TThread :: Synchronize（）>读取表单组件属性时？

Question

My Environment:

• C++ Builder XE4
• using VCL component

I have a question about TThread:Synchronize().

Usually, I use Synchronize() when I update Form component (eg Text->Caption) from the TThread routine().

__fastcall TThreadSample::Execute()
{
    Synchronize(&updateFormText);
}

where the updateFormText() is a function to update Form Text->Caption.

On the other hand, when I read caption from the Form text, I used followings without Synchronize().

__fastcall TThreadSample::DoRead()
{
    String acap = CFormXXX::GetTextCaption();
}

void __fastcall CFormXXX::GetTextCaption()
{
    return FormXXX->TextXXX->Text;
}

Question: Do I have to use Synchronize() also when I read Form component properties from a TThread routine?

Answer 1

Yes .

Properties are in fact syntactic sugar for function calls. Reading one also means a function is called ( well, most of the time ^[1] ).

In other words, if, in your code, you do:

x = MyVCLObj->SomeProperty;

the C++Builder compiler in fact generates a call to the (usually private) getter function for the property:

x = MyVCLObj->GetSomeProperty();

That runs in the context of the main thread, so it must be accessed using Synchronize() .

---

[1] I know that this is not true for all properties, and you may well be accessing the member field (eg FSomeProperty ) directly, but do you really want to check the docs each time? And this may change in a future version of the class too. So you should generally treat a property access like a function call.