In multi-threaded programming, memory barriers play a vital role in ensuring the correct ordering of memory operations. One of the memory barrier types commonly used is the Acquire-Release memory barrier.

The Acquire-Release memory barrier is a synchronization primitive that enforces an ordering constraint between memory operations. It ensures that certain memory operations that occur before the barrier are visible to other threads when they execute certain memory operations that come after the barrier.

How Does Acquire-Release Memory Barrier Work?

When a thread reaches an Acquire memory barrier, it enforces a synchronization point where all the memory operations preceding the barrier must complete and become visible to other threads before any memory operations following the barrier can be executed.

On the other hand, when a thread encounters a Release memory barrier, it ensures that all the memory operations following the barrier complete and become visible to other threads before any memory operations preceding the barrier can be executed.

Example Usage of Acquire-Release Memory Barrier

Let’s consider a scenario where multiple threads are accessing shared data protected by a lock. By using an Acquire-Release memory barrier, we can ensure that the changes made to the shared data by one thread are visible to other threads when they access the same data.

Here’s an example in C++ illustrating the usage of Acquire and Release memory barriers:

#include <atomic>

std::atomic<int> sharedData;
std::atomic<bool> dataReady;

void ThreadA()
{
    // Perform some computations to update the shared data
    sharedData.store(42, std::memory_order_release);

    // Set the dataReady flag to indicate that data is ready for other threads
    dataReady.store(true, std::memory_order_release);
}

void ThreadB()
{
    while (!dataReady.load(std::memory_order_acquire))
    {
        // Wait until data is ready
    }

    // Acquire the shared data
    int value = sharedData.load(std::memory_order_acquire);

    // Process the shared data
    // ...
}

In the above code, ThreadA updates the sharedData variable and sets the dataReady flag to indicate that data is ready for other threads. ThreadB waits until the dataReady flag is set and then acquires the sharedData using Acquire memory ordering.

By using Acquire-Release memory barriers, we ensure that the changes made by ThreadA to the sharedData variable are visible to ThreadB when it acquires the data.

#programming #multithreading