On Thu, 15 Jun 2006, Mark Andrews wrote:
Is there any good reason why "gcc -pthread" links in -lpthead except when -shared is specified?
Because one may want to build applications to use different threading libraries. Application A may work better with libthr, while application B prefers libpthread. Both applications may also rely on libfoo which needs a threading library in order to be MT-safe. If libfoo records a dependency on libpthread, and application A uses libthr, then that won't work (crashy crashy). I think we took the approach a long time ago that there were basically 2 reasons for a library to require threading: 1) To be MT-safe when used in the presence of a threaded application; and 2) To create threads behind the scenes in support of an application (i.e., a hypothetical libaio). In the case of 1, the library can use #pragma weak on pthread_create and detect whether or not a threads library is present and only use locking when pthread_create != NULL (libc provides stubs for all the pthread functions necessary for locking). In the case of 2, applications should know what libraries need threads and be required to supply -lpthread (or -lthr, or -pthread) when they are built. This may or may not change in the future because all the UNIX world is Linux :( (And for possible problems when using symbol versioning.)
Also the gcc man page does not match reality. -pthread Link a user-threaded process against libc_r instead of libc. man pthread mentions these libraries but provided no discussion on if or when you should include them on the command line. Nor does it mention "-pthread". LIBRARY POSIX Threads Library (libpthread, -lpthread) 1:1 Threading Library (libthr, -lthr) Reentrant C Library (libc_r, -lc_r) The hacker handbook seems to indicate that you shouldn't need to use -lpthread or -lc_r. http://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/dads-pthread.html
That's the porters handbook and they prefer to use PTHREAD_LIBS so one can override the default threading library when building the port. PTHREAD_LIBS defaults to -pthread because -pthread does the right thing on different archs where the default threading library varies (x86, amd64, ia64 use libpthread, sparc64 uses libthr, etc). -- DE _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"