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Re: [jgit-dev] nio exception

On 03/09/2012 04:28 PM, Shawn Pearce wrote:
> On Thu, Mar 8, 2012 at 22:57, Markus Duft <markus.duft@xxxxxxxxxx> wrote:
>> On 03/07/2012 04:30 PM, Shawn Pearce wrote:
>>> On Tue, Mar 6, 2012 at 23:17, Markus Duft <markus.duft@xxxxxxxxxx> wrote:
>>>> On 03/07/2012 03:32 AM, Shawn Pearce wrote:
>>>>> On Tue, Mar 6, 2012 at 05:16, Markus Duft <markus.duft@xxxxxxxxxx> wrote:
>>>> [snip]
>> [snip]
>>>> problematic here is the in.getChannel().size()... this uses a NIO channel to determine the size of the file (lol). This is the step that can fail. I'm not really sure what would be the best solution here, but i think a simple "final long sz = path.length();" would do instead. or is File.length() somehow bad? or more bad than Channel.size()?
>>> Whoops. The problem with path.length() is the inode could have changed
>>> out from under us between when the file was opened, and when the size
>>> was estimated. The only safe way to know is to use the channel to get
>>> at fstat() in the system, or to use the path.length() as an estimate
>>> for the buffer size but be prepared to grow or shrink our buffer if
>>> the actual file length is larger or smaller, as determined by when
>>> read() returns the EOF indicator.  :-)
>> are you really sure this is a problem? i checked the openjdk implementation of FileSystem.getLength() (which is used by File.length()), and it does a stat() on the path always. this should be for sure sufficient to not confuse anything :) it will also catch the case where inodes change. nothing is cached. nowhere. if there are java implementations that do cache - i think, _thats_ the bug then ;p
> Yes, it is a problem:
>   Thread 1:
>     FileInputStream in = new FileInputStream(....);
>   Thread 2:
>     echo hi >; mv config
>   Thread 1:
>       long len = path.length();  // now 3 instead of say 4000.

are you serious? you have to rewrite the file in between two code lines. you'll have to hit a nanoseconds timeframe?! other than that i think this is a little overkill, how about calling length() twice, once before, once after and then taking max() of the two ... ? :D the "be prepared to change buffer sizes" version sounds much harder to implement. any other ideas?


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