diff options
| -rw-r--r-- | guix/build/syscalls.scm | 35 |
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'. |