From 5d6dc5c742f827350490d8f33c4c89b203ae7460 Mon Sep 17 00:00:00 2001
From: Eric Wong <normalperson@yhbt.net>
Date: Fri, 10 Dec 2010 19:49:12 -0800
Subject: String#hash is not stable across processes :<

We need to implement our own hash functions for splitting
databases across multiple files.  This was totally fucking up
Rainbows!
---
 lib/metropolis.rb                   |  2 ++
 lib/metropolis/multi_hash.rb        | 24 ++++++++++++++++++++++++
 lib/metropolis/multi_hash/digest.rb | 23 +++++++++++++++++++++++
 lib/metropolis/multi_hash/to_i.rb   | 12 ++++++++++++
 lib/metropolis/tc/hdb.rb            |  6 ++++--
 lib/metropolis/tc/hdb/ex.rb         |  2 +-
 lib/metropolis/tc/hdb/ro.rb         |  2 +-
 lib/metropolis/tdb/multi.rb         |  4 +++-
 test/test_tdb.rb                    | 29 +++++++++++++++++++++++++++++
 9 files changed, 99 insertions(+), 5 deletions(-)
 create mode 100644 lib/metropolis/multi_hash.rb
 create mode 100644 lib/metropolis/multi_hash/digest.rb
 create mode 100644 lib/metropolis/multi_hash/to_i.rb

diff --git a/lib/metropolis.rb b/lib/metropolis.rb
index c38d4af..0af1465 100644
--- a/lib/metropolis.rb
+++ b/lib/metropolis.rb
@@ -9,6 +9,7 @@ module Metropolis
   autoload :TC, 'metropolis/tc'
   autoload :Hash, 'metropolis/hash'
   autoload :TDB, 'metropolis/tdb'
+  autoload :MultiHash, 'metropolis/multi_hash'
 
   def self.new(opts = {})
     opts = opts.dup
@@ -19,6 +20,7 @@ module Metropolis
       @query = @uri.query ? Rack::Utils.parse_query(@uri.query) : nil
       @path_pattern = opts[:path_pattern]
       @path = @uri.path if @uri.path != '/'
+      @multi_hash = opts[:multi_hash]
     end
 
     base = case uri.scheme
diff --git a/lib/metropolis/multi_hash.rb b/lib/metropolis/multi_hash.rb
new file mode 100644
index 0000000..65ed6fe
--- /dev/null
+++ b/lib/metropolis/multi_hash.rb
@@ -0,0 +1,24 @@
+# -*- encoding: binary -*-
+module Metropolis::MultiHash
+  autoload :Digest, 'metropolis/multi_hash/digest'
+  autoload :ToI, 'metropolis/multi_hash/to_i'
+
+  def self.extended(obj)
+    sym = obj.instance_eval {
+      case @multi_hash.to_s
+      when /\Ato_i/
+        extend Metropolis::MultiHash::ToI
+      when /\Adigest_/
+        extend Metropolis::MultiHash::Digest
+      when /\Atdb_hash_/
+        extend TDB::HashFunctions
+      end
+      @multi_hash
+    }
+    obj.respond_to?(sym) or
+      raise ArgumentError, "multi_hash=#{sym} not supported"
+    (class << obj; self; end).instance_eval do
+      alias_method :multi_hash, sym
+    end
+  end
+end
diff --git a/lib/metropolis/multi_hash/digest.rb b/lib/metropolis/multi_hash/digest.rb
new file mode 100644
index 0000000..974d7ac
--- /dev/null
+++ b/lib/metropolis/multi_hash/digest.rb
@@ -0,0 +1,23 @@
+# -*- encoding: binary -*-
+require 'digest'
+module Metropolis::MultiHash::Digest
+  def digest_sha1(key)
+    ::Digest::SHA1.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_md5(key)
+    ::Digest::MD5.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha256(key)
+    ::Digest::SHA256.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha384(key)
+    ::Digest::SHA384.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha512(key)
+    ::Digest::SHA512.digest(key)[0,4].unpack("N")[0]
+  end
+end
diff --git a/lib/metropolis/multi_hash/to_i.rb b/lib/metropolis/multi_hash/to_i.rb
new file mode 100644
index 0000000..69b2819
--- /dev/null
+++ b/lib/metropolis/multi_hash/to_i.rb
@@ -0,0 +1,12 @@
+# -*- encoding: binary -*-
+# simple "hashing" method which converts keys to integers,
+# this may be useful for databases that only store numeric keys
+module Metropolis::MultiHash::ToI
+  def to_i(key)
+    key.to_i
+  end
+
+  def to_i_16(key)
+    key.to_i(16)
+  end
+end
diff --git a/lib/metropolis/tc/hdb.rb b/lib/metropolis/tc/hdb.rb
index d0833f8..e63b015 100644
--- a/lib/metropolis/tc/hdb.rb
+++ b/lib/metropolis/tc/hdb.rb
@@ -68,6 +68,8 @@ module Metropolis::TC::HDB
       end
       [ hdb, path ]
     end
+    @multi_hash ||= :digest_sha1
+    extend Metropolis::MultiHash
     extend(RO) if @readonly
     extend(EX) if @exclusive
   end
@@ -77,7 +79,7 @@ module Metropolis::TC::HDB
   end
 
   def writer(key, &block)
-    hdb, path = @dbv[key.hash % @nr_slots]
+    hdb, path = @dbv[multi_hash(key) % @nr_slots]
     hdb.open(path, @wr_flags) or ex!(:open, hdb)
     yield hdb
     ensure
@@ -85,7 +87,7 @@ module Metropolis::TC::HDB
   end
 
   def reader(key)
-    hdb, path = @dbv[key.hash % @nr_slots]
+    hdb, path = @dbv[multi_hash(key) % @nr_slots]
     hdb.open(path, @rd_flags) or ex!(:open, hdb)
     yield hdb
     ensure
diff --git a/lib/metropolis/tc/hdb/ex.rb b/lib/metropolis/tc/hdb/ex.rb
index 5bc7f39..d205a76 100644
--- a/lib/metropolis/tc/hdb/ex.rb
+++ b/lib/metropolis/tc/hdb/ex.rb
@@ -11,7 +11,7 @@ module Metropolis::TC::HDB::EX
   end
 
   def reader(key)
-    yield @ex_dbv[key.hash % @nr_slots]
+    yield @ex_dbv[multi_hash(key) % @nr_slots]
   end
 
   alias_method :writer, :reader
diff --git a/lib/metropolis/tc/hdb/ro.rb b/lib/metropolis/tc/hdb/ro.rb
index 62ededc..72fa968 100644
--- a/lib/metropolis/tc/hdb/ro.rb
+++ b/lib/metropolis/tc/hdb/ro.rb
@@ -14,6 +14,6 @@ module Metropolis::TC::HDB::RO
   end
 
   def reader(key)
-    yield @ro_dbv[key.hash % @nr_slots]
+    yield @ro_dbv[multi_hash(key) % @nr_slots]
   end
 end
diff --git a/lib/metropolis/tdb/multi.rb b/lib/metropolis/tdb/multi.rb
index b22e63b..68c8bf5 100644
--- a/lib/metropolis/tdb/multi.rb
+++ b/lib/metropolis/tdb/multi.rb
@@ -2,6 +2,8 @@
 module Metropolis::TDB::Multi
   def self.extended(obj)
     obj.instance_eval do
+      @multi_hash ||= :tdb_hash_murmur2
+      extend Metropolis::MultiHash
       @dbv = (0...@nr_slots).to_a.map do |slot|
         path = sprintf(@path_pattern, slot)
         ::TDB.new(path, @tdb_opts)
@@ -10,7 +12,7 @@ module Metropolis::TDB::Multi
   end
 
   def db(key, &block)
-    yield @dbv[key.hash % @nr_slots]
+    yield @dbv[multi_hash(key) % @nr_slots]
   end
 
   def close!
diff --git a/test/test_tdb.rb b/test/test_tdb.rb
index 0fead86..3f607d1 100644
--- a/test/test_tdb.rb
+++ b/test/test_tdb.rb
@@ -15,6 +15,35 @@ class Test_TDB < Test::Unit::TestCase
     @app_opts = { :uri => @uri, :path_pattern => @path_pattern }
   end
 
+  def test_alternate_hash
+    n = 7
+    @app = Metropolis.new(@app_opts.merge(:nr_slots => n, :multi_hash => :to_i))
+    req = Rack::MockRequest.new(app)
+    o = { :lint => true, :fatal => true, :input => "." }
+    (1..8).each do |i|
+      r = req.put("/#{i * n}", o)
+      assert_equal 201, r.status
+      assert_equal "Created\n", r.body
+    end
+    tmp = Hash.new { |h,k| h[k] = {} }
+    @app.instance_eval do
+      @dbv.each_with_index { |db,i| db.each { |k,v| tmp[i][k] = v } }
+    end
+    expect = {
+      0 => {
+        "7" => ".",
+        "14" => ".",
+        "21" => ".",
+        "28" => ".",
+        "35" => ".",
+        "42" => ".",
+        "49" => ".",
+        "56" => ".",
+      }
+    }
+    assert_equal expect, tmp
+  end
+
   def teardown
     Dir[@path_pattern.sub!(/%\d*x/, '*')].each { |x| File.unlink(x) }
   end
-- 
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