[Bug libstdc++/58929] condition_variable does not wait without -pthread
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58929 Victor Mataré changed: What|Removed |Added CC||mat...@fh-aachen.de --- Comment #8 from Victor Mataré --- This has just caused me major headache because the behavior is completely unexpected. The root problem to me seems to be that pthread_cond_wait is defined not just in libphread, but also in libc: # objdump -TC /lib/libc.so.6 | grep cond_wait 0014a570 gDF .text 0033 (GLIBC_2.0) pthread_cond_wait 0007f5c0 gDF .text 0033 GLIBC_2.3.2 pthread_cond_wait Why is that even in there? And if I apparently end up calling this implementation, why doesn't block the way it should?
[Bug libstdc++/58929] condition_variable does not wait without -pthread
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58929 --- Comment #10 from Victor Mataré --- (In reply to Jonathan Wakely from comment #9) > The GNU libc has no-op stubs for several pthread functions. I think that is > done so that single threaded programs which don't actually need those > functions can still link to libraries that have references to those > functions. > > They don't block because they're not for use in multithreaded programs. If > you need the real versions you need to link to libpthread. OK, thanks for the clarification. But I feel I need to point out that that's just a huge WTF. How is a C++ dev supposed to know from the standard docs they work with all day that a condition_variable has any relation to libpthread? Least of all if you're used to getting linker errors if you're missing an implementation. I've read up on it a little bit and I can understand the rationale for having no-op mutex-related stuff because that doesn't break behavior in single-threaded code. But wait conditions are supposed to (mostly) block, single-threaded or not. A no-op stub is a severe breach of protocol there because no one expects to get "spurious" wakeups at 100% CPU. Just think about something like this happening in a real-time system. Maybe this should rather be a glibc bug. Any opinions on that?
