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-rw-r--r--guix/build/syscalls.scm35
1 files changed, 33 insertions, 2 deletions
diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index bbf2531c79..a5a9c92a42 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -80,6 +80,7 @@
lock-file
unlock-file
with-file-lock
+ with-file-lock/no-wait
set-thread-name
thread-name
@@ -1087,10 +1088,10 @@ exception if it's already taken."
;; Presumably we got EAGAIN or so.
(throw 'flock-error err))))))
-(define (lock-file file)
+(define* (lock-file file #:key (wait? #t))
"Wait and acquire an exclusive lock on FILE. Return an open port."
(let ((port (open-file file "w0")))
- (fcntl-flock port 'write-lock)
+ (fcntl-flock port 'write-lock #:wait? wait?)
port))
(define (unlock-file port)
@@ -1119,10 +1120,40 @@ exception if it's already taken."
(when port
(unlock-file port))))))
+(define (call-with-file-lock/no-wait file thunk handler)
+ (let ((port (catch #t
+ (lambda ()
+ (lock-file file #:wait? #f))
+ (lambda (key . args)
+ (match key
+ ('flock-error
+ (handler args))
+ ('system-error
+ ;; When using the statically-linked Guile in the initrd,
+ ;; 'fcntl-flock' returns ENOSYS unconditionally. Ignore
+ ;; that error since we're typically the only process running
+ ;; at this point.
+ (if (= ENOSYS (system-error-errno (cons key args)))
+ #f
+ (apply throw args)))
+ (_ (apply throw key args)))))))
+ (dynamic-wind
+ (lambda ()
+ #t)
+ thunk
+ (lambda ()
+ (when port
+ (unlock-file port))))))
+
(define-syntax-rule (with-file-lock file exp ...)
"Wait to acquire a lock on FILE and evaluate EXP in that context."
(call-with-file-lock file (lambda () exp ...)))
+(define-syntax-rule (with-file-lock/no-wait file handler exp ...)
+ "Try to acquire a lock on FILE and evaluate EXP in that context. Execute
+handler if the lock is already held by another process."
+ (call-with-file-lock/no-wait file (lambda () exp ...) handler))
+
;;;
;;; Miscellaneous, aka. 'prctl'.