Question

我使用Parallel.ForEach来处理并发字典集合。 ConcurrentDictionary包含Key和Byte字段。

concurrentDictionary - 这里是Concurrent Dictionary集合。

Parallel.ForEach(concurentDictionary, (item) =>
{
    var mailObject = dbContext.MailObjects.Where(x=> x.MailObjectId == item.key).Select(y=> y);
    mailObject.MailBody = ConvertToPdf(item.Value.MailBody);
} 
dbContext.SaveChanges();

如果任何特定项目的最大时间设置为60秒，我想设置超时。如果它需要超过60秒，我想退出并且不保存该特定项目。其余项目应通过dbContext.SaveChanges()方法保存。如何在Parallel.ForEach中实现这一目标？

Answer 1

这样的事情可能接近你想要的东西。

CancellationTokenSource cts = new CancellationTokenSource();

ParallelOptions parallelOptions = new ParallelOptions();
parallelOptions.CancellationToken = cts.Token;
parallelOptions.MaxDegreeOfParallelism = System.Environment.ProcessorCount;

Timer timer = new Timer(callback => { cts.Cancel(); }, null, 60*1000, Timeout.Infinite);

try
{
    Parallel.ForEach(concurentDictionary, parallelOptions, (item) =>
    {
        var mailObject = dbContext.MailObjects.Where(x => x.MailObjectId == item.key).Select(y => y);
        mailObject.MailBody = ConvertToPdf(item.Value.MailBody);
        parallelOptions.CancellationToken.ThrowIfCancellationRequested();
    });
}
catch (OperationCanceledException e)
{
    // Log the cancellation event...
}
finally
{
    dbContext.SaveChanges();
    cts.Dispose();
}

这里是解决方案的完整修订版，为每次迭代调整计时器的范围。如果一个（或多个）超过时间限制，它利用loopstate来停止迭代，而不是取消令牌。这不依赖于异常来退出循环。但是，在编写此代码时，任何异常也将触发所有循环停止。请注意，这不会立即停止所有循环，并将完成现有循环的执行，直到它们也完成或超时。

{
    if (Parallel.ForEach(concurentDictionary, (item, loopState) =>
        {
            Timer timer = new Timer(callback => { loopState.Stop(); }, null, 60 * 1000, Timeout.Infinite);

            try
            {
                if (loopState.ShouldExitCurrentIteration || loopState.IsExceptional)
                    loopState.Stop();

                var mailObject = dbContext.MailObjects.Where(x => x.MailObjectId == item.key).Select(y => y);
                mailObject.MailBody = ConvertToPdf(item.Value.MailBody);

                if (loopState.ShouldExitCurrentIteration || loopState.IsExceptional)
                    loopState.Stop();
            }
            catch (Exception)
            {
                loopState.Stop();
                throw;
            }
            finally
            {
                timer.Dispose();
            }
        }
    ).IsCompleted)
    {
        // All events complete
    }

}
catch (AggregateException)
{
    // Execution will not get to this point until all of the iterations have completed (or one 
    // has failed, and all that were running when that failure occurred complete).
}

在Parallel.ForEach中为项设置超时

1 个答案: