introduce mcache class for caching audio metadata

We often waste cycles rerunning commands we don't need
to run frequently.  Introduce a short term cache for
these.

1 files changed, 31 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