c++ - OpenMP "master"编译指示不得包含在 "parallel for"编译指示中

Question

为什么英特尔编译器不允许我指定 openmp parallel for block 中的某些操作应该仅由主线程执行？

如果没有这种功能，我该如何实现我想要实现的目标？

我想做的是通过并行回调来更新进度条:

long num_items_computed = 0;

#pragma omp parallel for schedule (guided)
for (...a range of items...)
{
    //update item count
    #pragma omp atomic
        num_items_computed++;

    //update progress bar with number of items computed
    //master thread only due to com marshalling
    #pragma omp master
        set_progressor_callback(num_items_computed);

    //actual computation goes here
    ...blah...
}

我只希望主线程调用回调，因为如果我不强制执行(比如使用 omp critical 来确保一次只有一个线程使用回调)，我会得到以下运行时异常:

The application called an interface that was marshalled for a different thread.

...因此希望将所有回调保留在主线程中。

提前致谢。

Answer 1

#include <omp.h>
void f(){}
int main()
{
#pragma omp parallel for schedule (guided)
    for (int i = 0; i < 100; ++i)
    {
        #pragma omp master
        f();
    }
    return 0;
}

编译器错误 C3034OpenMP“master”指令不能直接嵌套在“parallel for”指令中Visual Studio 2010 OpenMP 2.0

可能是这样:

long num_items_computed = 0;

#pragma omp parallel for schedule (guided)
for (...a range of items...)
{
    //update item count
    #pragma omp atomic
        num_items_computed++;

    //update progress bar with number of items computed
    //master thread only due to com marshalling
    //#pragma omp master it is error
    //#pragma omp critical it is right
    if (omp_get_thread_num() == 0) // may be good
        set_progressor_callback(num_items_computed);

    //actual computation goes here
    ...blah...
}