07.12.2013 22:35 пользователь "Ted Unangst" <t...@tedunangst.com> написал: > > On Sat, Dec 07, 2013 at 21:32, Vadim Zhukov wrote: > > 2013/12/7 Ted Unangst <t...@tedunangst.com>: > >> On Sat, Dec 07, 2013 at 14:11, Vadim Zhukov wrote: > >>> This patch fixes problems in KDE4, that relies on sharing (process-shared) > >>> semaphores via mmap(). This feature is used in the wild, so if we claim > >>> that we support process-shared semaphores, we have to implement it, too. > >>> > >>> This changes the sem_t definition: it becomes a synonim to struct __sem > >>> instead of being a pointer to it. This way we allow apps to have sem_t in > >>> shared memory via sem_init() and thus share it between processes (by, > >>> e.g., mmap()'ing the same file). Of course, this forces a major library > >>> version bump. > >> > >> This requires more thought. If the introduction of pshared support is > >> breaking things, maybe just that part can be reverted for now. > > > > Well, it's the half-done introduction of pshared support is breaking > > things. I do not see any fallout now that sharing unnamed semaphores > > works. But what we'll gain with revert? Except that it's still better > > than current situation. > > One of the hallmarks of the original libpthread was that all data > structures were opaque, and hidden via pointers. That in turn made it > possible to write a binary compatible librthread. I never would have > started librthread if it hadn't been for that compatibility. So I > don't like turning my back on it. Exposing the size of sem_t is a > *major* step.
Then we have to state that we won't support process-shared semaphores, as well as mutexes and other locks, ever. Because all of them should have ability to live in shared memory. The only other way to achieve process-shared locks I see, is to use sem_t and others as indexes in some kernel structures (like file descriptors), moving most of librthread into the kernel. That sounds too crazy even for me. :) I like opaque types of librthread, too. And I hate what I did with one of them already. Too bad for us that the world does not care. :(
