is it correct to use memory_order_relaxed in ProducerConsumerQueue::read

[Derek]

ProducerConsumerQueue::read has below code in the beginning to check if queue is empty, memory_order_relaxed looks bit suspicious. Presume the reason isEmpty is not called here is to avoid load readIndex twice, but isEmpty uses memory_order_consume on both readIndex and writeIndex.

    auto const currentRead = readIndex_.load(std::memory_order_relaxed);

    if (currentRead == writeIndex_.load(std::memory_order_acquire)) {

      // queue is empty

      return false;

    }

[Derek]

realized I was wrong when looking at write function. Since read will only be called by the reader thread, and readIndex is increased by reader thread only, memory_order_relaxed should be fine for reader thread.