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@

1 files changed, 41 insertions, 217 deletions

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);
 }