CODEWITHSUNDEEP
javaperformance
bli00
bli00

Reputation: 2797

ConcurrentLinkedQueue and poll()

I'm going to use ConcurrentLinkedQueue and Java as an example to a more general question. Let me first explain the question with regards to ConcurrentLinkedQueue. Consider:

ConcurrentLinkedQueue<Integer> queue = new ConcurrentLinkedQueue<>();
while (true) {
    Integer item = queue.poll();
    if (item != null) {
        // do some stuff
    }
}

ConcurrentLinkedQueue::poll does not block. So if I was to run this code (and only this code) in its own thread. It would constantly do a redundant operation. Compare this to using something like LinkedBlockingQueue::take that blocks until something is available. How much of a difference does it make?

I realize that the question is very vague and specific to the language and data-structure's implementation. But the questions generalizes to something like this:

How resource consuming is it to run a forever loop that does some small, repetitive operation (like queue.poll())?

Because the operation is small but repetitive, each iteration finishes faster but the loop also runs at a higher frequency, which makes me think that it's worse.

Upvotes: 0

Views: 985

Answers (1)

Simulant
Simulant

Reputation: 20122

As you have an infinite number of operations to execute, scheduled by the while (true) loop, you would bring one CPU core to constantly 100% utilisation with the polling implementation. Which is not a good idea.

On the other hand take blocks the thread until an item is available. The thread can be put in the background, while other threads can be executed on the CPU. A blocked thread does not consume resources. It is wake up, when an item is available and only then scheduled to be executed on the CPU.

The context switch of the scheduling of a background thread might give you a slightly slower reaction time (this depends on the operation system implementation of thread scheduling and handling interrupts), but over all it should be way better than putting constantly 100% utilisation on the CPU.

Upvotes: 2

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