Change to non-line buffered output if output is not a TTY #64861
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r? @KodrAus (rust_highfive has picked a reviewer for you, use r? to override) |
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This matches glibc behavior. This is determined using the `isatty` function on Unixes, and not attempted at all for other operating systems. Fixes rust-lang#60673.
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I get a 4x speed up for the worst case of the old implementation: fn main() {
for _ in 0..(1<<20) {
println!("y");
}
}The old program is doing 1048576 Changing the program to use an infinite loop, I get a throughput of 3MB/s vs 20MB/s. |
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An interesting question here is what we should do This doesn't output the |
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KodrAus
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Oct 10, 2019
| StdioReader::Fake => Ok(0), | ||
| } | ||
| } | ||
| #[inline] |
| pub fn should_be_line_buffered(&self) -> bool { | ||
| // FIXME: Fill in. I don't know how to check whether output is | ||
| // redirected on Windows. | ||
| true |
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For UWP I think we can also use GetConsoleMode.
| pub fn should_be_line_buffered(&self) -> bool { | ||
| // FIXME: Fill in. I don't know how to check whether output is | ||
| // redirected on Windows. | ||
| true |
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On Windows there's a GetConsoleMode function you can call. It's used in the atty library's Windows implementation. It looks like that crate also has some more complex heuristics for Windows but those might not be so important here.
| /// A writer that can either be line-buffered, buffered, unbuffered or fake. | ||
| /// | ||
| /// If it is fake, all outputs just succeed and are dropped silently. | ||
| enum StdioWriter<W: Write> { |
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There was a comment in the original FIXME suggesting we should call flush when dropping the handle if we're panicking. Did you have any thoughts on this @tbu-?
bluss
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Oct 15, 2019
| StdioWriter::LineBuffered(i) => i.write_vectored(bufs), | ||
| StdioWriter::Buffered(i) => i.write_vectored(bufs), | ||
| StdioWriter::Unbuffered(i) => i.write_vectored(bufs), | ||
| StdioWriter::Fake => Ok(bufs.iter().map(|b| b.len()).sum()), |
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This sum could probably wrap around, seems like it should saturate instead (not sure what's reasonable), or return the first non-empty len.
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@tbu- waiting for you to answer the review |
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Ping from Triage: @tbu- any updates? |
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Too little time right now. |
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This matches glibc behavior.
This is determined using the
isattyfunction on Unixes, and notattempted at all for other operating systems.
Fixes #60673.