Merge branch 'master' into index-slots

lib/strokedb/data_structures/simple_skiplist.rb

@@ -144,7 +144,7 @@ def first_key
       return first ? first[1] : nil
     end
 
-    # Insert a key-value pair. If key already exists,
+    # Insert a key-value pair. If the key already exists,
     # value will be overwritten.
     #
     #  <i> is a new node
@@ -179,6 +179,36 @@ def insert(key, value, __level = nil)
     	self
   	end
 
+  	# Remove a key-value pair. If the key does not exist,
+    # no action is performed.
+    #
+    #  <d> is a node to be removed
+    #  <M> is a marked node in a update_list
+    #  <N> is next node to <M> which reference must be updated. 
+    #
+    #  M-----------------> d <---------------- N ...
+    #  o ------> M ------> d <------ N ... 
+    #  o -> o -> o -> M -> d <- N ....
+    #
+    def delete(key)
+      @mutex.synchronize do
+        x = anchor
+        level = node_level(x)
+        update = Array.new(level)
+        x = find_with_update(x, level, key, update)
+
+        # remove existing key
+  	    if node_compare(x, key) == 0
+  	      level = node_level(x)
+  	      while level > 0
+  	        level -= 1
+  	        node_delete_after!(x, update[level], level)
+          end
+    	  end
+      end
+    	self
+  	end
+
   	def find_with_update(x, level, key, update) #:nodoc:
   	  while level > 0
         level -= 1
@@ -421,6 +451,25 @@ def node_insert_after!(x, prev, level)
       netx[3][level] = x
     end
 
+    # before: 
+    #   prev -> x -> next
+    #   prev <- x -> next
+    #
+    # after:
+    #
+    #  prev -> next
+    #  prev <- next
+    #
+    def node_delete_after!(x, prev, level)
+      netx = node_next(x, level)  # 'next' is a reserved word in ruby
+
+      # forward links
+      prev[0][level] = netx
+
+      # backward links
+      netx[3][level] = prev
+    end
+
     def new_node(level, key, value)
       [ 
         [nil]*level, 

spec/lib/strokedb/data_structures/simple_skiplist_spec.rb

@@ -98,6 +98,25 @@
   end
 
 
+  describe "Deleting from skiplist" do
+    before(:each) do
+      @list = SimpleSkiplist.new
+      @list.insert "1a", "a"
+      @list.insert "1b", "b"
+      @list.insert "1c", "c"
+      @list.insert "1d", "d"
+    end
+    it "should store nil" do
+      @list.insert("1b", nil)
+      @list.search("1", "1", 3, 0, false, false).should == ["a", nil, "c"]
+    end
+    it "should delete item" do
+      @list.delete("1b")
+      @list.search("1", "1", 3, 0, false, false).should == ["a", "c", "d"]
+    end
+  end
+
+
   describe "Big skiplist [#{lang}]" do
     before(:each) do
       @maxlevel    = 8