From owner-svn-src-head@FreeBSD.ORG Wed Mar 21 07:12:53 2012 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 15D57106566C; Wed, 21 Mar 2012 07:12:53 +0000 (UTC) (envelope-from davidxu@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c]) by mx1.freebsd.org (Postfix) with ESMTP id EB0888FC08; Wed, 21 Mar 2012 07:12:52 +0000 (UTC) Received: from svn.freebsd.org (localhost [127.0.0.1]) by svn.freebsd.org (8.14.4/8.14.4) with ESMTP id q2L7CqSC059191; Wed, 21 Mar 2012 07:12:52 GMT (envelope-from davidxu@svn.freebsd.org) Received: (from davidxu@localhost) by svn.freebsd.org (8.14.4/8.14.4/Submit) id q2L7Cqs1059189; Wed, 21 Mar 2012 07:12:52 GMT (envelope-from davidxu@svn.freebsd.org) Message-Id: <201203210712.q2L7Cqs1059189@svn.freebsd.org> From: David Xu Date: Wed, 21 Mar 2012 07:12:52 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Subject: svn commit: r233262 - head/lib/libc/gen X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 21 Mar 2012 07:12:53 -0000 Author: davidxu Date: Wed Mar 21 07:12:52 2012 New Revision: 233262 URL: http://svn.freebsd.org/changeset/base/233262 Log: Use version 2 of semaphore provided by kernel umtx code, now if there is no waiters, we still increase and decrease count in user mode without entering kernel, once there is a waiter, sem_post will enter kernel to increase count and wake thread up, this is atomicy and allow us to gracefully destroy semaphore after sem_wait returned. Modified: head/lib/libc/gen/sem_new.c Modified: head/lib/libc/gen/sem_new.c ============================================================================== --- head/lib/libc/gen/sem_new.c Wed Mar 21 07:07:43 2012 (r233261) +++ head/lib/libc/gen/sem_new.c Wed Mar 21 07:12:52 2012 (r233262) @@ -61,7 +61,8 @@ __weak_reference(_sem_unlink, sem_unlink __weak_reference(_sem_wait, sem_wait); #define SEM_PREFIX "/tmp/SEMD" -#define SEM_MAGIC ((u_int32_t)0x73656d31) +#define SEM_MAGIC1 ((u_int32_t)0x73656d31) +#define SEM_MAGIC ((u_int32_t)0x73656d32) struct sem_nameinfo { int open_count; @@ -109,7 +110,7 @@ static inline int sem_check_validity(sem_t *sem) { - if (sem->_magic == SEM_MAGIC) + if (sem->_magic == SEM_MAGIC || sem->_magic == SEM_MAGIC1) return (0); else { errno = EINVAL; @@ -130,7 +131,7 @@ _sem_init(sem_t *sem, int pshared, unsig sem->_magic = SEM_MAGIC; sem->_kern._count = (u_int32_t)value; sem->_kern._has_waiters = 0; - sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0; + sem->_kern._flags = (pshared ? USYNC_PROCESS_SHARED : 0) | SEM_VER2; return (0); } @@ -207,7 +208,7 @@ _sem_open(const char *name, int flags, . tmp._magic = SEM_MAGIC; tmp._kern._has_waiters = 0; tmp._kern._count = value; - tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED; + tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED | SEM_VER2; if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) { flock(fd, LOCK_UN); goto error; @@ -325,20 +326,11 @@ _sem_getvalue(sem_t * __restrict sem, in if (sem_check_validity(sem) != 0) return (-1); - *sval = (int)sem->_kern._count; + *sval = (int)sem->_kern._count & ~SEM_WAITERS; return (0); } static __inline int -usem_wake(struct _usem *sem) -{ - rmb(); - if (!sem->_has_waiters) - return (0); - return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL); -} - -static __inline int usem_wait(struct _usem *sem, const struct timespec *abstime) { struct _umtx_time *tm_p, timeout; @@ -358,48 +350,51 @@ usem_wait(struct _usem *sem, const struc (void *)tm_size, __DECONST(void*, tm_p)); } +static inline int +_trywait(sem_t *sem) +{ + int count; + + if ((sem->_kern._flags & SEM_VER2) != 0) { + while (((count = sem->_kern._count) & ~SEM_WAITERS) > 0) { + if (atomic_cmpset_acq_int(&sem->_kern._count, count, count - 1)) + return (0); + } + } else { + while ((count = sem->_kern._count) > 0) { + if (atomic_cmpset_acq_int(&sem->_kern._count, count, count - 1)) + return (0); + } + } + return (EAGAIN); +} + int _sem_trywait(sem_t *sem) { - int val; + int status; if (sem_check_validity(sem) != 0) return (-1); - - while ((val = sem->_kern._count) > 0) { - if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1)) - return (0); - } - errno = EAGAIN; + if ((status = _trywait(sem)) == 0) + return (0); + errno = status; return (-1); } -#define TIMESPEC_SUB(dst, src, val) \ - do { \ - (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec; \ - (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \ - if ((dst)->tv_nsec < 0) { \ - (dst)->tv_sec--; \ - (dst)->tv_nsec += 1000000000; \ - } \ - } while (0) - - int _sem_timedwait(sem_t * __restrict sem, const struct timespec * __restrict abstime) { - int val, retval; + int retval; if (sem_check_validity(sem) != 0) return (-1); retval = 0; for (;;) { - while ((val = sem->_kern._count) > 0) { - if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1)) - return (0); - } + if (_trywait(sem) == 0) + return (0); if (retval) { _pthread_testcancel(); @@ -438,10 +433,36 @@ _sem_wait(sem_t *sem) int _sem_post(sem_t *sem) { + int count; if (sem_check_validity(sem) != 0) return (-1); - atomic_add_rel_int(&sem->_kern._count, 1); - return usem_wake(&sem->_kern); + if ((sem->_kern._flags & SEM_VER2) != 0) { + for (;;) { + count = sem->_kern._count; + if ((count & SEM_WAITERS) == 0) { + if (__predict_false(count == SEM_VALUE_MAX)) { + errno = ERANGE; + return (-1); + } + if (atomic_cmpset_rel_int(&sem->_kern._count, count, count+1)) + return (0); + } else { + return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL); + } + } + } else { + do { + count = sem->_kern._count; + if (__predict_false(count == SEM_VALUE_MAX)) { + errno = ERANGE; + return (-1); + } + } while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count+1)); + rmb(); + if (!sem->_kern._has_waiters) + return (0); + return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL); + } }