Hey guys

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Hey guys,

How do I create thread-local variables in Delphi? Do I use some class or attribute for flag that the variable is thread-local? Do I use "threadvar" modifier for this purpose?

Thanks in advance :D

Comments

  1. Andrea RaimondiMay 8, 2015 at 10:43 PM

    threadvar .

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  2. A. BouchezMay 9, 2015 at 12:10 AM

    Yes, threadvar are how to create thread-local variables. But they are global variables, not tied to particular class.
    Be aware that threadvar have a cost: each threadvar will consume some resource for all threads, even if it is not used.
    And note also that there is no mean of automatic releasing the memory used by a threadvar: for instance, a string, an interface or a dynamic array won't be released automatically (as a standard var) when the thread finishes. You have to release the memory by hand.

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  3. Paul TOTHMay 10, 2015 at 1:43 AM

    what is the benefice of a threadvar against a TThread member ? I'm not a 100% OOP man, but I don't remember any case where I need a per thread global var.

    BTW Sytem.Threading TTask class use :
     class threavar FCurrentTask: TTask

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  4. A. BouchezMay 10, 2015 at 1:46 AM

    A class threadvar is just a global variable in disguise. ;) Just hide the global variable within the class type namespace...
    Sometimes, a global threadvar is needed, if you need to retrieve, e.g. the execution context. I use a threadvar e.g. to store the REST request context, where it is executed outside the scope of the TThread (which is part of the protocol implementation, so several TThread classes may appear).

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