Add BytesMut::zeroed
#517
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Add BytesMut::zeroed
#517
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lelongg
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bk2204
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When we freeze a BytesMut, we turn it into a Vec, and then convert that to a Bytes. Currently, this happen using Vec::into_boxed_slice, which reallocates to a slice of the same length as the Vev if the length and the capacity are not equal. This can pose a performance problem if the Vec is large or if this happens many times in a loop. Instead, let's compare the length and capacity, and if they're the same, continue to handle this using into_boxed_slice. Otherwise, since we have a type of vtable which can handle a separate capacity, the shared vtable, let's turn our Vec into that kind of Bytes. While this does not avoid allocation altogether, it performs a fixed size allocation and avoids any need to memcpy.
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This PR adds a convenient method
BytesMut::zeroedfor creating zero-filledBytesMut, which is more convenient than new aBytesMutand resize it with zero afterward.BytesMut::zeroedis also usually much faster.Closes #270