javax.imageio.ImageIO ThreadLocal use

[Alan Bateman]

On 09/05/2023 19:47, Duncan Gittins wrote:
> Alan
>
> thanks for the information. I'll wipe my allowSetThreadLocal calls and 
> add -Djdk.traceVirtualThreadLocals=true to monitor this from JDK21+.
>
> Unfortunately I'm not an expert on ImageIO - my observations (not 
> backed with solid JMH stats) are that JPG loading is quite slow, 
> disabling caching "ImageIO.setUseCache(false);" strangely appears to 
> make it faster, and for the NAS/USB storage devices I have it seems 
> that preloading a whole file into memory before calling 
> Image.read(InputStream) beats Image.read(File) directly. Not an issue 
> for loom-dev, and I may be incorrect anyway.
>
ImageIO.setUseCaches configures caching on the file system. From a quick 
look it doesn't appear to be caching in TLs. In any case, you've found 
the system property to help track down usages of TLs that might not 
scale with a lot of virtual threads.

-Alan