\page whats_new_AC_2_0 What's new in ApplicationCore 2.0
\section whats_new_2_0_initial_value Initial value propagation
- Initial values are propagated from the control system, from all application modules and all device variles.
- ApplicationModules are waiting to receive an initial value for *all* variables before entering the main loop. The code in the main loop can rely on having initial values for all inputs.
- As a consequence all ApplicationModules have to write initial values to all of their outputs at application start because these outputs usually are inputs to other modules.
\subsection whats_new_2_0_initial_value_app_change Required changes to existing applications
- Each application module has to **write all of its outputs** once **before the first blocking read**
- This can be done in two places
- Normally the initial values of the outputs are computed from the inital values of the inputs at the beginning of the ApplicationModule::mainLoop(). This is the preferred way.
- For constants or to break circulat dependencies between modules, initial values of the outpus can be written in ApplicationModule::prepare(). In this case they cannot be based in the initial values of the inputs, which are not available at this point in time. That's why sending initial values in ApplicationModule::prepare() should be avoided if possible.
@code
// Usual layout of an ApplicationModule::mainLoop() in AppclicationCore 1.x
// This can cause a blocking server in AppclicationCore 2.0
void mainLoop(){
while(true){
readAll(); // start with a blocking read
doComputationsFromInputs();
writeAll(); // write at the end of the loop
}
}
@endcode
@code
// Typical layout of an ApplicationModule::mainLoop() in AppclicationCore 2.0
void mainLoop(){
// when entering the main loop, all inputs have valid initial values
while(true){
doComputationsFromInputs(); // in the first round calcuations are based on initial values
writeAll();
readAll(); // blocking read before returning to the beginning of the loop
