diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 0c9effe..77b05b1 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -336,8 +336,10 @@ typedef HANDLE mdb_mutex_t, mdb_mutexref_t;
 #define pthread_mutex_lock(x)	WaitForSingleObject(*x, INFINITE)
 #define pthread_cond_signal(x)	SetEvent(*x)
 #define pthread_cond_wait(cond,mutex)	do{SignalObjectAndWait(*mutex, *cond, INFINITE, FALSE); WaitForSingleObject(*mutex, INFINITE);}while(0)
-#define THREAD_CREATE(thr,start,arg)	thr=CreateThread(NULL,0,start,arg,0,NULL)
-#define THREAD_FINISH(thr)	WaitForSingleObject(thr, INFINITE)
+#define THREAD_CREATE(thr,start,arg) \
+	(((thr) = CreateThread(NULL, 0, start, arg, 0, NULL)) ? 0 : ErrCode())
+#define THREAD_FINISH(thr) \
+	(WaitForSingleObject(thr, INFINITE) ? ErrCode() : 0)
 #define LOCK_MUTEX0(mutex)		WaitForSingleObject(mutex, INFINITE)
 #define UNLOCK_MUTEX(mutex)		ReleaseMutex(mutex)
 #define mdb_mutex_consistent(mutex)	0
@@ -9637,11 +9639,12 @@ mdb_put(MDB_txn *txn, MDB_dbi dbi,
 #ifndef MDB_WBUF
 #define MDB_WBUF	(1024*1024)
 #endif
+#define MDB_EOF		0x10	/**< #mdb_env_copyfd1() is done reading */
 
-	/** State needed for a compacting copy. */
+	/** State needed for a double-buffering compacting copy. */
 typedef struct mdb_copy {
 	pthread_mutex_t mc_mutex;
-	pthread_cond_t mc_cond;
+	pthread_cond_t mc_cond;	/**< Condition variable for #mc_new */
 	char *mc_wbuf[2];
 	char *mc_over[2];
 	MDB_env *mc_env;
@@ -9650,10 +9653,9 @@ typedef struct mdb_copy {
 	int mc_olen[2];
 	pgno_t mc_next_pgno;
 	HANDLE mc_fd;
-	int mc_status;
-	volatile int mc_new;
-	int mc_toggle;
-
+	int mc_toggle;			/**< Buffer number in provider */
+	int mc_new;				/**< (0-2 buffers to write) | (#MDB_EOF at end) */
+	volatile int mc_error;	/**< Error code, never cleared if set */
 } mdb_copy;
 
 	/** Dedicated writer thread for compacting copy. */
@@ -9672,20 +9674,16 @@ mdb_env_copythr(void *arg)
 #endif
 
 	pthread_mutex_lock(&my->mc_mutex);
-	my->mc_new = 0;
-	pthread_cond_signal(&my->mc_cond);
 	for(;;) {
 		while (!my->mc_new)
 			pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
-		if (my->mc_new < 0) {
-			my->mc_new = 0;
+		if (my->mc_new == 0 + MDB_EOF) /* 0 buffers, just EOF */
 			break;
-		}
-		my->mc_new = 0;
 		wsize = my->mc_wlen[toggle];
 		ptr = my->mc_wbuf[toggle];
 again:
-		while (wsize > 0) {
+		rc = MDB_SUCCESS;
+		while (wsize > 0 && !my->mc_error) {
 			DO_WRITE(rc, my->mc_fd, ptr, wsize, len);
 			if (!rc) {
 				rc = ErrCode();
@@ -9701,8 +9699,7 @@ again:
 			}
 		}
 		if (rc) {
-			my->mc_status = rc;
-			break;
+			my->mc_error = rc;
 		}
 		/* If there's an overflow page tail, write it too */
 		if (my->mc_olen[toggle]) {
@@ -9713,31 +9710,34 @@ again:
 		}
 		my->mc_wlen[toggle] = 0;
 		toggle ^= 1;
+		/* Return the empty buffer to provider */
+		my->mc_new--;
 		pthread_cond_signal(&my->mc_cond);
 	}
-	pthread_cond_signal(&my->mc_cond);
 	pthread_mutex_unlock(&my->mc_mutex);
 	return (THREAD_RET)0;
 #undef DO_WRITE
 }
 
-	/** Tell the writer thread there's a buffer ready to write */
+	/** Give buffer and/or #MDB_EOF to writer thread, await unused buffer.
+	 *
+	 * @param[in] my control structure.
+	 * @param[in] adjust (1 to hand off 1 buffer) | (MDB_EOF when ending).
+	 */
 static int ESECT
-mdb_env_cthr_toggle(mdb_copy *my, int st)
+mdb_env_cthr_toggle(mdb_copy *my, int adjust)
 {
-	int toggle = my->mc_toggle ^ 1;
 	pthread_mutex_lock(&my->mc_mutex);
-	if (my->mc_status) {
-		pthread_mutex_unlock(&my->mc_mutex);
-		return my->mc_status;
-	}
-	while (my->mc_new == 1)
-		pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
-	my->mc_new = st;
-	my->mc_toggle = toggle;
+	my->mc_new += adjust;
 	pthread_cond_signal(&my->mc_cond);
+	while (my->mc_new & 2)		/* both buffers in use */
+		pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
 	pthread_mutex_unlock(&my->mc_mutex);
-	return 0;
+
+	my->mc_toggle ^= (adjust & 1);
+	/* Both threads reset mc_wlen, to be safe from threading errors */
+	my->mc_wlen[my->mc_toggle] = 0;
+	return my->mc_error;
 }
 
 	/** Depth-first tree traversal for compacting copy. */
@@ -9803,6 +9803,7 @@ mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
 						}
 
 						memcpy(&pg, NODEDATA(ni), sizeof(pg));
+						memcpy(NODEDATA(ni), &my->mc_next_pgno, sizeof(pgno_t));
 						rc = mdb_page_get(&mc, pg, &omp, NULL);
 						if (rc)
 							goto done;
@@ -9825,7 +9826,6 @@ mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
 								goto done;
 							toggle = my->mc_toggle;
 						}
-						memcpy(NODEDATA(ni), &mo->mp_pgno, sizeof(pgno_t));
 					} else if (ni->mn_flags & F_SUBDATA) {
 						MDB_db db;
 
@@ -9903,47 +9903,51 @@ mdb_env_copyfd1(MDB_env *env, HANDLE fd)
 {
 	MDB_meta *mm;
 	MDB_page *mp;
-	mdb_copy my;
+	mdb_copy my = {0};
 	MDB_txn *txn = NULL;
 	pthread_t thr;
-	int rc;
+	int rc = MDB_SUCCESS;
 
 #ifdef _WIN32
-	my.mc_mutex = CreateMutex(NULL, FALSE, NULL);
-	my.mc_cond = CreateEvent(NULL, FALSE, FALSE, NULL);
+	if (!(my.mc_mutex = CreateMutex(NULL, FALSE, NULL)) ||
+		!(my.mc_cond = CreateEvent(NULL, FALSE, FALSE, NULL))) {
+		rc = ErrCode();
+		goto done;
+	}
 	my.mc_wbuf[0] = _aligned_malloc(MDB_WBUF*2, env->me_os_psize);
-	if (my.mc_wbuf[0] == NULL)
-		return errno;
+	if (my.mc_wbuf[0] == NULL) {
+		/* _aligned_malloc() sets errno, but we use Windows error codes */
+		rc = ERROR_NOT_ENOUGH_MEMORY;
+		goto done;
+	}
 #else
-	pthread_mutex_init(&my.mc_mutex, NULL);
-	pthread_cond_init(&my.mc_cond, NULL);
+	if ((rc = pthread_mutex_init(&my.mc_mutex, NULL)) ||
+		(rc = pthread_cond_init(&my.mc_cond, NULL)))
+		return rc;
 #ifdef HAVE_MEMALIGN
 	my.mc_wbuf[0] = memalign(env->me_os_psize, MDB_WBUF*2);
-	if (my.mc_wbuf[0] == NULL)
-		return errno;
+	if (my.mc_wbuf[0] == NULL) {
+		rc = errno;
+		goto done;
+	}
 #else
 	rc = posix_memalign((void **)&my.mc_wbuf[0], env->me_os_psize, MDB_WBUF*2);
 	if (rc)
-		return rc;
+		goto done;
 #endif
 #endif
 	memset(my.mc_wbuf[0], 0, MDB_WBUF*2);
 	my.mc_wbuf[1] = my.mc_wbuf[0] + MDB_WBUF;
-	my.mc_wlen[0] = 0;
-	my.mc_wlen[1] = 0;
-	my.mc_olen[0] = 0;
-	my.mc_olen[1] = 0;
 	my.mc_next_pgno = NUM_METAS;
-	my.mc_status = 0;
-	my.mc_new = 1;
-	my.mc_toggle = 0;
 	my.mc_env = env;
 	my.mc_fd = fd;
-	THREAD_CREATE(thr, mdb_env_copythr, &my);
+	rc = THREAD_CREATE(thr, mdb_env_copythr, &my);
+	if (rc)
+		goto done;
 
 	rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
 	if (rc)
-		return rc;
+		goto finish;
 
 	mp = (MDB_page *)my.mc_wbuf[0];
 	memset(mp, 0, NUM_METAS * env->me_psize);
@@ -9969,6 +9973,8 @@ mdb_env_copyfd1(MDB_env *env, HANDLE fd)
 		mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
 		while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
 			freecount += *(MDB_ID *)data.mv_data;
+		if (rc != MDB_NOTFOUND)
+			goto finish;
 		freecount += txn->mt_dbs[FREE_DBI].md_branch_pages +
 			txn->mt_dbs[FREE_DBI].md_leaf_pages +
 			txn->mt_dbs[FREE_DBI].md_overflow_pages;
@@ -9985,31 +9991,26 @@ mdb_env_copyfd1(MDB_env *env, HANDLE fd)
 	}
 	my.mc_wlen[0] = env->me_psize * NUM_METAS;
 	my.mc_txn = txn;
-	pthread_mutex_lock(&my.mc_mutex);
-	while(my.mc_new)
-		pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
-	pthread_mutex_unlock(&my.mc_mutex);
 	rc = mdb_env_cwalk(&my, &txn->mt_dbs[MAIN_DBI].md_root, 0);
-	if (rc == MDB_SUCCESS && my.mc_wlen[my.mc_toggle])
-		rc = mdb_env_cthr_toggle(&my, 1);
-	mdb_env_cthr_toggle(&my, -1);
-	pthread_mutex_lock(&my.mc_mutex);
-	while(my.mc_new)
-		pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
-	pthread_mutex_unlock(&my.mc_mutex);
-	THREAD_FINISH(thr);
 
+finish:
+	if (rc)
+		my.mc_error = rc;
+	mdb_env_cthr_toggle(&my, 1 | MDB_EOF);
+	rc = THREAD_FINISH(thr);
 	mdb_txn_abort(txn);
+
+done:
 #ifdef _WIN32
-	CloseHandle(my.mc_cond);
-	CloseHandle(my.mc_mutex);
+	if (my.mc_cond)  CloseHandle(my.mc_cond);
+	if (my.mc_mutex) CloseHandle(my.mc_mutex);
 	_aligned_free(my.mc_wbuf[0]);
 #else
 	pthread_cond_destroy(&my.mc_cond);
 	pthread_mutex_destroy(&my.mc_mutex);
 	free(my.mc_wbuf[0]);
 #endif
-	return rc;
+	return rc ? rc : my.mc_error;
 }
 
 	/** Copy environment as-is. */