Java Reference
In-Depth Information
Figure 12.1.
TimedPutTakeTest
with Various Buffer Capacities.
It may be somewhat puzzling at first that adding a lot more threads degrades performance
only slightly. The reason is hard to see from the data, but easy to see on a CPU performance
meter such as
perfbar
while the test is running: even with many threads, not much compu-
tation is going on, and most of it is spent blocking and unblocking threads. So there is plenty
of CPU slack for more threads to do the same thing without hurting performance very much.
However, be careful about concluding from this data that you can always add more threads to
a producer-consumer program that uses a bounded buffer. This test is fairly artificial in how it
simulates the
application
; the producers do almost no work to generate the item placed on the
queue, and the consumers do almost no work with the item retrieved. If the worker threads in
a real producer-consumer application do some nontrivial work to produce and consume items
(as is generally the case), then this slack would disappear and the effects of having too many
threads could be very noticeable. The primary purpose of this test is to measure what con-
straints the producer-consumer handoff via the bounded buffer imposes on overall through-
put.
