I am working on a custom VCL-only date edit component. Am planning on using the System.SysUtils.FormatDateTime function to convert a TDate to a string. There are two versions of FormatDateTime--one is thread-safe and the other is not. Since the VCL is not thread-safe, should I prefer the thread-safe version or is the non thread-safe version okay to use?
0
votes
Visual components are not thread-safe, so it doesn't matter which you use. The component cannot be used from a thread.
- Ken White
The overload is not just about thread safety. It's more about customizing the format settings without affecting global settings. If your component needs to convert a date/time to a string in a specific format, use the overload, regardless of threading.
- Remy Lebeau
2 Answers
2
votes
tl;dr use threadsafe version
If you use the non threadsafe version then you constrain any consumer of your component not to use that same non threadsafe version in a thread.
That's not an unreasonable constraint by any measure. Using the non threadsafe version is only really viable in a program that never does so away from the main thread. So a program would have to be breaking the rules in the first place for your component to be caught up in the fallout.
Having said that, a component author should as a principle avoid making any assumptions about the consuming program. So best practice is to call the threadsafe version. Then there can be no debate. Your program cannot be involved in any thread safety issue with these locale global variables.
1
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So long the caller will be the main thread, it doesn't matter if you choose a non thread safe variant of the function. Which in this case seems to be (if you are not creating inside of your component a worker thread from which you were calling that function, and you adhere to the rule that you won't use your control inside any worker thread, you'll be safe with it).
But there's more to consider. If you have recent Delphi version and keep UpdateFormatSettings property enabled, a globally declared format settings variable used in non thread safe overload of the FormatDateTime function will get updated when the user modifies their local settings on their system. I can't say anything about a control notification (so you could update the output) because I'm having only D2009 by hand right now and these changes has been added later.
