Trait AsyncVectoredWrite and related utilities #3092
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Darksonn
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Reintroduce vectored I/O facilities in the new module io::vec, starting from the poll_write_vectored method in the new AsyncVectoredWrite trait. Implement AsyncVectoredWrite for TcpStream.
io::Sink can consume vectored buffers just as well as it can do single buffers.
An extension trait providing async-friendly methods for all implementors of AsyncVectoredWrite.
Delegate these implementations to std::io::Write::write_vectored, no blocking when writing to byte containers in memory.
Fill the buffer more eagerly over consecutive calls to poll_write_vectored. At the first non-empty slice, the buffer is flushed if the slice does not fit completely, after which filling can continue until capacity is exhausted, or there is an oversized slice for direct writing, or there are no more slices to write.
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I believe this is obviated by #3149, which also adds an API for vectored writes. |
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Motivation
#2882 removed the
poll_write_bufmethod inAsyncWritethat could be implemented as a vectored write.There is still a desire to use vectored I/O facilities on objects that support them efficiently, especially on the writing side.
Solution
Introduce a new trait,
AsyncVectoredWrite, providing thepoll_write_vectoredmethod.In contrast to the earlier
poll_write_buf, the method is object-safe.AsyncVectoredWriteis implemented for:Sink;TcpStream,UnixStream, their write halves;AsyncVectoredWritetypes;io::WriteHalfof anAsyncVectoredWriteobject;BufWriter, as well as write-through delegations onBufStreamandBufReader.The latter implementation allows using
BufWriterand friends as buffering adapters in cases when generic code requiresAsyncVectoredWrite.The
AsyncVectoredWriteExtutility trait provides the async-friendly methodwrite_vectoredfor all types implementingAsyncVectoredWrite.