使用Linq to SQL进行多线程处理

Question

我正在构建一个应用程序,它要求我使用DataContext的内部线程.我的应用程序不断抛出InvalidOperationException类似于:

There is already an open DataReader associated with this Command which must be closed first

ExecuteReader requires an open and available Connection. The connection's current state is connecting

这些例外是间歇性的.

这是我的代码片段:

var repo = new Repository();
var entities = repo.GetAllEntities();
foreach (var entity in entities)
{
    ThreadPool.QueueUserWorkItem(
        delegate
        {
            try
            {
                 ProcessEntity(entity);
            }
            catch (Exception)
            {
                throw;
            }
        });
}

我认为将一个实体传递给主线程中的一个线程可能会有一些问题,因为一旦我尝试访问一个属性,错误似乎就会抛出entity.

任何人都知道为什么会发生这种情况以及如何解决它？

更新

这是我决定采用的:

var events = new Dictionary<int, AutoResetEvent>();
var repo = new Repository();
var entities = repo.GetAllEntities();
foreach (var entity in entities)
{
    events.Add(entity.ID, new AutoResetEvent(false));
    ThreadPool.QueueUserWorkItem(
        delegate
        {
            var repo = new Repository();
            try
            {
                ProcessHierarchy(repo.GetEntity(entity.ID), ReportRange.Weekly);
            }
            catch (Exception)
            {
                throw;
            }
            finally
            {
                events[entity.ID].Set();
            }
        });
}

WaitHandle.WaitAll(events.Values.ToArray());

欢迎改进/建议,但这似乎已经成功了.

Answer 1

抛出异常,因为实体的某些属性在先前的读取器尚未关闭时执行新查询.您不能同时对数据上下文执行多个查询.

作为一种解决方法,您可以"访问"您访问的属性,ProcessEntity()并在线程之前运行SQL.

例如:

var repo = new Repository();
var entities = repo.GetAllEntities();
foreach (var entity in entities)
{
    var localEntity = entity; // Verify the callback uses the correct instance
    var entityCustomers = localEntity.Customers;
    var entityOrders = localEntity.Orders;
    var invoices = entityOrders.Invoices;
    ThreadPool.QueueUserWorkItem(
        delegate
        {
            try
            {
                 ProcessEntity(localEntity);
            }
            catch (Exception)
            {
                throw;
            }
        });
}

此解决方法将仅在主线程上执行SQL,并且处理将在其他线程中完成.由于所有查询都在单个线程中完成,因此您在这里放松了一些效率.如果你有很多逻辑ProcessEntity()并且查询不是很重,那么这个解决方案很好.