compio_io/write/
buf.rs

1use std::future::ready;
2
3use compio_buf::{BufResult, IntoInner, IoBuf, IoVectoredBuf, buf_try};
4
5use crate::{
6    AsyncWrite, IoResult,
7    buffer::Buffer,
8    util::{DEFAULT_BUF_SIZE, slice_to_buf},
9};
10
11/// Wraps a writer and buffers its output.
12///
13/// It can be excessively inefficient to work directly with something that
14/// implements [`AsyncWrite`].  A `BufWriter<W>` keeps an in-memory buffer of
15/// data and writes it to an underlying writer in large, infrequent batches.
16//
17/// `BufWriter<W>` can improve the speed of programs that make *small* and
18/// *repeated* write calls to the same file or network socket. It does not
19/// help when writing very large amounts at once, or writing just one or a few
20/// times. It also provides no advantage when writing to a destination that is
21/// in memory, like a `Vec<u8>`.
22///
23/// Dropping `BufWriter<W>` also discards any bytes left in the buffer, so it is
24/// critical to call [`flush`] before `BufWriter<W>` is dropped. Calling
25/// [`flush`] ensures that the buffer is empty and thus no data is lost.
26///
27/// [`flush`]: AsyncWrite::flush
28
29#[derive(Debug)]
30pub struct BufWriter<W> {
31    writer: W,
32    buf: Buffer,
33}
34
35impl<W> BufWriter<W> {
36    /// Creates a new `BufWriter` with a default buffer capacity. The default is
37    /// currently 8 KB, but may change in the future.
38    pub fn new(writer: W) -> Self {
39        Self::with_capacity(DEFAULT_BUF_SIZE, writer)
40    }
41
42    /// Creates a new `BufWriter` with the specified buffer capacity.
43    pub fn with_capacity(cap: usize, writer: W) -> Self {
44        Self {
45            writer,
46            buf: Buffer::with_capacity(cap),
47        }
48    }
49}
50
51impl<W: AsyncWrite> BufWriter<W> {
52    async fn flush_if_needed(&mut self) -> IoResult<()> {
53        if self.buf.need_flush() {
54            self.flush().await?;
55        }
56        Ok(())
57    }
58}
59
60impl<W: AsyncWrite> AsyncWrite for BufWriter<W> {
61    async fn write<T: IoBuf>(&mut self, mut buf: T) -> BufResult<usize, T> {
62        // The previous flush may error because disk full. We need to make the buffer
63        // all-done before writing new data to it.
64        (_, buf) = buf_try!(self.flush_if_needed().await, buf);
65
66        let written = self
67            .buf
68            .with_sync(|w| {
69                let len = w.buf_len();
70                let mut w = w.slice(len..);
71                let written = slice_to_buf(buf.as_slice(), &mut w);
72                BufResult(Ok(written), w.into_inner())
73            })
74            .expect("Closure always return Ok");
75
76        (_, buf) = buf_try!(self.flush_if_needed().await, buf);
77
78        BufResult(Ok(written), buf)
79    }
80
81    async fn write_vectored<T: IoVectoredBuf>(&mut self, mut buf: T) -> BufResult<usize, T> {
82        (_, buf) = buf_try!(self.flush_if_needed().await, buf);
83
84        let written = self
85            .buf
86            .with(|mut w| {
87                let mut written = 0;
88                for buf in buf.iter_buf() {
89                    let len = w.buf_len();
90                    let mut slice = w.slice(len..);
91                    written += slice_to_buf(buf.as_slice(), &mut slice);
92                    w = slice.into_inner();
93
94                    if w.buf_len() == w.buf_capacity() {
95                        break;
96                    }
97                }
98                ready(BufResult(Ok(written), w))
99            })
100            .await
101            .expect("Closure always return Ok");
102
103        (_, buf) = buf_try!(self.flush_if_needed().await, buf);
104
105        BufResult(Ok(written), buf)
106    }
107
108    async fn flush(&mut self) -> IoResult<()> {
109        let Self { writer, buf } = self;
110
111        buf.flush_to(writer).await?;
112
113        Ok(())
114    }
115
116    async fn shutdown(&mut self) -> IoResult<()> {
117        self.flush().await?;
118        self.writer.shutdown().await
119    }
120}
121
122impl<W> IntoInner for BufWriter<W> {
123    type Inner = W;
124
125    fn into_inner(self) -> Self::Inner {
126        self.writer
127    }
128}
compio_io/write/buf.rs

compio_io/write/
buf.rs
