Thanks Alexander, that's exactly what I was suspecting. Parallel.ForEach() may not necessarily be using different threads to execute the tasks. Also, the latest stuff that can be implemented with async/await levers high parallelism without the need of multithreading. Only I'm afraid you have to post this on JIRA as well because Husain is probably not subscribed to the mailing list.

On 2017-04-07 10:31, Alexander Houben wrote:
Hello Husain,

I think the observed behavior lies in the implementation of Parallel.ForEach. All your assumptions seem correct to me except that Parallel.ForEach does not execute its actions on a separate thread or separate task each.

If you look at mscorlib with ILSpy and find System.Threading.Tasks.Parallel.ForEach you'll see that it does some heavy optimization to find the right ratio of threads/tasks and load.

IMHO it may be reusing a task where your "x-correlation-id" was set (if (i==3)) for other values of i, this is why you are seeing multiple modified log outputs.

cheers,
alex

On Fri, Apr 7, 2017 at 10:04 AM, Dominik Psenner (JIRA) <j...@apache.org <mailto:j...@apache.org>> wrote:


        [
    
https://issues.apache.org/jira/browse/LOG4NET-562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15960445#comment-15960445
    
<https://issues.apache.org/jira/browse/LOG4NET-562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15960445#comment-15960445>
    ]

    Dominik Psenner commented on LOG4NET-562:
    -----------------------------------------

    Have you tried to include the actual thread that the code executes
    in by logging System.Threading.Thread.CurrentThread.ManagedThreadId?

    > LogicalThreadContext is not per Thread
    > --------------------------------------
    >
    >                 Key: LOG4NET-562
    >                 URL:
    https://issues.apache.org/jira/browse/LOG4NET-562
    <https://issues.apache.org/jira/browse/LOG4NET-562>
    >             Project: Log4net
    >          Issue Type: Bug
    >          Components: Other
    >    Affects Versions: 2.0.8
    >         Environment: Windows 10, Visual Studio 17, .NET
    Framework 4.5.2
    >            Reporter: Husain Alshehhi
    >
    > LogicalThreadContext values are spread to many threads when they
    shouldn't.
    > This is an example:
    > {code:title=console.cs|borderStyle=solid}
    >             LogicalThreadContext.Properties["x-corralation-Id"]
    = "original-value";
    >             var list = new List<int> {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
    >             Parallel.ForEach(list, (i) =>
    >             {
    >                 if (i == 3)
> LogicalThreadContext.Properties["x-corralation-Id"] =
    "modified-value";
    >                 logger.Info($"thread {i}.");
    >             });
    > {code}
    > this is the result
    > {code:title=badresult.txt|borderStyle=solid}
    > {"timestamp":"2017-04-05T12:31:41.117Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 1.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.132Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 3.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 4.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 6.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.274Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 8.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.274Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 0.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.219Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 7.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.179Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 5.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 2.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.234Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 9.", "data":(null)}
    > {code}
    > This is what I was expecting:
    > {code:title=goodresult.txt|borderStyle=solid}
    > {"timestamp":"2017-04-05T12:31:41.117Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 1.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.132Z", "level":"INFO",
    "x-corralation-Id" : "modified-value", "logger":"logger",
    "message":"thread 3.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 4.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 6.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.274Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 8.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.274Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 0.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.219Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 7.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.179Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 5.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.273Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 2.", "data":(null)}
    > {"timestamp":"2017-04-05T12:31:41.234Z", "level":"INFO",
    "x-corralation-Id" : "original-value", "logger":"logger",
    "message":"thread 9.", "data":(null)}
    > {code}



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