Import guile-1.8 as multiple upstream tarball component

[lilypond.git] / guile18 / ice-9 / serialize.scm

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+;;;;   Copyright (C) 2003, 2006 Free Software Foundation, Inc.
+;;;;
+;;;; This library is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU Lesser General Public
+;;;; License as published by the Free Software Foundation; either
+;;;; version 2.1 of the License, or (at your option) any later version.
+;;;; 
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;; 
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+;;;;
+\f
+;;; Commentary:
+
+;; (serialize FORM1 ...) and (parallelize FORM1 ...) are useful when
+;; you don't trust the thread safety of most of your program, but
+;; where you have some section(s) of code which you consider can run
+;; in parallel to other sections.
+;;
+;; They "flag" (with dynamic extent) sections of code to be of
+;; "serial" or "parallel" nature and have the single effect of
+;; preventing a serial section from being run in parallel with any
+;; serial section (including itself).
+;;
+;; Both serialize and parallelize can be nested.  If so, the
+;; inner-most construct is in effect.
+;;
+;; NOTE 1: A serial section can run in parallel with a parallel
+;; section.
+;;
+;; NOTE 2: If a serial section S is "interrupted" by a parallel
+;; section P in the following manner: S = S1 P S2, S2 is not
+;; guaranteed to be resumed by the same thread that previously
+;; executed S1.
+;;
+;; WARNING: Spawning new threads within a serial section have
+;; undefined effects.  It is OK, though, to spawn threads in unflagged
+;; sections of code where neither serialize or parallelize is in
+;; effect.
+;;
+;; A typical usage is when Guile is used as scripting language in some
+;; application doing heavy computations.  If each thread is
+;; encapsulated with a serialize form, you can then put a parallelize
+;; form around the code performing the heavy computations (typically a
+;; C code primitive), enabling the computations to run in parallel
+;; while the scripting code runs single-threadedly.
+;; 
+
+;;; Code:
+
+(define-module (ice-9 serialize)
+  :use-module (ice-9 threads)
+  :export (call-with-serialization
+          call-with-parallelization)
+  :export-syntax (serialize
+                 parallelize))
+
+\f
+(define serialization-mutex (make-mutex))
+(define admin-mutex (make-mutex))
+(define owner #f)
+
+(define (call-with-serialization thunk)
+  (let ((outer-owner #f))
+    (dynamic-wind
+       (lambda ()
+         (lock-mutex admin-mutex)
+         (set! outer-owner owner)
+         (if (not (eqv? outer-owner (dynamic-root)))
+             (begin
+               (unlock-mutex admin-mutex)
+               (lock-mutex serialization-mutex)
+               (set! owner (dynamic-root)))
+             (unlock-mutex admin-mutex)))
+       thunk
+       (lambda ()
+         (lock-mutex admin-mutex)
+         (if (not (eqv? outer-owner (dynamic-root)))
+             (begin
+               (set! owner #f)
+               (unlock-mutex serialization-mutex)))
+         (unlock-mutex admin-mutex)))))
+
+(define-macro (serialize . forms)
+  `(call-with-serialization (lambda () ,@forms)))
+
+(define (call-with-parallelization thunk)
+  (let ((outer-owner #f))
+    (dynamic-wind
+       (lambda ()
+         (lock-mutex admin-mutex)
+         (set! outer-owner owner)
+         (if (eqv? outer-owner (dynamic-root))
+             (begin
+               (set! owner #f)
+               (unlock-mutex serialization-mutex)))
+         (unlock-mutex admin-mutex))
+       thunk
+       (lambda ()
+         (lock-mutex admin-mutex)
+         (if (eqv? outer-owner (dynamic-root))
+             (begin
+               (unlock-mutex admin-mutex)
+               (lock-mutex serialization-mutex)
+               (set! owner outer-owner))
+             (unlock-mutex admin-mutex))))))
+
+(define-macro (parallelize . forms)
+  `(call-with-parallelization (lambda () ,@forms)))