Parallel Task Not working properly

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When I run this code and Parallel == true all tasks access the properties of one task as they are static, so all the tasks that run will access the same proberties and the program will crash.

C#

private List<BackupTask> backupTasks = new List<BackupTask>();

public void RunBackup()
        {
            if (Parallel == false)
            {
                foreach (var item in backupTasks)
                {
                    item.RunBackup();
                }
            }
            else
            {
                List<Task> tasks = new List<Task>();
                foreach (var item in backupTasks)
                {
                    var t = Task.Factory.StartNew(() =>
                    {
                        item.RunBackup();
                    });
                    tasks.Add(t);
                }
                Task.WaitAll(tasks.ToArray());
            }
        }

Posted 7-Jan-13 1:57am

_Nizar

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Comments

Jibesh 7-Jan-13 14:19pm

You need to provide some more details about the crash and what's happening inside the method item.RunBackup, one method is to put the lock statement around your shared resources.

2 solutions

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_Nizar · Answer 1 · 2013-01-27T23:42:00

C#

public void RunBackup()
        {
            if (Parallel == false)
            {
                foreach (var item in backupTasks)
                {
                    item.RunBackup();
                }
            }
            else
            {
                //List<Task> tasks = new List<Task>();
                //foreach (var item in backupTasks)
                //{
                //    var t = Task.Factory.StartNew(() =>
                //    {
                //        item.RunBackup();
                //    });
                //    tasks.Add(t);
                //}
                //Task.WaitAll(tasks.ToArray());
                var tasks = new Task[backupTasks.Count];
                for (var i = 0; i < backupTasks.Count; i++)
                {
                    var x = i;
                    tasks[i] = Task.Factory.StartNew(() => backupTasks[x].RunBackup());
                }
                Task.WaitAll(tasks);
            }
        }

OriginalGriff · Answer 2 · 2013-01-07T02:10:00

Solution 1

Use the lock statement[^] - the link includes examples.

Posted 7-Jan-13 2:10am

OriginalGriff

Comments

_Nizar 8-Jan-13 2:48am

Using lock statement will be benefit if I'm using one object and i access its method from many threads.
But in my case I'm using one object per Task they share nothing, so why the access the same property (class variable).
I want to publish my program here but after i have fixed this problem.

_Nizar 8-Jan-13 4:31am

the tasks are independent from each other

OriginalGriff 8-Jan-13 4:34am

Except you say that they are using static data...
"all tasks access the properties of one task as they are static, so all the tasks that run will access the same proberties"

Which means they aren't independent.

_Nizar 9-Jan-13 5:37am

The data are not static.
Now after some investigation I found that when I run the code using the debugger so I give all the tasks time to finish before the next task will begin very thing work fine.
But if I run the code using also the debugger but with out giving the firs task time to finish before the next task the last task runs twice so a conflicting happen and the first task never runs.
I'm ready to give my program for investigation.
I have only this problem ales it is working fine in sequence.

thank you for your support