1# blocking
2
3[![Build](https://github.com/stjepang/blocking/workflows/Build%20and%20test/badge.svg)](
4https://github.com/stjepang/blocking/actions)
5![Rustc version](https://img.shields.io/badge/rustc-1.40+-lightgray.svg)
6[![License](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](
7https://github.com/stjepang/blocking)
8[![Cargo](https://img.shields.io/crates/v/blocking.svg)](
9https://crates.io/crates/blocking)
10[![Documentation](https://docs.rs/blocking/badge.svg)](
11https://docs.rs/blocking)
12
13A thread pool for isolating blocking I/O in async programs.
14
15Sometimes there's no way to avoid blocking I/O. Consider files or stdin, which have weak async
16support on modern operating systems. While [IOCP], [AIO], and [io_uring] are possible
17solutions, they're not always available or ideal.
18
19Since blocking is not allowed inside futures, we must move blocking I/O onto a special thread
20pool provided by this crate. The pool dynamically spawns and stops threads depending on the
21current number of running I/O jobs.
22
23Note that there is a limit on the number of active threads. Once that limit is hit, a running
24job has to finish before others get a chance to run. When a thread is idle, it waits for the
25next job or shuts down after a certain timeout.
26
27[IOCP]: https://en.wikipedia.org/wiki/Input/output_completion_port
28[AIO]: http://man7.org/linux/man-pages/man2/io_submit.2.html
29[io_uring]: https://lwn.net/Articles/776703
30
31## Examples
32
33Read the contents of a file:
34
35```rust
36use blocking::unblock;
37use std::fs;
38
39let contents = unblock(|| fs::read_to_string("file.txt")).await?;
40println!("{}", contents);
41```
42
43Read a file and pipe its contents to stdout:
44
45```rust
46use blocking::{unblock, Unblock};
47use futures_lite::io;
48use std::fs::File;
49
50let input = unblock(|| File::open("file.txt")).await?;
51let input = Unblock::new(input);
52let mut output = Unblock::new(std::io::stdout());
53
54io::copy(input, &mut output).await?;
55```
56
57Iterate over the contents of a directory:
58
59```rust
60use blocking::Unblock;
61use futures_lite::prelude::*;
62use std::fs;
63
64let mut dir = Unblock::new(fs::read_dir(".")?);
65while let Some(item) = dir.next().await {
66    println!("{}", item?.file_name().to_string_lossy());
67}
68```
69
70Spawn a process:
71
72```rust
73use blocking::unblock;
74use std::process::Command;
75
76let out = unblock(|| Command::new("dir").output()).await?;
77```
78
79## License
80
81Licensed under either of
82
83 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
84 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
85
86at your option.
87
88#### Contribution
89
90Unless you explicitly state otherwise, any contribution intentionally submitted
91for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
92dual licensed as above, without any additional terms or conditions.
93