view rust/hg-core/src/logging.rs @ 51109:687e192dae16

rust-matchers: fix quadratic complexity in `FileMatcher`

Concretely, this command:

```
$ echo hg up -r <nodeid>; time hg revert dir1 dir2 -r <othernode> --debug
hg up -r <nodeid>

real	0m14.690s
user	0m14.766s
sys	0m5.430s
```

was much slower despite using 16 cores before this change.
The approach taken here is the same one used in match.py, in exactmatcher.

This changeset was originally written by Valentin Gatien-Baron in a private
repository.
I have redacted the commit message and did a minor clean up of the code.

use crate::errors::{HgError, HgResultExt, IoErrorContext, IoResultExt};
use crate::vfs::Vfs;
use std::io::Write;

/// An utility to append to a log file with the given name, and optionally
/// rotate it after it reaches a certain maximum size.
///
/// Rotation works by renaming "example.log" to "example.log.1", after renaming
/// "example.log.1" to "example.log.2" etc up to the given maximum number of
/// files.
pub struct LogFile<'a> {
    vfs: Vfs<'a>,
    name: &'a str,
    max_size: Option<u64>,
    max_files: u32,
}

impl<'a> LogFile<'a> {
    pub fn new(vfs: Vfs<'a>, name: &'a str) -> Self {
        Self {
            vfs,
            name,
            max_size: None,
            max_files: 0,
        }
    }

    /// Rotate before writing to a log file that was already larger than the
    /// given size, in bytes. `None` disables rotation.
    pub fn max_size(mut self, value: Option<u64>) -> Self {
        self.max_size = value;
        self
    }

    /// Keep this many rotated files `{name}.1` up to `{name}.{max}`, in
    /// addition to the original `{name}` file.
    pub fn max_files(mut self, value: u32) -> Self {
        self.max_files = value;
        self
    }

    /// Append the given `bytes` as-is to the log file, after rotating if
    /// needed.
    ///
    /// No trailing newline is added. Make sure to include one in `bytes` if
    /// desired.
    pub fn write(&self, bytes: &[u8]) -> Result<(), HgError> {
        let path = self.vfs.join(self.name);
        let context = || IoErrorContext::WritingFile(path.clone());
        let open = || {
            std::fs::OpenOptions::new()
                .create(true)
                .append(true)
                .open(&path)
                .with_context(context)
        };
        let mut file = open()?;
        if let Some(max_size) = self.max_size {
            if file.metadata().with_context(context)?.len() >= max_size {
                // For example with `max_files == 5`, the first iteration of
                // this loop has `i == 4` and renames `{name}.4` to `{name}.5`.
                // The last iteration renames `{name}.1` to
                // `{name}.2`
                for i in (1..self.max_files).rev() {
                    self.vfs
                        .rename(
                            format!("{}.{}", self.name, i),
                            format!("{}.{}", self.name, i + 1),
                        )
                        .io_not_found_as_none()?;
                }
                // Then rename `{name}` to `{name}.1`. This is the
                // previously-opened `file`.
                self.vfs
                    .rename(self.name, format!("{}.1", self.name))
                    .io_not_found_as_none()?;
                // Finally, create a new `{name}` file and replace our `file`
                // handle.
                file = open()?;
            }
        }
        file.write_all(bytes).with_context(context)?;
        file.sync_all().with_context(context)
    }
}

#[test]
fn test_rotation() {
    let temp = tempfile::tempdir().unwrap();
    let vfs = Vfs { base: temp.path() };
    let logger = LogFile::new(vfs, "log").max_size(Some(3)).max_files(2);
    logger.write(b"one\n").unwrap();
    logger.write(b"two\n").unwrap();
    logger.write(b"3\n").unwrap();
    logger.write(b"four\n").unwrap();
    logger.write(b"five\n").unwrap();
    assert_eq!(vfs.read("log").unwrap(), b"five\n");
    assert_eq!(vfs.read("log.1").unwrap(), b"3\nfour\n");
    assert_eq!(vfs.read("log.2").unwrap(), b"two\n");
    assert!(vfs.read("log.3").io_not_found_as_none().unwrap().is_none());
}