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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: Directory.deleteFile confusingly throws IOException
Date Fri, 23 Apr 2010 10:20:02 GMT
Deletion can conceivably fail for a number of interesting reasons :)
File doesn't exist, permission is denied, file system corruption, some
kind of temporary resource starvation problem, etc...

And actually it looks like Java 7 (nio.2) has moved to throwing an
IOException (Path.delete) instead of returning a boolean
(File.delete):

    http://www.baptiste-wicht.com/2010/03/nio-2-path-api-java-7/

If only nio.2 exposed some way to madvise/posix_fadvise so segment
merging wouldn't obliterate the IO cache...

Mike

On Thu, Apr 22, 2010 at 11:45 PM, Shai Erera <serera@gmail.com> wrote:
> I understand your point Mike, but I don't think that returning a
> boolean will make the Dir API poor. Today boolean is as descriptive as
> an exception, only much more efficient to handle - given the current
> Dir impls in Lucene and that we don't think there are many impls out
> there …
>
> Also, I think the Java API makes sense - there cannot be too many
> reasons for failing to delete a file. So runtime SecurityException
> (which must be rarerly thrown) + boolean seems fine to me.
>
> But really, if you don't think we should change the API, let's drop it.
>
> Shai
>
> On Thursday, April 22, 2010, Michael McCandless
> <lucene@mikemccandless.com> wrote:
>> Actually they both seem consistent today?  Ie, Directory.deleteFile
>> returns nothing (void) and throws an IOE if the delete fails.
>>
>> Both FSDir and RAMDir throw IOE when the delete fails (yes, RAMDir
>> throws FNFE, but that's an IOE subclass).
>>
>> Just because the java API is poor (returns true or false instead of
>> throwing specific IOEs) doesn't mean we should make our Directory API
>> poor?
>>
>> And, how IFD deals with files that refuse to be deleted, seems
>> orthogonal to how Directory.deleteFile conveys the fact that the file
>> cannot be deleted...
>>
>> Mike
>>
>> On Wed, Apr 21, 2010 at 1:02 PM, Shai Erera <serera@gmail.com> wrote:
>>> I think today it's simply inconsistent - RAMDir throws FNFE if the file does
>>> not exist (and no other IOE) while FSDir throws IOE for whatever reason
>>> File.delete() returned false (not adding any information as to the cause).
>>> FSDir cannot do much more than what it does, because File.delete() does not
>>> throw any exception, except for the runtime SecurityException, which is
>>> ignored (propagated) by FSDir. I've never seen a SecurityException thrown by
>>> File.delete() ...
>>>
>>> And one can still (like IFD does) call dir.fileExist in case delete returned
>>> false to differentiate between "file exists and could not be deleted" to
>>> "file does not exist". As one can do w/ File. And then throw a more
>>> descriptive exception.
>>>
>>> Also, I think that given all the current impls don't add any (concrete)
>>> information as to why the file was not deleted, I think we should define the
>>> proper semantics: "Returns true iff the file was successfully deleted. If
>>> false is returned, it is advised to call #fileExists(String) to
>>> differentiate between a delete failure because the file does not exist, to
>>> another failure".
>>>
>>> We can keep the 'throws IOException' for "whatever other bad things
>>> happened", but I'd hate to do that, especially as there are probably not so
>>> many Directory implementations out there which can return more meaningful
>>> info then true/false. And if we keep the IOE, I think we should do something
>>> in IFD rather than swallow the exception and retry over if the file exists
>>> ... currently the code assumes the exception is temporary, which may not be
>>> the case w/ external Dir impls. And if we fix that ... well we need to fix
>>> 'deletePendingFiles' as well ... this becomes a mess.
>>>
>>> What do you think?
>>>
>>> Shai
>>>
>>> On Wed, Apr 21, 2010 at 7:01 PM, Michael McCandless
>>> <lucene@mikemccandless.com> wrote:
>>>>
>>>> I agree clarity is important so we should tighten up this spec.
>>>>
>>>> But, don't we potentially lose information if we just return true or
>>>> false?  (Ie why the deletion failed).  Failing because of FNFE vs a
>>>> "permission denied" or filesystem corruption are very different.  But,
>>>> then, our hands are tied anyway since File.delete returns boolean...
>>>> so maybe we should simply return a boolean...?
>>>>
>>>> Mike
>>>>
>>>> On Wed, Apr 21, 2010 at 11:32 AM, Shai Erera <serera@gmail.com> wrote:
>>>> > Hi
>>>> >
>>>> > While working on LUCENE-2402, I've noticed what I think is a confusing
>>>> > behavior of Dir.deleteFile. Its signature declares throwing an
>>>> > IOException,
>>>> > but w/ no documentation to when and why will this be thrown. And then
of
>>>> > course there are the two different implementations by FSDir and RAMDir:
>>>> > FSDir throws an IOException if File.delete() returns false while RAMDir
>>>> > throws FNFE if the file does not exist.
>>>> > In either case, an IOE is not thrown from the lower-level API (File
in
>>>> > FSDir
>>>> > case).
>>>> >
>>>> > Then, IFD.deleteFile declares "throws IOException", but never really
>>>> > throws
>>>> > it. Instead, it calls directory.deleteFile(), catches IOE, and calls
>>>> > dir.fileExists. If the latter returns true it adds the file to the list
>>>> > of
>>>> > pending to delete files, otherwise simply ignores the exception (!?).
>>>> >
>>>> > My feeling is that this exception should not be declared on Directory,
>>>> > but
>>>> > rather have deleteFile return true or false (like Java's File). In both
>>>> > current implementations, it's not a real IO error, and if there is any
>>>> > custom Dir impl out there, which really throws IOE, then IFD clearly
>>>> > ignores
>>>> > it, and will try to delete the file again next time.
>>>> >
>>>> > So it's more that Dir.deleteFile is confusing, than IFD is broken. And
I
>>>> > think clarity is important.
>>>> >
>>>> > What do you think?
>>>> >
>>
>
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