Tuesday, 15 December 2015
Producer/Consumer Problem:
Producers create items of some kind and add them to
a data structure; consumers
remove the items and process them.
Example: Event-driven programs are a good example. An
“event” is something that happens that requires the program to respond: the
user presses a key or moves the mouse, a block of data arrives from the disk, a
packet arrives from the network, a pending operation completes.
Whenever
an event occurs, a producer thread creates an event object and adds it to the
event buffer. Concurrently, consumer threads take events out of the buffer and
process them. In this case, the consumers are called “event handlers.”
Producer-consumer with
infinite buffer:
Basic Producer Code:
event =
waitForEvent()
buffer.add(event)
Basic
consumer code:
event
= buffer.get()
event.process()
Producer-consumer
initialization:
1 mutex =
Semaphore(1)
2 items =
Semaphore(0)
3 local event
Producer
solution:
1 event =
waitForEvent()
2 mutex.wait()
3
buffer.add(event)
4 mutex.signal()
5 items.signal()
Consumer
solution:
1 items.wait()
2 mutex.wait()
3 event =
buffer.get()
4 mutex.signal()
5 event.process()
Producer-consumer with a finite
buffer:
Initialization:
1 mutex = Semaphore(1)
2 items = Semaphore(0)
3 spaces = Semaphore(buffer.size())
consumer solution
1 items.wait()
2 mutex.wait()
3 event = buffer.get()
4 mutex.signal()
5 spaces.signal()
6 event.process()
producer solution:
1 event = waitForEvent()
2
3 spaces.wait()
4 mutex.wait()
5 buffer.add(event)
6 mutex.signal()
7 items.signal()
