使用TaskFactory.StartNew内部循环：状态对象不起作用

Question

First of all I initialize searchContext list:

var searchContexts = new List<SearchContext>();

for (byte pageNumber = 1; pageNumber < 6; pageNumber++)
{
    var searchContext = GetSearchContext(context, vendor, workRequest, pageNumber);

    searchContexts.Add(searchContext);
}     

where SearchContext is defined as follows:

public class SamoSearchContext
{
    public WorkRequest WorkRequest 
    { get; set; }

    public Vendor Vendor 
    { get; set; }

    public WorkResponse WorkResponse
    { get; set; }

    public byte PageNumber 
    { get; set; }
}

Then for each searchContext start new thread:

var tasks = new Task[taskCount];         
var taskScheduler = TaskScheduler.Default;

var index = 0;
foreach (var searchContext in searchContexts)
{

    var ssc = searchContext;

    tasks[index] = Task.Factory.StartNew((obj) => SendSearchRequest(ssc, token),
                ssc, token, TaskCreationOptions.AttachedToParent, taskScheduler);

    index++;
 }

SendSearchRequest() method call outside service to get the next search result page (by pageNumber). Here is the implementation:

 private void SendSearchRequest(SamoSearchContext context, CancellationToken token)
    {
        if (token.IsCancellationRequested)
            return;

        var workRequest = context.WorkRequest;

        workRequest.@params.PRICE_PAGE = context.PageNumber;

        context.WorkResponse = ServiceClient.GetWorkResponse<WorkRequest, WorkResponse>(ServiceOperations.GetPrice, workRequest, context.Vendor.UniformCode, context.Vendor.ID);

}

But reading logs after the loop execution I see that pageNumber is always = 4.

Could not understand what's wrong?

Answer 1

The matter is when I create SearchContext list, I indiscreetly used copy workRequest by reference (newSearchContext.WorkRequest = workRequest). So all SearchContexts in the list reference to the one workRequest instance. Then, in SendRequest() each time I've changed PRICE_PAGE field of this one instance. So it was the same, a bit strange that it always = 4, but not a random number from 1 to 5.

But, nevertheless, now I implement Clone() extension method for WorkRequest which copy the object field by field into a new instance. Now it works. Thanks everybody for participation!