如何通过替换顺序代码的 while 循环来添加 OpenMP for 循环

Question

以下代码是按顺序编写的。我想通过将 while 循环替换为 for 循环来实现 OpenMP，但不知道如何执行此操作。我知道 OpenMP 语法但无法实现。

进行并行的原因是为了检查顺序和并行技术之间的性能。有什么帮助吗？

  void block::mine_block(uint32_t difficulty) noexcept
{
    string str(difficulty, '0');

    auto start = system_clock::now();

    while (_hash.substr(0, difficulty) != str)
    {
        ++_nonce;
        _hash = calculate_hash();
    }

    auto end = system_clock::now();
    duration<double> diff = end - start;

    cout << "Block mined: " << _hash << " in " << diff.count() << " seconds" << endl;
}

@Matthieu Brucher - 这会是解决方案吗？

#pragma omp parallel    // start the parallel region
{
    #pragma omp single  // let the while loop execute by one thread and generate tasks
    while (time < TotalTime){

        #pragma omp task
        {
            // this code will be a task that may be executed immediately on a different core or deferred for later execution
        }

    } // end of while loop and single region
    // at this point we also wait until all tasks that were created have finished

} // end of parallel region

通过实现上述代码

#pragma omp parallel                        
    {
        #pragma omp single                      
        while (_hash.substr(0, difficulty) != str) {
            #pragma omp task                    
            {
                ++_nonce;
                _hash = calculate_hash();
            }
        }
    }

Answer 1

问题是您的循环中有依赖项。因此，不可能按原样并行化它。

一个好的第一种方法是使用多个起点并使用多个线程来创建新的哈希值。然后当其中一个线程找到一个很好的匹配时，你会打开一个全局 bool 标志并停止所有线程。