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//! A tool for use with the `hdrhistogram` crate, a rust port of HdrHistogram, that provides //! a clean interface with sane defaults for off-thread serialization of HdrHistogram interval //! logs to file. //! use std::sync::Arc; use std::time::{Instant, Duration, SystemTime, UNIX_EPOCH}; use std::path::{Path, PathBuf}; use std::thread::{self, JoinHandle}; use std::io; use std::{mem, fs}; use hdrhistogram::{Histogram}; use hdrhistogram::serialization::V2DeflateSerializer; use hdrhistogram::serialization::interval_log::{IntervalLogWriterBuilder, Tag}; use crossbeam_channel as channel; use chrono::Utc; type C = u64; /// Significant figure passed to `hdrhistogram::Histogram::new` upon /// construction pub const SIG_FIG: u8 = 3; /// Capacity of `crossbeam_channel::bounded` queue used to communicate /// between the measuring thread and the writer thread pub const CHANNEL_SIZE: usize = 8; /// Amount of time `HistLog::drop` will spin on a full channel to /// the writer thread to send a terminate signal pub const DROP_DEADLINE: Duration = Duration::from_millis(5); /// Returns `Duration` as number of nanoseconds (`u64`) /// /// # Examples /// ``` /// # use std::time::*; /// assert_eq!(histlog::nanos(Duration::from_secs(1)), 1_000_000_000u64); /// ``` pub fn nanos(d: Duration) -> u64 { d.as_secs() * 1_000_000_000_u64 + (d.subsec_nanos() as u64) } /// Provides off-thread serialization of HdrHistogram interval logs to file. /// /// # Purpose /// /// HdrHistogram is often used to measure latency. Generally, if something is important /// enough to measure latency, it's unlikely you want to write to a file on the same /// thread. /// /// One option would be to serialize to an in-memory buffer (e.g. `Vec<u8>`). However, /// this would still require allocating to the buffer, and would eventually require a /// lot of memory for a long-running process. /// /// `HistLog` allows the hot thread to pass off it's `hdrhistogram::Histogram` at regular intervals /// to a designated writer thread that can afford to dilly dally with IO. The interval /// log is written incrementally and can be inspected and analyzed while the program /// is still running. /// /// `HistLog` relies completely on the rust port of `HdrHistogram`, both for the in-memory /// recording of values and serialization. What it does provide is off-thread writing with /// a clean interface and sane defaults that make it relatively easy to use. /// /// # Examples /// /// A `HistLog` has a "series" name and a "tag." The HdrHistogram interval log format provides /// for one tag per entry. The series name is used to name the file the interval log is written to: /// /// ``` /// use std::time::*; /// /// let log_dir = "/tmp/path/to/logs"; /// let series = "server-latency"; // used to name the log file /// let tag = "xeon-e7-8891-v2"; // recorded with each entry /// let freq = Duration::from_secs(1); // how often results sent to writer thread /// /// // `HistLog::new` could fail creating file, `hdrhistogram::Histogram` /// let mut server1 = histlog::HistLog::new(log_dir, series, tag, freq).unwrap(); /// /// // use `HistLog::clone_with_tag` to serialize a separate tag to same file. /// let mut server2 = server1.clone_with_tag("xeon-e5-2670"); /// /// for i in 0..1000u64 { // dummy data /// server1.record(i).unwrap(); // call to `hdrhistogram::Histogram::record` could fail /// server2.record(i * 2).unwrap(); /// } /// /// assert_eq!(server1.path(), server2.path()); // both being saved to same file, via same writer thread /// ``` /// /// `HistLog`'s api design is built for event loops. Each iteration of the loop, new values are /// recorded, and the current time is checked to see whether the current `Histogram` should be /// passed off to the writer thread: /// /// ``` /// use std::time::*; /// /// let mut spintime = histlog::HistLog::new("/tmp/var/hist", "spintime", "main", Duration::from_secs(60)).unwrap(); /// /// let mut loop_time = Instant::now(); /// let mut prev: Instant; /// /// loop { /// prev = loop_time; /// loop_time = Instant::now(); /// spintime.record(histlog::nanos(loop_time - prev)).unwrap(); // nanos: Duration -> u64 /// spintime.check_send(loop_time); // sends to writer thread if elapsed > freq, /// // or... /// spintime.check_try_send(loop_time).unwrap(); // non-blocking equivalent (can fail) /// /// // do important stuff ... /// /// # break /// } /// ``` /// /// # Logs /// /// Logs are saved to `<log dir>/<series name>.<datetime>.hdrhistogram-interval-log.v2.gz`. /// /// Format of log is like this: /// /// ```console,ignore /// #[StartTime: 1544631293.283 (seconds since epoch)] /// #[BaseTime: 0.000 (seconds since epoch)] /// Tag=xeon-e7-8891-v2,1544631293.283,0.003,999.000,HISTFAAAAC94Ae3GMRUAMAgD0bRI6FovNVcHmGREAgNR [...] /// Tag=xeon-e5-2670,1544631293.283,0.003,999.000,HISTFAAAABx4AZNpmSzMwMDAxAABzFCaEUoz2X+AsQA/awK [...] /// [...] /// ``` /// /// Only the histogram data is compressed (deflate), so a `.gz` extension is perhaps misleading. /// /// Log file can be viewed/analyzed [here](https://hdrhistogram.github.io/HdrHistogramJSDemo/logparser.html) /// (javascript, runs locally) or with the Java-based [HistogramLogAnalyzer](https://github.com/HdrHistogram/HistogramLogAnalyzer). /// /// [Full documentation](https://docs.rs/hdrhistogram/6.1.1/hdrhistogram/serialization/interval_log/index.html) of log /// serialization available from the `hdrhistogram` crate. /// /// # Limitations /// /// - The series name and tags are currently limited to `&'static str` because the overhead of using /// `String` is prohibitive. This may change in future versions if a performant means of /// allowing dynamic tags presents itself that's not inordinately complicated to use. /// - `HistLog::check_send` and `HistLog::check_try_send` create a new `hdrhistogram::Histogram` /// and send the current/prev one to the writer thread each interval. Internally, an /// `hdrhistogram::Histogram` uses a `Vec` to store its counts, so there's an allocation involved. /// - Only `u64` values can be recorded, currently. /// pub struct HistLog { filename: PathBuf, series: &'static str, tag: &'static str, freq: Duration, last_sent: Instant, tx: channel::Sender<Option<Entry>>, hist: Histogram<C>, thread: Option<Arc<thread::JoinHandle<Result<usize, Error>>>>, } struct Entry { pub tag: &'static str, pub start: SystemTime, pub end: SystemTime, pub hist: Histogram<C>, } /// Unifies all the errors that might occur from using a `HistLog` in one enum. #[derive(Debug)] pub enum Error { Io(io::Error), //HdrCreation(hdrhistogram::errors::CreationError), HdrRecord(hdrhistogram::errors::RecordError), TrySend(channel::TrySendError<()>), } impl Clone for HistLog { fn clone(&self) -> Self { let thread = self.thread.as_ref().map(|x| Arc::clone(x)); Self { filename: self.filename.clone(), series: self.series.clone(), tag: self.tag.clone(), freq: self.freq.clone(), last_sent: Instant::now(), tx: self.tx.clone(), hist: self.hist.clone(), thread, } } } impl HistLog { /// Create a new `HistLog`. /// /// If `save_dir` does not exist, will attempt to create it (which could /// fail). Creating a new log file could fail. Spawning the writer thread could fail. pub fn new<P>(save_dir: P, series: &'static str, tag: &'static str, freq: Duration) -> Result<Self, Error> where P: AsRef<Path> { if !save_dir.as_ref().exists() { fs::create_dir_all(save_dir.as_ref()).map_err(Error::Io)?; } let save_dir = save_dir.as_ref().to_path_buf(); let filename = Self::get_filename(&save_dir, series); let (tx, rx) = channel::bounded(CHANNEL_SIZE); let thread = Some(Arc::new(Self::scribe(series, rx, filename.as_path())?)); let last_sent = Instant::now(); let hist = Histogram::new(SIG_FIG).expect("Histogram::new"); //.map_err(Error::HdrCreation)?; Ok(Self { filename, series, tag, freq, last_sent, tx, hist, thread }) } // not sure if this is a good thing to have // #[doc(hidden)] pub fn new_with_tag(&self, tag: &'static str) -> Result<Self, Error> { let mut save_dir = self.filename.clone(); if !save_dir.pop() { // `.pop` should remove the file name, leaving dir return Err(Error::Io(io::Error::new(io::ErrorKind::Other, "`filename.pop()` returned `false`! expected it to have a file name, return `true`."))) } Self::new(save_dir, self.series, tag, self.freq) } /// Returns the path of the log file the `HistLog` is writing to. /// pub fn path(&self) -> &Path { self.filename.as_path() } /// Record a new histogram with a `tag` that will serialize to the /// same interval log file as its parent. Each cloned `HistLog`'s entries /// will be written to their own lines in the log file, identifiable by tag. /// /// # Limitations /// /// No effort is made to check whether `tag` is a duplicate of a previous tag, /// and using a duplicate may produce unexpected results. pub fn clone_with_tag(&self, tag: &'static str) -> Self { assert!(self.thread.is_some(), "self.thread cannot be `None` unless `HistLog` was already dropped"); let thread = self.thread.as_ref().map(|x| Arc::clone(x)).unwrap(); let tx = self.tx.clone(); Self { filename: self.filename.clone(), series: self.series, tag, freq: self.freq, last_sent: Instant::now(), tx, hist: self.hist.clone(), thread: Some(thread), } } #[doc(hidden)] pub fn clone_with_tag_and_freq(&self, tag: &'static str, freq: Duration) -> Self { let mut clone = self.clone_with_tag(tag); clone.freq = freq; clone } /// Record a single value to the histogram. This could fail if the value /// is outside of the highest range permitted. See the /// [`hdrhistogram` docs](https://docs.rs/hdrhistogram/6.1.1/hdrhistogram/struct.Histogram.html#method.record) /// for further deails. The `hdrhistogram::Histogram` used by `HistLog` /// is created with a significant figure of 3 (`histlog::SIG_FIG` const). /// pub fn record(&mut self, value: u64) -> Result<(), Error> { self.hist.record(value).map_err(Error::HdrRecord) } /// Reset the state of the internal histogram and the last sent value. /// /// One situation this might be used is if there was a pause in recording. /// pub fn reset(&mut self) { self.hist.clear(); self.last_sent = Instant::now(); } fn send(&mut self, loop_time: Instant) { let end = SystemTime::now(); let start = end - (loop_time - self.last_sent); assert!(end > start, "end <= start!"); let mut next = Histogram::new_from(&self.hist); mem::swap(&mut self.hist, &mut next); self.tx.send(Some(Entry { tag: self.tag, start, end, hist: next })).ok(); //.expect("sending entry failed"); self.last_sent = loop_time; } fn try_send(&mut self, loop_time: Instant) -> Result<(), Error>{ let end = SystemTime::now(); let start = end - (loop_time - self.last_sent); assert!(end > start, "end <= start!"); let mut next = Histogram::new_from(&self.hist); mem::swap(&mut self.hist, &mut next); let entry = Entry { tag: self.tag, start, end, hist: next }; match self.tx.try_send(Some(entry)) { Ok(_) => { self.last_sent = loop_time; Ok(()) } Err(channel::TrySendError::Full(Some(Entry { mut hist, .. }))) => { // recoverable, swap rejected hist back in place // and continue trying... mem::swap(&mut self.hist, &mut hist); Err(Error::TrySend(channel::TrySendError::Full(()))) } Err(channel::TrySendError::Disconnected(_)) => { Err(Error::TrySend(channel::TrySendError::Disconnected(()))) } Err(channel::TrySendError::Full(None)) => { Err(Error::TrySend(channel::TrySendError::Full(()))) } } } /// Send the current histogram to the writer thread if the elapsed time /// since the last send is greater than the interval frequency. /// /// If the channel is disconnected, this will fail silently, instead of panicking. /// pub fn check_send(&mut self, loop_time: Instant) -> bool { let expired = loop_time > self.last_sent && loop_time - self.last_sent >= self.freq; if expired { self.send(loop_time); } expired } /// Non-blocking variant of `HistLog::check_send`, which will also return any errors, /// including a disconnected channel, encountered while trying to send to the /// writer thread. /// pub fn check_try_send(&mut self, loop_time: Instant) -> Result<bool, Error> { let expired = loop_time > self.last_sent && loop_time - self.last_sent >= self.freq; if expired { self.try_send(loop_time)?; } Ok(expired) } fn get_filename(save_dir: &PathBuf, series: &'static str) -> PathBuf { let now = Utc::now(); let filename = format!("{series}.{time}.hdrhistogram-interval-log.v2.gz", series = series, time = now.format("%Y-%m-%d-%H:%M:%SZ")); save_dir.join(&filename) } fn scribe( series: &'static str, rx: channel::Receiver<Option<Entry>>, filename: &Path, ) -> Result<JoinHandle<Result<usize, Error>>, Error> { let mut ser = V2DeflateSerializer::new(); let start_time = SystemTime::now(); let file = fs::File::create(filename).map_err(Error::Io)?; thread::Builder::new().name(format!("histlog:{}", series)).spawn(move || { let mut buf = io::LineWriter::new(file); let mut wtr = IntervalLogWriterBuilder::new() .with_base_time(UNIX_EPOCH) .with_start_time(start_time) .begin_log_with(&mut buf, &mut ser) .map_err(Error::Io)?; // unrecoverable, so exit early let mut n_rcvd = 0; loop { match rx.recv() { Ok(Some(Entry { tag, start, end, hist })) => { // TODO: this currently fails silently // // improved implementation might include a logger so there // is some record that it failed. // // alternatively, this could panic, so at least you know at // the end it didn't work. // // the fact that `file` is created before the thread is spawned // is mitigating, because typically if you can create the file, // you can write to it, too. // wtr.write_histogram(&hist, start.duration_since(UNIX_EPOCH).unwrap(), end.duration_since(start).unwrap(), Tag::new(tag)) .ok(); n_rcvd += 1; } Ok(None) => break, // terminate signal sent by `Drop` _ => thread::sleep(Duration::new(0, 1)), // nothing new, yield thread } } Ok(n_rcvd) }).map_err(Error::Io) } } impl Drop for HistLog { /// Checks if the current instance is the last remaining instance with a reference /// to the underlying writer thread, and, if so, sends a terminate signal to the /// writer thread and attempts to join it. /// /// # May Pause Up To 5ms /// /// In the event the channel to the writer thread is full, will continue trying /// to send a terminate command (busy polling the channel) until `DROP_DEADLINE` /// has expired (currently 5ms), upon which it will abort. /// /// If channel is disconnected, will simply abort without trying to join the /// writer thread. /// fn drop(&mut self) { // don't remember why this was added now ... presumably to // prepare the internal/queue state in some way. if !self.hist.is_empty() { self.send(Instant::now()) } if let Some(arc) = self.thread.take() { if let Ok(thread) = Arc::try_unwrap(arc) { let start = Instant::now(); while Instant::now() - start < DROP_DEADLINE { match self.tx.try_send(None) { Ok(_) => { let _ = thread.join(); break } Err(channel::TrySendError::Full(_)) => {} Err(_) => { break } } } } } } } #[allow(unused)] #[cfg(test)] mod tests { use super::*; #[test] fn create_histlog_record_one_and_drop() { let mut hist = HistLog::new("/tmp/histlog", "test", "red", Duration::from_millis(1)).unwrap(); for i in 0..1000u64 { hist.record(i).unwrap(); } assert_eq!(hist.check_send(Instant::now()), false); assert!(hist.check_try_send(Instant::now()).is_ok()); assert_eq!(hist.check_try_send(Instant::now()).unwrap(), false); thread::sleep(Duration::from_millis(3)); assert_eq!(hist.check_send(Instant::now()), true); let path = hist.filename.clone(); drop(hist); assert!(path.exists()); } #[test] fn clone_it() { let mut hist = HistLog::new("/tmp/histlog", "test", "red", Duration::from_millis(1)).unwrap(); let tx = hist.tx.clone(); let mut a = hist.clone_with_tag("blue"); for i in 0..1000u64 { hist.record(i).unwrap(); a.record(i * 2).unwrap(); } drop(hist); drop(a); match tx.try_send(None) { Err(channel::TrySendError::Disconnected(None)) => {}, other => panic!("unexpected variant: {:?}", other) } } }