What does this assert mean?

[mpuskas]

What does this assert mean?

[cameron314]

This could occur if there's more than one thread consuming from the queue.

Also, please update to the latest master, there were some fixes around signals while blocking on the semaphore at one point.

[mpuskas]

Good to know, thanks for the quick reply! We'll update to latest master and verify that we don't have multiple consumers.

[poor1017]

@cameron314 Hi, this issue is not fixed with the latest master. Can I just remove this assert directly? Thanks!

[cameron314]

No, if this assert is firing it indicates a bug somewhere, either in the queue or in the calling code. Can you share an example that reproduces?

[poor1017]

Here is the example source code:

#include <unistd.h>

#include <iostream>
#include <thread>

#include "readerwriterqueue.h"

typedef moodycamel::BlockingReaderWriterQueue<int> InputQueue;
auto input_queue = std::make_shared<InputQueue>();

void
startWorkLoop()
{
    while (true) {
        int input = 0;
        input_queue->wait_dequeue(input);
    }
}

void
startClientLoop()
{
    while (true) {
        sleep(2);
        std::cout << "enqueue ..." << std::endl;
        int input = 1;
        input_queue->enqueue(input);
    }
}

int
main(int argc, char **argv)
{
    std::shared_ptr<std::thread> thread1 = std::make_shared<std::thread>(&startWorkLoop);
    std::shared_ptr<std::thread> thread2 = std::make_shared<std::thread>(&startWorkLoop);

    std::shared_ptr<std::thread> client = std::make_shared<std::thread>(&startClientLoop);

    thread1->join();
    thread2->join();
    client->join();

    return 0;
}

Here is the CMakeLists.txt

cmake_minimum_required(VERSION 3.10.1)
project(verify)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -std=c++17 -pthread -W")
set(CMAKE_BUILD_TYPE "Debug")

add_executable(main main.cc)

OS: Ubuntu 20.04

[cameron314]

You have one producer thread but two consumer threads. This is an SPSC queue (supports single consumer only).

[poor1017]

This could occur if there's more than one thread consuming from the queue.

Also, please update to the latest master, there were some fixes around signals while blocking on the semaphore at one point.

I thought this had been fixed.

B.T.W. If I want to support multiple producers multiple consumers and keep consuming in order, what should I use?

Thanks.

[MagicKim]

This could occur if there's more than one thread consuming from the queue.
Also, please update to the latest master, there were some fixes around signals while blocking on the semaphore at one point.

I thought this had been fixed.

B.T.W. If I want to support multiple producers multiple consumers and keep consuming in order, what should I use?

Thanks.

Have you solved this issue? I am in a single producer and single consumer mode, and I have also encountered this error. I receive moodycamel::BlockingReaderWriterQueue enqueue from multiple network interfaces, and then wait_dequeue in a sub-thread.

[cameron314]

I thought this had been fixed.

The issue was with your example code.

B.T.W. If I want to support multiple producers multiple consumers and keep consuming in order, what should I use?

You'd need to find another queue implementation. I don't have an MPMC queue with global ordering.

I receive moodycamel::BlockingReaderWriterQueue enqueue from multiple network interfaces, and then wait_dequeue in a sub-thread.

Are you enqueueing from multiple threads?