As the worker processes are now properly spawned using fork-exec, they no longer inherit the stack size from the non-main coordinator thread, but get a main thread with reasonable stack size on their own. For this reason the coordinator threads can use the default stack size, and turn std::thread can be used as the only reason for the custom wrapper was to enlarge the stack. Change-Id: I1192474885abe9b0625ac483840b6e1a6a6a6964