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//! Inter-event timing metrics. //! //! This crate provides a `tracing::Subscriber` that keeps statistics on inter-event timing //! information. More concretely, given code like this: //! //! ```rust //! use tracing::*; //! use tracing_timing::{Builder, Histogram}; //! let subscriber = Builder::default().build(|| Histogram::new_with_max(1_000_000, 2).unwrap()); //! let dispatcher = Dispatch::new(subscriber); //! dispatcher::with_default(&dispatcher, || { //! trace_span!("request").in_scope(|| { //! // do a little bit of work //! trace!("fast"); //! // do a lot of work //! trace!("slow"); //! }) //! }); //! ``` //! //! You can produce something like this (see `examples/pretty.rs`): //! //! ```text //! fast: //! mean: 173.2µs, p50: 172µs, p90: 262µs, p99: 327µs, p999: 450µs, max: 778µs //! 25µs | * | 2.2th %-ile //! 50µs | * | 2.2th %-ile //! 75µs | * | 4.7th %-ile //! 100µs | *** | 11.5th %-ile //! 125µs | ***** | 24.0th %-ile //! 150µs | ******* | 41.1th %-ile //! 175µs | ******** | 59.2th %-ile //! 200µs | ******* | 75.4th %-ile //! 225µs | ** | 80.1th %-ile //! 250µs | *** | 87.3th %-ile //! 275µs | *** | 94.4th %-ile //! 300µs | ** | 97.8th %-ile //! //! slow: //! mean: 623.3µs, p50: 630µs, p90: 696µs, p99: 770µs, p999: 851µs, max: 950µs //! 500µs | * | 1.6th %-ile //! 525µs | ** | 4.8th %-ile //! 550µs | *** | 10.9th %-ile //! 575µs | ***** | 22.2th %-ile //! 600µs | ******* | 37.9th %-ile //! 625µs | ******** | 55.9th %-ile //! 650µs | ******* | 72.9th %-ile //! 675µs | ****** | 85.6th %-ile //! 700µs | **** | 93.5th %-ile //! 725µs | ** | 97.1th %-ile //! ``` //! //! When [`TimingSubscriber`] is used as the `tracing::Dispatch`, the time between each event in a //! span is measured using [`quanta`], and is recorded in "[high dynamic range histograms]" using //! [`hdrhistogram`]'s multi-threaded recording facilities. The recorded timing information is //! grouped using the [`SpanGroup`] and [`EventGroup`] traits, allowing you to combine recorded //! statistics across spans and events. //! //! ## Extracting timing histograms //! //! The crate does not implement a mechanism for recording the resulting histograms. Instead, you //! can implement this as you see fit using [`TimingSubscriber::with_histograms`]. It gives you //! access to the histograms for all groups. Note that you must call `refresh()` on each histogram //! to see its latest values (see [`hdrhistogram::SyncHistogram`]). //! //! To access the histograms later, use `tracing::Dispatch::downcast_ref`. If your type is hard to //! name, you can use a [`TimingSubscriber::downcaster`] instead. //! //! ```rust //! use tracing::*; //! use tracing_timing::{Builder, Histogram, TimingSubscriber}; //! let subscriber = Builder::default().build(|| Histogram::new_with_max(1_000_000, 2).unwrap()); //! let dispatch = Dispatch::new(subscriber); //! // ... //! // code that hands off clones of the dispatch //! // maybe to other threads //! // ... //! dispatch.downcast_ref::<TimingSubscriber>().unwrap().with_histograms(|hs| { //! for (span_group, hs) in hs { //! for (event_group, h) in hs { //! // make sure we see the latest samples: //! h.refresh(); //! // print the median: //! println!("{} -> {}: {}ns", span_group, event_group, h.value_at_quantile(0.5)) //! } //! } //! }); //! ``` //! //! See the documentation for [`hdrhistogram`] for more on what you can do once you have the //! histograms. //! //! ## Grouping samples //! //! By default, [`TimingSubscriber`] groups samples by the "name" of the containing span and the //! "message" of the relevant event. These are the first string parameter you pass to each of the //! relevant tracing macros. You can override this behavior either by providing your own //! implementation of [`SpanGroup`] and [`EventGroup`] to [`Builder::spans`] and //! [`Builder::events`] respectively. There are also a number of pre-defined "groupers" in the //! [`group`] module that cover the most common cases. //! //! # Timing information over time //! //! Every time you refresh a histogram, it incorporates any new timing samples recorded since the //! last call to `refresh`, allowing you to see timing metrics across all time. If you are //! monitoring the health of a continuously running system, you may instead wish to only see //! metrics across a limited window of time. You can do this by clearing the histogram in //! [`TimingSubscriber::with_histograms`] before refreshing them, or periodically as you see fit. //! //! # Usage notes: //! //! **Event timing is _per span_, not per span _per thread_.** This means that if you emit events //! for the same span concurrently from multiple threads, you may see weird timing information. //! //! **Span creation takes a lock.** This means that you will generally want to avoid creating //! extraneous spans. One technique that works well here is subsampling your application, for //! example by only creating tracking spans for _some_ of your requests. //! //! [high dynamic range histograms]: https://hdrhistogram.github.io/HdrHistogram/ //! [`hdrhistogram`]: https://docs.rs/hdrhistogram/ //! [`quanta`]: https://docs.rs/quanta/ //! [`hdrhistogram::SyncHistogram`]: https://docs.rs/hdrhistogram/6/hdrhistogram/sync/struct.SyncHistogram.html //! #![deny(missing_docs)] use crossbeam::channel; use crossbeam::sync::ShardedLock; use hdrhistogram::{sync::Recorder, SyncHistogram}; use indexmap::IndexMap; use slab::Slab; use std::cell::{RefCell, UnsafeCell}; use std::hash::Hash; use std::marker::PhantomData; use std::ops::{Deref, DerefMut}; use std::sync::{atomic, Mutex}; use tracing_core::*; /// A faster hasher for `tracing-timing` maps. pub type Hasher = fxhash::FxBuildHasher; /// A standard library `HashMap` with a faster hasher. pub type HashMap<K, V> = std::collections::HashMap<K, V, Hasher>; static TID: atomic::AtomicUsize = atomic::AtomicUsize::new(0); thread_local! { static SPAN: RefCell<Vec<span::Id>> = RefCell::new(Vec::new()); static MYTID: RefCell<Option<usize>> = RefCell::new(None); } mod builder; pub use builder::Builder; pub use hdrhistogram::Histogram; pub mod group; #[derive(Debug, Clone)] struct SpanGroupContext<S> { group: S, parent: Option<span::Id>, follows: Option<span::Id>, meta: &'static Metadata<'static>, } type Map<S, E, T> = HashMap<S, HashMap<E, T>>; /// Translate attributes from a tracing span into a timing span group. /// /// All spans whose attributes produce the same `Id`-typed value when passed through `group` /// share a namespace for the groups produced by [`EventGroup::group`] on their contained events. /// /// This trait is implemented for all functions with the appropriate signature. Note that you _may_ /// run into weird lifetime errors from the compiler when using a closure as a `SpanGroup`. This is /// a [known compiler issue]. You can work around it by adding a slight type hint to the arguments /// passed to the closure as follows (note the `: &_`): /// /// ```rust /// use tracing_timing::{Builder, Histogram}; /// use tracing::span; /// let s = Builder::default() /// .spans(|_: &span::Attributes| "all spans as one") /// .build(|| Histogram::new(3).unwrap()); /// ``` /// /// [known compiler issue]: https://github.com/rust-lang/rust/issues/41078 pub trait SpanGroup { /// The type of the timing span group. type Id; /// Extract the group for this span's attributes. fn group(&self, span: &span::Attributes) -> Self::Id; } /// Translate attributes from a tracing event into a timing event group. /// /// All events that share a [`SpanGroup`], and whose attributes produce the same `Id`-typed value /// when passed through `group`, are considered a single timing target, and have their samples /// recorded together. /// /// This trait is implemented for all functions with the appropriate signature. Note that you _may_ /// run into weird lifetime errors from the compiler when using a closure as an `EventGroup`. This /// is a [known compiler issue]. You can work around it by adding a slight type hint to the /// arguments passed to the closure as follows (note the `: &_`): /// /// ```rust /// use tracing_timing::{Builder, Histogram}; /// use tracing::Event; /// let s = Builder::default() /// .events(|_: &Event| "all events as one") /// .build(|| Histogram::new(3).unwrap()); /// ``` /// /// [known compiler issue]: https://github.com/rust-lang/rust/issues/41078 pub trait EventGroup { /// The type of the timing event group. type Id; /// Extract the group for this event. fn group(&self, event: &Event) -> Self::Id; } fn span_id_to_slab_idx(span: &span::Id) -> usize { span.into_u64() as usize - 1 } struct WriterState<S, E> { // We need fast access to the last event for each span. last_event: Slab<atomic::AtomicU64>, // how many references are there to each span id? // needed so we know when to reclaim refcount: Slab<atomic::AtomicUsize>, // note that many span::Ids can map to the same S spans: Slab<SpanGroupContext<S>>, // TID => (S + callsite) => E => thread-local Recorder tls: ThreadLocal<Map<S, E, Recorder<u64>>>, // used to produce a Recorder for a thread that has not recorded for a given sid/eid pair idle_recorders: Map<S, E, hdrhistogram::sync::IdleRecorder<Recorder<u64>, u64>>, // used to communicate new histograms to the reader created: channel::Sender<(S, E, SyncHistogram<u64>)>, // used to produce a new Histogram when a new sid/eid pair is encountered // // TODO: // placing this in a ShardedLock requires that it is Sync, but it's only ever used when you're // holding the write lock. not sure how to describe this in the type system. new_histogram: Box<dyn FnMut(&S, &E) -> Histogram<u64> + Send + Sync>, } struct ReaderState<S, E> { created: channel::Receiver<(S, E, SyncHistogram<u64>)>, histograms: HashMap<S, IndexMap<E, SyncHistogram<u64>, Hasher>>, } /// Timing-gathering tracing subscriber. /// /// This type is constructed using a [`Builder`]. /// /// See the [crate-level docs] for details. /// /// [crate-level docs]: ../ pub struct TimingSubscriber<S = group::ByName, E = group::ByMessage> where S: SpanGroup, E: EventGroup, S::Id: Hash + Eq, E::Id: Hash + Eq, { span_group: S, event_group: E, time: quanta::Clock, writers: ShardedLock<WriterState<S::Id, E::Id>>, reader: Mutex<ReaderState<S::Id, E::Id>>, } impl<S, E> TimingSubscriber<S, E> where S: SpanGroup, E: EventGroup, S::Id: Clone + Hash + Eq, E::Id: Clone + Hash + Eq, { fn time(&self, mut span: span::Id, event: &Event) { let start = self.time.now(); let inner = self.writers.read().unwrap(); let record = move |last_event: &Slab<atomic::AtomicU64>, r: &mut Recorder<u64>, span: &span::Id| { // NOTE: we substitute in the last possible timestamp to avoid measuring time spent // in accessing the various timing datastructures (like taking locks). this has the // effect of measuing Δt₁₂ = e₂.start - e₁.end, which is probably what users expect let previous = last_event[span_id_to_slab_idx(span)] .swap(self.time.now(), atomic::Ordering::AcqRel); if previous > start { // someone else recorded a sample _just_ now // the delta is effectively zero, but recording a 0 sample is misleading return; } r.saturating_record(start - previous) }; // who are we? let tid = ThreadId::default(); // fast path: sid/eid pair is known to this thread let eid = self.event_group.group(event); if let Some(ref tls) = inner.tls.get(&tid) { // we know no-one else has our TID: // NOTE: it's _not_ safe to use this after we drop the lock due to force_synchronize. let tls = unsafe { &mut *tls.get() }; loop { // the span id _must_ be known, as it's added when created let sgi = &inner.spans[span_id_to_slab_idx(&span)]; if let Some(ref mut recorder) = tls.get_mut(&sgi.group).and_then(|rs| rs.get_mut(&eid)) { // sid/eid already known and we already have a thread-local recorder! record(&inner.last_event, recorder, &span); } else if let Some(ref ir) = inner.idle_recorders[&sgi.group].get(&eid) { // we didn't know about the eid, but if there's already a recorder for it, // we can just create a local recorder from it and move on let mut recorder = ir.recorder(); record(&inner.last_event, &mut recorder, &span); let r = tls .entry(sgi.group.clone()) .or_insert_with(Default::default) .insert(eid.clone(), recorder); assert!(r.is_none()); } else { // we're the first thread to see this pair, so we need to make a histogram for it break; } if let Some(ref psi) = sgi.parent { // keep recording up the stack span = psi.clone(); } else { return; } } // at least one sid/eid pair was unknown } else { // this thread does not yet have TLS -- we'll have to take the lock } // slow path: either this thread is new, or a sid/eid pair was new // in either case, we need to take the write lock // to do that, we must first drop the read lock drop(inner); let mut inner = self.writers.write().unwrap(); let inner = &mut *inner; // if we don't have any thread-local state, construct that first let tls = inner.tls.entry(tid).or_insert_with(Default::default); // no-one else has our TID _and_ we have exclusive access to inner let tls = unsafe { &mut *tls.get() }; // use an existing recorder if one exists, or make a new histogram if one does not let nh = &mut inner.new_histogram; let created = &mut inner.created; let idle = &mut inner.idle_recorders; loop { let sgi = &inner.spans[span_id_to_slab_idx(&span)]; // since we're recursing up the tree, we _may_ find that we already have a recorder for // a _later_ span's sid/eid. make sure we don't create a new one in that case! let recorder = tls .entry(sgi.group.clone()) .or_insert_with(Default::default) .entry(eid.clone()) .or_insert_with(|| { // nope, get us a thread-local recorder idle.get_mut(&sgi.group) .unwrap() .entry(eid.clone()) .or_insert_with(|| { // no histogram exists! make one. let h = (nh)(&sgi.group, &eid).into_sync(); let ir = h.recorder().into_idle(); created.send((sgi.group.clone(), eid.clone(), h)).expect( "WriterState implies ReaderState, which holds the receiver", ); ir }) .recorder() }); // finally, we can record the sample record(&inner.last_event, recorder, &span); // recurse to parent if any if let Some(ref psi) = sgi.parent { span = psi.clone(); } else { break; } } } /// Force all current timing information to be refreshed immediately. /// /// Note that this will interrupt all concurrent metrics gathering until it returns. pub fn force_synchronize(&self) { // first, remove all thread-local recorders let mut inner = self.writers.write().unwrap(); // note that we don't remove the tls _entry_, // since that would make all writers take the write lock later! for tls in inner.tls.values_mut() { // we hold the write lock, so we know no other thread is using its tls. let tls = unsafe { &mut *tls.get() }; tls.clear(); } // now that we've done that, refresh all the histograms. we do it with a 0 timeout since we // know that dropping all the recorders above will cause refresh to see up-to-date values, // and we don't care about samples coming _after_ the clear above. drop(inner); self.with_histograms(|hs| { for hs in hs.values_mut() { for h in hs.values_mut() { h.refresh_timeout(std::time::Duration::new(0, 0)); } } }) } /// Access the timing histograms. /// /// Be aware that the contained histograms are not automatically updated to reflect recently /// gathered samples. For each histogram you wish to read from, you must call `refresh` or /// `refresh_timeout` to gather up-to-date samples. /// /// For information about what you can do with the histograms, see the [`hdrhistogram` /// documentation]. /// /// [`hdrhistogram` documentation]: https://docs.rs/hdrhistogram/ pub fn with_histograms<F, R>(&self, f: F) -> R where F: FnOnce(&mut HashMap<S::Id, IndexMap<E::Id, SyncHistogram<u64>, Hasher>>) -> R, { // writers never take this lock, so we don't hold them up should the user call refresh(), let mut reader = self.reader.lock().unwrap(); while let Ok((sid, eid, h)) = reader.created.try_recv() { let h = reader .histograms .entry(sid) .or_insert_with(IndexMap::default) .insert(eid, h); assert!( h.is_none(), "second histogram created for same sid/eid combination" ); } f(&mut reader.histograms) } } impl<S, E> Subscriber for TimingSubscriber<S, E> where S: SpanGroup + 'static, E: EventGroup + 'static, S::Id: Clone + Hash + Eq + 'static, E::Id: Clone + Hash + Eq + 'static, { fn enabled(&self, _: &Metadata) -> bool { // TODO: implement support for per-group subsampling true } fn new_span(&self, span: &span::Attributes) -> span::Id { let group = self.span_group.group(span); let parent = span .parent() .cloned() .or_else(|| SPAN.with(|current_span| current_span.borrow().last().cloned())); let sg = SpanGroupContext { group, parent, follows: None, meta: span.metadata(), }; let mut inner = self.writers.write().unwrap(); let id = inner.refcount.insert(atomic::AtomicUsize::new(1)); let id2 = inner.spans.insert(sg.clone()); assert_eq!(id, id2); inner .idle_recorders .entry(sg.group) .or_insert_with(HashMap::default); let id2 = inner .last_event .insert(atomic::AtomicU64::new(self.time.now())); assert_eq!(id, id2); span::Id::from_u64(id as u64 + 1) } fn record(&self, _: &span::Id, _: &span::Record) {} fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { let mut inner = self.writers.write().unwrap(); inner .spans .get_mut(span_id_to_slab_idx(span)) .unwrap() .follows = Some(follows.clone()); } fn event(&self, event: &Event) { let span = event.parent().cloned().or_else(|| { SPAN.with(|current_span| { let current_span = current_span.borrow(); current_span.last().cloned() }) }); if let Some(span) = span { self.time(span, event); } else { // recorded free-standing event -- ignoring } } fn enter(&self, span: &span::Id) { SPAN.with(|current_span| { current_span.borrow_mut().push(span.clone()); }) } fn exit(&self, span: &span::Id) { // we are guaranteed that one any given thread, spans are exited in reverse order SPAN.with(|current_span| { let leaving = current_span .borrow_mut() .pop() .expect("told to exit span when not in span"); assert_eq!( &leaving, span, "told to exit span that was not most recently entered" ); }) } fn clone_span(&self, span: &span::Id) -> span::Id { let inner = self.writers.read().unwrap(); inner.refcount[span_id_to_slab_idx(span)].fetch_add(1, atomic::Ordering::AcqRel); span.clone() } fn drop_span(&self, span: span::Id) { macro_rules! unwinding_lock { ($lock:expr) => { match $lock { Ok(g) => g, Err(_) if std::thread::panicking() => { // we're trying to take the span lock while panicking // the lock is poisoned, so the writer state is corrupt // so we might as well just return -- nothing more we can do return; } r @ Err(_) => r.unwrap(), } }; }; if 1 == unwinding_lock!(self.writers.read()).refcount[span_id_to_slab_idx(&span)] .fetch_sub(1, atomic::Ordering::AcqRel) { // span has ended! // reclaim its id let mut inner = unwinding_lock!(self.writers.write()); inner.last_event.remove(span_id_to_slab_idx(&span)); inner.refcount.remove(span_id_to_slab_idx(&span)); inner.spans.remove(span_id_to_slab_idx(&span)); // we _keep_ the entry in inner.recorders in place, since it may be used by other spans } } fn current_span(&self) -> span::Current { SPAN.with(|current_span| { current_span.borrow_mut().last().map(|sid| { span::Current::new( sid.clone(), self.writers.read().unwrap().spans[span_id_to_slab_idx(sid)].meta, ) }) }) .unwrap_or_else(span::Current::none) } } /// A convenience type for getting access to [`TimingSubscriber`] through a `Dispatch`. /// /// See [`TimingSubscriber::downcaster`]. #[derive(Debug, Copy)] pub struct Downcaster<S, E> { phantom: PhantomData<fn(S, E)>, } impl<S, E> Clone for Downcaster<S, E> { fn clone(&self) -> Self { Self { phantom: PhantomData, } } } impl<S, E> TimingSubscriber<S, E> where S: SpanGroup, E: EventGroup, S::Id: Clone + Hash + Eq, E::Id: Clone + Hash + Eq, { /// Returns an identifier that can later be used to get access to this [`TimingSubscriber`] /// after it has been turned into a `tracing::Dispatch`. /// /// ```rust /// use tracing::*; /// use tracing_timing::{Builder, Histogram, TimingSubscriber}; /// let subscriber = Builder::default().build(|| Histogram::new_with_max(1_000_000, 2).unwrap()); /// let downcaster = subscriber.downcaster(); /// let dispatch = Dispatch::new(subscriber); /// // ... /// // code that hands off clones of the dispatch /// // maybe to other threads /// // ... /// downcaster.downcast(&dispatch).unwrap().with_histograms(|hs| { /// for (span_group, hs) in hs { /// for (event_group, h) in hs { /// // make sure we see the latest samples: /// h.refresh(); /// // print the median: /// println!("{} -> {}: {}ns", span_group, event_group, h.value_at_quantile(0.5)) /// } /// } /// }); /// ``` /// pub fn downcaster(&self) -> Downcaster<S, E> { Downcaster { phantom: PhantomData, } } } impl<S, E> Downcaster<S, E> where S: SpanGroup + 'static, E: EventGroup + 'static, S::Id: Clone + Hash + Eq + 'static, E::Id: Clone + Hash + Eq + 'static, { /// Retrieve a reference to this ident's original [`TimingSubscriber`]. /// /// This method returns `None` if the given `Dispatch` is not holding a subscriber of the same /// type as this ident was created from. pub fn downcast<'a>(&self, d: &'a Dispatch) -> Option<&'a TimingSubscriber<S, E>> { d.downcast_ref() } } #[derive(Hash, Eq, PartialEq, Ord, PartialOrd, Debug, Copy, Clone)] #[repr(transparent)] struct ThreadId { tid: usize, _notsend: PhantomData<UnsafeCell<()>>, } impl Default for ThreadId { fn default() -> Self { MYTID.with(|mytid| { let mut mytid = mytid.borrow_mut(); if let Some(ref mytid) = *mytid { ThreadId { tid: *mytid, _notsend: PhantomData, } } else { let tid = TID.fetch_add(1, atomic::Ordering::AcqRel); *mytid = Some(tid); ThreadId { tid, _notsend: PhantomData, } } }) } } #[derive(Default)] struct ThreadLocal<T>(HashMap<ThreadId, UnsafeCell<T>>); impl<T> Deref for ThreadLocal<T> { type Target = HashMap<ThreadId, UnsafeCell<T>>; fn deref(&self) -> &Self::Target { &self.0 } } impl<T> DerefMut for ThreadLocal<T> { fn deref_mut(&mut self) -> &mut Self::Target { &mut self.0 } } unsafe impl<T: Send> Send for ThreadLocal<T> {} unsafe impl<T: Sync> Sync for ThreadLocal<T> {}