Use umtx to implement process sharable semaphore, to make this work,

now type sema_t is a structure which can be put in a shared memory area,
and multiple processes can operate it concurrently.
User can either use mmap(MAP_SHARED) + sem_init(pshared=1) or use sem_open()
to initialize a shared semaphore.
Named semaphore uses file system and is located in /tmp directory, and its
file name is prefixed with 'SEMD', so now it is chroot or jail friendly.
In simplist cases, both for named and un-named semaphore, userland code
does not have to enter kernel to reduce/increase semaphore's count.
The semaphore is designed to be crash-safe, it means even if an application
is crashed in the middle of operating semaphore, the semaphore state is
still safely recovered by later use, there is no waiter counter maintained
by userland code.
The main semaphore code is in libc and libthr only has some necessary stubs,
this makes it possible that a non-threaded application can use semaphore
without linking to thread library.
Old semaphore implementation is kept libc to maintain binary compatibility.
The kernel ksem API is no longer used in the new implemenation.

Discussed on: threads@

5 files changed, 165 insertions, 218 deletions

diff --git a/lib/libthr/thread/Makefile.inc b/lib/libthr/thread/Makefile.inc
index 4ce90b5..d3de74e 100644
--- a/lib/libthr/thread/Makefile.inc
+++ b/lib/libthr/thread/Makefile.inc
@@ -41,6 +41,7 @@ SRCS+= \
 	thr_rwlockattr.c \
 	thr_self.c \
 	thr_sem.c \
+	thr_sem_new.c \
 	thr_setprio.c \
 	thr_setschedparam.c \
 	thr_sig.c \
diff --git a/lib/libthr/thread/thr_init.c b/lib/libthr/thread/thr_init.c
index f96bba9..1bfdd28 100644
--- a/lib/libthr/thread/thr_init.c
+++ b/lib/libthr/thread/thr_init.c
@@ -246,7 +246,9 @@ static pthread_func_t jmp_table[][2] = {
 	{DUAL_ENTRY(_pthread_setcanceltype)},	/* PJT_SETCANCELTYPE */
 	{DUAL_ENTRY(_pthread_setspecific)},	/* PJT_SETSPECIFIC */
 	{DUAL_ENTRY(_pthread_sigmask)},		/* PJT_SIGMASK */
-	{DUAL_ENTRY(_pthread_testcancel)}	/* PJT_TESTCANCEL */
+	{DUAL_ENTRY(_pthread_testcancel)},	/* PJT_TESTCANCEL */
+	{DUAL_ENTRY(__pthread_cleanup_pop_imp)},/* PJT_CLEANUP_POP_IMP */
+	{DUAL_ENTRY(__pthread_cleanup_push_imp)}/* PJT_CLEANUP_PUSH_IMP */
 };
 
 static int init_once = 0;
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
index 57be0ae..415c1ec 100644
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -52,6 +52,20 @@
 #include <sys/thr.h>
 #include <pthread.h>
 
+#define	SYM_FB10(sym)			__CONCAT(sym, _fb10)
+#define	SYM_FBP10(sym)			__CONCAT(sym, _fbp10)
+#define	WEAK_REF(sym, alias)		__weak_reference(sym, alias)
+#define	SYM_COMPAT(sym, impl, ver)	__sym_compat(sym, impl, ver)
+#define	SYM_DEFAULT(sym, impl, ver)	__sym_default(sym, impl, ver)
+
+#define	FB10_COMPAT(func, sym)				\
+	WEAK_REF(func, SYM_FB10(sym));			\
+	SYM_COMPAT(sym, SYM_FB10(sym), FBSD_1.0)
+
+#define	FB10_COMPAT_PRIVATE(func, sym)			\
+	WEAK_REF(func, SYM_FBP10(sym));			\
+	SYM_DEFAULT(sym, SYM_FBP10(sym), FBSDprivate_1.0)
+
 #ifndef __hidden
 #define __hidden		__attribute__((visibility("hidden")))
 #endif
@@ -660,6 +674,9 @@ int	_schedparam_to_rtp(int policy, const struct sched_param *param,
 void	_thread_bp_create(void);
 void	_thread_bp_death(void);
 int	_sched_yield(void);
+void	_thr_sem_prefork(void);
+void	_thr_sem_postfork(void);
+void	_thr_sem_child_postfork(void);
 
 void	_pthread_cleanup_push(void (*)(void *), void *);
 void	_pthread_cleanup_pop(int);
diff --git a/lib/libthr/thread/thr_sem.c b/lib/libthr/thread/thr_sem.c
index 0dd5599..f20bde3 100644
--- a/lib/libthr/thread/thr_sem.c
+++ b/lib/libthr/thread/thr_sem.c
@@ -36,7 +36,6 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
-#include <semaphore.h>
 #include <stdlib.h>
 #include <time.h>
 #include <_semaphore.h>
@@ -44,248 +43,73 @@
 
 #include "thr_private.h"
 
-
-__weak_reference(_sem_init, sem_init);
-__weak_reference(_sem_destroy, sem_destroy);
-__weak_reference(_sem_getvalue, sem_getvalue);
-__weak_reference(_sem_trywait, sem_trywait);
-__weak_reference(_sem_wait, sem_wait);
-__weak_reference(_sem_timedwait, sem_timedwait);
-__weak_reference(_sem_post, sem_post);
-
-
-static inline int
-sem_check_validity(sem_t *sem)
-{
-
-	if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC))
-		return (0);
-	else {
-		errno = EINVAL;
-		return (-1);
-	}
-}
-
-static sem_t
-sem_alloc(unsigned int value, semid_t semid, int system_sem)
-{
-	sem_t sem;
-
-	if (value > SEM_VALUE_MAX) {
-		errno = EINVAL;
-		return (NULL);
-	}
-
-	sem = (sem_t)malloc(sizeof(struct sem));
-	if (sem == NULL) {
-		errno = ENOSPC;
-		return (NULL);
-	}
-	bzero(sem, sizeof(*sem));
-	/*
-	 * Fortunatly count and nwaiters are adjacency, so we can
-	 * use umtx_wait to wait on it, umtx_wait needs an address
-	 * can be accessed as a long interger.
-	 */
-	sem->count = (u_int32_t)value;
-	sem->nwaiters = 0;
-	sem->magic = SEM_MAGIC;
-	sem->semid = semid;
-	sem->syssem = system_sem;
-	return (sem);
-}
+FB10_COMPAT(_sem_init_compat, sem_init);
+FB10_COMPAT(_sem_destroy_compat, sem_destroy);
+FB10_COMPAT(_sem_getvalue_compat, sem_getvalue);
+FB10_COMPAT(_sem_trywait_compat, sem_trywait);
+FB10_COMPAT(_sem_wait_compat, sem_wait);
+FB10_COMPAT(_sem_timedwait_compat, sem_timedwait);
+FB10_COMPAT(_sem_post_compat, sem_post);
+
+typedef struct sem *sem_t;
+
+extern int _libc_sem_init_compat(sem_t *sem, int pshared, unsigned int value);
+extern int _libc_sem_destroy_compat(sem_t *sem);
+extern int _libc_sem_getvalue_compat(sem_t * __restrict sem, int * __restrict sval);
+extern int _libc_sem_trywait_compat(sem_t *sem);
+extern int _libc_sem_wait_compat(sem_t *sem);
+extern int _libc_sem_timedwait_compat(sem_t * __restrict sem,
+    const struct timespec * __restrict abstime);
+extern int _libc_sem_post_compat(sem_t *sem);
+
+int _sem_init_compat(sem_t *sem, int pshared, unsigned int value);
+int _sem_destroy_compat(sem_t *sem);
+int _sem_getvalue_compat(sem_t * __restrict sem, int * __restrict sval);
+int _sem_trywait_compat(sem_t *sem);
+int _sem_wait_compat(sem_t *sem);
+int _sem_timedwait_compat(sem_t * __restrict sem,
+    const struct timespec * __restrict abstime);
+int _sem_post_compat(sem_t *sem);
 
 int
-_sem_init(sem_t *sem, int pshared, unsigned int value)
+_sem_init_compat(sem_t *sem, int pshared, unsigned int value)
 {
-	semid_t semid;
-
-	semid = (semid_t)SEM_USER;
-	if ((pshared != 0) && (ksem_init(&semid, value) != 0))
-		return (-1);
-
-	(*sem) = sem_alloc(value, semid, pshared);
-	if ((*sem) == NULL) {
-		if (pshared != 0)
-			ksem_destroy(semid);
-		return (-1);
-	}
-	return (0);
+	return _libc_sem_init_compat(sem, pshared, value);
 }
 
 int
-_sem_destroy(sem_t *sem)
+_sem_destroy_compat(sem_t *sem)
 {
-	int retval;
-
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	/*
-	 * If this is a system semaphore let the kernel track it otherwise
-	 * make sure there are no waiters.
-	 */
-	if ((*sem)->syssem != 0)
-		retval = ksem_destroy((*sem)->semid);
-	else {
-		retval = 0;
-		(*sem)->magic = 0;
-	}
-	if (retval == 0)
-		free(*sem);
-	return (retval);
+	return _libc_sem_destroy_compat(sem);
 }
 
 int
-_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
+_sem_getvalue_compat(sem_t * __restrict sem, int * __restrict sval)
 {
-	int retval;
-
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	if ((*sem)->syssem != 0)
-		retval = ksem_getvalue((*sem)->semid, sval);
-        else {
-		*sval = (int)(*sem)->count;
-		retval = 0;
-	}
-	return (retval);
+	return _libc_sem_getvalue_compat(sem, sval);
 }
 
 int
-_sem_trywait(sem_t *sem)
-{
-	int val;
-
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	if ((*sem)->syssem != 0)
- 		return (ksem_trywait((*sem)->semid));
-
-	while ((val = (*sem)->count) > 0) {
-		if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
-			return (0);
-	}
-	errno = EAGAIN;
-	return (-1);
-}
-
-static void
-sem_cancel_handler(void *arg)
+_sem_trywait_compat(sem_t *sem)
 {
-	sem_t *sem = arg;
-
-	atomic_add_int(&(*sem)->nwaiters, -1);
-	if ((*sem)->nwaiters && (*sem)->count)
-		_thr_umtx_wake(&(*sem)->count, 1, 0);
+	return _libc_sem_trywait_compat(sem);
 }
 
 int
-_sem_wait(sem_t *sem)
+_sem_wait_compat(sem_t *sem)
 {
-	struct pthread *curthread;
-	int val, retval;
-
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	curthread = _get_curthread();
-	if ((*sem)->syssem != 0) {
-		_thr_cancel_enter(curthread);
-		retval = ksem_wait((*sem)->semid);
-		_thr_cancel_leave(curthread);
-		return (retval);
-	}
-
-	_pthread_testcancel();
-	do {
-		while ((val = (*sem)->count) > 0) {
-			if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
-				return (0);
-		}
-		atomic_add_int(&(*sem)->nwaiters, 1);
-		THR_CLEANUP_PUSH(curthread, sem_cancel_handler, sem);
-		_thr_cancel_enter(curthread);
-		retval = _thr_umtx_wait_uint(&(*sem)->count, 0, NULL, 0);
-		_thr_cancel_leave(curthread);
-		THR_CLEANUP_POP(curthread, 0);
-		atomic_add_int(&(*sem)->nwaiters, -1);
-	} while (retval == 0);
-	errno = retval;
-	return (-1);
+	return _libc_sem_wait_compat(sem);
 }
 
 int
-_sem_timedwait(sem_t * __restrict sem,
+_sem_timedwait_compat(sem_t * __restrict sem,
     const struct timespec * __restrict abstime)
 {
-	struct timespec ts, ts2;
-	struct pthread *curthread;
-	int val, retval;
-
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	curthread = _get_curthread();
-	if ((*sem)->syssem != 0) {
-		_thr_cancel_enter(curthread);
-		retval = ksem_timedwait((*sem)->semid, abstime);
-		_thr_cancel_leave(curthread);
-		return (retval);
-	}
-
-	/*
-	 * The timeout argument is only supposed to
-	 * be checked if the thread would have blocked.
-	 */
-	_pthread_testcancel();
-	do {
-		while ((val = (*sem)->count) > 0) {
-			if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
-				return (0);
-		}
-		if (abstime == NULL) {
-			errno = EINVAL;
-			return (-1);
-		}
-		clock_gettime(CLOCK_REALTIME, &ts);
-		TIMESPEC_SUB(&ts2, abstime, &ts);
-		atomic_add_int(&(*sem)->nwaiters, 1);
-		THR_CLEANUP_PUSH(curthread, sem_cancel_handler, sem);
-		_thr_cancel_enter(curthread);
-		retval = _thr_umtx_wait_uint((uint32_t*)&(*sem)->count, 0, &ts2, 0);
-		_thr_cancel_leave(curthread);
-		THR_CLEANUP_POP(curthread, 0);
-		atomic_add_int(&(*sem)->nwaiters, -1);
-	} while (retval == 0);
-	errno = retval;
-	return (-1);
+	return _libc_sem_timedwait_compat(sem, abstime);
 }
 
-/*
- * sem_post() is required to be safe to call from within
- * signal handlers, these code should work as that.
- */
-
 int
-_sem_post(sem_t *sem)
+_sem_post_compat(sem_t *sem)
 {
-	int retval = 0;
-	
-	if (sem_check_validity(sem) != 0)
-		return (-1);
-
-	if ((*sem)->syssem != 0)
-		return (ksem_post((*sem)->semid));
-
-	atomic_add_rel_int(&(*sem)->count, 1);
-
-	if ((*sem)->nwaiters) {
-		retval = _thr_umtx_wake(&(*sem)->count, 1, 0);
-		if (retval != 0)
-			retval = -1;
-	}
-	return (retval);
+	return _libc_sem_post_compat(sem);
 }
diff --git a/lib/libthr/thread/thr_sem_new.c b/lib/libthr/thread/thr_sem_new.c
new file mode 100644
index 0000000..689b252
--- /dev/null
+++ b/lib/libthr/thread/thr_sem_new.c
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2010 David Xu <davidxu@freebsd.org>.
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice(s), this list of conditions and the following disclaimer as
+ *    the first lines of this file unmodified other than the possible
+ *    addition of one or more copyright notices.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice(s), this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include "namespace.h"
+#include <sys/types.h>
+#include <sys/queue.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <time.h>
+#include <semaphore.h>
+#include "un-namespace.h"
+
+#include "thr_private.h"
+
+__weak_reference(_sem_init, sem_init);
+__weak_reference(_sem_destroy, sem_destroy);
+__weak_reference(_sem_getvalue, sem_getvalue);
+__weak_reference(_sem_trywait, sem_trywait);
+__weak_reference(_sem_wait, sem_wait);
+__weak_reference(_sem_timedwait, sem_timedwait);
+__weak_reference(_sem_post, sem_post);
+
+extern int _libc_sem_init(sem_t *sem, int pshared, unsigned int value);
+extern int _libc_sem_destroy(sem_t *sem);
+extern int _libc_sem_getvalue(sem_t * __restrict sem, int * __restrict sval);
+extern int _libc_sem_trywait(sem_t *sem);
+extern int _libc_sem_wait(sem_t *sem);
+extern int _libc_sem_timedwait(sem_t * __restrict sem,
+    const struct timespec * __restrict abstime);
+extern int _libc_sem_post(sem_t *sem);
+
+int
+_sem_init(sem_t *sem, int pshared, unsigned int value)
+{
+	return _libc_sem_init(sem, pshared, value);
+}
+
+int
+_sem_destroy(sem_t *sem)
+{
+	return _libc_sem_destroy(sem);
+}
+
+int
+_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
+{
+	return _libc_sem_getvalue(sem, sval);
+}
+
+int
+_sem_trywait(sem_t *sem)
+{
+	return _libc_sem_trywait(sem);
+}
+
+int
+_sem_wait(sem_t *sem)
+{
+	return _libc_sem_wait(sem);
+}
+
+int
+_sem_timedwait(sem_t * __restrict sem,
+    const struct timespec * __restrict abstime)
+{
+	return _libc_sem_timedwait(sem, abstime);
+}
+
+int
+_sem_post(sem_t *sem)
+{
+	return _libc_sem_post(sem);
+}