Concurrently cached values.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Concurrent/cache.ML	Thu Oct 01 22:39:06 2009 +0200
@@ -0,0 +1,32 @@
+(*  Title:      Pure/Concurrent/cache.ML
+    Author:     Makarius
+
+Concurrently cached values, with minimal locking time and singleton
+evaluation due to lazy storage.
+*)
+
+signature CACHE =
+sig
+  val create: 'table -> ('table -> 'key -> 'value lazy option) ->
+    ('key * 'value lazy -> 'table -> 'table) -> ('key -> 'value) -> 'key -> 'value
+end;
+
+structure Cache: CACHE =
+struct
+
+fun create empty lookup update f =
+  let
+    val cache = Synchronized.var "cache" empty;
+    fun apply x =
+      Synchronized.change_result cache
+        (fn tab =>
+          (case lookup tab x of
+            SOME y => (y, tab)
+          | NONE =>
+              let val y = Lazy.lazy (fn () => f x)
+              in (y, update (x, y) tab) end))
+      |> Lazy.force;
+  in apply end;
+
+end;
+

--- a/src/Pure/IsaMakefile	Thu Oct 01 20:47:26 2009 +0200
+++ b/src/Pure/IsaMakefile	Thu Oct 01 22:39:06 2009 +0200
@@ -42,37 +42,37 @@
 
 Pure: $(OUT)/Pure
 
-$(OUT)/Pure: $(BOOTSTRAP_FILES) Concurrent/future.ML			\
-  Concurrent/lazy.ML Concurrent/lazy_sequential.ML			\
-  Concurrent/mailbox.ML Concurrent/par_list.ML				\
-  Concurrent/par_list_sequential.ML Concurrent/simple_thread.ML		\
-  Concurrent/synchronized.ML Concurrent/synchronized_sequential.ML	\
-  Concurrent/task_queue.ML General/alist.ML General/antiquote.ML	\
-  General/balanced_tree.ML General/basics.ML General/binding.ML		\
-  General/buffer.ML General/file.ML General/graph.ML General/heap.ML	\
-  General/integer.ML General/long_name.ML General/markup.ML		\
-  General/name_space.ML General/ord_list.ML General/output.ML		\
-  General/path.ML General/position.ML General/pretty.ML			\
-  General/print_mode.ML General/properties.ML General/queue.ML		\
-  General/same.ML General/scan.ML General/secure.ML General/seq.ML	\
-  General/source.ML General/stack.ML General/symbol.ML			\
-  General/symbol_pos.ML General/table.ML General/url.ML General/xml.ML	\
-  General/yxml.ML Isar/args.ML Isar/attrib.ML Isar/auto_bind.ML		\
-  Isar/calculation.ML Isar/class.ML Isar/class_target.ML Isar/code.ML	\
-  Isar/constdefs.ML Isar/context_rules.ML Isar/element.ML		\
-  Isar/expression.ML Isar/isar_cmd.ML Isar/isar_document.ML		\
-  Isar/isar_syn.ML Isar/local_defs.ML Isar/local_syntax.ML		\
-  Isar/local_theory.ML Isar/locale.ML Isar/method.ML			\
-  Isar/object_logic.ML Isar/obtain.ML Isar/outer_keyword.ML		\
-  Isar/outer_lex.ML Isar/outer_parse.ML Isar/outer_syntax.ML		\
-  Isar/overloading.ML Isar/proof.ML Isar/proof_context.ML		\
-  Isar/proof_display.ML Isar/proof_node.ML Isar/rule_cases.ML		\
-  Isar/rule_insts.ML Isar/runtime.ML Isar/skip_proof.ML			\
-  Isar/spec_parse.ML Isar/specification.ML Isar/theory_target.ML	\
-  Isar/toplevel.ML Isar/value_parse.ML ML/ml_antiquote.ML		\
-  ML/ml_compiler.ML ML/ml_compiler_polyml-5.3.ML ML/ml_context.ML	\
-  ML/ml_env.ML ML/ml_lex.ML ML/ml_parse.ML ML/ml_syntax.ML		\
-  ML/ml_thms.ML ML-Systems/install_pp_polyml.ML				\
+$(OUT)/Pure: $(BOOTSTRAP_FILES) Concurrent/cache.ML			\
+  Concurrent/future.ML Concurrent/lazy.ML				\
+  Concurrent/lazy_sequential.ML Concurrent/mailbox.ML			\
+  Concurrent/par_list.ML Concurrent/par_list_sequential.ML		\
+  Concurrent/simple_thread.ML Concurrent/synchronized.ML		\
+  Concurrent/synchronized_sequential.ML Concurrent/task_queue.ML	\
+  General/alist.ML General/antiquote.ML General/balanced_tree.ML	\
+  General/basics.ML General/binding.ML General/buffer.ML		\
+  General/file.ML General/graph.ML General/heap.ML General/integer.ML	\
+  General/long_name.ML General/markup.ML General/name_space.ML		\
+  General/ord_list.ML General/output.ML General/path.ML			\
+  General/position.ML General/pretty.ML General/print_mode.ML		\
+  General/properties.ML General/queue.ML General/same.ML		\
+  General/scan.ML General/secure.ML General/seq.ML General/source.ML	\
+  General/stack.ML General/symbol.ML General/symbol_pos.ML		\
+  General/table.ML General/url.ML General/xml.ML General/yxml.ML	\
+  Isar/args.ML Isar/attrib.ML Isar/auto_bind.ML Isar/calculation.ML	\
+  Isar/class.ML Isar/class_target.ML Isar/code.ML Isar/constdefs.ML	\
+  Isar/context_rules.ML Isar/element.ML Isar/expression.ML		\
+  Isar/isar_cmd.ML Isar/isar_document.ML Isar/isar_syn.ML		\
+  Isar/local_defs.ML Isar/local_syntax.ML Isar/local_theory.ML		\
+  Isar/locale.ML Isar/method.ML Isar/object_logic.ML Isar/obtain.ML	\
+  Isar/outer_keyword.ML Isar/outer_lex.ML Isar/outer_parse.ML		\
+  Isar/outer_syntax.ML Isar/overloading.ML Isar/proof.ML		\
+  Isar/proof_context.ML Isar/proof_display.ML Isar/proof_node.ML	\
+  Isar/rule_cases.ML Isar/rule_insts.ML Isar/runtime.ML			\
+  Isar/skip_proof.ML Isar/spec_parse.ML Isar/specification.ML		\
+  Isar/theory_target.ML Isar/toplevel.ML Isar/value_parse.ML		\
+  ML/ml_antiquote.ML ML/ml_compiler.ML ML/ml_compiler_polyml-5.3.ML	\
+  ML/ml_context.ML ML/ml_env.ML ML/ml_lex.ML ML/ml_parse.ML		\
+  ML/ml_syntax.ML ML/ml_thms.ML ML-Systems/install_pp_polyml.ML		\
   ML-Systems/install_pp_polyml-5.3.ML ML-Systems/use_context.ML		\
   Proof/extraction.ML Proof/proof_rewrite_rules.ML			\
   Proof/proof_syntax.ML Proof/proofchecker.ML Proof/reconstruct.ML	\

--- a/src/Pure/ROOT.ML	Thu Oct 01 20:47:26 2009 +0200
+++ b/src/Pure/ROOT.ML	Thu Oct 01 22:39:06 2009 +0200
@@ -56,19 +56,25 @@
 (* concurrency within the ML runtime *)
 
 use "Concurrent/simple_thread.ML";
+
 use "Concurrent/synchronized.ML";
 if Multithreading.available then ()
 else use "Concurrent/synchronized_sequential.ML";
+
 use "Concurrent/mailbox.ML";
 use "Concurrent/task_queue.ML";
 use "Concurrent/future.ML";
+
 use "Concurrent/lazy.ML";
 if Multithreading.available then ()
 else use "Concurrent/lazy_sequential.ML";
+
 use "Concurrent/par_list.ML";
 if Multithreading.available then ()
 else use "Concurrent/par_list_sequential.ML";
 
+use "Concurrent/cache.ML";
+
 
 (* fundamental structures *)