diff --git a/headers/private/kernel/condition_variable.h b/headers/private/kernel/condition_variable.h
index 392d96ba24..0925a7162d 100644
--- a/headers/private/kernel/condition_variable.h
+++ b/headers/private/kernel/condition_variable.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007, Ingo Weinhold, bonefish@cs.tu-berlin.de.
+ * Copyright 2007-2008, Ingo Weinhold, bonefish@cs.tu-berlin.de.
  * Distributed under the terms of the MIT License.
  */
 #ifndef _KERNEL_CONDITION_VARIABLE_H
@@ -40,24 +40,16 @@ public:
 	inline	PrivateConditionVariable* Variable() const
 		{ return fVariable; }
 
-	class Private;
-
 protected:
-			bool				Add(const void* object);
-			status_t			Wait(uint32 flags);
+			bool				Add(const void* object, uint32 flags);
+			status_t			Wait();
 			status_t			Wait(const void* object, uint32 flags);
 
-private:
-			void				_Remove();
-
 protected:
 			PrivateConditionVariable* fVariable;
 			struct thread*		fThread;
-			uint32				fFlags;
-			status_t			fResult;
 
 			friend class PrivateConditionVariable;
-			friend class Private;
 };
 
 
@@ -103,8 +95,8 @@ public:
 template<typename Type = void>
 class ConditionVariableEntry : public PrivateConditionVariableEntry {
 public:
-	inline	bool				Add(const Type* object);
-	inline	status_t			Wait(uint32 flags = 0);
+	inline	bool				Add(const Type* object, uint32 flags = 0);
+	inline	status_t			Wait();
 	inline	status_t			Wait(const Type* object, uint32 flags = 0);
 };
 
@@ -143,17 +135,17 @@ ConditionVariable<Type>::NotifyAll(bool threadsLocked)
 
 template<typename Type>
 inline bool
-ConditionVariableEntry<Type>::Add(const Type* object)
+ConditionVariableEntry<Type>::Add(const Type* object, uint32 flags)
 {
-	return PrivateConditionVariableEntry::Add(object);
+	return PrivateConditionVariableEntry::Add(object, flags);
 }
 
 
 template<typename Type>
 inline status_t
-ConditionVariableEntry<Type>::Wait(uint32 flags)
+ConditionVariableEntry<Type>::Wait()
 {
-	return PrivateConditionVariableEntry::Wait(flags);
+	return PrivateConditionVariableEntry::Wait();
 }
 
 
@@ -170,8 +162,6 @@ extern "C" {
 
 struct thread;
 
-extern status_t condition_variable_interrupt_thread(struct thread* thread);
-
 extern void condition_variable_init();
 
 #ifdef __cplusplus
diff --git a/headers/private/kernel/sem.h b/headers/private/kernel/sem.h
index 756b53cdb4..6132125167 100644
--- a/headers/private/kernel/sem.h
+++ b/headers/private/kernel/sem.h
@@ -22,7 +22,6 @@ extern "C" {
 
 extern status_t sem_init(struct kernel_args *args);
 extern int sem_delete_owned_sems(team_id owner);
-extern status_t	sem_interrupt_thread(struct thread *t);
 extern int32 sem_used_sems(void);
 extern int32 sem_max_sems(void);
 
diff --git a/headers/private/kernel/thread.h b/headers/private/kernel/thread.h
index bd35d34fb6..1a93316c77 100644
--- a/headers/private/kernel/thread.h
+++ b/headers/private/kernel/thread.h
@@ -13,6 +13,11 @@
 #include <thread_types.h>
 #include <arch/thread.h>
 
+// For the thread blocking inline functions only.
+#include <kscheduler.h>
+#include <ksignal.h>
+
+
 struct kernel_args;
 struct select_info;
 
@@ -72,6 +77,12 @@ status_t deselect_thread(int32 object, struct select_info *info, bool kernel);
 
 #define syscall_64_bit_return_value() arch_syscall_64_bit_return_value()
 
+status_t thread_block();
+status_t thread_block_with_timeout(uint32 timeoutFlags, bigtime_t timeout);
+status_t thread_block_with_timeout_locked(uint32 timeoutFlags,
+			bigtime_t timeout);
+bool thread_unblock(status_t threadID, status_t status);
+
 // used in syscalls.c
 status_t _user_set_thread_priority(thread_id thread, int32 newPriority);
 status_t _user_rename_thread(thread_id thread, const char *name);
@@ -100,4 +111,87 @@ int _user_setrlimit(int resource, const struct rlimit * rlp);
 }
 #endif
 
+
+/*!
+	\a thread must be the current thread.
+	Thread lock can be, but doesn't need to be held.
+*/
+static inline bool
+thread_is_interrupted(struct thread* thread, uint32 flags)
+{
+	return ((flags & B_CAN_INTERRUPT)
+			&& (thread->sig_pending & ~thread->sig_block_mask) != 0)
+		|| ((flags & B_KILL_CAN_INTERRUPT)
+			&& (thread->sig_pending & KILL_SIGNALS));
+}
+
+
+static inline bool
+thread_is_blocked(struct thread* thread)
+{
+	return thread->wait.status == 1;
+}
+
+
+/*!
+	\a thread must be the current thread.
+	Thread lock can be, but doesn't need to be locked.
+*/
+static inline void
+thread_prepare_to_block(struct thread* thread, uint32 flags, uint32 type,
+	void* object)
+{
+	thread->wait.flags = flags;
+	thread->wait.type = type;
+	thread->wait.object = object;
+	atomic_set(&thread->wait.status, 1);
+		// Set status last to guarantee that the other fields are initialized
+		// when a thread is waiting.
+}
+
+
+static inline status_t
+thread_block_locked(struct thread* thread)
+{
+	if (thread->wait.status == 1) {
+		// check for signals, if interruptable
+		if (thread_is_interrupted(thread, thread->wait.flags)) {
+			thread->wait.status = B_INTERRUPTED;
+		} else {
+			thread->next_state = B_THREAD_WAITING;
+			scheduler_reschedule();
+		}
+	}
+
+	return thread->wait.status;
+}
+
+
+static inline bool
+thread_unblock_locked(struct thread* thread, status_t status)
+{
+	if (atomic_test_and_set(&thread->wait.status, status, 1) != 1)
+		return false;
+
+	// wake up the thread, if it is sleeping
+	if (thread->state == B_THREAD_WAITING)
+		scheduler_enqueue_in_run_queue(thread);
+
+	return true;
+}
+
+
+static inline status_t
+thread_interrupt(struct thread* thread, bool kill)
+{
+	if ((thread->wait.flags & B_CAN_INTERRUPT) != 0
+		|| (kill && (thread->wait.flags & B_KILL_CAN_INTERRUPT) != 0)) {
+		thread_unblock_locked(thread, B_INTERRUPTED);
+		return B_OK;
+	}
+
+	return B_NOT_ALLOWED;
+}
+
+
 #endif /* _THREAD_H */
diff --git a/headers/private/kernel/thread_types.h b/headers/private/kernel/thread_types.h
index ac7f02d0c9..014ebd2292 100644
--- a/headers/private/kernel/thread_types.h
+++ b/headers/private/kernel/thread_types.h
@@ -55,6 +55,15 @@ typedef enum job_control_state {
 #define THREAD_STOPPED				0x3
 #define THREAD_CONTINUED			0x4
 
+// The type of object a thread blocks on (thread::wait::type, set by
+// thread_prepare_to_block()).
+enum {
+	THREAD_BLOCK_TYPE_SEMAPHORE				= 0,
+	THREAD_BLOCK_TYPE_CONDITION_VARIABLE	= 1,
+	THREAD_BLOCK_TYPE_SNOOZE				= 2,
+	THREAD_BLOCK_TYPE_USER_BASE				= 10000
+};
+
 struct image;
 	// defined in image.c
 struct select_info;
@@ -233,12 +242,12 @@ struct thread {
 	bool			was_yielded;
 
 	struct {
-		sem_id		blocking;
-		int32		count;
-		int32		acquire_count;
-		status_t	acquire_status;
-		int32		flags;
-	} sem;
+		status_t	status;				// current wait status
+		uint32		flags;				// interrupable flags
+		uint32		type;				// type of the object waited on
+		void*		object;				// pointer to the object waited on
+		timer		unblock_timer;		// timer for block with timeout
+	} wait;
 
 	struct PrivateConditionVariableEntry *condition_variable_entry;
 
diff --git a/src/add-ons/kernel/drivers/tty/tty.cpp b/src/add-ons/kernel/drivers/tty/tty.cpp
index acb31a6503..afe467488f 100644
--- a/src/add-ons/kernel/drivers/tty/tty.cpp
+++ b/src/add-ons/kernel/drivers/tty/tty.cpp
@@ -408,14 +408,14 @@ RequestOwner::Wait(bool interruptable)
 
 		// add an entry to wait on
 		ConditionVariableEntry<> entry;
-		entry.Add(this);
+		entry.Add(this, interruptable ? B_CAN_INTERRUPT : 0);
 
 		locker.Unlock();
 
 		// wait
 		TRACE(("%p->RequestOwner::Wait(): waiting for condition...\n", this));
 
-		error = entry.Wait(interruptable ? B_CAN_INTERRUPT : 0);
+		error = entry.Wait();
 
 		TRACE(("%p->RequestOwner::Wait(): condition occurred: %lx\n", this,
 			error));
diff --git a/src/system/kernel/condition_variable.cpp b/src/system/kernel/condition_variable.cpp
index 148690802f..922371fe17 100644
--- a/src/system/kernel/condition_variable.cpp
+++ b/src/system/kernel/condition_variable.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007, Ingo Weinhold, bonefish@cs.tu-berlin.de.
+ * Copyright 2007-2008, Ingo Weinhold, bonefish@cs.tu-berlin.de.
  * Distributed under the terms of the MIT License.
  */
 
@@ -92,30 +92,36 @@ dump_condition_variable(int argc, char** argv)
 
 
 bool
-PrivateConditionVariableEntry::Add(const void* object)
+PrivateConditionVariableEntry::Add(const void* object, uint32 flags)
 {
 	ASSERT(object != NULL);
 
 	fThread = thread_get_current_thread();
-	fFlags = 0;
-	fResult = B_OK;
 
 	InterruptsLocker _;
 	SpinLocker locker(sConditionVariablesLock);
 
-	// add to the queue for the variable
 	fVariable = sConditionVariableHash.Lookup(object);
-	if (fVariable)
-		fVariable->fEntries.Add(this);
-	else
-		fResult = B_ENTRY_NOT_FOUND;
 
-	return (fVariable != NULL);
+	struct thread* thread = thread_get_current_thread();
+	thread_prepare_to_block(thread, flags, THREAD_BLOCK_TYPE_CONDITION_VARIABLE,
+		fVariable);
+
+	if (fVariable == NULL) {
+		SpinLocker threadLocker(thread_spinlock);
+		thread_unblock_locked(thread, B_ENTRY_NOT_FOUND);
+		return false;
+	}
+
+	// add to the queue for the variable
+	fVariable->fEntries.Add(this);
+
+	return true;
 }
 
 
 status_t
-PrivateConditionVariableEntry::Wait(uint32 flags)
+PrivateConditionVariableEntry::Wait()
 {
 	if (!are_interrupts_enabled()) {
 		panic("wait_for_condition_variable_entry() called with interrupts "
@@ -124,77 +130,32 @@ PrivateConditionVariableEntry::Wait(uint32 flags)
 	}
 
 	InterruptsLocker _;
+
 	SpinLocker threadLocker(thread_spinlock);
-	SpinLocker locker(sConditionVariablesLock);
-
-	// check whether this entry has already been notified
-	// (set the flags while at it)
-	if (fVariable == NULL)
-		return fResult;
-	fFlags = flags;
-
-	// When interruptable, check pending signals first
-	struct thread* thread = thread_get_current_thread();
-	if (((flags & B_CAN_INTERRUPT)
-			&& (thread->sig_pending & ~thread->sig_block_mask) != 0)
-		|| ((flags & B_KILL_CAN_INTERRUPT)
-			&& (thread->sig_pending & KILL_SIGNALS))) {
-		// remove entry from the variables
-		_Remove();
-		return B_INTERRUPTED;
-	}
-
-	// wait
-	thread->next_state = B_THREAD_WAITING;
-	thread->condition_variable_entry = this;
-	thread->sem.blocking = -1;
-
-	locker.Unlock();
-	scheduler_reschedule();
+	status_t error = thread_block_locked(thread_get_current_thread());
 	threadLocker.Unlock();
 
-	return fResult;
+	SpinLocker locker(sConditionVariablesLock);
+
+	// remove entry from variable, if not done yet
+	if (fVariable != NULL) {
+		fVariable->fEntries.Remove(this);
+		fVariable = NULL;
+	}
+
+	return error;
 }
 
 
 status_t
 PrivateConditionVariableEntry::Wait(const void* object, uint32 flags)
 {
-	if (Add(object))
-		return Wait(flags);
+	if (Add(object, flags))
+		return Wait();
 	return B_ENTRY_NOT_FOUND;
 }
 
 
-/*! Removes the entry from its variable.
-	Interrupts must be disabled, sConditionVariablesLock must be held.
-*/
-void
-PrivateConditionVariableEntry::_Remove()
-{
-	if (fVariable) {
-		fVariable->fEntries.Remove(this);
-		fVariable = NULL;
-	}
-}
-
-
-class PrivateConditionVariableEntry::Private {
-public:
-	inline Private(PrivateConditionVariableEntry& entry)
-		: fEntry(entry)
-	{
-	}
-
-	inline uint32 Flags() const				{ return fEntry.fFlags; }
-	inline void Remove() const				{ fEntry._Remove(); }
-	inline void SetResult(status_t result)	{ fEntry.fResult = result; }
-
-private:
-	PrivateConditionVariableEntry&	fEntry;
-};
-
-
 // #pragma mark - PrivateConditionVariable
 
 
@@ -306,15 +267,7 @@ PrivateConditionVariable::_Notify(bool all, status_t result)
 	while (PrivateConditionVariableEntry* entry = fEntries.RemoveHead()) {
 		entry->fVariable = NULL;
 
-		struct thread* thread = entry->fThread;
-
-		if (thread->condition_variable_entry != NULL)
-			thread->condition_variable_entry->fResult = result;
-
-		// wake up the thread
-		thread->condition_variable_entry = NULL;
-		if (thread->state == B_THREAD_WAITING)
-			scheduler_enqueue_in_run_queue(thread);
+		thread_unblock_locked(entry->fThread, B_OK);
 
 		if (!all)
 			break;
@@ -325,41 +278,6 @@ PrivateConditionVariable::_Notify(bool all, status_t result)
 // #pragma mark -
 
 
-/*!	Interrupts must be disabled, thread lock must be held.
-*/
-status_t
-condition_variable_interrupt_thread(struct thread* thread)
-{
-	SpinLocker locker(sConditionVariablesLock);
-
-	if (thread == NULL || thread->state != B_THREAD_WAITING
-		|| thread->condition_variable_entry == NULL) {
-		return B_BAD_VALUE;
-	}
-
-	PrivateConditionVariableEntry* entry = thread->condition_variable_entry;
-	uint32 flags = PrivateConditionVariableEntry::Private(*entry).Flags();
-
-	// interruptable?
-	if ((flags & B_CAN_INTERRUPT) == 0
-		&& ((flags & B_KILL_CAN_INTERRUPT) == 0
-			|| (thread->sig_pending & KILL_SIGNALS) == 0)) {
-		return B_NOT_ALLOWED;
-	}
-
-	PrivateConditionVariableEntry::Private(*entry).SetResult(B_INTERRUPTED);
-
-	// remove entry from its variable
-	PrivateConditionVariableEntry::Private(*entry).Remove();
-
-	// wake up the thread
-	thread->condition_variable_entry = NULL;
-	scheduler_enqueue_in_run_queue(thread);
-
-	return B_OK;
-}
-
-
 void
 condition_variable_init()
 {
@@ -383,4 +301,3 @@ condition_variable_init()
 		"\n"
 		"Lists all existing condition variables\n", 0);
 }
-
diff --git a/src/system/kernel/debug/user_debugger.cpp b/src/system/kernel/debug/user_debugger.cpp
index 879b86a667..ba4316e745 100644
--- a/src/system/kernel/debug/user_debugger.cpp
+++ b/src/system/kernel/debug/user_debugger.cpp
@@ -2366,12 +2366,13 @@ _user_debug_thread(thread_id threadID)
 				scheduler_enqueue_in_run_queue(thread);
 				break;
 
-			case B_THREAD_WAITING:
-				// thread waiting: interrupt it
-				if (thread->sem.blocking >= 0)
-					sem_interrupt_thread(thread);
-				else if (thread->condition_variable_entry)
-					condition_variable_interrupt_thread(thread);
+			default:
+				// thread may be waiting: interrupt it
+				thread_interrupt(thread, false);
+					// TODO: If the thread is already in the kernel and e.g.
+					// about to acquire a semaphore (before
+					// thread_prepare_to_block()), we won't interrupt it.
+					// Maybe we should rather send a signal (SIGTRAP).
 				break;
 		}
 	}
diff --git a/src/system/kernel/fs/fifo.cpp b/src/system/kernel/fs/fifo.cpp
index e594954603..d63d6e32d2 100644
--- a/src/system/kernel/fs/fifo.cpp
+++ b/src/system/kernel/fs/fifo.cpp
@@ -359,13 +359,13 @@ Inode::WriteDataToBuffer(const void *_data, size_t *_length, bool nonBlocking)
 				return B_WOULD_BLOCK;
 
 			ConditionVariableEntry<> entry;
-			entry.Add(this);
+			entry.Add(this, B_CAN_INTERRUPT);
 
 			WriteRequest request(minToWrite);
 			fWriteRequests.Add(&request);
 
 			benaphore_unlock(&fRequestLock);
-			status_t status = entry.Wait(B_CAN_INTERRUPT);
+			status_t status = entry.Wait();
 			benaphore_lock(&fRequestLock);
 
 			fWriteRequests.Remove(&request);
@@ -473,11 +473,11 @@ Inode::WaitForReadRequest(ReadRequest &request)
 
 	// add the entry to wait on
 	ConditionVariableEntry<> entry;
-	entry.Add(&request);
+	entry.Add(&request, B_CAN_INTERRUPT);
 
 	// wait
 	benaphore_unlock(&fRequestLock);
-	status_t status = entry.Wait(B_CAN_INTERRUPT);
+	status_t status = entry.Wait();
 	benaphore_lock(&fRequestLock);
 
 	// unpublish the condition variable
diff --git a/src/system/kernel/sem.cpp b/src/system/kernel/sem.cpp
index c21da57d9f..49b402dc86 100644
--- a/src/system/kernel/sem.cpp
+++ b/src/system/kernel/sem.cpp
@@ -1,4 +1,5 @@
 /*
+ * Copyright 2008, Ingo Weinhold, ingo_weinhold@gmx.de.
  * Copyright 2002-2008, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
  * Distributed under the terms of the MIT License.
  *
@@ -21,6 +22,8 @@
 #include <debug.h>
 #include <thread.h>
 #include <team.h>
+#include <util/AutoLock.h>
+#include <util/DoublyLinkedList.h>
 #include <vfs.h>
 #include <vm_low_memory.h>
 #include <vm_page.h>
@@ -34,13 +37,36 @@
 
 //#define TRACE_SEM
 #ifdef TRACE_SEM
-#	define TRACE(x) dprintf x
+#	define TRACE(x) dprintf_no_syslog x
 #else
 #	define TRACE(x) ;
 #endif
 
+//#define KTRACE_SEM
+#ifdef KTRACE_SEM
+#	define KTRACE(x...) ktrace_printf(x)
+#else
+#	define KTRACE(x...) do {} while (false)
+#endif
+
 #define DEBUG_LAST_ACQUIRER
 
+struct queued_thread : DoublyLinkedListLinkImpl<queued_thread> {
+	queued_thread(struct thread *thread, int32 count)
+		:
+		thread(thread),
+		count(count),
+		queued(false)
+	{
+	}
+
+	struct thread	*thread;
+	int32			count;
+	bool			queued;
+};
+
+typedef DoublyLinkedList<queued_thread> ThreadQueue;
+
 struct sem_entry {
 	sem_id		id;
 	spinlock	lock;	// protects only the id field when unused
@@ -48,12 +74,14 @@ struct sem_entry {
 		// when slot in use
 		struct {
 			int32				count;
-			struct thread_queue queue;
+			int32				net_count;
+									// count + acquisition count of all blocked
+									// threads
 			char				*name;
 			team_id				owner;	// if set to -1, means owned by a port
 			select_info			*select_infos;
-#ifdef DEBUG_LAST_ACQUIRER
 			thread_id			last_acquirer;
+#ifdef DEBUG_LAST_ACQUIRER
 			int32				last_acquire_count;
 			thread_id			last_releaser;
 			int32				last_release_count;
@@ -66,6 +94,8 @@ struct sem_entry {
 			struct sem_entry	*next;
 		} unused;
 	} u;
+
+	ThreadQueue			queue;	// should be in u.used, but has a constructor
 };
 
 static const int32 kMaxSemaphores = 131072;
@@ -84,24 +114,13 @@ static spinlock sem_spinlock = 0;
 #define GRAB_SEM_LOCK(s)         acquire_spinlock(&(s).lock)
 #define RELEASE_SEM_LOCK(s)      release_spinlock(&(s).lock)
 
-static int remove_thread_from_sem(struct thread *thread, struct sem_entry *sem,
-	struct thread_queue *queue, status_t acquireStatus, bool hasThreadLock);
-
-struct sem_timeout_args {
-	thread_id	blocked_thread;
-	sem_id		blocked_sem_id;
-	int32		sem_count;
-};
-
 
 static int
 dump_sem_list(int argc, char **argv)
 {
 	const char *name = NULL;
 	team_id owner = -1;
-#ifdef DEBUG_LAST_ACQUIRER
 	thread_id last = -1;
-#endif
 	int32 i;
 
 	if (argc > 2) {
@@ -109,38 +128,26 @@ dump_sem_list(int argc, char **argv)
 			owner = strtoul(argv[2], NULL, 0);
 		else if (!strcmp(argv[1], "name"))
 			name = argv[2];
-#ifdef DEBUG_LAST_ACQUIRER
 		else if (!strcmp(argv[1], "last"))
 			last = strtoul(argv[2], NULL, 0);
-#endif
 	} else if (argc > 1)
 		owner = strtoul(argv[1], NULL, 0);
 
-	kprintf("sem            id count   team"
-#ifdef DEBUG_LAST_ACQUIRER
-		"   last"
-#endif
-		"  name\n");
+	kprintf("sem            id count   team   last  name\n");
 
 	for (i = 0; i < sMaxSems; i++) {
 		struct sem_entry *sem = &sSems[i];
 		if (sem->id < 0
-#ifdef DEBUG_LAST_ACQUIRER
 			|| (last != -1 && sem->u.used.last_acquirer != last)
-#endif
 			|| (name != NULL && strstr(sem->u.used.name, name) == NULL)
 			|| (owner != -1 && sem->u.used.owner != owner))
 			continue;
 
 		kprintf("%p %6ld %5ld %6ld "
-#ifdef DEBUG_LAST_ACQUIRER
 			"%6ld "
-#endif
 			" %s\n", sem, sem->id, sem->u.used.count,
 			sem->u.used.owner,
-#ifdef DEBUG_LAST_ACQUIRER
 			sem->u.used.last_acquirer > 0 ? sem->u.used.last_acquirer : 0,
-#endif
 			sem->u.used.name);
 	}
 
@@ -158,12 +165,10 @@ dump_sem(struct sem_entry *sem)
 		kprintf("owner:   %ld\n", sem->u.used.owner);
 		kprintf("count:   %ld\n", sem->u.used.count);
 		kprintf("queue:  ");
-		if (sem->u.used.queue.head != NULL) {
-			struct thread *thread = sem->u.used.queue.head;
-			while (thread != NULL) {
-				kprintf(" %ld", thread->id);
-				thread = thread->queue_next;
-			}
+		if (!sem->queue.IsEmpty()) {
+			ThreadQueue::Iterator it = sem->queue.GetIterator();
+			while (queued_thread* entry = it.Next())
+				kprintf(" %ld", entry->thread->id);
 			kprintf("\n");
 		} else
 			kprintf(" -\n");
@@ -178,16 +183,19 @@ dump_sem(struct sem_entry *sem)
 		kprintf("last released by: %ld, count: %ld\n", sem->u.used.last_releaser,
 			sem->u.used.last_release_count);
 
+		if (sem->u.used.last_releaser != 0)
+			set_debug_variable("_releaser", sem->u.used.last_releaser);
+		else
+			unset_debug_variable("_releaser");
+#else
+		kprintf("last acquired by: %ld\n", sem->u.used.last_acquirer);
+#endif
+
 		if (sem->u.used.last_acquirer != 0)
 			set_debug_variable("_acquirer", sem->u.used.last_acquirer);
 		else
 			unset_debug_variable("_acquirer");
 
-		if (sem->u.used.last_releaser != 0)
-			set_debug_variable("_releaser", sem->u.used.last_releaser);
-		else
-			unset_debug_variable("_releaser");
-#endif
 	} else {
 		kprintf("next:    %p\n", sem->u.unused.next);
 		kprintf("next_id: %ld\n", sem->u.unused.next_id);
@@ -238,13 +246,6 @@ dump_sem_info(int argc, char **argv)
 }
 
 
-static inline void
-clear_thread_queue(struct thread_queue *queue)
-{
-	queue->head = queue->tail = NULL;
-}
-
-
 /*!	\brief Appends a semaphore slot to the free list.
 
 	The semaphore list must be locked.
@@ -281,56 +282,6 @@ notify_sem_select_events(struct sem_entry* sem, uint16 events)
 }
 
 
-/*! Called from a timer handler. Wakes up a semaphore */
-static int32
-sem_timeout(timer *data)
-{
-	struct sem_timeout_args *args = (struct sem_timeout_args *)data->user_data;
-	struct thread *thread;
-	int slot;
-	int state;
-	struct thread_queue wakeupQueue;
-
-	thread = thread_get_thread_struct(args->blocked_thread);
-	if (thread == NULL)
-		return B_HANDLED_INTERRUPT;
-	slot = args->blocked_sem_id % sMaxSems;
-
-	state = disable_interrupts();
-	GRAB_SEM_LOCK(sSems[slot]);
-
-	TRACE(("sem_timeout: called on %p sem %ld, thread %ld\n",
-		data, args->blocked_sem_id, args->blocked_thread));
-
-	if (sSems[slot].id != args->blocked_sem_id) {
-		// this thread was not waiting on this semaphore
-		panic("sem_timeout: thread %ld was trying to wait on sem %ld which "
-			"doesn't exist!\n", args->blocked_thread, args->blocked_sem_id);
-
-		RELEASE_SEM_LOCK(sSems[slot]);
-		restore_interrupts(state);
-		return B_HANDLED_INTERRUPT;
-	}
-
-	clear_thread_queue(&wakeupQueue);
-	remove_thread_from_sem(thread, &sSems[slot], &wakeupQueue, B_TIMED_OUT,
-		false);
-
-	RELEASE_SEM_LOCK(sSems[slot]);
-
-	GRAB_THREAD_LOCK();
-	// put the threads in the run q here to make sure we dont deadlock in sem_interrupt_thread
-	while ((thread = thread_dequeue(&wakeupQueue)) != NULL)
-		scheduler_enqueue_in_run_queue(thread);
-
-	RELEASE_THREAD_LOCK();
-
-	restore_interrupts(state);
-
-	return B_INVOKE_SCHEDULER;
-}
-
-
 /*!	Fills the thread_info structure with information from the specified
 	thread.
 	The thread lock must be held when called.
@@ -342,13 +293,7 @@ fill_sem_info(struct sem_entry *sem, sem_info *info, size_t size)
 	info->team = sem->u.used.owner;
 	strlcpy(info->name, sem->u.used.name, sizeof(info->name));
 	info->count = sem->u.used.count;
-
-	// ToDo: not sure if this is the latest holder, or the next
-	// holder...
-	if (sem->u.used.queue.head != NULL)
-		info->latest_holder = sem->u.used.queue.head->id;
-	else
-		info->latest_holder = -1;
+	info->latest_holder = sem->u.used.last_acquirer;
 }
 
 
@@ -389,17 +334,12 @@ sem_init(kernel_args *args)
 	add_debugger_command_etc("sems", &dump_sem_list,
 		"Dump a list of all active semaphores (for team, with name, etc.)",
 		"[ ([ \"team\" | \"owner\" ] <team>) | (\"name\" <name>) ]"
-#ifdef DEBUG_LAST_ACQUIRER
-			" | (\"last\" <last acquirer>)"
-#endif
-		"\n"
+			" | (\"last\" <last acquirer>)\n"
 		"Prints a list of all active semaphores meeting the given\n"
 		"requirement. If no argument is given, all sems are listed.\n"
 		"  <team>             - The team owning the semaphores.\n"
 		"  <name>             - Part of the name of the semaphores.\n"
-#ifdef DEBUG_LAST_ACQUIRER
 		"  <last acquirer>    - The thread that last acquired the semaphore.\n"
-#endif
 		, 0);
 	add_debugger_command_etc("sem", &dump_sem_info,
 		"Dump info about a particular semaphore",
@@ -478,7 +418,8 @@ create_sem_etc(int32 count, const char *name, team_id owner)
 		GRAB_SEM_LOCK(*sem);
 		sem->id = sem->u.unused.next_id;
 		sem->u.used.count = count;
-		clear_thread_queue(&sem->u.used.queue);
+		sem->u.used.net_count = count;
+		new(&sem->queue) ThreadQueue;
 		sem->u.used.name = tempName;
 		sem->u.used.owner = owner;
 		sem->u.used.select_infos = NULL;
@@ -486,6 +427,9 @@ create_sem_etc(int32 count, const char *name, team_id owner)
 		RELEASE_SEM_LOCK(*sem);
 
 		atomic_add(&sUsedSems, 1);
+
+		KTRACE("create_sem_etc(count: %ld, name: %s, owner: %ld) -> %ld",
+			count, name, owner, id);
 	}
 
 	RELEASE_SEM_LIST_LOCK();
@@ -572,95 +516,52 @@ deselect_sem(int32 id, struct select_info* info, bool kernel)
 }
 
 
-/*! Wake up a thread that's blocked on a semaphore
-	this function must be entered with interrupts disabled and THREADLOCK held
-*/
-status_t
-sem_interrupt_thread(struct thread *thread)
-{
-	struct thread_queue wakeupQueue;
-	int32 slot;
-
-	TRACE(("sem_interrupt_thread: called on thread %p (%ld), blocked on sem %ld\n",
-		thread, thread->id, thread->sem.blocking));
-
-	if (thread->state != B_THREAD_WAITING || thread->sem.blocking < 0)
-		return B_BAD_VALUE;
-	if ((thread->sem.flags & B_CAN_INTERRUPT) == 0
-		&& ((thread->sem.flags & B_KILL_CAN_INTERRUPT) == 0
-			|| (thread->sig_pending & KILL_SIGNALS) == 0)) {
-		return B_NOT_ALLOWED;
-	}
-
-	slot = thread->sem.blocking % sMaxSems;
-
-	GRAB_SEM_LOCK(sSems[slot]);
-
-	if (sSems[slot].id != thread->sem.blocking) {
-		panic("sem_interrupt_thread: thread %ld blocks on sem %ld, but that "
-			"sem doesn't exist!\n", thread->id, thread->sem.blocking);
-	}
-
-	clear_thread_queue(&wakeupQueue);
-	status_t result = remove_thread_from_sem(thread, &sSems[slot],
-		&wakeupQueue, B_INTERRUPTED, true);
-
-	RELEASE_SEM_LOCK(sSems[slot]);
-
-	if (result != B_OK) {
-		// The thread is not in the wait queue anymore. Probably it just timed
-		// out before we locked the sem.
-		return result;
-	}
-
-	while ((thread = thread_dequeue(&wakeupQueue)) != NULL)
-		scheduler_enqueue_in_run_queue(thread);
-
-	return B_OK;
-}
-
-
 /*!	Forcibly removes a thread from a semaphores wait queue. May have to wake up
-	other threads in the process. All threads that need to be woken up are added
-	to the passed in thread_queue.
-	Must be called with semaphore lock held.
+	other threads in the process.
+	Must be called with semaphore lock held. The thread lock must not be held.
 */
-static int
-remove_thread_from_sem(struct thread *thread, struct sem_entry *sem,
-	struct thread_queue *queue, status_t acquireStatus, bool hasThreadLock)
+static void
+remove_thread_from_sem(queued_thread *entry, struct sem_entry *sem)
 {
-	// remove the thread from the queue and place it in the supplied queue
-	if (thread_dequeue_id(&sem->u.used.queue, thread->id) != thread)
-		return B_ENTRY_NOT_FOUND;
+	if (!entry->queued)
+		return;
 
-	sem->u.used.count += thread->sem.acquire_count;
-	thread->sem.acquire_status = acquireStatus;
-	thread_enqueue(thread, queue);
+	sem->queue.Remove(entry);
+	entry->queued = false;
+	sem->u.used.count += entry->count;
 
-	// now see if more threads need to be woken up
-	while (sem->u.used.count > 0
-		   && thread_lookat_queue(&sem->u.used.queue) != NULL) {
-		int32 delta = min_c(thread->sem.count, sem->u.used.count);
+	// We're done with this entry. We only have to check, if other threads
+	// need unblocking, too.
 
-		thread->sem.count -= delta;
-		if (thread->sem.count <= 0) {
-			thread = thread_dequeue(&sem->u.used.queue);
-			thread_enqueue(thread, queue);
+	// Now see if more threads need to be woken up. We get the thread lock for
+	// that time, so the blocking state of threads won't change. We need that
+	// lock anyway when unblocking a thread.
+	GRAB_THREAD_LOCK();
+
+	while ((entry = sem->queue.Head()) != NULL) {
+		if (thread_is_blocked(entry->thread)) {
+			// The thread is still waiting. If its count is satisfied, unblock
+			// it. Otherwise we can't unblock any other thread.
+			if (entry->count > sem->u.used.net_count)
+				break;
+
+			thread_unblock_locked(entry->thread, B_OK);
+			sem->u.used.net_count -= entry->count;
+		} else {
+			// The thread is no longer waiting, but still queued, which means
+			// acquiration failed and we can just remove it.
+			sem->u.used.count += entry->count;
 		}
-		sem->u.used.count -= delta;
+
+		sem->queue.Remove(entry);
+		entry->queued = false;
 	}
 
-	if (sem->u.used.count > 0 && sem->u.used.select_infos != NULL) {
-		if (hasThreadLock)
-			RELEASE_THREAD_LOCK();
+	RELEASE_THREAD_LOCK();
 
+	// select notification, if the semaphore is now acquirable
+	if (sem->u.used.count > 0)
 		notify_sem_select_events(sem, B_EVENT_ACQUIRE_SEMAPHORE);
-
-		if (hasThreadLock)
-			GRAB_THREAD_LOCK();
-	}
-
-	return B_OK;
 }
 
 
@@ -732,21 +633,14 @@ create_sem(int32 count, const char *name)
 status_t
 delete_sem(sem_id id)
 {
-	struct thread_queue releaseQueue;
-	int32 releasedThreads;
-	struct thread *thread;
-	cpu_status state;
-	int32 slot;
-	char *name;
-
 	if (sSemsActive == false)
 		return B_NO_MORE_SEMS;
 	if (id < 0)
 		return B_BAD_SEM_ID;
 
-	slot = id % sMaxSems;
+	int32 slot = id % sMaxSems;
 
-	state = disable_interrupts();
+	cpu_status state = disable_interrupts();
 	GRAB_SEM_LOCK(sSems[slot]);
 
 	if (sSems[slot].id != id) {
@@ -756,22 +650,21 @@ delete_sem(sem_id id)
 		return B_BAD_SEM_ID;
 	}
 
+	KTRACE("delete_sem(sem: %ld)", id);
+
 	notify_sem_select_events(&sSems[slot], B_EVENT_INVALID);
 	sSems[slot].u.used.select_infos = NULL;
 
-	releasedThreads = 0;
-	clear_thread_queue(&releaseQueue);
-
 	// free any threads waiting for this semaphore
-	while ((thread = thread_dequeue(&sSems[slot].u.used.queue)) != NULL) {
-		thread->sem.acquire_status = B_BAD_SEM_ID;
-		thread->sem.count = 0;
-		thread_enqueue(thread, &releaseQueue);
-		releasedThreads++;
+	GRAB_THREAD_LOCK();
+	while (queued_thread* entry = sSems[slot].queue.RemoveHead()) {
+		entry->queued = false;
+		thread_unblock_locked(entry->thread, B_BAD_SEM_ID);
 	}
+	RELEASE_THREAD_LOCK();
 
 	sSems[slot].id = -1;
-	name = sSems[slot].u.used.name;
+	char *name = sSems[slot].u.used.name;
 	sSems[slot].u.used.name = NULL;
 
 	RELEASE_SEM_LOCK(sSems[slot]);
@@ -782,15 +675,6 @@ delete_sem(sem_id id)
 	atomic_add(&sUsedSems, -1);
 	RELEASE_SEM_LIST_LOCK();
 
-	if (releasedThreads > 0) {
-		GRAB_THREAD_LOCK();
-		while ((thread = thread_dequeue(&releaseQueue)) != NULL)	
-			scheduler_enqueue_in_run_queue(thread);
-
-		scheduler_reschedule();
-		RELEASE_THREAD_LOCK();
-	}
-
 	restore_interrupts(state);
 
 	free(name);
@@ -876,21 +760,20 @@ switch_sem_etc(sem_id semToBeReleased, sem_id id, int32 count,
 		}
 	}
 
+	KTRACE("switch_sem_etc(semToBeReleased: %ld, sem: %ld, count: %ld, "
+		"flags: 0x%lx, timeout: %lld)", semToBeReleased, id, count, flags,
+		timeout);
+
 	if ((sSems[slot].u.used.count -= count) < 0) {
 		// we need to block
 		struct thread *thread = thread_get_current_thread();
-		timer timeoutTimer;
-			// stick it on the stack, since we may be blocking here
-		struct sem_timeout_args args;
 
 		TRACE(("switch_sem_etc(id = %ld): block name = %s, thread = %p,"
 			" name = %s\n", id, sSems[slot].u.used.name, thread, thread->name));
 
 		// do a quick check to see if the thread has any pending signals
 		// this should catch most of the cases where the thread had a signal
-		if (((flags & B_CAN_INTERRUPT) && (thread->sig_pending & ~thread->sig_block_mask) != 0)
-			|| ((flags & B_KILL_CAN_INTERRUPT)
-				&& (thread->sig_pending & KILL_SIGNALS))) {
+		if (thread_is_interrupted(thread, flags)) {
 			sSems[slot].u.used.count += count;
 			status = B_INTERRUPTED;
 				// the other semaphore will be released later
@@ -900,90 +783,55 @@ switch_sem_etc(sem_id semToBeReleased, sem_id id, int32 count,
 		if ((flags & (B_RELATIVE_TIMEOUT | B_ABSOLUTE_TIMEOUT)) == 0)
 			timeout = B_INFINITE_TIMEOUT;
 
-		thread->next_state = B_THREAD_WAITING;
-		thread->sem.flags = flags;
-		thread->sem.blocking = id;
-		thread->sem.acquire_count = count;
-		thread->sem.count = min_c(-sSems[slot].u.used.count, count);
-			// store the count we need to restore upon release
-		thread->sem.acquire_status = B_NO_ERROR;
-		thread_enqueue(thread, &sSems[slot].u.used.queue);
+		// enqueue in the semaphore queue and get ready to wait
+		queued_thread queueEntry(thread, count);
+		sSems[slot].queue.Add(&queueEntry);
+		queueEntry.queued = true;
 
-		if (timeout != B_INFINITE_TIMEOUT) {
-			TRACE(("switch_sem_etc: setting timeout sem for %Ld usecs, sem %ld, thread %ld\n",
-				timeout, id, thread->id));
-
-			// set up an event to go off with the thread struct as the data
-			args.blocked_sem_id = id;
-			args.blocked_thread = thread->id;
-			args.sem_count = count;
-
-			timeoutTimer.user_data = &args;
-			add_timer(&timeoutTimer, &sem_timeout, timeout,
-				flags & B_RELATIVE_TIMEOUT ?
-					B_ONE_SHOT_RELATIVE_TIMER : B_ONE_SHOT_ABSOLUTE_TIMER);			
-		}
+		thread_prepare_to_block(thread, flags, THREAD_BLOCK_TYPE_SEMAPHORE,
+			(void*)(addr_t)id);
 
 		RELEASE_SEM_LOCK(sSems[slot]);
 
-		if (semToBeReleased >= B_OK) {
+		// release the other semaphore, if any
+		if (semToBeReleased >= 0) {
 			release_sem_etc(semToBeReleased, 1, B_DO_NOT_RESCHEDULE);
 			semToBeReleased = -1;
 		}
 
 		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
-		if (((flags & B_CAN_INTERRUPT)
-				&& (thread->sig_pending & ~thread->sig_block_mask) != 0)
-			|| ((flags & B_KILL_CAN_INTERRUPT)
-				&& (thread->sig_pending & KILL_SIGNALS))) {
-			struct thread_queue wakeupQueue;
-			// ok, so a tiny race happened where a signal was delivered to this thread while
-			// it was setting up the sem. We can only be sure a signal wasn't delivered
-			// here, since the threadlock is held. The previous check would have found most
-			// instances, but there was a race, so we have to handle it. It'll be more messy...
-			clear_thread_queue(&wakeupQueue);
-			GRAB_SEM_LOCK(sSems[slot]);
-			if (sSems[slot].id == id) {
-				remove_thread_from_sem(thread, &sSems[slot], &wakeupQueue,
-					B_INTERRUPTED, true);
-			}
-			RELEASE_SEM_LOCK(sSems[slot]);
 
-			struct thread *wakeupThread;
-			while ((wakeupThread = thread_dequeue(&wakeupQueue)) != NULL)
-				scheduler_enqueue_in_run_queue(wakeupThread);
+		status_t acquireStatus = timeout == B_INFINITE_TIMEOUT
+			? thread_block_locked(thread)
+			: thread_block_with_timeout_locked(flags, timeout);
 
-			// fall through and reschedule since another thread with a higher priority may have been woken up
-		}
-		scheduler_reschedule();
 		RELEASE_THREAD_LOCK();
+		GRAB_SEM_LOCK(sSems[slot]);
 
-		if (timeout != B_INFINITE_TIMEOUT) {
-			if (thread->sem.acquire_status != B_TIMED_OUT) {
-				// cancel the timer event, the sem may have been deleted or interrupted
-				// with the timer still active
-				cancel_timer(&timeoutTimer);
-			}
-		}
+		// If we're still queued, this means the acquiration failed, and we
+		// need to remove our entry and (potentially) wake up other threads.
+		if (queueEntry.queued)
+			remove_thread_from_sem(&queueEntry, &sSems[slot]);
 
-#ifdef DEBUG_LAST_ACQUIRER
-		if (thread->sem.acquire_status >= B_OK) {
+		if (acquireStatus >= B_OK) {
 			sSems[slot].u.used.last_acquirer = thread_get_current_thread_id();
+#ifdef DEBUG_LAST_ACQUIRER
 			sSems[slot].u.used.last_acquire_count = count;
-		}
 #endif
+		}
 
+		RELEASE_SEM_LOCK(sSems[slot]);
 		restore_interrupts(state);
 
 		TRACE(("switch_sem_etc(sem %ld): exit block name %s, "
 			"thread %ld (%s)\n", id, sSems[slot].u.used.name, thread->id,
 			thread->name));
-		return thread->sem.acquire_status;
+		KTRACE("switch_sem_etc() done: 0x%lx", acquireStatus);
+		return acquireStatus;
 	} else {
-#ifdef DEBUG_LAST_ACQUIRER
+		sSems[slot].u.used.net_count -= count;
 		sSems[slot].u.used.last_acquirer = thread_get_current_thread_id();
+#ifdef DEBUG_LAST_ACQUIRER
 		sSems[slot].u.used.last_acquire_count = count;
 #endif
 	}
@@ -1004,6 +852,8 @@ err:
 	_user_debugger("Thread tried to acquire kernel semaphore.");
 #endif
 
+	KTRACE("switch_sem_etc() done: 0x%lx", status);
+
 	return status;
 }
 
@@ -1018,10 +868,7 @@ release_sem(sem_id id)
 status_t
 release_sem_etc(sem_id id, int32 count, uint32 flags)
 {
-	struct thread_queue releaseQueue;
 	int32 slot = id % sMaxSems;
-	cpu_status state;
-	status_t status = B_OK;
 
 	if (kernel_startup)
 		return B_OK;
@@ -1032,13 +879,12 @@ release_sem_etc(sem_id id, int32 count, uint32 flags)
 	if (count <= 0 && (flags & B_RELEASE_ALL) == 0)
 		return B_BAD_VALUE;
 
-	state = disable_interrupts();
-	GRAB_SEM_LOCK(sSems[slot]);
+	InterruptsLocker _;
+	SpinLocker semLocker(sSems[slot].lock);
 
 	if (sSems[slot].id != id) {
 		TRACE(("sem_release_etc: invalid sem_id %ld\n", id));
-		status = B_BAD_SEM_ID;
-		goto err;
+		return B_BAD_SEM_ID;
 	}
 
 	// ToDo: the B_CHECK_PERMISSION flag should be made private, as it
@@ -1047,81 +893,80 @@ release_sem_etc(sem_id id, int32 count, uint32 flags)
 		&& sSems[slot].u.used.owner == team_get_kernel_team_id()) {
 		dprintf("thread %ld tried to release kernel semaphore.\n",
 			thread_get_current_thread_id());
-		status = B_NOT_ALLOWED;
-		goto err;
+		return B_NOT_ALLOWED;
 	}
 
-#ifdef DEBUG_LAST_ACQUIRER
+	KTRACE("release_sem_etc(sem: %ld, count: %ld, flags: 0x%lx)", id, count,
+		flags);
+
 	sSems[slot].u.used.last_acquirer = -sSems[slot].u.used.last_acquirer;
+#ifdef DEBUG_LAST_ACQUIRER
 	sSems[slot].u.used.last_releaser = thread_get_current_thread_id();
 	sSems[slot].u.used.last_release_count = count;
 #endif
 
-	// clear out a queue we will use to hold all of the threads that we will have to
-	// put back into the run list. This is done so the thread lock wont be held
-	// while this sems lock is held since the two locks are grabbed in the other
-	// order in sem_interrupt_thread.
-	clear_thread_queue(&releaseQueue);
-
 	if (flags & B_RELEASE_ALL) {
-		count = -sSems[slot].u.used.count;
+		count = sSems[slot].u.used.net_count - sSems[slot].u.used.count;
 
 		// is there anything to do for us at all?
 		if (count == 0)
-			goto err;
+			return B_OK;
+
+		// Don't release more than necessary -- there might be interrupted/
+		// timed out threads in the queue.
+		flags |= B_RELEASE_IF_WAITING_ONLY;
 	}
 
+	SpinLocker threadLocker(thread_spinlock);
+
 	while (count > 0) {
-		int delta = count;
-		if (sSems[slot].u.used.count < 0) {
-			struct thread *thread = thread_lookat_queue(&sSems[slot].u.used.queue);
-
-			delta = min_c(count, thread->sem.count);
-			thread->sem.count -= delta;
-			if (thread->sem.count <= 0) {
-				// release this thread
-				thread = thread_dequeue(&sSems[slot].u.used.queue);
-				thread_enqueue(thread, &releaseQueue);
-				thread->sem.count = 0;
+		queued_thread* entry = sSems[slot].queue.Head();
+		if (entry == NULL) {
+			if ((flags & B_RELEASE_IF_WAITING_ONLY) == 0) {
+				sSems[slot].u.used.count += count;
+				sSems[slot].u.used.net_count += count;
 			}
-		} else if (flags & B_RELEASE_IF_WAITING_ONLY)
 			break;
+		}
 
-		sSems[slot].u.used.count += delta;
-		count -= delta;
+		if (thread_is_blocked(entry->thread)) {
+			// The thread is still waiting. If its count is satisfied,
+			// unblock it. Otherwise we can't unblock any other thread.
+			if (entry->count > sSems[slot].u.used.net_count + count) {
+				sSems[slot].u.used.count += count;
+				sSems[slot].u.used.net_count += count;
+				break;
+			}
+
+			thread_unblock_locked(entry->thread, B_OK);
+
+			int delta = min_c(count, entry->count);
+			sSems[slot].u.used.count += delta;
+			sSems[slot].u.used.net_count += delta - entry->count;
+			count -= delta;
+		} else {
+			// The thread is no longer waiting, but still queued, which
+			// means acquiration failed and we can just remove it.
+			sSems[slot].u.used.count += entry->count;
+		}
+
+		sSems[slot].queue.Remove(entry);
+		entry->queued = false;
 	}
 
+	threadLocker.Unlock();
+
 	if (sSems[slot].u.used.count > 0)
 		notify_sem_select_events(&sSems[slot], B_EVENT_ACQUIRE_SEMAPHORE);
 
-	RELEASE_SEM_LOCK(sSems[slot]);
-
-	// pull off any items in the release queue and put them in the run queue
-	if (releaseQueue.head != NULL) {
-		struct thread *thread;
-
-		GRAB_THREAD_LOCK();
-		while ((thread = thread_dequeue(&releaseQueue)) != NULL) {
-#if 0
-			// temporarily place thread in a run queue with a higher priority to boost it up
-			thread->next_priority = thread->priority >= B_FIRST_REAL_TIME_PRIORITY ?
-				thread->priority : thread->priority + 1;
-#endif
-			scheduler_enqueue_in_run_queue(thread);
-		}
-		if ((flags & B_DO_NOT_RESCHEDULE) == 0)
-			scheduler_reschedule();
-
-		RELEASE_THREAD_LOCK();
+	// reschedule, if we've not explicitly been told not to
+	if ((flags & B_DO_NOT_RESCHEDULE) == 0) {
+		semLocker.Unlock();
+		threadLocker.Lock();
+		scheduler_reschedule();
 	}
-	goto outnolock;
 
-err:
-	RELEASE_SEM_LOCK(sSems[slot]);
-outnolock:
-	restore_interrupts(state);
-
-	return status;
+	return B_OK;
 }
 
 
diff --git a/src/system/kernel/signal.cpp b/src/system/kernel/signal.cpp
index 1e739adc86..5d6f18c139 100644
--- a/src/system/kernel/signal.cpp
+++ b/src/system/kernel/signal.cpp
@@ -459,20 +459,6 @@ is_signal_blocked(int signal)
 }
 
 
-/*!	Tries to interrupt a thread waiting for a semaphore or a condition variable.
-	Interrupts must be disabled, the thread lock be held.
-*/
-static status_t
-signal_interrupt_thread(struct thread* thread)
-{
-	if (thread->sem.blocking >= 0)
-		return sem_interrupt_thread(thread);
-	else if (thread->condition_variable_entry)
-		return condition_variable_interrupt_thread(thread);
-	return B_BAD_VALUE;
-}
-
-
 /*!	Delivers the \a signal to the \a thread, but doesn't handle the signal -
 	it just makes sure the thread gets the signal, ie. unblocks it if needed.
 	This function must be called with interrupts disabled and the
@@ -505,19 +491,13 @@ deliver_signal(struct thread *thread, uint signal, uint32 flags)
 
 			mainThread->sig_pending |= SIGNAL_TO_MASK(SIGKILLTHR);
 			// Wake up main thread
-			if (mainThread->state == B_THREAD_SUSPENDED)
-				scheduler_enqueue_in_run_queue(mainThread);
-			else if (mainThread->state == B_THREAD_WAITING)
-				signal_interrupt_thread(mainThread);
+			thread_interrupt(mainThread, true);
 
 			// Supposed to fall through
 		}
 		case SIGKILLTHR:
 			// Wake up suspended threads and interrupt waiting ones
-			if (thread->state == B_THREAD_SUSPENDED)
-				scheduler_enqueue_in_run_queue(thread);
-			else if (thread->state == B_THREAD_WAITING)
-				signal_interrupt_thread(thread);
+			thread_interrupt(thread, true);
 			break;
 
 		case SIGCONT:
@@ -536,8 +516,7 @@ deliver_signal(struct thread *thread, uint signal, uint32 flags)
 			if (thread->sig_pending
 				& (~thread->sig_block_mask | SIGNAL_TO_MASK(SIGCHLD))) {
 				// Interrupt thread if it was waiting
-				if (thread->state == B_THREAD_WAITING)
-					signal_interrupt_thread(thread);
+				thread_interrupt(thread, false);
 			}
 			break;
 	}
diff --git a/src/system/kernel/team.cpp b/src/system/kernel/team.cpp
index 595faae505..2d228da1eb 100644
--- a/src/system/kernel/team.cpp
+++ b/src/system/kernel/team.cpp
@@ -1745,7 +1745,7 @@ wait_for_child(pid_t child, uint32 flags, int32 *_reason,
 		ConditionVariableEntry<team_dead_children> deadWaitEntry;
 
 		if (status == B_WOULD_BLOCK && (flags & WNOHANG) == 0)
-			deadWaitEntry.Add(team->dead_children);
+			deadWaitEntry.Add(team->dead_children, B_CAN_INTERRUPT);
 
 		locker.Unlock();
 
@@ -1766,7 +1766,7 @@ wait_for_child(pid_t child, uint32 flags, int32 *_reason,
 			return status;
 		}
 
-		status = deadWaitEntry.Wait(B_CAN_INTERRUPT);
+		status = deadWaitEntry.Wait();
 		if (status == B_INTERRUPTED) {
 			T(WaitForChildDone(status));
 			return status;
diff --git a/src/system/kernel/thread.cpp b/src/system/kernel/thread.cpp
index 3bf6babb96..734d17a809 100644
--- a/src/system/kernel/thread.cpp
+++ b/src/system/kernel/thread.cpp
@@ -78,8 +78,6 @@ static thread_id sNextThreadID = 1;
 static int32 sMaxThreads = 4096;
 static int32 sUsedThreads = 0;
 
-static sem_id sSnoozeSem = -1;
-
 // death stacks - used temporarily as a thread cleans itself up
 struct death_stack {
 	area_id	area;
@@ -226,8 +224,6 @@ create_thread_struct(struct thread *inthread, const char *name,
 	thread->id = threadID >= 0 ? threadID : allocate_thread_id();
 	thread->team = NULL;
 	thread->cpu = cpu;
-	thread->sem.blocking = -1;
-	thread->condition_variable_entry = NULL;
 	thread->fault_handler = 0;
 	thread->page_faults_allowed = 1;
 	thread->kernel_stack_area = -1;
@@ -659,6 +655,28 @@ thread_exit2(void *_args)
 }
 
 
+static sem_id
+get_thread_wait_sem(struct thread* thread)
+{
+	if (thread->state == B_THREAD_WAITING
+		&& thread->wait.type == THREAD_BLOCK_TYPE_SEMAPHORE) {
+		return (sem_id)(addr_t)thread->wait.object;
+	}
+	return -1;
+}
+
+
+static PrivateConditionVariable*
+get_thread_wait_cvar(struct thread* thread)
+{
+	if (thread->state == B_THREAD_WAITING
+		&& thread->wait.type == THREAD_BLOCK_TYPE_CONDITION_VARIABLE) {
+		return (PrivateConditionVariable*)thread->wait.object;
+	}
+	return NULL;
+}
+
+
 /*!
 	Fills the thread_info structure with information from the specified
 	thread.
@@ -673,25 +691,37 @@ fill_thread_info(struct thread *thread, thread_info *info, size_t size)
 	strlcpy(info->name, thread->name, B_OS_NAME_LENGTH);
 
 	if (thread->state == B_THREAD_WAITING) {
-		if (thread->sem.blocking == sSnoozeSem)
-			info->state = B_THREAD_ASLEEP;
-		else if (thread->sem.blocking == thread->msg.read_sem)
-			info->state = B_THREAD_RECEIVING;
-		else
-			info->state = B_THREAD_WAITING;
+		info->state = B_THREAD_WAITING;
+
+		switch (thread->wait.type) {
+			case THREAD_BLOCK_TYPE_SNOOZE:
+				info->state = B_THREAD_ASLEEP;
+				break;
+
+			case THREAD_BLOCK_TYPE_SEMAPHORE:
+			{
+				sem_id sem = (sem_id)(addr_t)thread->wait.object;
+				if (sem == thread->msg.read_sem)
+					info->state = B_THREAD_RECEIVING;
+				break;
+			}
+
+			case THREAD_BLOCK_TYPE_CONDITION_VARIABLE:
+			default:
+				break;
+		}
 	} else
 		info->state = (thread_state)thread->state;
 
 	info->priority = thread->priority;
-	info->sem = thread->sem.blocking;
 	info->user_time = thread->user_time;
 	info->kernel_time = thread->kernel_time;
 	info->stack_base = (void *)thread->user_stack_base;
 	info->stack_end = (void *)(thread->user_stack_base
 		+ thread->user_stack_size);
+	info->sem = get_thread_wait_sem(thread);
 }
 
-
 static status_t
 send_data_etc(thread_id id, int32 code, const void *buffer,
 	size_t bufferSize, int32 flags)
@@ -989,12 +1019,26 @@ state_to_text(struct thread *thread, int32 state)
 			return "running";
 
 		case B_THREAD_WAITING:
-			if (thread->sem.blocking == sSnoozeSem)
-				return "zzz";
-			if (thread->sem.blocking == thread->msg.read_sem)
-				return "receive";
+		{
+			switch (thread->wait.type) {
+				case THREAD_BLOCK_TYPE_SNOOZE:
+					return "zzz";
+	
+				case THREAD_BLOCK_TYPE_SEMAPHORE:
+				{
+					sem_id sem = (sem_id)(addr_t)thread->wait.object;
+					if (sem == thread->msg.read_sem)
+						return "receive";
+					break;
+				}
+	
+				case THREAD_BLOCK_TYPE_CONDITION_VARIABLE:
+				default:
+					break;
+			}
 
 			return "waiting";
+		}
 
 		case B_THREAD_SUSPENDED:
 			return "suspended";
@@ -1029,14 +1073,8 @@ _dump_thread_info(struct thread *thread)
 	kprintf("sig_pending:        %#lx (blocked: %#lx)\n", thread->sig_pending,
 		thread->sig_block_mask);
 	kprintf("in_kernel:          %d\n", thread->in_kernel);
-	kprintf("  sem.blocking:     %ld\n", thread->sem.blocking);
-	kprintf("  sem.count:        %ld\n", thread->sem.count);
-	kprintf("  sem.acquire_status: %#lx\n", thread->sem.acquire_status);
-	kprintf("  sem.flags:        %#lx\n", thread->sem.flags);
-
-	PrivateConditionVariableEntry* entry = thread->condition_variable_entry;
-	kprintf("condition variable: %p\n", entry ? entry->Variable() : NULL);
-
+	kprintf("sem blocking:       %ld\n", get_thread_wait_sem(thread));
+	kprintf("condition variable: %p\n", get_thread_wait_cvar(thread));
 	kprintf("fault_handler:      %p\n", (void *)thread->fault_handler);
 	kprintf("args:               %p %p\n", thread->args1, thread->args2);
 	kprintf("entry:              %p\n", (void *)thread->entry);
@@ -1165,7 +1203,7 @@ dump_thread_list(int argc, char **argv)
 		if ((requiredState && thread->state != requiredState)
 			|| (calling && !arch_debug_contains_call(thread, callSymbol,
 					callStart, callEnd))
-			|| (sem > 0 && thread->sem.blocking != sem)
+			|| (sem > 0 && get_thread_wait_sem(thread) != sem)
 			|| (team > 0 && thread->team->id != team)
 			|| (realTimeOnly && thread->priority < B_REAL_TIME_DISPLAY_PRIORITY))
 			continue;
@@ -1175,10 +1213,10 @@ dump_thread_list(int argc, char **argv)
 
 		// does it block on a semaphore or a condition variable?
 		if (thread->state == B_THREAD_WAITING) {
-			if (thread->condition_variable_entry)
-				kprintf("%p  ", thread->condition_variable_entry->Variable());
+			if (get_thread_wait_cvar(thread))
+				kprintf("%p  ", get_thread_wait_cvar(thread));
 			else
-				kprintf("%10ld  ", thread->sem.blocking);
+				kprintf("%10ld  ", get_thread_wait_sem(thread));
 		} else
 			kprintf("      -     ");
 
@@ -1881,13 +1919,6 @@ thread_init(kernel_args *args)
 	// zero out the dead thread structure q
 	memset(&dead_q, 0, sizeof(dead_q));
 
-	// allocate snooze sem
-	sSnoozeSem = create_sem(0, "snooze sem");
-	if (sSnoozeSem < 0) {
-		panic("error creating snooze sem\n");
-		return sSnoozeSem;
-	}
-
 	if (arch_thread_init(args) < B_OK)
 		panic("arch_thread_init() failed!\n");
 
@@ -2039,6 +2070,77 @@ thread_preboot_init_percpu(struct kernel_args *args, int32 cpuNum)
 	return B_OK;
 }
 
+
+//	#pragma mark - thread blocking API
+
+
+static status_t
+thread_block_timeout(timer* timer)
+{
+	// The timer has been installed with B_TIMER_ACQUIRE_THREAD_LOCK, so
+	// we're holding the thread lock already. This makes things comfortably
+	// easy.
+
+	struct thread* thread = (struct thread*)timer->user_data;
+	if (thread_unblock_locked(thread, B_TIMED_OUT))
+		return B_INVOKE_SCHEDULER;
+
+	return B_HANDLED_INTERRUPT;
+}
+
+
+status_t
+thread_block()
+{
+	InterruptsSpinLocker _(thread_spinlock);
+	return thread_block_locked(thread_get_current_thread());
+}
+
+
+bool
+thread_unblock(status_t threadID, status_t status)
+{
+	InterruptsSpinLocker _(thread_spinlock);
+
+	struct thread* thread = thread_get_thread_struct_locked(threadID);
+	if (thread == NULL)
+		return false;
+	return thread_unblock_locked(thread, status);
+}
+
+
+status_t
+thread_block_with_timeout_locked(uint32 timeoutFlags, bigtime_t timeout)
+{
+	struct thread* thread = thread_get_current_thread();
+
+	if (thread->wait.status != 1)
+		return thread->wait.status;
+
+	// Timer flags: absolute/relative + "acquire thread lock". The latter
+	// avoids nasty race conditions and deadlock problems that could otherwise
+	// occur between our cancel_timer() and a concurrently executing
+	// thread_block_timeout().
+	uint32 timerFlags = (timeoutFlags & B_RELATIVE_TIMEOUT)
+		? B_ONE_SHOT_RELATIVE_TIMER : B_ONE_SHOT_ABSOLUTE_TIMER;
+	timerFlags |= B_TIMER_ACQUIRE_THREAD_LOCK;
+
+	// install the timer
+	thread->wait.unblock_timer.user_data = thread;
+	add_timer(&thread->wait.unblock_timer, &thread_block_timeout, timeout,
+		timerFlags);
+
+	// block
+	status_t error = thread_block_locked(thread);
+
+	// cancel timer, if it didn't fire
+	if (error != B_TIMED_OUT)
+		cancel_timer(&thread->wait.unblock_timer);
+
+	return error;
+}
+
+
 //	#pragma mark - public kernel API
 
 
@@ -2297,7 +2399,12 @@ snooze_etc(bigtime_t timeout, int timebase, uint32 flags)
 	if (timebase != B_SYSTEM_TIMEBASE)
 		return B_BAD_VALUE;
 
-	status = acquire_sem_etc(sSnoozeSem, 1, flags, timeout);
+	InterruptsSpinLocker _(thread_spinlock);
+	struct thread* thread = thread_get_current_thread();
+
+	thread_prepare_to_block(thread, flags, THREAD_BLOCK_TYPE_SNOOZE, NULL);
+	status = thread_block_with_timeout_locked(flags, timeout);
+
 	if (status == B_TIMED_OUT || status == B_WOULD_BLOCK)
 		return B_OK;