diff --git a/headers/os/kernel/OS.h b/headers/os/kernel/OS.h
index b738d747b9..7ad1f346ca 100644
--- a/headers/os/kernel/OS.h
+++ b/headers/os/kernel/OS.h
@@ -170,6 +170,11 @@ extern status_t	acquire_sem(sem_id id);
 extern status_t	acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout);
 extern status_t	release_sem(sem_id id);
 extern status_t	release_sem_etc(sem_id id, int32 count, uint32 flags);
+// ToDo: the following two calls are not part of the BeOS API, and might be
+//	changed or even removed for the final release of Haiku R1
+extern status_t	switch_sem(sem_id semToBeReleased, sem_id id);
+extern status_t	switch_sem_etc(sem_id semToBeReleased, sem_id id, int32 count,
+					uint32 flags, bigtime_t timeout);
 extern status_t	get_sem_count(sem_id id, int32 *threadCount);
 extern status_t	set_sem_owner(sem_id id, team_id team);
 
diff --git a/headers/private/kernel/sem.h b/headers/private/kernel/sem.h
index ac0a7eea9d..684ec9db43 100755
--- a/headers/private/kernel/sem.h
+++ b/headers/private/kernel/sem.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2004, Axel Dörfler, axeld@pinc-software.de.
+ * Copyright 2002-2005, Axel Dörfler, axeld@pinc-software.de.
  * Distributed under the terms of the MIT License.
  *
  * Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
@@ -12,7 +12,6 @@
 #include <OS.h>
 #include <thread.h>
 
-
 struct kernel_args;
 
 
@@ -33,6 +32,8 @@ sem_id _user_create_sem(int32 count, const char *name);
 status_t _user_delete_sem(sem_id id);
 status_t _user_acquire_sem(sem_id id);
 status_t _user_acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout);
+status_t _user_switch_sem(sem_id releaseSem, sem_id id);
+status_t _user_switch_sem_etc(sem_id releaseSem, sem_id id, int32 count, uint32 flags, bigtime_t timeout);
 status_t _user_release_sem(sem_id id);
 status_t _user_release_sem_etc(sem_id id, int32 count, uint32 flags);
 status_t _user_get_sem_count(sem_id id, int32* thread_count);
diff --git a/headers/private/kernel/syscalls.h b/headers/private/kernel/syscalls.h
index 3c7fe18b7c..39c6736448 100644
--- a/headers/private/kernel/syscalls.h
+++ b/headers/private/kernel/syscalls.h
@@ -46,6 +46,9 @@ extern status_t		_kern_get_safemode_option(const char *parameter, char *buffer,
 /* sem functions */
 extern sem_id		_kern_create_sem(int count, const char *name);
 extern status_t		_kern_delete_sem(sem_id id);
+extern status_t		_kern_switch_sem(sem_id releaseSem, sem_id id);
+extern status_t		_kern_switch_sem_etc(sem_id releaseSem, sem_id id, uint32 count,
+						uint32 flags, bigtime_t timeout);
 extern status_t		_kern_acquire_sem(sem_id id);
 extern status_t		_kern_acquire_sem_etc(sem_id id, uint32 count, uint32 flags, bigtime_t timeout);
 extern status_t		_kern_release_sem(sem_id id);
diff --git a/src/kernel/core/sem.c b/src/kernel/core/sem.c
index 07dac4fdf9..47df6fa40f 100644
--- a/src/kernel/core/sem.c
+++ b/src/kernel/core/sem.c
@@ -407,12 +407,29 @@ sem_timeout(timer *data)
 status_t
 acquire_sem(sem_id id)
 {
-	return acquire_sem_etc(id, 1, 0, 0);
+	return switch_sem_etc(-1, id, 1, 0, 0);
 }
 
+
 status_t
 acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout)
 {
+	return switch_sem_etc(-1, id, count, flags, timeout);
+}
+
+
+status_t
+switch_sem(sem_id toBeReleased, sem_id toBeAcquired)
+{
+	return switch_sem_etc(toBeReleased, toBeAcquired, 1, 0, 0);
+}
+
+
+status_t
+switch_sem_etc(sem_id semToBeReleased, sem_id id, int32 count,
+	uint32 flags, bigtime_t timeout)
+{
+	// ToDo: add support for B_CHECK_PERMISSION
 	int slot = id % sMaxSems;
 	int state;
 	status_t status = B_OK;
@@ -494,6 +511,10 @@ acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout)
 		}
 
 		RELEASE_SEM_LOCK(sSems[slot]);
+
+		if (semToBeReleased >= B_OK)
+			release_sem_etc(semToBeReleased, 1, B_DO_NOT_RESCHEDULE);
+
 		GRAB_THREAD_LOCK();
 		// check again to see if a signal is pending.
 		// it may have been delivered while setting up the sem, though it's pretty unlikely
@@ -553,6 +574,7 @@ release_sem(sem_id id)
 status_t
 release_sem_etc(sem_id id, int32 count, uint32 flags)
 {
+	// ToDo: add support for B_CHECK_PERMISSION
 	struct thread_queue releaseQueue;
 	int32 slot = id % sMaxSems;
 	cpu_status state;
@@ -998,28 +1020,42 @@ _user_delete_sem(sem_id id)
 status_t
 _user_acquire_sem(sem_id id)
 {
-	return _user_acquire_sem_etc(id, 1, 0, 0);
+	return switch_sem_etc(-1, id, 1, B_CAN_INTERRUPT | B_CHECK_PERMISSION, 0);
 }
 
 
 status_t
 _user_acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout)
 {
-	return acquire_sem_etc(id, count, flags | B_CAN_INTERRUPT, timeout);
+	return switch_sem_etc(-1, id, count, flags | B_CAN_INTERRUPT | B_CHECK_PERMISSION, timeout);
+}
+
+
+status_t
+_user_switch_sem(sem_id releaseSem, sem_id id)
+{
+	return switch_sem_etc(releaseSem, id, 1, B_CAN_INTERRUPT | B_CHECK_PERMISSION, 0);
+}
+
+
+status_t
+_user_switch_sem_etc(sem_id releaseSem, sem_id id, int32 count, uint32 flags, bigtime_t timeout)
+{
+	return switch_sem_etc(releaseSem, id, count, flags | B_CAN_INTERRUPT | B_CHECK_PERMISSION, timeout);
 }
 
 
 status_t
 _user_release_sem(sem_id id)
 {
-	return release_sem_etc(id, 1, 0);
+	return release_sem_etc(id, 1, B_CHECK_PERMISSION);
 }
 
 
 status_t
 _user_release_sem_etc(sem_id id, int32 count, uint32 flags)
 {
-	return release_sem_etc(id, count, flags);
+	return release_sem_etc(id, count, flags | B_CHECK_PERMISSION);
 }
 
 
diff --git a/src/kernel/libroot/os/sem.c b/src/kernel/libroot/os/sem.c
index ca5921375c..b07143d05f 100644
--- a/src/kernel/libroot/os/sem.c
+++ b/src/kernel/libroot/os/sem.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2004, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
+ * Copyright 2002-2005, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
  * Distributed under the terms of the MIT License.
  */
 
@@ -36,6 +36,23 @@ acquire_sem_etc(sem_id id, int32 count, uint32 flags, bigtime_t timeout)
 }
 
 
+// ToDo: the next two calls (switch_sem()) are not yet public API; no decision
+//	has been made yet, so they may get changed or removed until R1
+
+status_t
+switch_sem(sem_id releaseSem, sem_id id)
+{
+	return _kern_switch_sem(releaseSem, id);
+}
+
+
+status_t
+switch_sem_etc(sem_id releaseSem, sem_id id, int32 count, uint32 flags, bigtime_t timeout)
+{
+	return _kern_switch_sem_etc(releaseSem, id, count, flags, timeout);
+}
+
+
 status_t
 release_sem(sem_id id)
 {