c# - 运行多个任务重用同一个对象实例

Question

这是一个有趣的。我有一个创建一堆 Task 的服务。目前列表中只配置了两个任务。但是，如果我在 Task 操作中放置一个断点并检查 schedule.Name 的值，则会使用相同的计划名称命中两次。但是，在计划列表中配置了两个单独的计划。谁能解释为什么任务重用循环中的最后一个时间表？这是范围问题吗？

// make sure that we can log any exceptions thrown by the tasks
TaskScheduler.UnobservedTaskException += new EventHandler<UnobservedTaskExceptionEventArgs>(TaskScheduler_UnobservedTaskException);

// kick off all enabled tasks
foreach (IJobSchedule schedule in _schedules)
{
    if (schedule.Enabled)
    {
        Task.Factory.StartNew(() =>
                                {
                                    // breakpoint at line below. Inspecting "schedule.Name" always returns the name 
                                    // of the last schedule in the list. List contains 2 separate schedule items.
                                    IJob job = _kernel.Get<JobFactory>().CreateJob(schedule.Name);
                                    JobRunner jobRunner = new JobRunner(job, schedule);
                                    jobRunner.Run();
                                },
                                CancellationToken.None, 
                                TaskCreationOptions.LongRunning, 
                                TaskScheduler.Default
                                );
    }
} // next schedule

Answer 1

如果您在 foreach 循环中使用临时变量，它应该可以解决您的问题。

foreach (IJobSchedule schedule in _schedules)
{
    var tmpSchedule = schedule;
    if (tmpSchedule.Enabled)
    {
        Task.Factory.StartNew(() =>
                                {
                                    // breakpoint at line below. Inspecting "schedule.Name" always returns the name 
                                    // of the last schedule in the list. List contains 2 separate schedule items.
                                    IJob job = _kernel.Get<JobFactory>().CreateJob(tmpSchedule.Name);
                                    JobRunner jobRunner = new JobRunner(job, tmpSchedule);
                                    jobRunner.Run();
                                },
                                CancellationToken.None, 
                                TaskCreationOptions.LongRunning, 
                                TaskScheduler.Default
                                );
    }


} //

有关闭包和循环变量的进一步引用，请参阅 Closing over the loop variable considered harmful