RFR: 8304745: Lazily initialize byte[] in java.io.BufferedInputStream

[Sergey Tsypanov]

On Wed, 22 Mar 2023 23:01:32 GMT, Chen Liang <liach at openjdk.org> wrote:

> This change exposes the CLOSED array

Otherwise we have to either call `getInIfOpen()`/`getBufIfOpen` making them at least protected or dodge this somehow via `SharedSecrets`

> I mean that additional API exposure is acceptable and backward compatible, but the previous contract to subclasses that the protected `buf` is initialized after superclass constructor execution breaks. Before this change proceeds, we have to check how many subclasses of `BufferedInputStream` access this `buf` in a wide range of libraries and evaluate the impact, which I anticipate to be huge.
> 
> A slightly less impactful approach would be sharing a `byte[0]` for a newly initialized state, like in ArrayList, so users anticipating a closed `BufferedInputStream` to have a null `buf` will still work. But users anticipating a usable buf after constructor will still break: for instance, since `getBufIfOpen` is private but the `buf` field it uses is protected, nothing prevents subclasses from copying the same implementation over; and the same implementation will stop working with this new optimization.

@liach with your approach tests are green

> src/java.base/share/classes/java/io/BufferedInputStream.java line 78:
> 
>> 76:     private final InternalLock lock;
>> 77: 
>> 78:     /**
> 
> These should be reverted, now that the subclasses will see the same behavior as before.

But it's just comment clean up

> src/java.base/share/classes/java/io/BufferedInputStream.java line 211:
> 
>> 209:             throw new IllegalArgumentException("Buffer size <= 0");
>> 210:         }
>> 211:         buf = new byte[0];
> 
> Two recommendations:
> 1. This `new byte[0]` can be safely shared, so I recommend you to put it in a static final field to avoid reallocation
> 2. The subclass compatibility can be retained by:
> Suggestion:
> 
>         buf = (getClass() == BufferedInputStream.class) ? new byte[0] : new byte[size];

Good point, done!

> src/java.base/share/classes/java/io/BufferedInputStream.java line 216:
> 
>> 214:             throw new IllegalArgumentException("Buffer size <= 0");
>> 215:         }
>> 216:         buf = getClass() == BufferedInputStream.class ? EMPTY : new byte[size];
> 
> Actually, you can merge this `getClass()` check with the one below for locks.

Done

-------------

PR Comment: https://git.openjdk.org/jdk/pull/13150#issuecomment-1480701591
PR Comment: https://git.openjdk.org/jdk/pull/13150#issuecomment-1481236336
PR Review Comment: https://git.openjdk.org/jdk/pull/13150#discussion_r1146316757
PR Review Comment: https://git.openjdk.org/jdk/pull/13150#discussion_r1146321335
PR Review Comment: https://git.openjdk.org/jdk/pull/13150#discussion_r1146414668