If the engine receives a special comment line # gtpengine-sleep n, it will sleep for n seconds before reading the next line.
This feature can be used for adding simulated delays in test GTP scripts (e.g. to test pondering functionality). Note that the start time for sleeping is at the start of the previous command, not when the response to the previous command is received, because GtpEngine continues reading the stream while the previous command is in progress. This functionality is only enabled, if GtpEngine was compiled with GTPENGINE_INTERRUPT.