The following include is missing in gecode/support/thread/pthreads.hpp causing compilation to fail for me (unknown sleep(3) and usleep(3)) in both 3.1.0 and trunk: #ifdef GECODE_HAS_UNISTD_H #include <unistd.h> #endif or perhaps more correctly: #ifdef GECODE_HAS_UNISTD_H extern "C" { #include <unistd.h> } #endif --Denys