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From: "sthlm58 at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/67434] New: std::chrono::duration acts like static even if instantiated every time Date: Wed, 02 Sep 2015 11:15:00 -0000 [thread overview] Message-ID: <bug-67434-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67434 Bug ID: 67434 Summary: std::chrono::duration acts like static even if instantiated every time Product: gcc Version: 5.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: sthlm58 at gmail dot com Target Milestone: --- For some reason std::chrono:duration maintains state (when instantiated as local variable) if compiled together with std::random_device in the same scope. Found on GCC: Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/5.2.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ./configure --prefix=/usr/local --disable-multilib --without-mpc --without-mpfr --without-gmp --without-cloog --without-isl --enable-languages=c,c++ Thread model: posix gcc version 5.2.0 (GCC) Reproduce with: #include <iostream> #include <algorithm> #include <random> #include <chrono> std::chrono::duration<double> benchmark( ) { std::random_device rd; std::chrono::duration<double> total; for (int i = 0; i < 100; i++) { auto t1 = std::chrono::high_resolution_clock::now(); auto t2 = std::chrono::high_resolution_clock::now(); total += std::chrono::duration_cast<std::chrono::duration<double>>(t2 - t1); } return total; } int main() { for (int i = 0; i < 10; i++) { std::cout << "time: " << benchmark().count() << std::endl; } return 0; } Build & run: g++ -std=c++14 -O2 main.cpp -Wall -Wextra && ./a.out Output (e.g.): http://coliru.stacked-crooked.com/a/0d4dcd432a4b0f51 time: 0.000112018 time: 0.000222767 time: 0.000333607 time: 0.000444344 time: 0.000554722 time: 0.00066537 time: 0.000775786 time: 0.000886287 time: 0.000996599 time: 0.0011071 Expected output (when commenting line 8) (e.g.): http://coliru.stacked-crooked.com/a/e1f9fa0323d4d3f4 time: 0.00010953 time: 0.000110805 time: 0.000111902 time: 0.000112299 time: 0.000109301 time: 0.000109781 time: 0.000109413 time: 0.000109506 time: 0.000109258 time: 0.000110727
next reply other threads:[~2015-09-02 11:15 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-09-02 11:15 sthlm58 at gmail dot com [this message] 2015-09-02 11:28 ` [Bug libstdc++/67434] " redi at gcc dot gnu.org 2015-09-03 11:55 ` sthlm58 at gmail dot com
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