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@

3 files changed, 2 insertions, 89 deletions

diff --git a/sys/kern/uipc_sem.c b/sys/kern/uipc_sem.c
index 5ca13f8..f41b49c 100644
--- a/sys/kern/uipc_sem.c
+++ b/sys/kern/uipc_sem.c
@@ -51,7 +51,6 @@ __FBSDID("$FreeBSD$");
 #include <sys/priv.h>
 #include <sys/proc.h>
 #include <sys/posix4.h>
-#include <sys/semaphore.h>
 #include <sys/_semaphore.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
diff --git a/sys/sys/_semaphore.h b/sys/sys/_semaphore.h
index df3c5da..5266d04 100644
--- a/sys/sys/_semaphore.h
+++ b/sys/sys/_semaphore.h
@@ -31,26 +31,9 @@
 typedef intptr_t semid_t;
 struct timespec;
 
-#ifndef _KERNEL
-
-#include <sys/cdefs.h>
+#define SEM_VALUE_MAX  __INT_MAX
 
-/*
- * Semaphore definitions.
- */
-struct sem {
-#define SEM_MAGIC       ((u_int32_t) 0x09fa4012)
-        u_int32_t       magic;
-        pthread_mutex_t lock;
-        pthread_cond_t  gtzero;
-        u_int32_t       count;
-        u_int32_t       nwaiters;
-#define SEM_USER        (NULL)
-        semid_t         semid;  /* semaphore id if kernel (shared) semaphore */
-        int             syssem; /* 1 if kernel (shared) semaphore */
-        LIST_ENTRY(sem) entry;
-        struct sem      **backpointer;
-};
+#ifndef _KERNEL
 
 __BEGIN_DECLS
 
diff --git a/sys/sys/semaphore.h b/sys/sys/semaphore.h
deleted file mode 100644
index 34ede7b..0000000
--- a/sys/sys/semaphore.h
+++ /dev/null
@@ -1,69 +0,0 @@
-/*-
- * Copyright (c) 1996, 1997
- *	HD Associates, Inc.  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, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by HD Associates, Inc
- * 4. Neither the name of the author nor the names of any co-contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY HD ASSOCIATES AND CONTRIBUTORS ``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 HD ASSOCIATES OR CONTRIBUTORS 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.
- *
- * $FreeBSD$
- */
-
-/* semaphore.h: POSIX 1003.1b semaphores */
-
-#ifndef _SEMAPHORE_H_
-#define _SEMAPHORE_H_
-
-#include <machine/_limits.h>
-
-/* Opaque type definition. */
-struct sem;
-typedef	struct sem *	sem_t;
-
-#define	SEM_FAILED	((sem_t *)0)
-#define	SEM_VALUE_MAX	__INT_MAX
-
-#ifndef _KERNEL
-#include <sys/cdefs.h>
-
-struct timespec;
-
-__BEGIN_DECLS
-int	 sem_close(sem_t *);
-int	 sem_destroy(sem_t *);
-int	 sem_getvalue(sem_t * __restrict, int * __restrict);
-int	 sem_init(sem_t *, int, unsigned int);
-sem_t	*sem_open(const char *, int, ...);
-int	 sem_post(sem_t *);
-int	 sem_timedwait(sem_t * __restrict, const struct timespec * __restrict);
-int	 sem_trywait(sem_t *);
-int	 sem_unlink(const char *);
-int	 sem_wait(sem_t *);
-__END_DECLS
-
-#endif
-
-#endif /* !_SEMAPHORE_H_ */