Why are stdin actually blocks and how to make it truly non-blocking?

[katyo]

Version

termion-tokio v0.1.0
└── tokio v0.1.11
├── tokio-codec v0.1.1
│ └── tokio-io v0.1.9
├── tokio-current-thread v0.1.3
│ └── tokio-executor v0.1.5
├── tokio-executor v0.1.5 ()
├── tokio-fs v0.1.3
│ ├── tokio-io v0.1.9 ()
│ └── tokio-threadpool v0.1.7
│ └── tokio-executor v0.1.5 ()
│ └── tokio-io v0.1.9 ()
├── tokio-io v0.1.9 ()
├── tokio-reactor v0.1.6
│ ├── tokio-executor v0.1.5 ()
│ └── tokio-io v0.1.9 ()
├── tokio-tcp v0.1.2
│ ├── tokio-io v0.1.9 ()
│ └── tokio-reactor v0.1.6 ()
├── tokio-threadpool v0.1.7 ()
├── tokio-timer v0.2.7
│ └── tokio-executor v0.1.5 ()
├── tokio-udp v0.1.2
│ ├── tokio-codec v0.1.1 ()
│ ├── tokio-io v0.1.9 ()
│ └── tokio-reactor v0.1.6 ()
└── tokio-uds v0.2.2
├── tokio-io v0.1.9 ()
└── tokio-reactor v0.1.6 ()

Platform

Linux debi 4.9.0-7-amd64 #1 SMP Debian 4.9.110-3+deb9u2 (2018-08-13) x86_64 GNU/Linux

Description

When I tried to use tokio stdin (i.e. using FramedRead with self-written Decoder) it unexpectedly blocks process until any input happens.

I working with this repository: https://github.com/katyo/termion-tokio/
To reproduce you can run example: cargo run --example input.

Expected behavior: Periodical ticks happens independently from user input.
Actual behavior: No periodical ticks until any user input happens.

[carllerche]

Switching stdin / stdout to non-blocking is a process global operation and could have unintended impact on other code.

You can always switch the FD to non-blocking mode yourself, but that also means you cannot reliably use things like println! anymore.

[carllerche]

I'm going to close this issue as the documentation problem is tracked in the doc-push repo (tokio-rs/doc-push#85).