@@ -144,7 +144,7 @@ module StrokeDB 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 @@ module StrokeDB 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 @@ module StrokeDB 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, lib/strokedb/data_structures/simple_skiplist.rb @@ -98,6 +98,25 @@ SimpleSkiplist.with_optimizations(OPTIMIZATIONS) do |lang| 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 spec/lib/strokedb/data_structures/simple_skiplist_spec.rb 03795003ae925546efc24a45b3bb5047d76b6c36 Oleg Andreev oleganza@idbns.com http://github.com/yrashk/strokedb/commit/70bd2f5d26937659ae299c333f890a6baece162a 70bd2f5d26937659ae299c333f890a6baece162a 2008-05-24T13:48:35-07:00 2008-05-24T13:48:35-07:00 added SimpleSkiplist#delete 9eb462feabb90124dec9c4f9327b6c0738139538 Oleg Andreev oleganza@idbns.com