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    <p>Writing a thread safe code in Delphi involves the basic care you would have in any other language, which means to deal with <strong>race conditions</strong>. A race condition happens when different threads access the <strong>same data</strong>. A good way to deal with that is to declare an instance of <strong>TCriticalSection</strong> and wrap the <em>dangerous</em> code in it.</p> <p>The code below shows a getter and a setter of a property that, by hypotesis, has a race condition.</p> <pre><code>constructor TMyThread.Create; begin CriticalX := TCriticalSection.Create; end; destructor TMyThread.Destroy; override; begin FreeAndNil(CriticalX); end; function TMyThread.GetX: string; begin CriticalX.Enter; try Result := FX; finally CriticalX.Leave; end; end; procedure TMyThread.SetX(const value: string); begin CriticalX.Enter; try FX := Value; finally CriticalX.Leave; end; end; </code></pre> <p>Notice the use of a single instance of <strong>TCriticalSection</strong> (<strong>CriticalX</strong>) to serialize the access to the data member <strong>FX</strong>.</p> <p>However, with Delphi you have an aditional consideration! VCL is not thread safe, so in order to avoid VCL race conditions, any operation that results in <strong>screen changing</strong> must run in the main thread. You get that by calling such a code inside a <strong>Synchronize</strong> method. Considering the class above, you should do something like this:</p> <pre><code>procedure TMyThread.ShowX; begin Synchronize(SyncShowX); end; procedure TMyThread.SyncShowX; begin ShowMessage(IntToStr(FX)); end; </code></pre> <p>If you have <strong>Delphi 2010</strong> or later, there is an easier way that makes use of anonymous methods:</p> <pre><code>procedure TMyThread.ShowX; begin Synchronize(procedure begin ShowMessage(IntToStr(FX)); end); end; </code></pre> <p>I hope this helps!</p>
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    1. COCan you please stop calling **critical section** s - and even **event** s in an other post - **Mutex**? It could be a source of confusion if you know what a Mutex is, and can not help understand your code if you don't.
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