On 5 August 2010 04:54, <marcos_david.di...@sophia.inria.fr> wrote: > On Wed, August 4, 2010 8:45 pm, Jonathan Wakely wrote: >> On 4 August 2010 13:56, Marcos Dione wrote: >>> so, in short: does a simple Thread model have any impact on C-only >>> programs that could use threads? in particular, how it does impact >>> Boehm's GC usage in a C-only program? if the impact is negative, would >> >> IIUC GCC's thread model doesn't affect how you use threads in your own >> program, only how GCC's libraries (e.g. the C++ and ObjC runtimes) use >> threads. > > so it is wrong that some projects (in particular, Boehm's GC) test > thread availability by looking at the output of 'gcc -v' because that > would be assuming that it will use the same libraries compiled along > with that gcc?
I don't know that it's "wrong," it might just be a requirement of using that project that you use suitable runtime libraries that match the compiler used to build the project. It's not up to GCC to decide other projects' requirements. > in particular, this platform uses its own libc > implementation... also, you don't mention libc at all. is it different I have no idea, that's something you'd have to ask the libc maintainers, not the GCC list. > with it? and last one: can anyone explain *how* it affects stdlibc++ > and others? The library is called libstdc++, see http://gcc.gnu.org/onlinedocs/libstdc++/manual/ext_concurrency.html and http://gcc.gnu.org/onlinedocs/libstdc++/manual/using_concurrency.html and for more details see the code. With thread model "single" all calls to atomic operations are always turned into plain integer arithmetic. So for example, std::string reference counting uses simple increments and decrements, with no memory synchronisation and no protection against data races. You could still write a multithreaded program which uses std::string, but the library will behave as though you have a single-threaded program so if you share objects between threads you will get problems. Additionally, features of the library which require thread-related components such as mutexes will be disabed and unavailable if GCC was configured without a supported thread model.
