Date: Mon, 30 Oct 2006 16:49:26 +0800 From: David Xu <davidxu@freebsd.org> To: freebsd-threads@freebsd.org Subject: libthr status Message-ID: <200610301649.26429.davidxu@freebsd.org>
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Hi, As some of you may know that I have been working on 1:1 threading for years on FreeBSD. In the past years, I have polished it again and again. 1) The current status of libthr is that all features listed in /usr/include/pthread.h and /usr/include/pthread_np.h are supported by libthr except followings: 1.1) libthr does not support PROCESS scope, a threads created in libthr is SYSTEM scope threads, a kernel thread within system contention scope. The PROCESS scope is supported by libpthread using userland scheduler. 1.2) libthr does not support PROCESS SHARED mutex and other pthread synchronous objects. Study pthread_mutexattr_setpshared if you are interested. libpthread does not support the feature too. But libthr has better potential than libpthread to support it, since our kernel umtx code support shared memory map, study kern_umtx.c if you are interested. 1.3) libthr does not support some level of robust mutex which is found in recent Linux kernel and glibc and Solaris, this is only required if PROCESS SHARED mutex is supported. libpthread does not support the feature too. This is not required by POSIX, but in some commercial implementations. 1.4) pthread_getconcurrency and pthread_setconcurrency in libthr are no-op, because it is 1:1 and does not have PROCESS scope thread. it is supported by libpthread to tune number of UPCALL structures. 1.5) pthread_switch_add_np and pthread_switch_delete_np are no-op in libthr, they are remanet of libc_r. 1.6) setrlimit for number of kenrel threads, it is not done, one-day work. 1.7 CPU binding API, not done in libthr, found in other OSes. libpthread does not support it either. 1.8 C++ object unwinding when pthread_exit is called(), I found it is support by debian Linux and Solaris, I have sample implementation for libthr. 1.9) I forgot something. 2) Things can only be used by root: 2.1) the real-time scheduling options can only be used by root, e.g, if you call pthread_attr_setschedpolicy() with parameter SCHED_FIFO or SCHED_RR, the thread can only be created by root, normal user will get EPERM errno. you can use it in libpthread, but it is not real-time, it is a static priority scheduling in userland scheduler, if you want to preemptable other threads or processes in the system when playing real-time multimedia or military program, no way! 2.2) the real-time scheduling is not safe, it can deadlock itself and the whole system if program behavors incorrectly, it should only be used by trusted programs. David Xu
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