SharedVariable1.cs

public void Execute(IServiceProvider serviceProvider)
{
   // Obtain the tracing service
   ITracingService tracingService = (ITracingService)serviceProvider.GetService(typeof(ITracingService));

   // Obtain the execution context from the service provider.  
    IPluginExecutionContext executionContext = (IPluginExecutionContext)
    serviceProvider.GetService(typeof(IPluginExecutionContext))
    
    int counter = 0;

    //Check existence of shared variable and fetch the value from executionContext
    if (executionContext.ParentContext != null && executionContext.ParentContext.SharedVariables.ContainsKey("Counter"))
    {
        counter = (int)executionContext.SharedVariables.ContainsKey("Counter");
    }
    
    executionContext.SharedVariables.Add("Counter",counter++);
    
    // your logic

}