D并行循环

Question

首先,D如何创建并行foreach(底层逻辑)？

int main(string[] args)
{
    int[] arr;
    arr.length = 100000000;
    /* Why it is working?, it's simple foreach which working with
       reference to int from arr, parallel function return ParallelForeach!R
       (ParallelForeach!int[]), but I don't know what it is.
       Parallel function is part od phobos library, not D builtin function, then what
       kind of magic is used for this? */
    foreach (ref e;parallel(arr))
    {
        e = 100;
    }
    foreach (ref e;parallel(arr))
    {
        e *= e;
    }
    return 0;
}

第二,为什么它比简单的foreach慢？最后,如果我创建自己的taskPool(并且不使用全局taskPool对象),程序永远不会结束.为什么？

Answer 1

parallel返回一个ParallelForeach实现opApply(int delegate(...))foreach重载的struct(类型).

在调用时,struct向private提交一个并行函数,该函数submitAndExecute将相同的任务提交给池中的所有线程.

这样做:

scope(failure)
{
    // If an exception is thrown, all threads should bail.
    atomicStore(shouldContinue, false);
}

while (atomicLoad(shouldContinue))
{
    immutable myUnitIndex = atomicOp!"+="(workUnitIndex, 1);
    immutable start = workUnitSize * myUnitIndex;
    if(start >= len)
    {
        atomicStore(shouldContinue, false);
        break;
    }

    immutable end = min(len, start + workUnitSize);

    foreach(i; start..end)
    {
        static if(withIndex)
        {
            if(dg(i, range[i])) foreachErr();
        }
        else
        {
            if(dg(range[i])) foreachErr();
        }
    }
}

where workUnitIndex和shouldContinue是共享变量,dg是foreach委托

它变慢的原因仅仅是因为将函数传递给池中的线程并原子地访问共享变量所需的开销.

您的自定义池未关闭的原因可能是您没有关闭线程池 finish