Struct async_std::io::BufWriter [−][src]
pub struct BufWriter<W> { /* fields omitted */ }Expand description
Wraps a writer and buffers its output.
It can be excessively inefficient to work directly with something that
implements Write. For example, every call to
write on TcpStream results in a system call. A
BufWriter keeps an in-memory buffer of data and writes it to an underlying
writer in large, infrequent batches.
BufWriter can improve the speed of programs that make small and
repeated write calls to the same file or network socket. It does not
help when writing very large amounts at once, or writing just one or a few
times. It also provides no advantage when writing to a destination that is
in memory, like a Vec<u8>.
Unlike the BufWriter type in std, this type does not write out the
contents of its buffer when it is dropped. Therefore, it is absolutely
critical that users explicitly flush the buffer before dropping a
BufWriter.
This type is an async version of std::io::BufWriter.
Examples
Let’s write the numbers one through ten to a TcpStream:
use async_std::net::TcpStream;
use async_std::prelude::*;
let mut stream = TcpStream::connect("127.0.0.1:34254").await?;
for i in 0..10 {
let arr = [i+1];
stream.write(&arr).await?;
}Because we’re not buffering, we write each one in turn, incurring the
overhead of a system call per byte written. We can fix this with a
BufWriter:
use async_std::io::BufWriter;
use async_std::net::TcpStream;
use async_std::prelude::*;
let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
for i in 0..10 {
let arr = [i+1];
stream.write(&arr).await?;
};
stream.flush().await?;By wrapping the stream with a BufWriter, these ten writes are all grouped
together by the buffer, and will all be written out in one system call when
stream.flush() completes. (As mentioned above, dropping a BufWriter
does not flush its buffers, so a flush call is essential.)
Implementations
Creates a new BufWriter with a default buffer capacity. The default is currently 8 KB,
but may change in the future.
Examples
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);Creates a new BufWriter with the specified buffer capacity.
Examples
Creating a buffer with a buffer of a hundred bytes.
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let stream = TcpStream::connect("127.0.0.1:34254").await?;
let mut buffer = BufWriter::with_capacity(100, stream);Gets a reference to the underlying writer.
Examples
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
// We can use reference just like buffer
let reference = buffer.get_ref();Gets a mutable reference to the underlying writer.
It is inadvisable to directly write to the underlying writer.
Examples
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
// We can use reference just like buffer
let reference = buffer.get_mut();Consumes BufWriter, returning the underlying writer
This method will not write leftover data, it will be lost.
For method that will attempt to write before returning the writer see poll_into_inner
Examples
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34251").await?);
// unwrap the TcpStream and flush the buffer
let stream = buf_writer.into_inner().await.unwrap();Returns a reference to the internally buffered data.
Examples
use async_std::io::BufWriter;
use async_std::net::TcpStream;
let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34251").await?);
// See how many bytes are currently buffered
let bytes_buffered = buf_writer.buffer().len();Trait Implementations
Seek to the offset, in bytes, in the underlying writer.
Seeking always writes out the internal buffer before seeking.
Attempt to write bytes from buf into the object.
Attempt to flush the object, ensuring that any buffered data reach their destination. Read more
Attempt to close the object.
Attempt to write bytes from bufs into the object using vectored IO operations.
Writes some bytes into the byte stream. Read more
Flushes the stream to ensure that all buffered contents reach their destination. Read more
Writes an entire buffer into the byte stream. Read more