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authorEric Wong <e@80x24.org>2016-12-26 23:04:57 +0000
committerEric Wong <e@80x24.org>2016-12-26 23:10:53 +0000
commitefd81f4f6be4e91225aa893787d4ede84b46ed5e (patch)
treeb0bccd43e292a08c538794b5ee85d289eeb1e538
parent53c3abbbb222e3ab84c565498b8461009a3059c0 (diff)
downloaddtas-efd81f4f6be4e91225aa893787d4ede84b46ed5e.tar.gz
We often waste cycles rerunning commands we don't need
to run frequently.  Introduce a short term cache for
these.
-rw-r--r--lib/dtas/mcache.rb31
-rw-r--r--test/test_mcache.rb19
2 files changed, 50 insertions, 0 deletions
diff --git a/lib/dtas/mcache.rb b/lib/dtas/mcache.rb
new file mode 100644
index 0000000..b638a23
--- /dev/null
+++ b/lib/dtas/mcache.rb
@@ -0,0 +1,31 @@
+# Copyright (C) 2016 all contributors <dtas-all@nongnu.org>
+# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
+# frozen_string_literal: true
+# encoding: binary
+require_relative '../dtas'
+
+class DTAS::Mcache
+  def initialize(shift = 8, ttl = 60)
+    @mask = (1 << shift) - 1
+    @ttl = ttl
+    @tbl = []
+  end
+
+  def lookup(infile)
+    bucket = infile.hash & @mask
+    if cur = @tbl[bucket]
+      if cur[:infile] == infile && (DTAS.now - cur[:btime]) < @ttl
+        return cur
+      end
+    end
+    return unless block_given?
+    @tbl[bucket] = begin
+      cur = cur ? cur.clear : {}
+      if ret = yield(infile, cur)
+        ret[:infile] = infile.frozen? ? infile : infile.dup.freeze
+        ret[:btime] = DTAS.now
+      end
+      ret
+    end
+  end
+end
diff --git a/test/test_mcache.rb b/test/test_mcache.rb
new file mode 100644
index 0000000..6957021
--- /dev/null
+++ b/test/test_mcache.rb
@@ -0,0 +1,19 @@
+# Copyright (C) 2016 all contributors <dtas-all@nongnu.org>
+# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
+# frozen_string_literal: true
+require './test/helper'
+require 'dtas/mcache'
+
+class TestMcache < Testcase
+  def test_mcache
+    mc = DTAS::Mcache.new
+    exist = nil
+    mc.lookup('hello') { |infile, hash| exist = hash }
+    assert_kind_of Hash, exist
+    assert_equal 'hello', exist[:infile]
+    assert_operator exist[:btime], :<=, DTAS.now
+    assert_same exist, mc.lookup('hello')
+    assert_nil mc.lookup('HELLO')
+    assert_same exist, mc.lookup('hello'), 'no change after miss'
+  end
+end