InstallAware

AFAIK according to MSI guidelines it is not recommended that more than one (MSI) installation is running at a time for instance nested installations are well known troublemakers. I know from InstallShield Setups that they automatically prevent that two setups entering execution sequence simultaneously. IA Setups has no such check and it is possible that multiple setups are entering their execution sequence (Apply Install) at the same time. I already observed some problems if I for instance run a big InstallShield created setup and then a InstallAware generated setup. It seems like both are blocking each other. The IA setup is in a loop (progresstext is "Windows Installer..") and does not go on until the IS setup has finished.
In the other way round (start IA setup and then IS setup) it seems to work: running IA does not prevent IS setup from entering his execution sequence. Also two IA setups are running apparently without trouble at the same time.

Now my question: can I run two IA generated installations at the same time and set mymind at rest or should I implement mechanisms that prevent such a scenario?

Dear alibaba,

In fact, you do not need to worry about this at all - the InstallAware engine works with a mutex, and other setups wait until this mutex is free. This will never cause conflicts among IA setups because they will all wait until the mutex is free, polling regularly.

Ah okay I understand, thank you! But this does not explain why or if an IA setup is waiting for an IS setup. And an IS setup also will not wait for an IA setup I think. In our company we have also some older product lines which setups are created with InnstallShield so this scenario should be considered as well.
So I think I will have to implement a check for running msiexec.exe bevore calling Apply Install to make sure that no non IA generated setup is running,am I right ?

Right, so the IA MSI holds a mutex locked and we cannot install other IA MSIs until this mutex is released. However, f the moment the setup grabs the mutex, another MSI setup is also being run than those other setups may fail due to that mutex.
Therefore, some sort of sequencing would be necessary here.