Release Jackson BufferRecycler to its pool in encoders#37059
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bclozel merged 1 commit intoJul 16, 2026
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Both encoders acquire a pooled BufferRecycler via factory._getBufferRecycler() but never return it. Jackson 3 changed the default pool from a ThreadLocal to a per-factory ConcurrentDequePool that only refills on an explicit releaseToPool(), so the gap leaves the pool empty and every encode allocates a fresh recycler and buffers. Hold the recycler in a local and release it once the generator and byte builder are done: in encodeValue's finally, and in the streaming path's doAfterTerminate after generator.close() and byteBuilder.release(). releaseToPool() is idempotent, so sharing the recycler with the generator cannot double-release. Closes spring-projectsgh-37059 Signed-off-by: samlightfoot <samueldlightfoot@gmail.com>
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Thanks so much @samueldlightfoot for your contribution! |
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Summary
Both encoders acquire a pooled BufferRecycler via factory._getBufferRecycler() but never return it. Jackson 3 changed the default pool from a ThreadLocal to a per-factory ConcurrentDequePool that only refills on an explicit releaseToPool(), so the gap leaves the pool empty and every encode allocates a fresh recycler and buffers.
Hold the recycler in a local and release it once the generator and byte builder are done: in encodeValue's finally, and in the streaming path's doAfterTerminate after generator.close() and byteBuilder.release(). releaseToPool() is idempotent, so sharing the recycler with the generator cannot double-release.
Allocation profile
Setup: Bytes allocated per
encodeValuecall, measured with HotSpotThreadMXBean.getThreadAllocatedBytes()single-threaded at steady state (200k warmup, 500k ops/round × 7, median), using a default Jackson 3JsonMapper; the only difference between arms is the addedBufferRecycler.releaseToPool().The fix removes a fixed ~18 KB of recycler-buffer allocation per encode — constant in absolute terms, so the percentage just tracks payload size.