James,
Some reading is required to understand your code (never used volatile!) but
thanks for direction.
I will try this way.
W dniu piątek, 31 lipca 2015 17:39:50 UTC+2 użytkownik James Reeves napisał:
>
> The way I'd do it is to write a function that caches the output writer or
> stream. When the cache expires, the function closes the old writer and
> opens a new one to the new file.
>
> In the example below, I'm assuming you have a function that returns the
> same name for the same hour.
>
> (let [cache (volatile! nil)]
> (defn get-output-writer []
> (locking cache
> (let [filename (get-output-filename-for-this-hour)]
> (when (or (nil? @cache) (not= (:filename @cache) filename))
> (if-let [writer (:writer @cache)] (.close writer))
> (vreset! cache {:filename filename, :writer (io/writer filename)
> })))
> (:writer @cache))))
>
> Note that I'm using the locking macro to ensure that the function cannot
> be executed simultaneously by multiple threads.
>
> - James
>
>
> On 31 July 2015 at 13:23, Marcin Jurczuk <mjur...@gmail.com <javascript:>>
> wrote:
>
>> Hi all,
>>
>> This is my first post here so please be compassionate :)
>>
>> I'm evaluating clojure for some of my purposes and I've stuck on task
>> that I don't know to handle.
>> I have applicatin that is receiving a lot of data and writing some
>> results to a file.
>> However once per hour this output file must be changes so data are in
>> chunks.
>> I have working solution with writing to one file but I don't know where
>> to start code for changeing "this on the fly".
>> What I need is to avoid open-close cycle with every piece of data to save
>> since data stream is big.I need only close one file and open another one
>> (name generated on some rules) where data will be continously written once
>> per hour.
>>
>> I have this app written in golang where there are just two goroutines and
>> main code retriving data.
>> Writing goroutine beside data to write channel also have filename channel
>> and when it receives message here it just close current file and open
>> another but file handle var (i.e outFile) is always the same.
>> This file swap is made with mutex arround and other protection so there
>> is no case when write is made to a closed file.
>>
>> There is another timer goroutine that every ~§1h just calculate new
>> filename and sends message to write goroutine.
>> Works like expected :)
>>
>> As a proof of concept I'm trying to rewrite this in clojure.
>> Summary it's like kind of syslog which have to change destination file
>> periodically.
>>
>> Kind regards to everyone.
>>
>> Marcin.
>>
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