Add element acquire/release capabilities to rtree.

This makes it possible to acquire short-term "ownership" of rtree
elements so that it is possible to read an extent pointer *and* read the
extent's contents with a guarantee that the element will not be modified
until the ownership is released.  This is intended as a mechanism for
resolving rtree read/write races rather than as a way to lock extents.

include/jemalloc/internal/chunk.h

@@ -87,7 +87,7 @@ JEMALLOC_INLINE extent_t *
 chunk_lookup(const void *ptr, bool dependent)
 {
 
-	return (rtree_get(&chunks_rtree, (uintptr_t)ptr, dependent));
+	return (rtree_read(&chunks_rtree, (uintptr_t)ptr, dependent));
 }
 #endif
 

include/jemalloc/internal/private_symbols.txt

@@ -457,18 +457,24 @@ register_zone
 rtree_child_read
 rtree_child_read_hard
 rtree_child_tryread
+rtree_clear
 rtree_delete
-rtree_get
 rtree_new
 rtree_node_valid
-rtree_set
+rtree_elm_acquire
+rtree_elm_lookup
+rtree_elm_read
+rtree_elm_read_acquired
+rtree_elm_release
+rtree_elm_write
+rtree_elm_write_acquired
+rtree_read
 rtree_start_level
 rtree_subkey
 rtree_subtree_read
 rtree_subtree_read_hard
 rtree_subtree_tryread
-rtree_val_read
+rtree_write
-rtree_val_write
 run_quantize_ceil
 run_quantize_floor
 s2u

include/jemalloc/internal/rtree.h

@@ -6,7 +6,7 @@
  */
 #ifdef JEMALLOC_H_TYPES
 
-typedef struct rtree_node_elm_s rtree_node_elm_t;
+typedef struct rtree_elm_s rtree_elm_t;
 typedef struct rtree_level_s rtree_level_t;
 typedef struct rtree_s rtree_t;
 
@@ -21,25 +21,24 @@ typedef struct rtree_s rtree_t;
     ((1U << (LG_SIZEOF_PTR+3)) / RTREE_BITS_PER_LEVEL)
 
 /* Used for two-stage lock-free node initialization. */
-#define	RTREE_NODE_INITIALIZING	((rtree_node_elm_t *)0x1)
+#define	RTREE_NODE_INITIALIZING	((rtree_elm_t *)0x1)
 
 /*
  * The node allocation callback function's argument is the number of contiguous
- * rtree_node_elm_t structures to allocate, and the resulting memory must be
+ * rtree_elm_t structures to allocate, and the resulting memory must be zeroed.
- * zeroed.
  */
-typedef rtree_node_elm_t *(rtree_node_alloc_t)(size_t);
+typedef rtree_elm_t *(rtree_node_alloc_t)(size_t);
-typedef void (rtree_node_dalloc_t)(rtree_node_elm_t *);
+typedef void (rtree_node_dalloc_t)(rtree_elm_t *);
 
 #endif /* JEMALLOC_H_TYPES */
 /******************************************************************************/
 #ifdef JEMALLOC_H_STRUCTS
 
-struct rtree_node_elm_s {
+struct rtree_elm_s {
 	union {
 		void		*pun;
-		rtree_node_elm_t	*child;
+		rtree_elm_t	*child;
-		extent_t		*val;
+		extent_t	*extent;
 	};
 };
 
@@ -60,7 +59,7 @@ struct rtree_level_s {
 	 *
 	 *   levels[1] : [<unused> | 0x00000001**** | 0x00000002**** | ... ]
 	 *
-	 *   levels[2] : [val(0x000000000000) | val(0x000000000001) | ...]
+	 *   levels[2] : [extent(0x000000000000) | extent(0x000000000001) | ...]
 	 *
 	 * This has practical implications on x64, which currently uses only the
 	 * lower 47 bits of virtual address space in userland, thus leaving
@@ -68,7 +67,7 @@ struct rtree_level_s {
 	 */
 	union {
 		void		*subtree_pun;
-		rtree_node_elm_t	*subtree;
+		rtree_elm_t	*subtree;
 	};
 	/* Number of key bits distinguished by this level. */
 	unsigned		bits;
@@ -98,10 +97,9 @@ struct rtree_s {
 bool rtree_new(rtree_t *rtree, unsigned bits, rtree_node_alloc_t *alloc,
     rtree_node_dalloc_t *dalloc);
 void	rtree_delete(rtree_t *rtree);
-rtree_node_elm_t	*rtree_subtree_read_hard(rtree_t *rtree,
+rtree_elm_t	*rtree_subtree_read_hard(rtree_t *rtree, unsigned level);
+rtree_elm_t	*rtree_child_read_hard(rtree_t *rtree, rtree_elm_t *elm,
     unsigned level);
-rtree_node_elm_t	*rtree_child_read_hard(rtree_t *rtree,
-    rtree_node_elm_t *elm, unsigned level);
 
 #endif /* JEMALLOC_H_EXTERNS */
 /******************************************************************************/
@@ -111,22 +109,27 @@ rtree_node_elm_t	*rtree_child_read_hard(rtree_t *rtree,
 unsigned	rtree_start_level(rtree_t *rtree, uintptr_t key);
 uintptr_t	rtree_subkey(rtree_t *rtree, uintptr_t key, unsigned level);
 
-bool	rtree_node_valid(rtree_node_elm_t *node);
+bool	rtree_node_valid(rtree_elm_t *node);
-rtree_node_elm_t	*rtree_child_tryread(rtree_node_elm_t *elm,
+rtree_elm_t	*rtree_child_tryread(rtree_elm_t *elm, bool dependent);
-    bool dependent);
+rtree_elm_t	*rtree_child_read(rtree_t *rtree, rtree_elm_t *elm,
-rtree_node_elm_t	*rtree_child_read(rtree_t *rtree, rtree_node_elm_t *elm,
     unsigned level, bool dependent);
-extent_t	*rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm,
+extent_t	*rtree_elm_read(rtree_elm_t *elm, bool dependent);
+void	rtree_elm_write(rtree_elm_t *elm, const extent_t *extent);
+rtree_elm_t	*rtree_subtree_tryread(rtree_t *rtree, unsigned level,
     bool dependent);
-void	rtree_val_write(rtree_t *rtree, rtree_node_elm_t *elm,
+rtree_elm_t	*rtree_subtree_read(rtree_t *rtree, unsigned level,
-    const extent_t *val);
-rtree_node_elm_t	*rtree_subtree_tryread(rtree_t *rtree, unsigned level,
-    bool dependent);
-rtree_node_elm_t	*rtree_subtree_read(rtree_t *rtree, unsigned level,
     bool dependent);
+rtree_elm_t	*rtree_elm_lookup(rtree_t *rtree, uintptr_t key,
+    bool dependent, bool init_missing);
 
-extent_t	*rtree_get(rtree_t *rtree, uintptr_t key, bool dependent);
+bool	rtree_write(rtree_t *rtree, uintptr_t key, const extent_t *extent);
-bool	rtree_set(rtree_t *rtree, uintptr_t key, const extent_t *val);
+extent_t	*rtree_read(rtree_t *rtree, uintptr_t key, bool dependent);
+rtree_elm_t	*rtree_elm_acquire(rtree_t *rtree, uintptr_t key,
+    bool dependent, bool init_missing);
+extent_t	*rtree_elm_read_acquired(rtree_elm_t *elm);
+void	rtree_elm_write_acquired(rtree_elm_t *elm, const extent_t *extent);
+void	rtree_elm_release(rtree_elm_t *elm);
+void	rtree_clear(rtree_t *rtree, uintptr_t key);
 #endif
 
 #if (defined(JEMALLOC_ENABLE_INLINE) || defined(JEMALLOC_RTREE_C_))
@@ -154,18 +157,18 @@ rtree_subkey(rtree_t *rtree, uintptr_t key, unsigned level)
 }
 
 JEMALLOC_ALWAYS_INLINE bool
-rtree_node_valid(rtree_node_elm_t *node)
+rtree_node_valid(rtree_elm_t *node)
 {
 
 	return ((uintptr_t)node > (uintptr_t)RTREE_NODE_INITIALIZING);
 }
 
-JEMALLOC_ALWAYS_INLINE rtree_node_elm_t *
+JEMALLOC_ALWAYS_INLINE rtree_elm_t *
-rtree_child_tryread(rtree_node_elm_t *elm, bool dependent)
+rtree_child_tryread(rtree_elm_t *elm, bool dependent)
 {
-	rtree_node_elm_t *child;
+	rtree_elm_t *child;
 
-	/* Double-checked read (first read may be stale. */
+	/* Double-checked read (first read may be stale). */
 	child = elm->child;
 	if (!dependent && !rtree_node_valid(child))
 		child = atomic_read_p(&elm->pun);
@@ -173,11 +176,11 @@ rtree_child_tryread(rtree_node_elm_t *elm, bool dependent)
 	return (child);
 }
 
-JEMALLOC_ALWAYS_INLINE rtree_node_elm_t *
+JEMALLOC_ALWAYS_INLINE rtree_elm_t *
-rtree_child_read(rtree_t *rtree, rtree_node_elm_t *elm, unsigned level,
+rtree_child_read(rtree_t *rtree, rtree_elm_t *elm, unsigned level,
     bool dependent)
 {
-	rtree_node_elm_t *child;
+	rtree_elm_t *child;
 
 	child = rtree_child_tryread(elm, dependent);
 	if (!dependent && unlikely(!rtree_node_valid(child)))
@@ -187,40 +190,46 @@ rtree_child_read(rtree_t *rtree, rtree_node_elm_t *elm, unsigned level,
 }
 
 JEMALLOC_ALWAYS_INLINE extent_t *
-rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm, bool dependent)
+rtree_elm_read(rtree_elm_t *elm, bool dependent)
 {
+	extent_t *extent;
 
 	if (dependent) {
 		/*
-		 * Reading a val on behalf of a pointer to a valid allocation is
+		 * Reading a value on behalf of a pointer to a valid allocation
-		 * guaranteed to be a clean read even without synchronization,
+		 * is guaranteed to be a clean read even without
-		 * because the rtree update became visible in memory before the
+		 * synchronization, because the rtree update became visible in
-		 * pointer came into existence.
+		 * memory before the pointer came into existence.
 		 */
-		return (elm->val);
+		extent = elm->extent;
 	} else {
 		/*
 		 * An arbitrary read, e.g. on behalf of ivsalloc(), may not be
 		 * dependent on a previous rtree write, which means a stale read
 		 * could result if synchronization were omitted here.
 		 */
-		return (atomic_read_p(&elm->pun));
+		extent = (extent_t *)atomic_read_p(&elm->pun);
 	}
+
+	/* Mask the lock bit. */
+	extent = (extent_t *)((uintptr_t)extent & ~((uintptr_t)0x1));
+
+	return (extent);
 }
 
 JEMALLOC_INLINE void
-rtree_val_write(rtree_t *rtree, rtree_node_elm_t *elm, const extent_t *val)
+rtree_elm_write(rtree_elm_t *elm, const extent_t *extent)
 {
 
-	atomic_write_p(&elm->pun, val);
+	atomic_write_p(&elm->pun, extent);
 }
 
-JEMALLOC_ALWAYS_INLINE rtree_node_elm_t *
+JEMALLOC_ALWAYS_INLINE rtree_elm_t *
 rtree_subtree_tryread(rtree_t *rtree, unsigned level, bool dependent)
 {
-	rtree_node_elm_t *subtree;
+	rtree_elm_t *subtree;
 
-	/* Double-checked read (first read may be stale. */
+	/* Double-checked read (first read may be stale). */
 	subtree = rtree->levels[level].subtree;
 	if (!dependent && unlikely(!rtree_node_valid(subtree)))
 		subtree = atomic_read_p(&rtree->levels[level].subtree_pun);
@@ -228,10 +237,10 @@ rtree_subtree_tryread(rtree_t *rtree, unsigned level, bool dependent)
 	return (subtree);
 }
 
-JEMALLOC_ALWAYS_INLINE rtree_node_elm_t *
+JEMALLOC_ALWAYS_INLINE rtree_elm_t *
 rtree_subtree_read(rtree_t *rtree, unsigned level, bool dependent)
 {
-	rtree_node_elm_t *subtree;
+	rtree_elm_t *subtree;
 
 	subtree = rtree_subtree_tryread(rtree, level, dependent);
 	if (!dependent && unlikely(!rtree_node_valid(subtree)))
@@ -240,16 +249,20 @@ rtree_subtree_read(rtree_t *rtree, unsigned level, bool dependent)
 	return (subtree);
 }
 
-JEMALLOC_ALWAYS_INLINE extent_t *
+JEMALLOC_ALWAYS_INLINE rtree_elm_t *
-rtree_get(rtree_t *rtree, uintptr_t key, bool dependent)
+rtree_elm_lookup(rtree_t *rtree, uintptr_t key, bool dependent,
+    bool init_missing)
 {
 	uintptr_t subkey;
 	unsigned start_level;
-	rtree_node_elm_t *node;
+	rtree_elm_t *node;
+
+	assert(!dependent || !init_missing);
 
 	start_level = rtree_start_level(rtree, key);
 
-	node = rtree_subtree_tryread(rtree, start_level, dependent);
+	node = init_missing ? rtree_subtree_read(rtree, start_level, dependent)
+	    : rtree_subtree_tryread(rtree, start_level, dependent);
 #define	RTREE_GET_BIAS	(RTREE_HEIGHT_MAX - rtree->height)
 	switch (start_level + RTREE_GET_BIAS) {
 #define	RTREE_GET_SUBTREE(level)					\
@@ -259,7 +272,9 @@ rtree_get(rtree_t *rtree, uintptr_t key, bool dependent)
 			return (NULL);					\
 		subkey = rtree_subkey(rtree, key, level -		\
 		    RTREE_GET_BIAS);					\
-		node = rtree_child_tryread(&node[subkey], dependent);	\
+		node = init_missing ? rtree_child_read(rtree,		\
+		    &node[subkey], level - RTREE_GET_BIAS, dependent) :	\
+		    rtree_child_tryread(&node[subkey], dependent);	\
 		/* Fall through. */
 #define	RTREE_GET_LEAF(level)						\
 	case level:							\
@@ -272,8 +287,7 @@ rtree_get(rtree_t *rtree, uintptr_t key, bool dependent)
 		 * node is a leaf, so it contains values rather than	\
 		 * child pointers.					\
 		 */							\
-		return (rtree_val_read(rtree, &node[subkey],		\
+		return (&node[subkey]);
-		    dependent));
 #if RTREE_HEIGHT_MAX > 1
 	RTREE_GET_SUBTREE(0)
 #endif
@@ -332,33 +346,94 @@ rtree_get(rtree_t *rtree, uintptr_t key, bool dependent)
 }
 
 JEMALLOC_INLINE bool
-rtree_set(rtree_t *rtree, uintptr_t key, const extent_t *val)
+rtree_write(rtree_t *rtree, uintptr_t key, const extent_t *extent)
 {
-	uintptr_t subkey;
+	rtree_elm_t *elm;
-	unsigned i, start_level;
-	rtree_node_elm_t *node, *child;
 
-	start_level = rtree_start_level(rtree, key);
+	assert(extent != NULL); /* Use rtree_clear() for this case. */
+	assert(((uintptr_t)extent & (uintptr_t)0x1) == (uintptr_t)0x0);
 
-	node = rtree_subtree_read(rtree, start_level, false);
+	elm = rtree_elm_lookup(rtree, key, false, true);
-	if (node == NULL)
+	if (elm == NULL)
 		return (true);
-	for (i = start_level; /**/; i++, node = child) {
+	assert(rtree_elm_read(elm, false) == NULL);
-		subkey = rtree_subkey(rtree, key, i);
+	rtree_elm_write(elm, extent);
-		if (i == rtree->height - 1) {
+
-			/*
-			 * node is a leaf, so it contains values rather than
-			 * child pointers.
-			 */
-			rtree_val_write(rtree, &node[subkey], val);
 	return (false);
 }
-		assert(i + 1 < rtree->height);
+
-		child = rtree_child_read(rtree, &node[subkey], i, false);
+JEMALLOC_ALWAYS_INLINE extent_t *
-		if (child == NULL)
+rtree_read(rtree_t *rtree, uintptr_t key, bool dependent)
-			return (true);
+{
+	rtree_elm_t *elm;
+
+	elm = rtree_elm_lookup(rtree, key, dependent, false);
+	if (elm == NULL)
+		return (NULL);
+
+	return (rtree_elm_read(elm, dependent));
 }
-	not_reached();
+
+JEMALLOC_INLINE rtree_elm_t *
+rtree_elm_acquire(rtree_t *rtree, uintptr_t key, bool dependent,
+    bool init_missing)
+{
+	rtree_elm_t *elm;
+
+	elm = rtree_elm_lookup(rtree, key, dependent, init_missing);
+	if (!dependent && elm == NULL)
+		return (NULL);
+	{
+		extent_t *extent;
+		void *s;
+
+		do {
+			extent = rtree_elm_read(elm, false);
+			/* The least significant bit serves as a lock. */
+			s = (void *)((uintptr_t)extent | (uintptr_t)0x1);
+		} while (atomic_cas_p(&elm->pun, (void *)extent, s));
+	}
+
+	return (elm);
+}
+
+JEMALLOC_INLINE extent_t *
+rtree_elm_read_acquired(rtree_elm_t *elm)
+{
+	extent_t *extent;
+
+	assert(((uintptr_t)elm->pun & (uintptr_t)0x1) == (uintptr_t)0x1);
+	extent = (extent_t *)((uintptr_t)elm->pun & ~((uintptr_t)0x1));
+	assert(((uintptr_t)extent & (uintptr_t)0x1) == (uintptr_t)0x0);
+
+	return (extent);
+}
+
+JEMALLOC_INLINE void
+rtree_elm_write_acquired(rtree_elm_t *elm, const extent_t *extent)
+{
+
+	assert(((uintptr_t)extent & (uintptr_t)0x1) == (uintptr_t)0x0);
+	assert(((uintptr_t)elm->pun & (uintptr_t)0x1) == (uintptr_t)0x1);
+	elm->pun = (void *)((uintptr_t)extent | (uintptr_t)0x1);
+	assert(rtree_elm_read_acquired(elm) == extent);
+}
+
+JEMALLOC_INLINE void
+rtree_elm_release(rtree_elm_t *elm)
+{
+
+	rtree_elm_write(elm, rtree_elm_read_acquired(elm));
+}
+
+JEMALLOC_INLINE void
+rtree_clear(rtree_t *rtree, uintptr_t key)
+{
+	rtree_elm_t *elm;
+
+	elm = rtree_elm_acquire(rtree, key, true, false);
+	rtree_elm_write_acquired(elm, NULL);
+	rtree_elm_release(elm);
 }
 #endif
 

src/chunk.c

@@ -146,7 +146,7 @@ chunk_register(tsdn_t *tsdn, const void *chunk, const extent_t *extent)
 
 	assert(extent_addr_get(extent) == chunk);
 
-	if (rtree_set(&chunks_rtree, (uintptr_t)chunk, extent))
+	if (rtree_write(&chunks_rtree, (uintptr_t)chunk, extent))
 		return (true);
 	if (config_prof && opt_prof) {
 		size_t size = extent_size_get(extent);
@@ -170,10 +170,8 @@ chunk_register(tsdn_t *tsdn, const void *chunk, const extent_t *extent)
 void
 chunk_deregister(const void *chunk, const extent_t *extent)
 {
-	bool err;
 
-	err = rtree_set(&chunks_rtree, (uintptr_t)chunk, NULL);
+	rtree_clear(&chunks_rtree, (uintptr_t)chunk);
-	assert(!err);
 	if (config_prof && opt_prof) {
 		size_t size = extent_size_get(extent);
 		size_t nsub = (size == 0) ? 1 : size / chunksize;
@@ -684,12 +682,12 @@ chunk_merge_default(void *chunk_a, size_t size_a, void *chunk_b, size_t size_b,
 	return (false);
 }
 
-static rtree_node_elm_t *
+static rtree_elm_t *
 chunks_rtree_node_alloc(size_t nelms)
 {
 
-	return ((rtree_node_elm_t *)base_alloc(tsdn_fetch(), nelms *
+	return ((rtree_elm_t *)base_alloc(tsdn_fetch(), nelms *
-	    sizeof(rtree_node_elm_t)));
+	    sizeof(rtree_elm_t)));
 }
 
 bool

src/rtree.c

@@ -8,7 +8,10 @@ hmin(unsigned ha, unsigned hb)
 	return (ha < hb ? ha : hb);
 }
 
-/* Only the most significant bits of keys passed to rtree_[gs]et() are used. */
+/*
+ * Only the most significant bits of keys passed to rtree_{read,write}() are
+ * used.
+ */
 bool
 rtree_new(rtree_t *rtree, unsigned bits, rtree_node_alloc_t *alloc,
     rtree_node_dalloc_t *dalloc)
@@ -62,7 +65,7 @@ rtree_new(rtree_t *rtree, unsigned bits, rtree_node_alloc_t *alloc,
 }
 
 static void
-rtree_delete_subtree(rtree_t *rtree, rtree_node_elm_t *node, unsigned level)
+rtree_delete_subtree(rtree_t *rtree, rtree_elm_t *node, unsigned level)
 {
 
 	if (level + 1 < rtree->height) {
@@ -70,7 +73,7 @@ rtree_delete_subtree(rtree_t *rtree, rtree_node_elm_t *node, unsigned level)
 
 		nchildren = ZU(1) << rtree->levels[level].bits;
 		for (i = 0; i < nchildren; i++) {
-			rtree_node_elm_t *child = node[i].child;
+			rtree_elm_t *child = node[i].child;
 			if (child != NULL)
 				rtree_delete_subtree(rtree, child, level + 1);
 		}
@@ -84,16 +87,16 @@ rtree_delete(rtree_t *rtree)
 	unsigned i;
 
 	for (i = 0; i < rtree->height; i++) {
-		rtree_node_elm_t *subtree = rtree->levels[i].subtree;
+		rtree_elm_t *subtree = rtree->levels[i].subtree;
 		if (subtree != NULL)
 			rtree_delete_subtree(rtree, subtree, i);
 	}
 }
 
-static rtree_node_elm_t *
+static rtree_elm_t *
-rtree_node_init(rtree_t *rtree, unsigned level, rtree_node_elm_t **elmp)
+rtree_node_init(rtree_t *rtree, unsigned level, rtree_elm_t **elmp)
 {
-	rtree_node_elm_t *node;
+	rtree_elm_t *node;
 
 	if (atomic_cas_p((void **)elmp, NULL, RTREE_NODE_INITIALIZING)) {
 		/*
@@ -114,15 +117,15 @@ rtree_node_init(rtree_t *rtree, unsigned level, rtree_node_elm_t **elmp)
 	return (node);
 }
 
-rtree_node_elm_t *
+rtree_elm_t *
 rtree_subtree_read_hard(rtree_t *rtree, unsigned level)
 {
 
 	return (rtree_node_init(rtree, level, &rtree->levels[level].subtree));
 }
 
-rtree_node_elm_t *
+rtree_elm_t *
-rtree_child_read_hard(rtree_t *rtree, rtree_node_elm_t *elm, unsigned level)
+rtree_child_read_hard(rtree_t *rtree, rtree_elm_t *elm, unsigned level)
 {
 
 	return (rtree_node_init(rtree, level, &elm->child));

test/unit/rtree.c

@@ -1,20 +1,24 @@
 #include "test/jemalloc_test.h"
 
-static rtree_node_elm_t *
+static rtree_elm_t *
 node_alloc(size_t nelms)
 {
+	rtree_elm_t *node;
 
-	return ((rtree_node_elm_t *)calloc(nelms, sizeof(rtree_node_elm_t)));
+	node = (rtree_elm_t *)calloc(nelms, sizeof(rtree_elm_t));
+	assert_ptr_not_null(node, "Unexpected calloc() failure");
+
+	return (node);
 }
 
 static void
-node_dalloc(rtree_node_elm_t *node)
+node_dalloc(rtree_elm_t *node)
 {
 
 	free(node);
 }
 
-TEST_BEGIN(test_rtree_get_empty)
+TEST_BEGIN(test_rtree_read_empty)
 {
 	unsigned i;
 
@@ -22,13 +26,89 @@ TEST_BEGIN(test_rtree_get_empty)
 		rtree_t rtree;
 		assert_false(rtree_new(&rtree, i, node_alloc, node_dalloc),
 		    "Unexpected rtree_new() failure");
-		assert_ptr_null(rtree_get(&rtree, 0, false),
+		assert_ptr_null(rtree_read(&rtree, 0, false),
-		    "rtree_get() should return NULL for empty tree");
+		    "rtree_read() should return NULL for empty tree");
 		rtree_delete(&rtree);
 	}
 }
 TEST_END
 
+#define	NTHREADS	8
+#define	MAX_NBITS	18
+#define	NITERS		1000
+#define	SEED		42
+
+typedef struct {
+	unsigned	nbits;
+	rtree_t		rtree;
+	uint32_t	seed;
+} thd_start_arg_t;
+
+static void *
+thd_start(void *varg)
+{
+	thd_start_arg_t *arg = (thd_start_arg_t *)varg;
+	sfmt_t	*sfmt;
+	extent_t *extent;
+	unsigned i;
+
+	sfmt = init_gen_rand(arg->seed);
+	extent = (extent_t *)malloc(sizeof(extent));
+	assert_ptr_not_null(extent, "Unexpected malloc() failure");
+
+	for (i = 0; i < NITERS; i++) {
+		uintptr_t key = (uintptr_t)gen_rand64(sfmt);
+		if (i % 2 == 0) {
+			rtree_elm_t *elm;
+
+			elm = rtree_elm_acquire(&arg->rtree, key, false, true);
+			assert_ptr_not_null(elm,
+			    "Unexpected rtree_elm_acquire() failure");
+			rtree_elm_write_acquired(elm, extent);
+			rtree_elm_release(elm);
+
+			elm = rtree_elm_acquire(&arg->rtree, key, true, false);
+			assert_ptr_not_null(elm,
+			    "Unexpected rtree_elm_acquire() failure");
+			rtree_elm_read_acquired(elm);
+			rtree_elm_release(elm);
+		} else
+			rtree_read(&arg->rtree, key, false);
+	}
+
+	free(extent);
+	fini_gen_rand(sfmt);
+	return (NULL);
+}
+
+TEST_BEGIN(test_rtree_concurrent)
+{
+	thd_start_arg_t arg;
+	thd_t thds[NTHREADS];
+	sfmt_t *sfmt;
+	unsigned i, j;
+
+	sfmt = init_gen_rand(SEED);
+	for (i = 1; i < MAX_NBITS; i++) {
+		arg.nbits = i;
+		assert_false(rtree_new(&arg.rtree, arg.nbits, node_alloc,
+		    node_dalloc), "Unexpected rtree_new() failure");
+		arg.seed = gen_rand32(sfmt);
+		for (j = 0; j < NTHREADS; j++)
+			thd_create(&thds[j], thd_start, (void *)&arg);
+		for (j = 0; j < NTHREADS; j++)
+			thd_join(thds[j], NULL);
+		rtree_delete(&arg.rtree);
+	}
+	fini_gen_rand(sfmt);
+}
+TEST_END
+
+#undef NTHREADS
+#undef MAX_NBITS
+#undef NITERS
+#undef SEED
+
 TEST_BEGIN(test_rtree_extrema)
 {
 	unsigned i;
@@ -39,16 +119,16 @@ TEST_BEGIN(test_rtree_extrema)
 		assert_false(rtree_new(&rtree, i, node_alloc, node_dalloc),
 		    "Unexpected rtree_new() failure");
 
-		assert_false(rtree_set(&rtree, 0, &extent_a),
+		assert_false(rtree_write(&rtree, 0, &extent_a),
-		    "Unexpected rtree_set() failure");
+		    "Unexpected rtree_write() failure, i=%u", i);
-		assert_ptr_eq(rtree_get(&rtree, 0, true), &extent_a,
+		assert_ptr_eq(rtree_read(&rtree, 0, true), &extent_a,
-		    "rtree_get() should return previously set value");
+		    "rtree_read() should return previously set value, i=%u", i);
 
-		assert_false(rtree_set(&rtree, ~((uintptr_t)0), &extent_b),
+		assert_false(rtree_write(&rtree, ~((uintptr_t)0), &extent_b),
-		    "Unexpected rtree_set() failure");
+		    "Unexpected rtree_write() failure, i=%u", i);
-		assert_ptr_eq(rtree_get(&rtree, ~((uintptr_t)0), true),
+		assert_ptr_eq(rtree_read(&rtree, ~((uintptr_t)0), true),
 		    &extent_b,
-		    "rtree_get() should return previously set value");
+		    "rtree_read() should return previously set value, i=%u", i);
 
 		rtree_delete(&rtree);
 	}
@@ -69,22 +149,21 @@ TEST_BEGIN(test_rtree_bits)
 		    "Unexpected rtree_new() failure");
 
 		for (j = 0; j < sizeof(keys)/sizeof(uintptr_t); j++) {
-			assert_false(rtree_set(&rtree, keys[j], &extent),
+			assert_false(rtree_write(&rtree, keys[j], &extent),
-			    "Unexpected rtree_set() failure");
+			    "Unexpected rtree_write() failure");
 			for (k = 0; k < sizeof(keys)/sizeof(uintptr_t); k++) {
-				assert_ptr_eq(rtree_get(&rtree, keys[k], true),
+				assert_ptr_eq(rtree_read(&rtree, keys[k], true),
-				    &extent, "rtree_get() should return "
+				    &extent, "rtree_read() should return "
 				    "previously set value and ignore "
 				    "insignificant key bits; i=%u, j=%u, k=%u, "
 				    "set key=%#"FMTxPTR", get key=%#"FMTxPTR, i,
 				    j, k, keys[j], keys[k]);
 			}
-			assert_ptr_null(rtree_get(&rtree,
+			assert_ptr_null(rtree_read(&rtree,
 			    (((uintptr_t)1) << (sizeof(uintptr_t)*8-i)), false),
 			    "Only leftmost rtree leaf should be set; "
 			    "i=%u, j=%u", i, j);
-			assert_false(rtree_set(&rtree, keys[j], NULL),
+			rtree_clear(&rtree, keys[j]);
-			    "Unexpected rtree_set() failure");
 		}
 
 		rtree_delete(&rtree);
@@ -105,31 +184,36 @@ TEST_BEGIN(test_rtree_random)
 		extent_t extent;
 		unsigned j;
 		rtree_t rtree;
+		rtree_elm_t *elm;
 
 		assert_false(rtree_new(&rtree, i, node_alloc, node_dalloc),
 		    "Unexpected rtree_new() failure");
 
 		for (j = 0; j < NSET; j++) {
 			keys[j] = (uintptr_t)gen_rand64(sfmt);
-			assert_false(rtree_set(&rtree, keys[j], &extent),
+			elm = rtree_elm_acquire(&rtree, keys[j], false, true);
-			    "Unexpected rtree_set() failure");
+			assert_ptr_not_null(elm,
-			assert_ptr_eq(rtree_get(&rtree, keys[j], true), &extent,
+			    "Unexpected rtree_elm_acquire() failure");
-			    "rtree_get() should return previously set value");
+			rtree_elm_write_acquired(elm, &extent);
+			rtree_elm_release(elm);
+			assert_ptr_eq(rtree_read(&rtree, keys[j], true),
+			    &extent,
+			    "rtree_read() should return previously set value");
 		}
 		for (j = 0; j < NSET; j++) {
-			assert_ptr_eq(rtree_get(&rtree, keys[j], true), &extent,
+			assert_ptr_eq(rtree_read(&rtree, keys[j], true),
-			    "rtree_get() should return previously set value");
+			    &extent, "rtree_read() should return previously "
+			    "set value, j=%u", j);
 		}
 
 		for (j = 0; j < NSET; j++) {
-			assert_false(rtree_set(&rtree, keys[j], NULL),
+			rtree_clear(&rtree, keys[j]);
-			    "Unexpected rtree_set() failure");
+			assert_ptr_null(rtree_read(&rtree, keys[j], true),
-			assert_ptr_null(rtree_get(&rtree, keys[j], true),
+			    "rtree_read() should return previously set value");
-			    "rtree_get() should return previously set value");
 		}
 		for (j = 0; j < NSET; j++) {
-			assert_ptr_null(rtree_get(&rtree, keys[j], true),
+			assert_ptr_null(rtree_read(&rtree, keys[j], true),
-			    "rtree_get() should return previously set value");
+			    "rtree_read() should return previously set value");
 		}
 
 		rtree_delete(&rtree);
@@ -145,7 +229,8 @@ main(void)
 {
 
 	return (test(
-	    test_rtree_get_empty,
+	    test_rtree_read_empty,
+	    test_rtree_concurrent,
 	    test_rtree_extrema,
 	    test_rtree_bits,
 	    test_rtree_random));