency
Slide 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;
Slide7CS 140 Lecture Notes: Concurrency
Slide 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;
Slide8CS 140 Lecture Notes: Concurrency
Slide 8