The following commands are used to start the simulator in its own thread, halt the simulation and resume it again. The extra (background) thread enables the caller to continue with other tasks in the main thread, e.g. watching its own event loop. Of course you have to take care that the caller will not exit before ngspice is finished, otherwise you immediately will loose all data. After having halted the simulator by suspending the background thread, you may assess data, change ngspice parameters, or read output data using the caller's main thread, before you resume simulation using a background thread again. While the background thread is running, ngspice will reject any other command sent by ngSpice_Command.

Typical usage:

ngSpice_Command("bg_run");
...
ngSpice_Command("bg_halt");
...
ngSpice_Command("bg_resume");

Basically you may send the commands 'run' or 'resume' (no prefix bg_), starting ngspice within the main thread. The caller then has to wait until ngspice returns from simulation. A command 'halt' is not available then.

After simulation is finished (test with callback 19.3.3.6), you may send other commands from Chapt. 17.5, emulating any .control script. These commands are executed in the main thread, which should be okay because execution time is typically short.