direct buffer preference should not depend on unsafe presence#15381
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direct buffer preference should not depend on unsafe presence#15381
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I had a small conversation about this with @chrisvest yesterday on discord: https://canary.discord.com/channels/936310574684438528/936310574684438532/1385254901654749244 |
franz1981
reviewed
Jun 20, 2025
| * applies for buffers allocated via {@link #allocateDirect(int)} and when using the {@code clean} method of the | ||
| * returned {@link CleanableDirectBuffer}. | ||
| */ | ||
| public static boolean canReliabilyFreeDirectBuffers() { |
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it could be even boolean hasCleaner but not a strong preference
chrisvest
approved these changes
Jun 20, 2025
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Motivation:
Currently, the preference if a direct buffer should be allocated by, for example,
ByteBufAllocator.buffer()orByteBufAllocator.ioBuffer()depends on the fact if unsafe is available. It seems like this was originally introduced as only with unsafe it was possible to get the cleaner of a ByteBuffer to clean it. However, with the changes introduced in #15231, it doesn't make sense anymore to depend on this as unsafe could be unavailable but MemorySegments will still be freeable.Modification:
Switch the check for unsafe to a check that validates if the current cleaner implementation is able to free the allocated buffers (each implementation can do this except the no-op one). This ensures that direct buffers are actually preferred when they're backed by something cleanable and still unpreferred when unsafe is unavailable and buffers cannot be freed in a controlled way.
Result:
Direct buffers will be preferred when they're cleanable in a controlled way unrelated to the fact if unsafe is available.