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utils: Add 'fcntl-flock'.
* guix/utils.scm (%struct-flock, F_SETLKW, F_xxLCK): New variables. (fcntl-flock): New procedure. * tests/utils.scm ("fcntl-flock"): New test.
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2 changed files with 95 additions and 3 deletions
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@ -1,5 +1,5 @@
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;;; GNU Guix --- Functional package management for GNU
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2013 Mark H Weaver <mhw@netris.org>
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;;; Copyright © 2013 Mark H Weaver <mhw@netris.org>
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;;;
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;;;
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;;; This file is part of GNU Guix.
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;;; This file is part of GNU Guix.
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@ -34,7 +34,7 @@ (define-module (guix utils)
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#:use-module (ice-9 regex)
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#:use-module (ice-9 regex)
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#:use-module (ice-9 match)
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#:use-module (ice-9 match)
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#:use-module (ice-9 format)
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#:use-module (ice-9 format)
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#:autoload (system foreign) (pointer->procedure)
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#:use-module (system foreign)
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#:export (bytevector->base16-string
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#:export (bytevector->base16-string
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base16-string->bytevector
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base16-string->bytevector
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@ -43,6 +43,7 @@ (define-module (guix utils)
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nixpkgs-derivation*
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nixpkgs-derivation*
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compile-time-value
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compile-time-value
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fcntl-flock
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memoize
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memoize
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default-keyword-arguments
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default-keyword-arguments
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substitute-keyword-arguments
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substitute-keyword-arguments
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@ -222,6 +223,67 @@ (define-syntax-rule (nixpkgs-derivation* attribute)
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"Evaluate the given Nixpkgs derivation at compile-time."
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"Evaluate the given Nixpkgs derivation at compile-time."
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(compile-time-value (nixpkgs-derivation attribute)))
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(compile-time-value (nixpkgs-derivation attribute)))
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;;;
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;;; Advisory file locking.
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;;;
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(define %struct-flock
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;; 'struct flock' from <fcntl.h>.
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(list short ; l_type
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short ; l_whence
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size_t ; l_start
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size_t ; l_len
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int)) ; l_pid
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(define F_SETLKW
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;; On Linux-based systems, this is usually 7, but not always
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;; (exceptions include SPARC.) On GNU/Hurd, it's 9.
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(compile-time-value
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(cond ((string-contains %host-type "sparc") 9) ; sparc-*-linux-gnu
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((string-contains %host-type "linux") 7) ; *-linux-gnu
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(else 9)))) ; *-gnu*
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(define F_xxLCK
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;; The F_RDLCK, F_WRLCK, and F_UNLCK constants.
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(compile-time-value
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(cond ((string-contains %host-type "sparc") #(1 2 3)) ; sparc-*-linux-gnu
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((string-contains %host-type "hppa") #(1 2 3)) ; hppa-*-linux-gnu
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((string-contains %host-type "linux") #(0 1 2)) ; *-linux-gnu
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(else #(1 2 3))))) ; *-gnu*
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(define fcntl-flock
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(let* ((ptr (dynamic-func "fcntl" (dynamic-link)))
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(proc (pointer->procedure int ptr `(,int ,int *))))
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(lambda (fd-or-port operation)
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"Perform locking OPERATION on the file beneath FD-OR-PORT. OPERATION
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must be a symbol, one of 'read-lock, 'write-lock, or 'unlock."
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(define (operation->int op)
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(case op
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((read-lock) (vector-ref F_xxLCK 0))
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((write-lock) (vector-ref F_xxLCK 1))
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((unlock) (vector-ref F_xxLCK 2))
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(else (error "invalid fcntl-flock operation" op))))
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(define fd
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(if (port? fd-or-port)
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(fileno fd-or-port)
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fd-or-port))
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;; XXX: 'fcntl' is a vararg function, but here we happily use the
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;; standard ABI; crossing fingers.
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(let ((err (proc fd
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F_SETLKW ; lock & wait
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(make-c-struct %struct-flock
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(list (operation->int operation)
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SEEK_SET
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0 0 ; whole file
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0)))))
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(or (zero? err)
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;; Presumably we got EAGAIN or so.
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(throw 'flock-error fd))))))
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;;;
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;;;
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;;; Miscellaneous.
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;;; Miscellaneous.
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@ -1,5 +1,5 @@
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;;; GNU Guix --- Functional package management for GNU
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;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
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;;; Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
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;;;
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;;;
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;;; This file is part of GNU Guix.
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;;; This file is part of GNU Guix.
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;;;
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;;;
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@ -139,6 +139,36 @@ (define-module (test-utils)
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(append pids1 pids2)))
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(append pids1 pids2)))
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(equal? (get-bytevector-all decompressed) data)))))
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(equal? (get-bytevector-all decompressed) data)))))
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(test-equal "fcntl-flock"
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0 ; the child's exit status
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(let ((file (open-input-file (search-path %load-path "guix.scm"))))
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(fcntl-flock file 'read-lock)
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(match (primitive-fork)
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(0
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(dynamic-wind
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(const #t)
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(lambda ()
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;; Taking a read lock should be OK.
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(fcntl-flock file 'read-lock)
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(fcntl-flock file 'unlock)
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(catch 'flock-error
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(lambda ()
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;; Taking an exclusive lock should raise an exception.
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(fcntl-flock file 'write-lock))
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(lambda args
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(primitive-exit 0)))
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(primitive-exit 1))
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(lambda ()
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(primitive-exit 2))))
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(pid
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(match (waitpid pid)
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((_ . status)
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(let ((result (status:exit-val status)))
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(fcntl-flock file 'unlock)
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(close-port file)
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result)))))))
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;; This is actually in (guix store).
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;; This is actually in (guix store).
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(test-equal "store-path-package-name"
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(test-equal "store-path-package-name"
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"bash-4.2-p24"
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"bash-4.2-p24"
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