diff --git a/evthread.c b/evthread.c
new file mode 100644
index 0000000..90e195d
--- /dev/null
+++ b/evthread.c
@@ -0,0 +1,445 @@
+/*
+ * Copyright (c) 2008-2012 Niels Provos, Nick Mathewson
+ *
+ * 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. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
+ */
+
+#include "event2/event-config.h"
+
+#ifndef _EVENT_DISABLE_THREAD_SUPPORT
+
+#include "event2/thread.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "log-internal.h"
+#include "mm-internal.h"
+#include "util-internal.h"
+#include "evthread-internal.h"
+
+#ifdef EVTHREAD_EXPOSE_STRUCTS
+#define GLOBAL
+#else
+#define GLOBAL static
+#endif
+
+/* globals */
+GLOBAL int _evthread_lock_debugging_enabled = 0;
+GLOBAL struct evthread_lock_callbacks _evthread_lock_fns = {
+	0, 0, NULL, NULL, NULL, NULL
+};
+GLOBAL unsigned long (*_evthread_id_fn)(void) = NULL;
+GLOBAL struct evthread_condition_callbacks _evthread_cond_fns = {
+	0, NULL, NULL, NULL, NULL
+};
+
+/* Used for debugging */
+static struct evthread_lock_callbacks _original_lock_fns = {
+	0, 0, NULL, NULL, NULL, NULL
+};
+static struct evthread_condition_callbacks _original_cond_fns = {
+	0, NULL, NULL, NULL, NULL
+};
+
+void
+evthread_set_id_callback(unsigned long (*id_fn)(void))
+{
+	_evthread_id_fn = id_fn;
+}
+
+int
+evthread_set_lock_callbacks(const struct evthread_lock_callbacks *cbs)
+{
+	struct evthread_lock_callbacks *target =
+	    _evthread_lock_debugging_enabled
+	    ? &_original_lock_fns : &_evthread_lock_fns;
+
+	if (!cbs) {
+		if (target->alloc)
+			event_warnx("Trying to disable lock functions after "
+			    "they have been set up will probaby not work.");
+		memset(target, 0, sizeof(_evthread_lock_fns));
+		return 0;
+	}
+	if (target->alloc) {
+		/* Uh oh; we already had locking callbacks set up.*/
+		if (target->lock_api_version == cbs->lock_api_version &&
+			target->supported_locktypes == cbs->supported_locktypes &&
+			target->alloc == cbs->alloc &&
+			target->free == cbs->free &&
+			target->lock == cbs->lock &&
+			target->unlock == cbs->unlock) {
+			/* no change -- allow this. */
+			return 0;
+		}
+		event_warnx("Can't change lock callbacks once they have been "
+		    "initialized.");
+		return -1;
+	}
+	if (cbs->alloc && cbs->free && cbs->lock && cbs->unlock) {
+		memcpy(target, cbs, sizeof(_evthread_lock_fns));
+		return event_global_setup_locks_(1);
+	} else {
+		return -1;
+	}
+}
+
+int
+evthread_set_condition_callbacks(const struct evthread_condition_callbacks *cbs)
+{
+	struct evthread_condition_callbacks *target =
+	    _evthread_lock_debugging_enabled
+	    ? &_original_cond_fns : &_evthread_cond_fns;
+
+	if (!cbs) {
+		if (target->alloc_condition)
+			event_warnx("Trying to disable condition functions "
+			    "after they have been set up will probaby not "
+			    "work.");
+		memset(target, 0, sizeof(_evthread_cond_fns));
+		return 0;
+	}
+	if (target->alloc_condition) {
+		/* Uh oh; we already had condition callbacks set up.*/
+		if (target->condition_api_version == cbs->condition_api_version &&
+			target->alloc_condition == cbs->alloc_condition &&
+			target->free_condition == cbs->free_condition &&
+			target->signal_condition == cbs->signal_condition &&
+			target->wait_condition == cbs->wait_condition) {
+			/* no change -- allow this. */
+			return 0;
+		}
+		event_warnx("Can't change condition callbacks once they "
+		    "have been initialized.");
+		return -1;
+	}
+	if (cbs->alloc_condition && cbs->free_condition &&
+	    cbs->signal_condition && cbs->wait_condition) {
+		memcpy(target, cbs, sizeof(_evthread_cond_fns));
+	}
+	if (_evthread_lock_debugging_enabled) {
+		_evthread_cond_fns.alloc_condition = cbs->alloc_condition;
+		_evthread_cond_fns.free_condition = cbs->free_condition;
+		_evthread_cond_fns.signal_condition = cbs->signal_condition;
+	}
+	return 0;
+}
+
+struct debug_lock {
+	unsigned locktype;
+	unsigned long held_by;
+	/* XXXX if we ever use read-write locks, we will need a separate
+	 * lock to protect count. */
+	int count;
+	void *lock;
+};
+
+static void *
+debug_lock_alloc(unsigned locktype)
+{
+	struct debug_lock *result = mm_malloc(sizeof(struct debug_lock));
+	if (!result)
+		return NULL;
+	if (_original_lock_fns.alloc) {
+		if (!(result->lock = _original_lock_fns.alloc(
+				locktype|EVTHREAD_LOCKTYPE_RECURSIVE))) {
+			mm_free(result);
+			return NULL;
+		}
+	} else {
+		result->lock = NULL;
+	}
+	result->locktype = locktype;
+	result->count = 0;
+	result->held_by = 0;
+	return result;
+}
+
+static void
+debug_lock_free(void *lock_, unsigned locktype)
+{
+	struct debug_lock *lock = lock_;
+	EVUTIL_ASSERT(lock->count == 0);
+	EVUTIL_ASSERT(locktype == lock->locktype);
+	if (_original_lock_fns.free) {
+		_original_lock_fns.free(lock->lock,
+		    lock->locktype|EVTHREAD_LOCKTYPE_RECURSIVE);
+	}
+	lock->lock = NULL;
+	lock->count = -100;
+	mm_free(lock);
+}
+
+static void
+evthread_debug_lock_mark_locked(unsigned mode, struct debug_lock *lock)
+{
+	++lock->count;
+	if (!(lock->locktype & EVTHREAD_LOCKTYPE_RECURSIVE))
+		EVUTIL_ASSERT(lock->count == 1);
+	if (_evthread_id_fn) {
+		unsigned long me;
+		me = _evthread_id_fn();
+		if (lock->count > 1)
+			EVUTIL_ASSERT(lock->held_by == me);
+		lock->held_by = me;
+	}
+}
+
+static int
+debug_lock_lock(unsigned mode, void *lock_)
+{
+	struct debug_lock *lock = lock_;
+	int res = 0;
+	if (lock->locktype & EVTHREAD_LOCKTYPE_READWRITE)
+		EVUTIL_ASSERT(mode & (EVTHREAD_READ|EVTHREAD_WRITE));
+	else
+		EVUTIL_ASSERT((mode & (EVTHREAD_READ|EVTHREAD_WRITE)) == 0);
+	if (_original_lock_fns.lock)
+		res = _original_lock_fns.lock(mode, lock->lock);
+	if (!res) {
+		evthread_debug_lock_mark_locked(mode, lock);
+	}
+	return res;
+}
+
+static void
+evthread_debug_lock_mark_unlocked(unsigned mode, struct debug_lock *lock)
+{
+	if (lock->locktype & EVTHREAD_LOCKTYPE_READWRITE)
+		EVUTIL_ASSERT(mode & (EVTHREAD_READ|EVTHREAD_WRITE));
+	else
+		EVUTIL_ASSERT((mode & (EVTHREAD_READ|EVTHREAD_WRITE)) == 0);
+	if (_evthread_id_fn) {
+		EVUTIL_ASSERT(lock->held_by == _evthread_id_fn());
+		if (lock->count == 1)
+			lock->held_by = 0;
+	}
+	--lock->count;
+	EVUTIL_ASSERT(lock->count >= 0);
+}
+
+static int
+debug_lock_unlock(unsigned mode, void *lock_)
+{
+	struct debug_lock *lock = lock_;
+	int res = 0;
+	evthread_debug_lock_mark_unlocked(mode, lock);
+	if (_original_lock_fns.unlock)
+		res = _original_lock_fns.unlock(mode, lock->lock);
+	return res;
+}
+
+static int
+debug_cond_wait(void *_cond, void *_lock, const struct timeval *tv)
+{
+	int r;
+	struct debug_lock *lock = _lock;
+	EVUTIL_ASSERT(lock);
+	EVLOCK_ASSERT_LOCKED(_lock);
+	evthread_debug_lock_mark_unlocked(0, lock);
+	r = _original_cond_fns.wait_condition(_cond, lock->lock, tv);
+	evthread_debug_lock_mark_locked(0, lock);
+	return r;
+}
+
+void
+evthread_enable_lock_debuging(void)
+{
+	struct evthread_lock_callbacks cbs = {
+		EVTHREAD_LOCK_API_VERSION,
+		EVTHREAD_LOCKTYPE_RECURSIVE,
+		debug_lock_alloc,
+		debug_lock_free,
+		debug_lock_lock,
+		debug_lock_unlock
+	};
+	if (_evthread_lock_debugging_enabled)
+		return;
+	memcpy(&_original_lock_fns, &_evthread_lock_fns,
+	    sizeof(struct evthread_lock_callbacks));
+	memcpy(&_evthread_lock_fns, &cbs,
+	    sizeof(struct evthread_lock_callbacks));
+
+	memcpy(&_original_cond_fns, &_evthread_cond_fns,
+	    sizeof(struct evthread_condition_callbacks));
+	_evthread_cond_fns.wait_condition = debug_cond_wait;
+	_evthread_lock_debugging_enabled = 1;
+
+	/* XXX return value should get checked. */
+	event_global_setup_locks_(0);
+}
+
+int
+_evthread_is_debug_lock_held(void *lock_)
+{
+	struct debug_lock *lock = lock_;
+	if (! lock->count)
+		return 0;
+	if (_evthread_id_fn) {
+		unsigned long me = _evthread_id_fn();
+		if (lock->held_by != me)
+			return 0;
+	}
+	return 1;
+}
+
+void *
+_evthread_debug_get_real_lock(void *lock_)
+{
+	struct debug_lock *lock = lock_;
+	return lock->lock;
+}
+
+void *
+evthread_setup_global_lock_(void *lock_, unsigned locktype, int enable_locks)
+{
+	/* there are four cases here:
+	   1) we're turning on debugging; locking is not on.
+	   2) we're turning on debugging; locking is on.
+	   3) we're turning on locking; debugging is not on.
+	   4) we're turning on locking; debugging is on. */
+
+	if (!enable_locks && _original_lock_fns.alloc == NULL) {
+		/* Case 1: allocate a debug lock. */
+		EVUTIL_ASSERT(lock_ == NULL);
+		return debug_lock_alloc(locktype);
+	} else if (!enable_locks && _original_lock_fns.alloc != NULL) {
+		/* Case 2: wrap the lock in a debug lock. */
+		struct debug_lock *lock;
+		EVUTIL_ASSERT(lock_ != NULL);
+
+		if (!(locktype & EVTHREAD_LOCKTYPE_RECURSIVE)) {
+			/* We can't wrap it: We need a recursive lock */
+			_original_lock_fns.free(lock_, locktype);
+			return debug_lock_alloc(locktype);
+		}
+		lock = mm_malloc(sizeof(struct debug_lock));
+		if (!lock) {
+			_original_lock_fns.free(lock_, locktype);
+			return NULL;
+		}
+		lock->lock = lock_;
+		lock->locktype = locktype;
+		lock->count = 0;
+		lock->held_by = 0;
+		return lock;
+	} else if (enable_locks && ! _evthread_lock_debugging_enabled) {
+		/* Case 3: allocate a regular lock */
+		EVUTIL_ASSERT(lock_ == NULL);
+		return _evthread_lock_fns.alloc(locktype);
+	} else {
+		/* Case 4: Fill in a debug lock with a real lock */
+		struct debug_lock *lock = lock_;
+		EVUTIL_ASSERT(enable_locks &&
+		              _evthread_lock_debugging_enabled);
+		EVUTIL_ASSERT(lock->locktype == locktype);
+		EVUTIL_ASSERT(lock->lock == NULL);
+		lock->lock = _original_lock_fns.alloc(
+			locktype|EVTHREAD_LOCKTYPE_RECURSIVE);
+		if (!lock->lock) {
+			lock->count = -200;
+			mm_free(lock);
+			return NULL;
+		}
+		return lock;
+	}
+}
+
+
+#ifndef EVTHREAD_EXPOSE_STRUCTS
+unsigned long
+_evthreadimpl_get_id()
+{
+	return _evthread_id_fn ? _evthread_id_fn() : 1;
+}
+void *
+_evthreadimpl_lock_alloc(unsigned locktype)
+{
+	return _evthread_lock_fns.alloc ?
+	    _evthread_lock_fns.alloc(locktype) : NULL;
+}
+void
+_evthreadimpl_lock_free(void *lock, unsigned locktype)
+{
+	if (_evthread_lock_fns.free)
+		_evthread_lock_fns.free(lock, locktype);
+}
+int
+_evthreadimpl_lock_lock(unsigned mode, void *lock)
+{
+	if (_evthread_lock_fns.lock)
+		return _evthread_lock_fns.lock(mode, lock);
+	else
+		return 0;
+}
+int
+_evthreadimpl_lock_unlock(unsigned mode, void *lock)
+{
+	if (_evthread_lock_fns.unlock)
+		return _evthread_lock_fns.unlock(mode, lock);
+	else
+		return 0;
+}
+void *
+_evthreadimpl_cond_alloc(unsigned condtype)
+{
+	return _evthread_cond_fns.alloc_condition ?
+	    _evthread_cond_fns.alloc_condition(condtype) : NULL;
+}
+void
+_evthreadimpl_cond_free(void *cond)
+{
+	if (_evthread_cond_fns.free_condition)
+		_evthread_cond_fns.free_condition(cond);
+}
+int
+_evthreadimpl_cond_signal(void *cond, int broadcast)
+{
+	if (_evthread_cond_fns.signal_condition)
+		return _evthread_cond_fns.signal_condition(cond, broadcast);
+	else
+		return 0;
+}
+int
+_evthreadimpl_cond_wait(void *cond, void *lock, const struct timeval *tv)
+{
+	if (_evthread_cond_fns.wait_condition)
+		return _evthread_cond_fns.wait_condition(cond, lock, tv);
+	else
+		return 0;
+}
+int
+_evthreadimpl_is_lock_debugging_enabled(void)
+{
+	return _evthread_lock_debugging_enabled;
+}
+
+int
+_evthreadimpl_locking_enabled(void)
+{
+	return _evthread_lock_fns.lock != NULL;
+}
+#endif
+
+#endif