Thread local storage

Question

what is the best way to store some variable local to each thread?

score 57 · Answer 1 · edited Jun 03 '13 at 15:37

57

If you use .Net 4.0 or above, as far as I know, the recommended way is to use System.Threading.ThreadLocal<T> which also gives lazy initialization as a bonus.

edited Jun 03 '13 at 15:37

Sam Harwell

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answered Dec 30 '11 at 12:42

Ali Ferhat

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This method is also not limited to static fields. – Sam Harwell Jun 03 '13 at 15:37

score 44 · Accepted Answer · edited Jun 03 '13 at 15:36

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You can indicate that static variables should be stored per-thread using the [ThreadStatic] attribute:

[ThreadStatic]
private static int foo;

edited Jun 03 '13 at 15:36

Sam Harwell

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answered Nov 16 '10 at 02:49

James Kovacs

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Can I store static List of objects per-thread with this attribute? – Dainius Kreivys Oct 26 '16 at 13:22
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@DainiusKreivys Yes! No matter what the type of variable is, its unique instance will be maintained per thread as long as you are using `[ThreadStatic]` attribute. I did a quick test using `[ThreadStatic] private static List foo = new List { 20, 30 };`. Then, on another thread I initialized the same foo variable with a list containing three integers and when that thread ended my original list containing two elements referred by main thread remained intact. – RBT Jun 01 '17 at 02:02

score 19 · Answer 3 · edited Jun 03 '13 at 15:24

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Another option in the case that scope is an issue you can used Named Data Slots e.g.

    //setting
    LocalDataStoreSlot lds =  System.Threading.Thread.AllocateNamedDataSlot("foo");
    System.Threading.Thread.SetData(lds, "SomeValue");

    //getting
    LocalDataStoreSlot lds = System.Threading.Thread.GetNamedDataSlot("foo");
    string somevalue = System.Threading.Thread.GetData(lds).ToString();

This is only a good idea if you can't do what James Kovacs and AdamSane described

edited Jun 03 '13 at 15:24

NibblyPig

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answered Nov 16 '10 at 04:12

Conrad Frix

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Does named data slots work with the new `async Task` model? Is there something extra needed to make a slot available in the task? – Jaans Nov 13 '14 at 10:20
@Jaans See https://stackoverflow.com/questions/23555255/how-to-maintain-thread-context-across-async-await-model-in-c – Dai Nov 16 '21 at 09:04

score 7 · Answer 4 · answered Nov 16 '10 at 02:51

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Other option is to pass in a parameter into the thread start method. You will need to keep in in scope, but it may be easier to debug and maintain.

answered Nov 16 '10 at 02:51

AdamSane

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Thread local storage

4 Answers4

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