使用TPL的Parallel.ForEach时跟踪进度

Question

以下是跟踪进度的最佳方法

long total = Products.LongCount();
long current = 0;
double Progress = 0.0;

Parallel.ForEach(Products, product =>
{
    try
    {
        var price = GetPrice(SystemAccount, product);
        SavePrice(product,price);
    }
    finally
    {
        Interlocked.Decrement(ref this.current);
    }});

我想将进度变量从0.0更新为1.0(当前/总)但我不想使用会对并行性产生负面影响的任何内容.

Answer 1

Jon的解决方案很好,如果您需要这样的简单同步,您的第一次尝试应该几乎总是使用lock.但是,如果你测量锁定减慢了太多的东西,你应该考虑使用类似的东西Interlocked.

在这种情况下,我将使用Interlocked.Increment增加当前计数,并更改Progress为属性:

private long total;
private long current;
public double Progress
{
    get
    {
        if (total == 0)
            return 0;
        return (double)current / total;
    }
}

…

this.total = Products.LongCount();
this.current = 0;

Parallel.ForEach(Products, product =>
{
    try
    {
        var price = GetPrice(SystemAccount, product);
        SavePrice(product, price);
    }
    finally
    {
        Interlocked.Increment(ref this.current);
    }
});

此外,您可能想要考虑如何处理异常,我不确定以异常结束的迭代应该计为完成.

Answer 2

由于您只是进行一些快速计算，因此通过锁定适当的对象来确保原子性：

long total = Products.LongCount();
long current = 0;
double Progress = 0.0;
var lockTarget = new object();

Parallel.ForEach(Products, product =>
{
    try
    {
        var price = GetPrice(SystemAccount, product);
        SavePrice(product,price);
    }
    finally
    {
        lock (lockTarget) {
            Progress = ++this.current / total;
        }
    }});