diff --git a/.gitignore b/.gitignore
index 11c9110..12f423e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 **/*.xlog
 **/*.snap
+.DS_Store
\ No newline at end of file
diff --git a/examples/example-locks/init.lua b/examples/example-locks/init.lua
new file mode 100644
index 0000000..b378126
--- /dev/null
+++ b/examples/example-locks/init.lua
@@ -0,0 +1,59 @@
+box.cfg{
+	-- listen = '127.0.0.1:4221'
+}
+-- box.once('access:v1', function()
+--         box.schema.user.grant('guest', 'read,write,execute', 'universe')
+-- end)
+
+require 'strict'.on()
+
+-- box.once('schema',function()
+	local format = {
+		{name = "id",      type = "string"},
+		{name = "status",  type = "string"},
+		{name = "lock",    type = "number", nullable=true},
+
+		{name = "action", type = "string"},
+		{name = "attr",   type = "*"},
+		{name = "runat",   type = "number"},
+	}
+	box.schema.space.create('tasks', { if_not_exists = true, format = format })
+
+	box.space.tasks:create_index('primary', { unique = true, parts = {'id'}, if_not_exists = true})
+	box.space.tasks:create_index('xq', { unique = false, parts = { 'status', 'id' }, if_not_exists = true})
+	box.space.tasks:create_index('lock', { unique = false, parts = { 'lock', 'status', 'id' }, if_not_exists = true})
+	box.space.tasks:create_index('runat', { unique = false, parts = { 'runat', 'id' }, if_not_exists = true})
+-- end)
+
+if not package.path:match('%.%./%?%.lua;') then
+	package.path = '../?.lua;' .. package.path
+end
+
+require 'xqueue' ( box.space.tasks, {
+	debug = true;
+	fields = {
+		status = 'status';
+		lock  = 'lock';
+		runat  = 'runat';
+	};
+	features = {
+		id = 'uuid',
+		delayed = true,
+		ttl = true,
+	};
+	workers = 0;
+	worker = function(task)
+		print(require'fiber'.self().id(), "got task",task.id, require'yaml'.encode(box.space.tasks:select()))
+		require'fiber'.sleep(10)
+	end;
+} )
+
+
+print(require'yaml'.encode(box.space.tasks:select()))
+-- for i = 1, 5 do
+-- 	local t = box.space.tasks:put{ lock=1, action = "doit", attr = {} }
+-- 	print('inserted', t.id, t.status)
+-- end
+
+require'console'.start()
+os.exit()
diff --git a/example-putwait/init.lua b/examples/example-putwait/init.lua
similarity index 100%
rename from example-putwait/init.lua
rename to examples/example-putwait/init.lua
diff --git a/example-runat/init.lua b/examples/example-runat/init.lua
similarity index 100%
rename from example-runat/init.lua
rename to examples/example-runat/init.lua
diff --git a/example-tube/init.lua b/examples/example-tube/init.lua
similarity index 100%
rename from example-tube/init.lua
rename to examples/example-tube/init.lua
diff --git a/example-worker/init.lua b/examples/example-worker/init.lua
similarity index 100%
rename from example-worker/init.lua
rename to examples/example-worker/init.lua
diff --git a/example1/init.lua b/examples/example1/init.lua
similarity index 100%
rename from example1/init.lua
rename to examples/example1/init.lua
diff --git a/rockspecs/xqueue-scm-6.rockspec b/rockspecs/xqueue-scm-6.rockspec
new file mode 100644
index 0000000..a118904
--- /dev/null
+++ b/rockspecs/xqueue-scm-6.rockspec
@@ -0,0 +1,20 @@
+package = "xqueue"
+version = "scm-6"
+source = {
+   url = "git://github.com/ktsstudio/xqueue.git",
+   branch = "locks",
+}
+description = {
+   summary = "Package for loading external lua config",
+   homepage = "https://github.com/moonlibs/xqueue.git",
+   license = "BSD"
+}
+dependencies = {
+   "lua ~> 5.1"
+}
+build = {
+   type = "builtin",
+   modules = {
+      xqueue = "xqueue.lua"
+   }
+}
diff --git a/xqueue.lua b/xqueue.lua
index 5911e61..31dfe4a 100644
--- a/xqueue.lua
+++ b/xqueue.lua
@@ -84,6 +84,9 @@ Status:
 
 	D - done - task was processed and ack'ed and permanently left in database
 		enabled when keep feature is set
+
+	L - locked - task is locked via `lock' index. Tasks will be processed only 
+		if there are no older tasks by `lock` index
 	
 	X - reserved for statistics
 
@@ -102,6 +105,7 @@ Interface:
 			status   = 'status_field_name'    | status_field_no,
 			runat    = 'runat_field_name'     | runat_field_no,
 			priority = 'priority_field_name'  | priority_field_no,
+			lock     = 'lock_field_name'      | lock_field_no,
 		},
 		features = {
 			id = 'auto_increment' | 'uuid' | 'required' | function
@@ -243,6 +247,7 @@ function M.upgrade(space,opts,depth)
 		self.taken = space.xq.taken
 		self._stat = space.xq._stat
 		self.bysid = space.xq.bysid
+		self.sid_take_fids = space.xq.sid_take_fids
 		self._lock = space.xq._lock
 		self.take_wait = space.xq.take_wait
 		self.take_chans = space.xq.take_chans or setmetatable({}, { __mode = 'v' })
@@ -252,6 +257,7 @@ function M.upgrade(space,opts,depth)
 	else
 		self.taken = {}
 		self.bysid = {}
+		self.sid_take_fids = {}
 		-- byfid = {};
 		self._lock = {}
 		self.put_wait = setmetatable({}, { __mode = 'v' })
@@ -300,7 +306,7 @@ function M.upgrade(space,opts,depth)
 	-- 1. fields check
 	local fields = {}
 	local fieldmap = {}
-	for _,f in pairs({{"status","str"},{"runat","num"},{"priority","num"},{"tube","str"}}) do
+	for _,f in pairs({{"status","str"},{"runat","num"},{"priority","num"},{"tube","str"},{"lock","*"}}) do
 		local fname,ftype = f[1], f[2]
 		local num = opts.fields[fname]
 		if num then
@@ -320,7 +326,7 @@ function M.upgrade(space,opts,depth)
 				error(string.format("wrong type %s for field %s, number or string required",type(num),fname),2 + depth)
 			end
 			-- check type
-			if format[num] then
+			if format[num] and ftype ~= "*" then
 				if not typeeq(format[num].type, ftype) then
 					error(string.format("type mismatch for field %s, required %s, got %s",fname, ftype, format[fname].type),2+depth)
 				end
@@ -457,6 +463,23 @@ function M.upgrade(space,opts,depth)
 				end
 			end
 		end
+
+		if fields.lock then
+			local lock_index
+			for _,index in pairs(space.index) do
+				if type(_) == 'number' and #index.parts >= 2 then
+					if index.parts[1].fieldno == fields.lock and index.parts[2].fieldno == fields.status then
+						-- print("found lock index", index.name)
+						lock_index = index
+						break
+					end
+				end
+			end
+			if not lock_index then
+				error(string.format("fields.lock requires tree index with at least fields (`lock', `status', ...)"), 2+depth)
+			end
+			self.lock_index = lock_index
+		end
 	end
 
 	local runat_index
@@ -626,6 +649,10 @@ function M.upgrade(space,opts,depth)
 		features.tube = true
 	end
 
+	if fields.lock then
+		features.lockable = true
+	end
+
 	self.gen_id = gen_id
 	self.features = features
 	self.space = space.id
@@ -649,6 +676,50 @@ function M.upgrade(space,opts,depth)
 		return t[pkf.no]
 	end
 
+	function self:register_take_fid()
+		local sid = box.session.id()
+		local fid = fiber.id()
+		if self.sid_take_fids[sid] == nil then
+			self.sid_take_fids[sid] = {}
+		end
+		self.sid_take_fids[sid][fid] = true
+	end
+
+	function self:deregister_take_fid()
+		local sid = box.session.id()
+		local fid = fiber.id()
+		if self.sid_take_fids[sid] == nil then
+			return
+		end
+
+		self.sid_take_fids[sid][fid] = nil
+	end
+
+	function self:wakeup_locked_task(t)
+		local locker_t = self.lock_index:select({ t[ self.fieldmap.lock ], 'L' }, {limit=1})[1]
+		if locker_t ~= nil then
+			locker_t = box.space[self.space]:update({ locker_t[ self.key.no ] }, {
+				{ '=', self.fields.status, 'R' }
+			})
+			log.info("Unlock: L->R {%s} (by %s) from %s/sid=%s/fid=%s",
+				self:getkey(locker_t), self:getkey(t), box.session.storage.peer, box.session.id(), fiber.id() )
+			self:wakeup(locker_t)
+		end
+		return locker_t
+	end
+
+	function self:find_locker_task(lock_value)
+		local locker_t
+		for _, status in ipairs({'L', 'T', 'R'}) do
+			locker_t = self.lock_index:select({ lock_value, status }, {limit=1})[1]
+			if locker_t ~= nil then
+				-- there is a task that should be processed first
+				return locker_t
+			end
+		end
+		return nil
+	end
+
 	-- Notify producer if it is still waiting us.
 	-- Producer waits only for successfully processed task
 	-- or for task which would never be processed.
@@ -709,7 +780,7 @@ function M.upgrade(space,opts,depth)
 				if xq.ready then xq.ready:get() end
 				log.info("I am worker %s",i)
 				if box.info.ro then
-					log.notice("Shutting down on ro instance")
+					log.info("Shutting down on ro instance")
 					return
 				end
 				while box.space[space.name] and space.xq == xq do
@@ -747,7 +818,7 @@ function M.upgrade(space,opts,depth)
 			local chan = xq.runat_chan
 			log.info("Runat started")
 			if box.info.ro then
-				log.notice("Shutting down on ro instance")
+				log.info("Shutting down on ro instance")
 				return
 			end
 			local maxrun = 1000
@@ -769,25 +840,35 @@ function M.upgrade(space,opts,depth)
 						if #collect >= maxrun then remaining = 0 break end
 					end
 					
+					local status
 					for _,t in ipairs(collect) do
 						-- log.info("Runat: %s, %s", _, t)
-						if t[xq.fields.status] == 'W' then
-							log.info("Runat: W->R %s",xq:keyfield(t))
+						status = t[ xq.fields.status ]
+
+						if status == 'W' then
+							local target_status = 'R'
+							if xq.features.lockable and t[ xq.fieldmap.lock ] ~= nil then
+								-- check if we need to set status L or R by looking up locker task
+								if xq:find_locker_task(t[ xq.fieldmap.lock ]) ~= nil then
+									target_status = 'L'
+								end
+							end
+							log.info("Runat: W->%s %s",target_status,xq:keyfield(t))
 							-- TODO: default ttl?
 							local u = space:update({ xq:keyfield(t) },{
-								{ '=',xq.fields.status,'R' },
+								{ '=',xq.fields.status,target_status },
 								{ '=',xq.fields.runat, xq.NEVER }
 							})
 							xq:wakeup(u)
-						elseif t[xq.fields.status] == 'R' and xq.features.ttl then
+						elseif (status == 'R' or status == 'L') and xq.features.ttl then
 							local key = xq:keyfield(t)
 							log.info("Runat: Kill R by ttl %s (%+0.2fs)", key, fiber.time() - t[ xq.fields.runat ])
 							t = space:delete{key}
 							notify_producer(key, t)
-						elseif t[xq.fields.status] == 'Z' and xq.features.zombie then
+						elseif status == 'Z' and xq.features.zombie then
 							log.info("Runat: Kill Zombie %s",xq:keyfield(t))
 							space:delete{ xq:keyfield(t) }
-						elseif t[xq.fields.status] == 'T' and xq.features.ttr then
+						elseif status == 'T' and xq.features.ttr then
 							local key = xq:keypack(t)
 							local sid = xq.taken[ key ]
 							local peer = peers[sid] or sid
@@ -803,7 +884,7 @@ function M.upgrade(space,opts,depth)
 							end
 							xq:wakeup(u)
 						else
-							log.error("Runat: unsupported status %s for %s",t[xq.fields.status], tostring(t))
+							log.error("Runat: unsupported status %s for %s",status, tostring(t))
 							space:update({ xq:keyfield(t) },{
 								{ '=',xq.fields.runat, xq.NEVER }
 							})
@@ -967,6 +1048,15 @@ function M.upgrade(space,opts,depth)
 			end
 			self.bysid[sid] = nil
 		end
+
+		if self.sid_take_fids[sid] then
+			for fid in pairs(self.sid_take_fids[sid]) do
+				log.info('Killing take fiber %d in sid %d', fid, sid)
+				fiber.kill(fid)
+			end
+
+			self.sid_take_fids[sid] = nil
+		end
 	end, self._on_dis)
 	
 	rawset(space,'xq',self)
@@ -1104,6 +1194,14 @@ function methods:put(t, opts)
 		t[ xq.fieldmap.status ] = 'R'
 	end
 
+	-- check lock index
+	if xq.features.lockable and t[ xq.fieldmap.status ] == 'R' and t[ xq.fieldmap.lock ] ~= nil then
+		-- check if we need to set status L or R by looking up tasks in L, R or T states
+		if xq:find_locker_task(t[ xq.fieldmap.lock ]) ~= nil then
+			t[ xq.fieldmap.status ] = 'L'
+		end
+	end
+
 	local tuple = xq.tuple(t)
 	local key = tuple[ xq.key.no ]
 
@@ -1142,6 +1240,7 @@ local wait_for = {
 	R = true,
 	T = true,
 	W = true,
+	L = true,
 }
 
 function methods:wait(key, timeout)
@@ -1228,6 +1327,7 @@ function methods:take(timeout, opts)
 		start_with = {'R'}
 	end
 
+	local wait_chan = (tube_chan or xq.take_wait)
 	local now = fiber.time()
 	local key
 	local found
@@ -1244,8 +1344,14 @@ function methods:take(timeout, opts)
 		if not found then
 			local left = (now + timeout) - fiber.time()
 			if left <= 0 then goto finish end
-
-			(tube_chan or xq.take_wait):get(left)
+			
+			self.xq:register_take_fid()
+			local ok, r = pcall(wait_chan.get, wait_chan, left)
+			self.xq:deregister_take_fid()
+			if not ok then 
+				log.info('take finished abruptly: %s', r)
+				goto finish 
+			end
 			if box.session.storage.destroyed then goto finish end
 		end
 	end
@@ -1415,6 +1521,11 @@ function methods:ack(key, attr)
 			log.info("Ack: %s->delete {%s} +%s from %s/sid=%s/fid=%s", old,
 				key, attr.delay, box.session.storage.peer, box.session.id(), fiber.id() )
 		end
+
+		if xq.features.lockable and t[ xq.fieldmap.lock ] ~= nil then
+			-- find any task that is locked
+			xq:wakeup_locked_task(t)
+		end
 	end)
 
 	xq:putback(t) -- in real drop form taken key
@@ -1443,6 +1554,10 @@ function methods:bury(key, attr)
 			xq.runat_chan:put(true,0)
 		end
 		log.info("Bury {%s} by %s, sid=%s, fid=%s", key, box.session.storage.peer, box.session.id(), fiber.id())
+
+		if xq.features.lockable and t[ xq.fieldmap.lock ] ~= nil then
+ 			xq:wakeup_locked_task(t)
+		end
 	end)
 
 	xq:putback(t)
@@ -1497,6 +1612,10 @@ function methods:kill(key)
 		end
 		xq.taken[key] = nil
 		xq._lock[key] = nil
+
+		if xq.features.lockable and t[ xq.fieldmap.lock ] ~= nil then
+			xq:wakeup_locked_task(task)
+		end
 	end
 end
 
@@ -1527,6 +1646,7 @@ local pretty_st = {
 	B = "Buried",
 	Z = "Zombie",
 	D = "Done",
+	L = "Locked",
 }
 
 function methods:stats(pretty)