A monitor is a synchronization approach that
allows threads to wait until a condition is
satisfied while enforcing mutual exclusion. A
classic example of this would be the
producer-consumer problem where the consumer
not only has mutual exclusive access to a list
of items, but also needs to wait if there are
insufficient items on the list. Monitors in
Java are provided using the synchronized
keyword along with the wait and notify,
notifyAll methods for the object.
The example here defines an empty list (with just an integer) and create 4 producers and 4 consumers that produce/consume 1-4 items at a time. If there are insufficient items for a consumer, it waits until they are available.
Course: Concurrent Data Structures, Monsoon 2020
Taught by: Prof. Govindarajulu Regeti
producer(n):
1. Lock on items
2. Produce "n" items
3. Notify all consumers
4. Unlock on items
... loop
(.notifyAll: Unlock + notifyAll + Lock)consumer(n):
1. Lock on items
2. Wait until atleast "n" items present
3. Consume "n" items
4. Unlock on items
... loop
(.wait: Unlock + wait + Lock)## OUTPUT
4 producers and 4 consumers ...
P1: items=0
P1: new items=1
P4: items=1
P4: new items=5
C4: items=5
C4: new items=1
C3: items=1
C3: too few items=1
C2: items=1
C2: too few items=1
P3: items=1
P3: new items=4
C1: items=4
C1: new items=3
P2: items=3
P2: new items=5
C2: new items=3
C3: new items=0
C2: items=0
C2: too few items=0
C4: items=0
C4: too few items=0
C3: items=0
C3: too few items=0
P4: items=0
P4: new items=4
C2: new items=2
C3: too few items=2
C4: too few items=2
C1: items=2
C1: new items=1
P3: items=1
P3: new items=4
C3: new items=1
C4: too few items=1
C3: items=1
C3: too few items=1
P1: items=1
P1: new items=2
C4: too few items=2
C3: too few items=2
...