14ea4621ab
See ["mtime comparison considered harmful"](https://apenwarr.ca/log/20181113) for details of why comparators other than equality/inequality should not be used with mtime. Release Notes: - N/A
49 lines
2 KiB
Rust
49 lines
2 KiB
Rust
use collections::HashMap;
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use fs::MTime;
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use std::{path::Path, sync::Arc};
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const MAX_FILES_BEFORE_RESUMMARIZE: usize = 4;
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const MAX_BYTES_BEFORE_RESUMMARIZE: u64 = 1_000_000; // 1 MB
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#[derive(Default, Debug)]
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pub struct SummaryBacklog {
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/// Key: path to a file that needs summarization, but that we haven't summarized yet. Value: that file's size on disk, in bytes, and its mtime.
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files: HashMap<Arc<Path>, (u64, Option<MTime>)>,
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/// Cache of the sum of all values in `files`, so we don't have to traverse the whole map to check if we're over the byte limit.
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total_bytes: u64,
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}
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impl SummaryBacklog {
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/// Store the given path in the backlog, along with how many bytes are in it.
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pub fn insert(&mut self, path: Arc<Path>, bytes_on_disk: u64, mtime: Option<MTime>) {
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let (prev_bytes, _) = self
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.files
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.insert(path, (bytes_on_disk, mtime))
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.unwrap_or_default(); // Default to 0 prev_bytes
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// Update the cached total by subtracting out the old amount and adding the new one.
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self.total_bytes = self.total_bytes - prev_bytes + bytes_on_disk;
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}
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/// Returns true if the total number of bytes in the backlog exceeds a predefined threshold.
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pub fn needs_drain(&self) -> bool {
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self.files.len() > MAX_FILES_BEFORE_RESUMMARIZE ||
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// The whole purpose of the cached total_bytes is to make this comparison cheap.
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// Otherwise we'd have to traverse the entire dictionary every time we wanted this answer.
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self.total_bytes > MAX_BYTES_BEFORE_RESUMMARIZE
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}
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/// Remove all the entries in the backlog and return the file paths as an iterator.
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#[allow(clippy::needless_lifetimes)] // Clippy thinks this 'a can be elided, but eliding it gives a compile error
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pub fn drain<'a>(&'a mut self) -> impl Iterator<Item = (Arc<Path>, Option<MTime>)> + 'a {
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self.total_bytes = 0;
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self.files
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.drain()
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.map(|(path, (_size, mtime))| (path, mtime))
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}
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pub fn len(&self) -> usize {
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self.files.len()
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}
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}
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