SD wrote:
# Create libtest.so g++ -shared -fPIC test.cpp -o libtest.so # link boost_regex before libtest.so g++ main.cpp -lboost_regex${BOOST_EXT} -ltest -L${PWD} -o main_fast # link boost_regex after libtest.so g++ main.cpp -ltest -lboost_regex${BOOST_EXT} -L${PWD} -o main_slow
time env LD_LIBRARY_PATH=${PWD} ./main_slow # real 0m0.753s, user 0m0.746s, sys 0m0.004s time env LD_LIBRARY_PATH=${PWD} ./main_fast # real 0m0.104s, user 0m0.103s, sys 0m0.002s
As the results show the order which libs are being linked to the program has significant performance impacts on execution time: main_fast is about 7 times faster than main_slow. .... I would appreciate if someone could explain these surprising results.
Before we go on guessing what could cause this -- do you get the same timings on successive runs of any given executable?
Yes, the runtimes vary only minimally.
Does running ldd on both binaries report that the same boost_regexp binary is being linked to? I don't see why different ones would be linked to, but still. If this theory is wrong, can you create a self-contained archive with all the necessary files, and send it, so that I (and others) can try to reproduce. This sounds truly bizarre. - Volodya