ZnCharacterEncoder default instances

>
> Hi Sven and Everyone,
>
> Instantiation of character encoders is relatively expensive, as can be
> seen by the following code snippet:
>
> | count str ba enc new old |
>
> count := 10000.
> str := 'test-äöü'.
> new := [
>     count timesRepeat: [
>         (ZnCharacterEncoder newForEncoding: 'utf8') encodeString: str
> ] ] timeToRunWithoutGC.
> enc := ZnCharacterEncoder newForEncoding: 'utf8'.
> old := [
>     count timesRepeat: [
>         enc encodeString: str ] ] timeToRunWithoutGC.
> { old. new. }
>
> " #(14 122)"
>
> What do you think of the idea of caching default instances of encoders?
>
> My idea was to have a dictionary in ZnCharacterEncoder and add a class
> method #forEncoding:.  This would lazily create an instance, store it
> in the dictionary, and then re-use the instance whenever that encoder
> is requested.  If people really want their own instance (not sure why,
> there aren't any instance variables, and so there's no state), they
> can use the existing #newForEncoding:.
>
> For example, sending #exists to a file reference currently
> instantiates two encoders.
>
> This was actually previously fixed by #20273[1], but seems to have
> been lost with the refactoring of FilePluginPrims to File.  From
> memory, Cyril's application saved 12 seconds by caching the encoder.
> But in that case the instance was private to the file plugin
> primitives.  This would be a more general solution.
>
> [1] https://pharo.fogbugz.com/f/cases/20273/FilePluginPrims-could-save-an-encoder-to-speedup-some-methods

> On 28 Aug 2018, at 12:43, Alistair Grant <[hidden email]> wrote:
>
> Hi Sven and Everyone,
>
> Instantiation of character encoders is relatively expensive, as can be
> seen by the following code snippet:
>
> | count str ba enc new old |
>
> count := 10000.
> str := 'test-äöü'.
> new := [
>    count timesRepeat: [
>        (ZnCharacterEncoder newForEncoding: 'utf8') encodeString: str
> ] ] timeToRunWithoutGC.
> enc := ZnCharacterEncoder newForEncoding: 'utf8'.
> old := [
>    count timesRepeat: [
>        enc encodeString: str ] ] timeToRunWithoutGC.
> { old. new. }
>
> " #(14 122)"
>
> What do you think of the idea of caching default instances of encoders?
>
> My idea was to have a dictionary in ZnCharacterEncoder and add a class
> method #forEncoding:.  This would lazily create an instance, store it
> in the dictionary, and then re-use the instance whenever that encoder
> is requested.  If people really want their own instance (not sure why,
> there aren't any instance variables, and so there's no state), they
> can use the existing #newForEncoding:.
>
> For example, sending #exists to a file reference currently
> instantiates two encoders.
>
> This was actually previously fixed by #20273[1], but seems to have
> been lost with the refactoring of FilePluginPrims to File.  From
> memory, Cyril's application saved 12 seconds by caching the encoder.
> But in that case the instance was private to the file plugin
> primitives.  This would be a more general solution.
>
> [1] https://pharo.fogbugz.com/f/cases/20273/FilePluginPrims-could-save-an-encoder-to-speedup-some-methods
>
> Thanks,
> Alistair
>

>
> Hi Alistair,
>
> Thanks for the feedback, but consider:
>
> count := 10000.
> str := 'test-äöü'.
> [
>    count timesRepeat: [
>        ZnCharacterEncoder utf8 encodeString: str
> ] ] timeToRunWithoutGC.
>
> => 8
>
> #newForEncoding: is indeed slow as it has to look through all known encoders, which also involves a subclasses search, which is a PITA.
>
> ZnCharacterEncoder class>>#utf8 actually uses a cached default instance (see ZnUTF8Encoder class>>#default). As this is the most used encoder, with no customization options, it makes sense. For example, #utf8Encoded and #utf8Decoded use this instance.
>
> However, some (byte, utf16, utf32) encoders do have state (endianness, strictness, ...), so global caching could be an issue.
>
> Users of the encoders are free to cache their own instances.
>
> I am not (yet) convinced that a global cache is needed.