RFR: 8357647 : Stream gatherers forward upstream size information to downstream

[Viktor Klang]

On Fri, 23 May 2025 15:53:22 GMT, Johannes Döbler <duke at openjdk.org> wrote:

>> While it could be argued that unbounded Spliterators should not report SIZED / SUBSIZED, GatherSink should report an unknown emission size, so switching to downstream.begin(-1) rather than downstream.begin(size).
>> 
>> Includes a regression test which yields an OOME if this change is omitted.
>
> src/java.base/share/classes/java/util/stream/GathererOp.java line 153:
> 
>> 151:             if (initializer != Gatherer.defaultInitializer()) // Optimization
>> 152:                 state = initializer.get();
>> 153:             sink.begin(-1); // GathererOp does not know the size of the output
> 
> The Integrator of the SO question which motivated this PR _does_ know the size of the output. In general would it be worth to enhance Integrator with something like `default long estimateSize(long streamEstimate) { return -1; }` to allow Integrator implementations to weigh in?

@jdlib I guess that would depend on the definition of *value* and *cost* in this context.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/25418#discussion_r2104911643