Lock queue lock 52 how to#
Lock queue lock 52 software#
Lock queue lock 52 code#
Lock queue lock 52 free#

Lock queue lock 52 free#

The problem with lock free algorithms is that they maximize contention by allowing contending threads to continue to contend. That's a key reason they're not used nearly as frequently. Lock free algorithms generally perform more poorly than lock-based algorithms. Std::cout << '1234 was generated!' << std::endl Std::this_thread::sleep_for(std::chrono::microseconds(100)) Checks if 1234 was generated by the producer, returns if found. Std::this_thread::sleep_for(std::chrono::microseconds(rand() % 1000)) Īuto consumer = std::async(std::launch::async, () Sleep for random duration (0-999 microseconds) * Using the blocking queue, the mutex must be unlocked here.

* Using the blocking queue, the mutex must be locked here.

Lock queue lock 52 code#

What could be the reason for the performance loss?Įxmple code (Producer/Consumer) // c++11 compiler and boost library requiredĪuto producer = std::async(std::launch::async, () However, boost::lockfree::spsc_queue does not have a function like this, which, for me, implies that it does not rely on the hardware and that is is always lockfree - on any machine. To find out if these instructions are supported, boost::lockfree::queue has a method called bool is_lock_free(void) const. However this has the obvious drawback of losing the lock-free property.

Lock queue lock 52 software#

If it is not available in hardware, it can be emulated in software using guards. Not all hardware supports the same set of atomic instructions. On the remote machine however, the average went up to 800 microseconds, which is slower than it was before.įirst I thought this might be because the remote machine might not support the lock-free implementation:

On my local VM I could see a huge performance gain, the average is now on 200 microseconds. Then I 'upgraded' the std::queue to boost::lockfree::spsc_queue, so I could get rid of the mutexes protecting the queue. Using std::queue, the average was almost the same on both machines: ~750 microseconds. The times were measured on 2 machines: My local Ubuntu VM and a remote server. I measured the average time which a specific operation on this queue requires. In any case we advice to perform benchmarks with different data structures for a specific workload.Until now I was using std::queue in my project. In general we advise to consider if lock-free data structures are necessary or if concurrent data structures are sufficient. Lock-free data structures will be a better choice in order to optimize the latency of a system or to avoid priority inversion, which may be necessary in real-time applications. In order to maximise the throughput of an application one should consider high-performance concurrent data structures. Therefore lock-free data structures are not necessarily the best choice for every use case. The definition of 'lock-free' and 'wait-free' only mention the upper bound of an operation. When discussing the performance of non-blocking data structures, one has to distinguish between amortized and worst-case costs. It would typically increase the overall workload (spinlocks can waste a lot of processor cycles). > lock-free queue, which I assumed would reduce workload. This means that any thread either sees the state before or after the operation, but no intermediate state can be observed. Instead of relying on guards, non-blocking data structures require atomic operations (specific CPU instructions executed without interruption). Non-blocking data structures do not rely on locks and mutexes to ensure thread-safety. See this example from boost (using boost::lockfree::queue).

Lock queue lock 52 how to#

> So I am unsure how to have threads without a lock, on a lock-free queue. Inside the loop the unique lock with an associated condition variable verifies if the queue is indeed not empty before popping. The benefit of a condition variable is that it sleeps while waiting, thus minimising CPU cycle usage.Ĭurrently there are 2 threads, each in a while (true) loop. The producer would then wake the condition with a notify(). The question I have is how to have multiple threads consume without spinning, Before using MPMCQueue.h I was using std::queue and using a unique_lock with a condition variable. The idea with a multi producer multi consumer lock-free queue is that multiple threads can push and pop to and from the queue without having a lock and optionally a condition variable (if a unique_lock). The reason I chose MPMCQueue.h is it looked simple enough, only having 180 lines of code. I decided to use MPMCQueue.h available on github, having found numerous examples. I've listened to Herb Stutter's youtube talks on lock-free data structures and I wanted to try and use a lock-free queue.