[OpenJDK 2D-Dev] RFR: 8261282: Lazy initialization of built-in ICC_Profile/ColorSpace classes is too lazy

[Alexander Zvegintsev]

On Sun, 7 Feb 2021 05:36:52 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> Short fix description:
> 
> The fix changes the initialization of the built-in color profiles/spaces from the lazy initialization per requested profile via static synchronization to the lazy initialization of all profiles/spaces on the first request via class initialization(holder idiom).
> 
> Long fix description:
> 
> 1. A long time ago the factory method ICC_Profile#getInstance() was a heavyweight method. For each requested profile it used the data of the icc file(ex: sRGB: 6kb and pycc: 200kb).
> As a result, in our code, we have tried to skip this method as much as possible or delay its usage. But we found that we have to use it anyway during startup. So we implemented the deferral mechanic for the sRGB profile. When this profile is requested we did not read the data but return the stub that contained some known in advance properties, such as num of color components, etc. The icc data is used only if the user request some of it later -> in this case we "activate" the profile and drop the stub data.
> 
> 2. Later we found that we may need some other profiles at startup, and the deferral mechanics was implemented for all profiles by the JDK-6793818. But profile activation was implemented as one step for all profiles at once, so if one profile such as sRGB was activated then the next profiles returned from the "ICC_Profile#getInstance" if not requested before was activated as well(used the icc file data).
> 
> 3. The deferral mechanics were updated in the JDK-6986863. Now activation of one profile does not affect other profiles and as a result, the "ICC_Profile#getInstance" always returns the stubs of the requested profiles.
> 
> 4. Each profile stub contains just a few lightweight objects, but still, use the heavyweight static synchronization to access/create it, see:
>    https://github.com/openjdk/jdk/blob/9d59dec200490f11bfc1c661b30f10c7edee3a6d/src/java.desktop/share/classes/java/awt/color/ICC_Profile.java#L821
>    Note that we have separate blocks for each profile("stub"). That looks an overkill.
>    
> 5. Note that in theory, it is not necessary to create these stubs lazily, each stub is a ICC_Profile object and ProfileDeferralInfo object, so we can use them as static fields in the ICC_Profile class. But here that classes initialization order come to play -> it is a bad idea to refer to the ICC_ProfileRGB(a subclass of the ICC_Profile) in the static block of ICC_Profile class because this could cause a deadlock.
> 
> 6. So this change merged initialization of all stubs to the one-step, still initialize stubs lazily, and maintains the singleton property.

Marked as reviewed by azvegint (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/2447