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monads, gexp: Prevent redefinition of syntax parameters.

Fixes <https://bugs.gnu.org/27476>.

This fixes multi-threaded compilation of this code where syntax
parameters could end up being redefined and where a race condition could
lead a thread to see the "wrong" value of the syntax parameter.

* guix/monads.scm (define-syntax-parameter-once): New macro.
(>>=, return): Use it.
* guix/gexp.scm (define-syntax-parameter-once): New macro.
(current-imported-modules, current-imported-extensions): Use it.
wip-deploy2
Ludovic Courtès 3 years ago
parent
commit
8245bb74fc
No known key found for this signature in database GPG Key ID: 90B11993D9AEBB5
  1. 15
      guix/gexp.scm
  2. 15
      guix/monads.scm

15
guix/gexp.scm

@ -920,7 +920,18 @@ and in the current monad setting (system type, etc.)"
(simple-format #f "~a:~a" line column)))
"<unknown location>")))
(define-syntax-parameter current-imported-modules
(define-syntax-rule (define-syntax-parameter-once name proc)
;; Like 'define-syntax-parameter' but ensure the top-level binding for NAME
;; does not get redefined. This works around a race condition in a
;; multi-threaded context with Guile <= 2.2.4: <https://bugs.gnu.org/27476>.
(eval-when (load eval expand compile)
(define name
(if (module-locally-bound? (current-module) 'name)
(module-ref (current-module) 'name)
(make-syntax-transformer 'name 'syntax-parameter
(list proc))))))
(define-syntax-parameter-once current-imported-modules
;; Current list of imported modules.
(identifier-syntax '()))
@ -931,7 +942,7 @@ environment."
(identifier-syntax modules)))
body ...))
(define-syntax-parameter current-imported-extensions
(define-syntax-parameter-once current-imported-extensions
;; Current list of extensions.
(identifier-syntax '()))

15
guix/monads.scm

@ -274,12 +274,23 @@ more optimizations."
(_
#'generic-name))))))))))
(define-syntax-parameter >>=
(define-syntax-rule (define-syntax-parameter-once name proc)
;; Like 'define-syntax-parameter' but ensure the top-level binding for NAME
;; does not get redefined. This works around a race condition in a
;; multi-threaded context with Guile <= 2.2.4: <https://bugs.gnu.org/27476>.
(eval-when (load eval expand compile)
(define name
(if (module-locally-bound? (current-module) 'name)
(module-ref (current-module) 'name)
(make-syntax-transformer 'name 'syntax-parameter
(list proc))))))
(define-syntax-parameter-once >>=
;; The name 'bind' is already taken, so we choose this (obscure) symbol.
(lambda (s)
(syntax-violation '>>= ">>= (bind) used outside of 'with-monad'" s)))
(define-syntax-parameter return
(define-syntax-parameter-once return
(lambda (s)
(syntax-violation 'return "return used outside of 'with-monad'" s)))

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