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Re: [PATCH] Futures: Avoid creating the worker pool more than once
From: |
Mark H Weaver |
Subject: |
Re: [PATCH] Futures: Avoid creating the worker pool more than once |
Date: |
Wed, 07 Nov 2012 08:46:40 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) |
Here's an improved version the patch that gracefully handles the case
where creation of the worker pool is unsuccessful due to an exception or
cancelled thread.
What do you think?
Mark
>From b0d936a348b916e73e9071abeb7baae3d7c126d3 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Wed, 7 Nov 2012 08:39:42 -0500
Subject: [PATCH] Futures: Avoid creating the worker pool more than once.
* module/ice-9/futures.scm (%create-workers!): Use 'with-mutex' in case
an exception is thrown. Within the critical section, check to make
sure the worker pool hasn't already been created by another thread.
---
module/ice-9/futures.scm | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/module/ice-9/futures.scm b/module/ice-9/futures.scm
index 0f64b5c..7fbccf6 100644
--- a/module/ice-9/futures.scm
+++ b/module/ice-9/futures.scm
@@ -19,6 +19,7 @@
(define-module (ice-9 futures)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
+ #:use-module (ice-9 threads)
#:use-module (ice-9 q)
#:export (future make-future future? touch))
@@ -157,15 +158,20 @@ touched."
(define %workers '())
(define (%create-workers!)
- (lock-mutex %futures-mutex)
- (set! %workers
- (unfold (lambda (i) (>= i %worker-count))
- (lambda (i)
- (call-with-new-thread process-futures))
- 1+
- 0))
- (set! create-workers! (lambda () #t))
- (unlock-mutex %futures-mutex))
+ (with-mutex
+ %futures-mutex
+ ;; Setting 'create-workers!' to a no-op is an optimization, but it is
+ ;; still possible for '%create-workers!' to be called more than once
+ ;; from different threads. Therefore, to avoid creating %workers more
+ ;; than once (and thus creating too many threads), we check to make
+ ;; sure %workers is empty within the critical section.
+ (when (null? %workers)
+ (set! %workers
+ (unfold (lambda (i) (>= i %worker-count))
+ (lambda (i) (call-with-new-thread process-futures))
+ 1+
+ 0))
+ (set! create-workers! (lambda () #t)))))
(define create-workers!
(lambda () (%create-workers!)))
--
1.7.10.4