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//! Spans represent periods of time in which a program was executing in a //! particular context. //! //! A span consists of [fields], user-defined key-value pairs of arbitrary data //! that describe the context the span represents, and a set of fixed attributes //! that describe all `tracing` spans and events. Attributes describing spans //! include: //! //! - An [`Id`] assigned by the subscriber that uniquely identifies it in relation //! to other spans. //! - The span's [parent] in the trace tree. //! - [Metadata] describing that describes static characteristics of all spans //! originating from that callsite, such as its name, source code location, //! [verbosity level], and the names of its fields. //! //! # Creating Spans //! //! Spans are created using the [`span!`] macro. This macro is invoked with the //! following arguments, in order: //! //! - The [`target`] and/or [`parent`](parent) attributes, if the user wishes to override //! their default values. //! - The span's [verbosity level] //! - A string literal providing the span's name. //! - Finally, between zero and 32 arbitrary key/value fields. //! //! [parent]: #span-relationships //! [`target`]: ../struct.Metadata.html#method.target //! //! For example: //! ```rust //! #[macro_use] //! extern crate tracing; //! use tracing::Level; //! //! # fn main() { //! /// Construct a new span at the `INFO` level named "my_span", with a single //! /// field named answer , with the value `42`. //! let my_span = span!(Level::INFO, "my_span", answer = 42); //! # } //! ``` //! //! The documentation for the [`span!`] macro provides additional examples of //! the various options that exist when creating spans. //! //! The [`trace_span!`], [`debug_span!`], [`info_span!`], [`warn_span!`], and //! [`error_span!`] exist as shorthand for constructing spans at various //! verbosity levels. //! //! ## Recording Span Creation //! //! The [`Attributes`] type contains data associated with a span, and is //! provided to the [`Subscriber`] when a new span is created. It contains //! the span's metadata, the ID of [the span's parent] if one was explicitly set, //! and any fields whose values were recorded when the span was constructed. //! The subscriber, which is responsible for recording `tracing` data, can then //! store or record these values. //! //! [the span's parent]: #span-relationships //! //! # The Span Lifecycle //! //! ## Entering a Span //! //! A thread of execution is said to _enter_ a span when it begins executing, //! and _exit_ the span when it switches to another context. Spans may be //! entered through the [`enter`] and [`in_scope`] methods. //! //! The `enter` method enters a span, returning a [guard] that exits the span //! when dropped //! ``` //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! let my_var: u64 = 5; //! let my_span = span!(Level::TRACE, "my_span", my_var); //! //! // `my_span` exists but has not been entered. //! //! // Enter `my_span`... //! let _enter = my_span.enter(); //! //! // Perform some work inside of the context of `my_span`... //! // Dropping the `_enter` guard will exit the span. //! # } //!``` //! //! `in_scope` takes a closure or function pointer and executes it inside the //! span. //! ``` //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! let my_var: u64 = 5; //! let my_span = span!(Level::TRACE, "my_span", my_var = &my_var); //! //! my_span.in_scope(|| { //! // perform some work in the context of `my_span`... //! }); //! //! // Perform some work outside of the context of `my_span`... //! //! my_span.in_scope(|| { //! // Perform some more work in the context of `my_span`. //! }); //! # } //! ``` //! //! **Note:** Since entering a span takes `&self`, and `Span`s are `Clone`, //! `Send`, and `Sync`, it is entirely valid for multiple threads to enter the //! same span concurrently. //! //! ## Span Relationships //! //! Spans form a tree structure — unless it is a root span, all spans have a //! _parent_, and may have one or more _children_. When a new span is created, //! the current span becomes the new span's parent. The total execution time of //! a span consists of the time spent in that span and in the entire subtree //! represented by its children. Thus, a parent span always lasts for at least //! as long as the longest-executing span in its subtree. //! //! ``` //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! // this span is considered the "root" of a new trace tree: //! span!(Level::INFO, "root").in_scope(|| { //! // since we are now inside "root", this span is considered a child //! // of "root": //! span!(Level::DEBUG, "outer_child").in_scope(|| { //! // this span is a child of "outer_child", which is in turn a //! // child of "root": //! span!(Level::TRACE, "inner_child").in_scope(|| { //! // and so on... //! }); //! }); //! // another span created here would also be a child of "root". //! }); //! # } //!``` //! //! In addition, the parent of a span may be explicitly specified in //! the `span!` macro. For example: //! //! ```rust //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! // Create, but do not enter, a span called "foo". //! let foo = span!(Level::INFO, "foo"); //! //! // Create and enter a span called "bar". //! let bar = span!(Level::INFO, "bar"); //! let _enter = bar.enter(); //! //! // Although we have currently entered "bar", "baz"'s parent span //! // will be "foo". //! let baz = span!(parent: &foo, Level::INFO, "baz"); //! # } //! ``` //! //! A child span should typically be considered _part_ of its parent. For //! example, if a subscriber is recording the length of time spent in various //! spans, it should generally include the time spent in a span's children as //! part of that span's duration. //! //! In addition to having zero or one parent, a span may also _follow from_ any //! number of other spans. This indicates a causal relationship between the span //! and the spans that it follows from, but a follower is *not* typically //! considered part of the duration of the span it follows. Unlike the parent, a //! span may record that it follows from another span after it is created, using //! the [`follows_from`] method. //! //! As an example, consider a listener task in a server. As the listener accepts //! incoming connections, it spawns new tasks that handle those connections. We //! might want to have a span representing the listener, and instrument each //! spawned handler task with its own span. We would want our instrumentation to //! record that the handler tasks were spawned as a result of the listener task. //! However, we might not consider the handler tasks to be _part_ of the time //! spent in the listener task, so we would not consider those spans children of //! the listener span. Instead, we would record that the handler tasks follow //! from the listener, recording the causal relationship but treating the spans //! as separate durations. //! //! ## Closing Spans //! //! Execution may enter and exit a span multiple times before that span is //! _closed_. Consider, for example, a future which has an associated //! span and enters that span every time it is polled: //! ```rust //! # extern crate tracing; //! # extern crate futures; //! # use futures::{Future, Poll, Async}; //! struct MyFuture { //! // data //! span: tracing::Span, //! } //! //! impl Future for MyFuture { //! type Item = (); //! type Error = (); //! //! fn poll(&mut self) -> Poll<Self::Item, Self::Error> { //! let _enter = self.span.enter(); //! // Do actual future work... //! # Ok(Async::Ready(())) //! } //! } //! ``` //! //! If this future was spawned on an executor, it might yield one or more times //! before `poll` returns `Ok(Async::Ready)`. If the future were to yield, then //! the executor would move on to poll the next future, which may _also_ enter //! an associated span or series of spans. Therefore, it is valid for a span to //! be entered repeatedly before it completes. Only the time when that span or //! one of its children was the current span is considered to be time spent in //! that span. A span which is not executing and has not yet been closed is said //! to be _idle_. //! //! Because spans may be entered and exited multiple times before they close, //! [`Subscriber`]s have separate trait methods which are called to notify them //! of span exits and when span handles are dropped. When execution exits a //! span, [`exit`] will always be called with that span's ID to notify the //! subscriber that the span has been exited. When span handles are dropped, the //! [`drop_span`] method is called with that span's ID. The subscriber may use //! this to determine whether or not the span will be entered again. //! //! If there is only a single handle with the capacity to exit a span, dropping //! that handle "closes" the span, since the capacity to enter it no longer //! exists. For example: //! ``` //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! { //! span!(Level::TRACE, "my_span").in_scope(|| { //! // perform some work in the context of `my_span`... //! }); // --> Subscriber::exit(my_span) //! //! // The handle to `my_span` only lives inside of this block; when it is //! // dropped, the subscriber will be informed via `drop_span`. //! //! } // --> Subscriber::drop_span(my_span) //! # } //! ``` //! //! However, if multiple handles exist, the span can still be re-entered even if //! one or more is dropped. For determining when _all_ handles to a span have //! been dropped, `Subscriber`s have a [`clone_span`] method, which is called //! every time a span handle is cloned. Combined with `drop_span`, this may be //! used to track the number of handles to a given span — if `drop_span` has //! been called one more time than the number of calls to `clone_span` for a //! given ID, then no more handles to the span with that ID exist. The //! subscriber may then treat it as closed. //! //! # When to use spans //! //! As a rule of thumb, spans should be used to represent discrete units of work //! (e.g., a given request's lifetime in a server) or periods of time spent in a //! given context (e.g., time spent interacting with an instance of an external //! system, such as a database). //! //! Which scopes in a program correspond to new spans depend somewhat on user //! intent. For example, consider the case of a loop in a program. Should we //! construct one span and perform the entire loop inside of that span, like: //! //! ```rust //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! # let n = 1; //! let span = span!(Level::TRACE, "my_loop"); //! let _enter = span.enter(); //! for i in 0..n { //! # let _ = i; //! // ... //! } //! # } //! ``` //! Or, should we create a new span for each iteration of the loop, as in: //! ```rust //! # #[macro_use] extern crate tracing; //! # use tracing::Level; //! # fn main() { //! # let n = 1u64; //! for i in 0..n { //! let span = span!(Level::TRACE, "my_loop", iteration = i); //! let _enter = span.enter(); //! // ... //! } //! # } //! ``` //! //! Depending on the circumstances, we might want to do either, or both. For //! example, if we want to know how long was spent in the loop overall, we would //! create a single span around the entire loop; whereas if we wanted to know how //! much time was spent in each individual iteration, we would enter a new span //! on every iteration. //! //! [fields]: ../field/index.html //! [Metadata]: ../struct.Metadata.html //! [`Id`]: struct.Id.html //! [verbosity level]: ../struct.Level.html //! [`span!`]: ../macro.span.html //! [`trace_span!`]: ../macro.trace_span.html //! [`debug_span!`]: ../macro.debug_span.html //! [`info_span!`]: ../macro.info_span.html //! [`warn_span!`]: ../macro.warn_span.html //! [`error_span!`]: ../macro.error_span.html //! [`clone_span`]: ../subscriber/trait.Subscriber.html#method.clone_span //! [`drop_span`]: ../subscriber/trait.Subscriber.html#method.drop_span //! [`exit`]: ../subscriber/trait.Subscriber.html#tymethod.exit //! [`Subscriber`]: ../subscriber/trait.Subscriber.html //! [`Attributes`]: struct.Attributes.html //! [`enter`]: struct.Span.html#method.enter //! [`in_scope`]: struct.Span.html#method.in_scope //! [`follows_from`]: struct.Span.html#method.follows_from //! [guard]: struct.Entered.html pub use tracing_core::span::{Attributes, Id, Record}; use crate::stdlib::{ cmp, fmt, hash::{Hash, Hasher}, }; use crate::{ dispatcher::{self, Dispatch}, field, Metadata, }; /// Trait implemented by types which have a span `Id`. pub trait AsId: crate::sealed::Sealed { /// Returns the `Id` of the span that `self` corresponds to, or `None` if /// this corresponds to a disabled span. fn as_id(&self) -> Option<&Id>; } /// A handle representing a span, with the capability to enter the span if it /// exists. /// /// If the span was rejected by the current `Subscriber`'s filter, entering the /// span will silently do nothing. Thus, the handle can be used in the same /// manner regardless of whether or not the trace is currently being collected. #[derive(Clone)] pub struct Span { /// A handle used to enter the span when it is not executing. /// /// If this is `None`, then the span has either closed or was never enabled. inner: Option<Inner>, /// Metadata describing the span. /// /// This might be `Some` even if `inner` is `None`, in the case that the /// span is disabled but the metadata is needed for `log` support. meta: Option<&'static Metadata<'static>>, } /// A handle representing the capacity to enter a span which is known to exist. /// /// Unlike `Span`, this type is only constructed for spans which _have_ been /// enabled by the current filter. This type is primarily used for implementing /// span handles; users should typically not need to interact with it directly. #[derive(Debug)] pub(crate) struct Inner { /// The span's ID, as provided by `subscriber`. id: Id, /// The subscriber that will receive events relating to this span. /// /// This should be the same subscriber that provided this span with its /// `id`. subscriber: Dispatch, } /// A guard representing a span which has been entered and is currently /// executing. /// /// When the guard is dropped, the span will be exited. /// /// This is returned by the [`Span::enter`] function. /// /// [`Span::enter`]: ../struct.Span.html#method.enter #[derive(Debug)] #[must_use = "once a span has been entered, it should be exited"] pub struct Entered<'a> { span: &'a Span, } // ===== impl Span ===== impl Span { /// Constructs a new `Span` with the given [metadata] and set of /// [field values]. /// /// The new span will be constructed by the currently-active [`Subscriber`], /// with the current span as its parent (if one exists). /// /// After the span is constructed, [field values] and/or [`follows_from`] /// annotations may be added to it. /// /// [metadata]: ../metadata /// [`Subscriber`]: ../subscriber/trait.Subscriber.html /// [field values]: ../field/struct.ValueSet.html /// [`follows_from`]: ../struct.Span.html#method.follows_from #[inline] pub fn new(meta: &'static Metadata<'static>, values: &field::ValueSet<'_>) -> Span { let new_span = Attributes::new(meta, values); Self::make(meta, new_span) } /// Constructs a new `Span` as the root of its own trace tree, with the /// given [metadata] and set of [field values]. /// /// After the span is constructed, [field values] and/or [`follows_from`] /// annotations may be added to it. /// /// [metadata]: ../metadata /// [field values]: ../field/struct.ValueSet.html /// [`follows_from`]: ../struct.Span.html#method.follows_from #[inline] pub fn new_root(meta: &'static Metadata<'static>, values: &field::ValueSet<'_>) -> Span { Self::make(meta, Attributes::new_root(meta, values)) } /// Constructs a new `Span` as child of the given parent span, with the /// given [metadata] and set of [field values]. /// /// After the span is constructed, [field values] and/or [`follows_from`] /// annotations may be added to it. /// /// [metadata]: ../metadata /// [field values]: ../field/struct.ValueSet.html /// [`follows_from`]: ../struct.Span.html#method.follows_from pub fn child_of( parent: impl Into<Option<Id>>, meta: &'static Metadata<'static>, values: &field::ValueSet<'_>, ) -> Span { let new_span = match parent.into() { Some(parent) => Attributes::child_of(parent, meta, values), None => Attributes::new_root(meta, values), }; Self::make(meta, new_span) } /// Constructs a new disabled span with the given `Metadata`. /// /// This should be used when a span is constructed from a known callsite, /// but the subscriber indicates that it is disabled. /// /// Entering, exiting, and recording values on this span will not notify the /// `Subscriber` but _may_ record log messages if the `log` feature flag is /// enabled. #[inline(always)] pub fn new_disabled(meta: &'static Metadata<'static>) -> Span { Self { inner: None, meta: Some(meta), } } /// Constructs a new span that is *completely disabled*. /// /// This can be used rather than `Option<Span>` to represent cases where a /// span is not present. /// /// Entering, exiting, and recording values on this span will do nothing. pub const fn none() -> Span { Self { inner: None, meta: None, } } /// Returns a handle to the span [considered by the `Subscriber`] to be the /// currrent span. /// /// If the subscriber indicates that it does not track the current span, or /// that the thread from which this function is called is not currently /// inside a span, the returned span will be disabled. /// /// [considered by the `Subscriber`]: ../subscriber/trait.Subscriber.html#method.current pub fn current() -> Span { dispatcher::get_default(|dispatch| { if let Some((id, meta)) = dispatch.current_span().into_inner() { let id = dispatch.clone_span(&id); Self { inner: Some(Inner::new(id, dispatch)), meta: Some(meta), } } else { Self::none() } }) } fn make(meta: &'static Metadata<'static>, new_span: Attributes<'_>) -> Span { let attrs = &new_span; let inner = dispatcher::get_default(move |dispatch| { let id = dispatch.new_span(attrs); Some(Inner::new(id, dispatch)) }); let span = Self { inner, meta: Some(meta), }; #[cfg(feature = "log")] span.log(format_args!("++ {}; {}", meta.name(), FmtAttrs(attrs))); span } /// Enters this span, returning a guard that will exit the span when dropped. /// /// If this span is enabled by the current subscriber, then this function will /// call [`Subscriber::enter`] with the span's [`Id`], and dropping the guard /// will call [`Subscriber::exit`]. If the span is disabled, this does nothing. /// /// # Examples /// /// ``` /// #[macro_use] extern crate tracing; /// # use tracing::Level; /// # fn main() { /// let span = span!(Level::INFO, "my_span"); /// let guard = span.enter(); /// /// // code here is within the span /// /// drop(guard); /// /// // code here is no longer within the span /// /// # } /// ``` /// /// Guards need not be explicitly dropped: /// /// ``` /// #[macro_use] extern crate tracing; /// # fn main() { /// fn my_function() -> String { /// // enter a span for the duration of this function. /// let span = trace_span!("my_function"); /// let _enter = span.enter(); /// /// // anything happening in functions we call is still inside the span... /// my_other_function(); /// /// // returning from the function drops the guard, exiting the span. /// return "Hello world".to_owned(); /// } /// /// fn my_other_function() { /// // ... /// } /// # } /// ``` /// /// Sub-scopes may be created to limit the duration for which the span is /// entered: /// /// ``` /// #[macro_use] extern crate tracing; /// # fn main() { /// let span = info_span!("my_great_span"); /// /// { /// let _enter = span.enter(); /// /// // this event occurs inside the span. /// info!("i'm in the span!"); /// /// // exiting the scope drops the guard, exiting the span. /// } /// /// // this event is not inside the span. /// info!("i'm outside the span!") /// # } /// ``` /// /// [`Subscriber::enter`]: ../subscriber/trait.Subscriber.html#method.enter /// [`Subscriber::exit`]: ../subscriber/trait.Subscriber.html#method.exit /// [`Id`]: ../struct.Id.html pub fn enter<'a>(&'a self) -> Entered<'a> { if let Some(ref inner) = self.inner.as_ref() { inner.subscriber.enter(&inner.id); } #[cfg(feature = "log")] { if let Some(ref meta) = self.meta { self.log(format_args!("-> {}", meta.name())); } } Entered { span: self } } /// Executes the given function in the context of this span. /// /// If this span is enabled, then this function enters the span, invokes `f` /// and then exits the span. If the span is disabled, `f` will still be /// invoked, but in the context of the currently-executing span (if there is /// one). /// /// Returns the result of evaluating `f`. /// /// # Examples /// /// ``` /// # #[macro_use] extern crate tracing; /// # use tracing::Level; /// # fn main() { /// let my_span = span!(Level::TRACE, "my_span"); /// /// my_span.in_scope(|| { /// // this event occurs within the span. /// trace!("i'm in the span!"); /// }); /// /// // this event occurs outside the span. /// trace!("i'm not in the span!"); /// # } /// ``` /// /// Calling a function and returning the result: /// ``` /// # #[macro_use] extern crate tracing; /// # use tracing::Level; /// fn hello_world() -> String { /// "Hello world!".to_owned() /// } /// /// # fn main() { /// let span = info_span!("hello_world"); /// // the span will be entered for the duration of the call to /// // `hello_world`. /// let a_string = span.in_scope(hello_world); /// # } /// pub fn in_scope<F: FnOnce() -> T, T>(&self, f: F) -> T { let _enter = self.enter(); f() } /// Returns a [`Field`](../field/struct.Field.html) for the field with the /// given `name`, if one exists, pub fn field<Q: ?Sized>(&self, field: &Q) -> Option<field::Field> where Q: field::AsField, { self.metadata().and_then(|meta| field.as_field(meta)) } /// Returns true if this `Span` has a field for the given /// [`Field`](../field/struct.Field.html) or field name. #[inline] pub fn has_field<Q: ?Sized>(&self, field: &Q) -> bool where Q: field::AsField, { self.field(field).is_some() } /// Visits that the field described by `field` has the value `value`. pub fn record<Q: ?Sized, V>(&self, field: &Q, value: &V) -> &Self where Q: field::AsField, V: field::Value, { if let Some(ref meta) = self.meta { if let Some(field) = field.as_field(meta) { self.record_all( &meta .fields() .value_set(&[(&field, Some(value as &dyn field::Value))]), ); } } self } /// Visit all the fields in the span pub fn record_all(&self, values: &field::ValueSet<'_>) -> &Self { let record = Record::new(values); if let Some(ref inner) = self.inner { inner.record(&record); } #[cfg(feature = "log")] { if let Some(ref meta) = self.meta { self.log(format_args!("{}; {}", meta.name(), FmtValues(&record))); } } self } /// Returns `true` if this span was disabled by the subscriber and does not /// exist. #[inline] pub fn is_disabled(&self) -> bool { self.inner.is_none() } /// Indicates that the span with the given ID has an indirect causal /// relationship with this span. /// /// This relationship differs somewhat from the parent-child relationship: a /// span may have any number of prior spans, rather than a single one; and /// spans are not considered to be executing _inside_ of the spans they /// follow from. This means that a span may close even if subsequent spans /// that follow from it are still open, and time spent inside of a /// subsequent span should not be included in the time its precedents were /// executing. This is used to model causal relationships such as when a /// single future spawns several related background tasks, et cetera. /// /// If this span is disabled, or the resulting follows-from relationship /// would be invalid, this function will do nothing. pub fn follows_from(&self, from: impl for<'a> Into<Option<&'a Id>>) -> &Self { if let Some(ref inner) = self.inner { if let Some(from) = from.into() { inner.follows_from(from); } } self } /// Returns this span's `Id`, if it is enabled. pub fn id(&self) -> Option<Id> { self.inner.as_ref().map(Inner::id) } /// Returns this span's `Metadata`, if it is enabled. pub fn metadata(&self) -> Option<&'static Metadata<'static>> { self.meta.clone() } #[cfg(feature = "log")] #[inline] fn log(&self, message: fmt::Arguments) { if let Some(ref meta) = self.meta { let logger = log::logger(); let log_meta = log::Metadata::builder() .level(level_to_log!(meta.level())) .target(meta.target()) .build(); if logger.enabled(&log_meta) { logger.log( &log::Record::builder() .metadata(log_meta) .module_path(meta.module_path()) .file(meta.file()) .line(meta.line()) .args(message) .build(), ); } } } } impl cmp::PartialEq for Span { fn eq(&self, other: &Self) -> bool { match (&self.meta, &other.meta) { (Some(this), Some(that)) => { this.callsite() == that.callsite() && self.inner == other.inner } _ => false, } } } impl Hash for Span { fn hash<H: Hasher>(&self, hasher: &mut H) { self.inner.hash(hasher); } } impl fmt::Debug for Span { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { let mut span = f.debug_struct("Span"); if let Some(ref meta) = self.meta { span.field("name", &meta.name()) .field("level", &meta.level()) .field("target", &meta.target()); if let Some(ref inner) = self.inner { span.field("id", &inner.id()); } else { span.field("disabled", &true); } if let Some(ref path) = meta.module_path() { span.field("module_path", &path); } if let Some(ref line) = meta.line() { span.field("line", &line); } if let Some(ref file) = meta.file() { span.field("file", &file); } } else { span.field("none", &true); } span.finish() } } impl<'a> Into<Option<&'a Id>> for &'a Span { fn into(self) -> Option<&'a Id> { self.inner.as_ref().map(|inner| &inner.id) } } impl<'a> Into<Option<Id>> for &'a Span { fn into(self) -> Option<Id> { self.inner.as_ref().map(Inner::id) } } impl Into<Option<Id>> for Span { fn into(self) -> Option<Id> { self.inner.as_ref().map(Inner::id) } } impl Drop for Span { fn drop(&mut self) { if let Some(Inner { ref id, ref subscriber, }) = self.inner { if subscriber.try_close(id.clone()) { #[cfg(feature = "log")] { if let Some(ref meta) = self.meta { self.log(format_args!("-- {}", meta.name())); } } } } } } // ===== impl Inner ===== impl Inner { /// Indicates that the span with the given ID has an indirect causal /// relationship with this span. /// /// This relationship differs somewhat from the parent-child relationship: a /// span may have any number of prior spans, rather than a single one; and /// spans are not considered to be executing _inside_ of the spans they /// follow from. This means that a span may close even if subsequent spans /// that follow from it are still open, and time spent inside of a /// subsequent span should not be included in the time its precedents were /// executing. This is used to model causal relationships such as when a /// single future spawns several related background tasks, et cetera. /// /// If this span is disabled, this function will do nothing. Otherwise, it /// returns `Ok(())` if the other span was added as a precedent of this /// span, or an error if this was not possible. fn follows_from(&self, from: &Id) { self.subscriber.record_follows_from(&self.id, &from) } /// Returns the span's ID. fn id(&self) -> Id { self.id.clone() } fn record(&self, values: &Record<'_>) { self.subscriber.record(&self.id, values) } fn new(id: Id, subscriber: &Dispatch) -> Self { Inner { id, subscriber: subscriber.clone(), } } } impl cmp::PartialEq for Inner { fn eq(&self, other: &Self) -> bool { self.id == other.id } } impl Hash for Inner { fn hash<H: Hasher>(&self, state: &mut H) { self.id.hash(state); } } impl Clone for Inner { fn clone(&self) -> Self { Inner { id: self.subscriber.clone_span(&self.id), subscriber: self.subscriber.clone(), } } } // ===== impl Entered ===== impl<'a> Drop for Entered<'a> { #[inline] fn drop(&mut self) { // Dropping the guard exits the span. // // Running this behaviour on drop rather than with an explicit function // call means that spans may still be exited when unwinding. if let Some(inner) = self.span.inner.as_ref() { inner.subscriber.exit(&inner.id); } #[cfg(feature = "log")] { if let Some(ref meta) = self.span.meta { self.span.log(format_args!("<- {}", meta.name())); } } } } #[cfg(feature = "log")] struct FmtValues<'a>(&'a Record<'a>); #[cfg(feature = "log")] impl<'a> fmt::Display for FmtValues<'a> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let mut res = Ok(()); self.0.record(&mut |k: &field::Field, v: &dyn fmt::Debug| { res = write!(f, "{}={:?} ", k, v); }); res } } #[cfg(feature = "log")] struct FmtAttrs<'a>(&'a Attributes<'a>); #[cfg(feature = "log")] impl<'a> fmt::Display for FmtAttrs<'a> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let mut res = Ok(()); self.0.record(&mut |k: &field::Field, v: &dyn fmt::Debug| { res = write!(f, "{}={:?} ", k, v); }); res } } #[cfg(test)] mod test { use super::*; trait AssertSend: Send {} impl AssertSend for Span {} trait AssertSync: Sync {} impl AssertSync for Span {} }