priority_queue.md

Priority Queue

When to use the Priority Queue

The Priority Queue should be used when there are distinct priorities between elements to be enqueued, for instance different urgency signals between threads or packets of different priorities.

Note: At the moment, the Queue is only meant to be used for trivial types.

How to use

Shown here is an example of typical use:

• Initialization

#include "lockfree.hpp"
// --snip--
lockfree::spsc::PriorityQueue<Event, 64, 3> queue_events;

• Producer thread/interrupt

Event event = actor1.Run();
// --snip--
while(!queue_events.Push(event, priority)) {}

• Consumer thread/interrupt

Event event_in;
bool read_success = queue_events.Pop(read);
if (read_success) {
    actor2.ProcessEvent(event_in);
}

There is also a std::optional API for Pop:

auto read = queue_events.PopOptional();

if (read) {
    actor2.ProcessEvent(read);
}

Performance and memory use

This implementation has O(1) time complexity for Push and O(current_max_priority) for Pop making it extremely fast.

On the other hand the memory usage is a function of size * priority_count, so adequately chosing the number of priorities is necessary.