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doc clarifications and tests for some file-locking corners

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This commit is contained in:
Matthew Flatt 2011-09-16 20:56:58 -06:00
parent 4c59f02cb0
commit 376efea754
2 changed files with 30 additions and 4 deletions
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27
collects/scribblings/reference/file-ports.scrbl
View File

@ -317,10 +317,31 @@ either it is released with @racket[port-file-unlock] or the port is closed
Depending on the platform, locks may be merely advisory (i.e., locks Depending on the platform, locks may be merely advisory (i.e., locks
affect only the ability of processes to acquire locks) or they may affect only the ability of processes to acquire locks) or they may
correspond to mandatory locks that prevent reads and writes to the correspond to mandatory locks that prevent reads and writes to the
locked file. Specifically, locks are mandatory on Windows and locked file. Specifically, locks are mandatory on Windows and advisory
advisory on other platforms. on other platforms. Multiple tries for a @racket['shared] lock on a
single port can succeed; on Unix and Mac OS X, a single
@racket[port-file-unlock] release the lock, while on other Windows, a
@racket[port-file-unlock] is needed for each successful
@racket[port-try-file-lock?]. On Unix and Mac OS X, multiple tries for
a @racket['exclusive] lock can succeed and a single
@racket[port-file-unlock] releases the lock, while on Windows, a try
for an @racket['exclusive] lock fails for a given port if the port
already holds the lock.
Typically, locking is supported only for file ports, and attempting to A lock acquired for an input port from @racket[open-input-output-file]
can be released through @racket[port-file-unlock] on the corresponding
output port, and vice versa. If the output port from
@racket[open-input-output-file] holds an @racket['exclusive] lock, the
corresponding input port can still acquire a @racket['shared] lock,
even multiple times; on Windows, a @racket[port-file-unlock] is needed
for each successful lock try, while a single @racket[port-file-unlock]
balances the lock tries on Unix and Mac OS X. A @racket['shared] lock on
an input port can be upgraded to an @racket['exclusive] lock through the
corresponding output port on Unix and Mac OS X, in which case a single
@racket[port-file-unlock] (on either port) releases the lock, while
such upgrades are not allowed on Windows.
Locking is normally supported only for file ports, and attempting to
acquire a lock with other kinds of file-stream ports raises an acquire a lock with other kinds of file-stream ports raises an
@racket[exn:fail:filesystem] exception.} @racket[exn:fail:filesystem] exception.}

7
collects/tests/racket/file.rktl
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@ -695,6 +695,7 @@
(check-test-file "tmp2") (check-test-file "tmp2")
(let-values ([(p p-out) (open-input-output-file "tmp2" #:exists 'update)]) (let-values ([(p p-out) (open-input-output-file "tmp2" #:exists 'update)])
(test #t port-try-file-lock? p 'shared)
(test #t port-try-file-lock? p 'shared) (test #t port-try-file-lock? p 'shared)
(let ([p2 (open-input-file "tmp2")]) (let ([p2 (open-input-file "tmp2")])
(test #t port-try-file-lock? p2 'shared) (test #t port-try-file-lock? p2 'shared)
@ -704,8 +705,12 @@
(let ([p3 (open-output-file "tmp2" #:exists 'update)]) (let ([p3 (open-output-file "tmp2" #:exists 'update)])
(test #f port-try-file-lock? p3 'exclusive) (test #f port-try-file-lock? p3 'exclusive)
(test (void) port-file-unlock p) (test (void) port-file-unlock p)
(when (eq? (system-type) 'windows)
;; need another unlock, since we got a 'shared lock twice
(test #f port-try-file-lock? p3 'exclusive)
(test (void) port-file-unlock p))
(test #t port-try-file-lock? p3 'exclusive) (test #t port-try-file-lock? p3 'exclusive)
(test #t port-try-file-lock? p3 'exclusive) (test (not (eq? 'windows (system-type))) port-try-file-lock? p3 'exclusive)
(test #f port-try-file-lock? p 'shared) (test #f port-try-file-lock? p 'shared)
(close-output-port p3)) (close-output-port p3))
(err/rt-test (port-try-file-lock? p 'exclusive)) (err/rt-test (port-try-file-lock? p 'exclusive))