| //! Collectors collect and record trace data. |
| use crate::{span, Dispatch, Event, LevelFilter, Metadata}; |
| |
| use crate::stdlib::{ |
| any::{Any, TypeId}, |
| boxed::Box, |
| sync::Arc, |
| }; |
| |
| /// Trait representing the functions required to collect trace data. |
| /// |
| /// Crates that provide implementations of methods for collecting or recording |
| /// trace data should implement the `Subscriber` interface. This trait is |
| /// intended to represent fundamental primitives for collecting trace events and |
| /// spans — other libraries may offer utility functions and types to make |
| /// subscriber implementations more modular or improve the ergonomics of writing |
| /// subscribers. |
| /// |
| /// A subscriber is responsible for the following: |
| /// - Registering new spans as they are created, and providing them with span |
| /// IDs. Implicitly, this means the subscriber may determine the strategy for |
| /// determining span equality. |
| /// - Recording the attachment of field values and follows-from annotations to |
| /// spans. |
| /// - Filtering spans and events, and determining when those filters must be |
| /// invalidated. |
| /// - Observing spans as they are entered, exited, and closed, and events as |
| /// they occur. |
| /// |
| /// When a span is entered or exited, the subscriber is provided only with the |
| /// [ID] with which it tagged that span when it was created. This means |
| /// that it is up to the subscriber to determine whether and how span _data_ — |
| /// the fields and metadata describing the span — should be stored. The |
| /// [`new_span`] function is called when a new span is created, and at that |
| /// point, the subscriber _may_ choose to store the associated data if it will |
| /// be referenced again. However, if the data has already been recorded and will |
| /// not be needed by the implementations of `enter` and `exit`, the subscriber |
| /// may freely discard that data without allocating space to store it. |
| /// |
| /// ## Overriding default impls |
| /// |
| /// Some trait methods on `Subscriber` have default implementations, either in |
| /// order to reduce the surface area of implementing `Subscriber`, or for |
| /// backward-compatibility reasons. However, many subscribers will likely want |
| /// to override these default implementations. |
| /// |
| /// The following methods are likely of interest: |
| /// |
| /// - [`register_callsite`] is called once for each callsite from which a span |
| /// event may originate, and returns an [`Interest`] value describing whether or |
| /// not the subscriber wishes to see events or spans from that callsite. By |
| /// default, it calls [`enabled`], and returns `Interest::always()` if |
| /// `enabled` returns true, or `Interest::never()` if enabled returns false. |
| /// However, if the subscriber's interest can change dynamically at runtime, |
| /// it may want to override this function to return `Interest::sometimes()`. |
| /// Additionally, subscribers which wish to perform a behaviour once for each |
| /// callsite, such as allocating storage for data related to that callsite, |
| /// can perform it in `register_callsite`. |
| /// |
| /// See also the [documentation on the callsite registry][cs-reg] for details |
| /// on [`register_callsite`]. |
| /// |
| /// - [`event_enabled`] is called once before every call to the [`event`] |
| /// method. This can be used to implement filtering on events once their field |
| /// values are known, but before any processing is done in the `event` method. |
| /// - [`clone_span`] is called every time a span ID is cloned, and [`try_close`] |
| /// is called when a span ID is dropped. By default, these functions do |
| /// nothing. However, they can be used to implement reference counting for |
| /// spans, allowing subscribers to free storage for span data and to determine |
| /// when a span has _closed_ permanently (rather than being exited). |
| /// Subscribers which store per-span data or which need to track span closures |
| /// should override these functions together. |
| /// |
| /// [ID]: super::span::Id |
| /// [`new_span`]: Subscriber::new_span |
| /// [`register_callsite`]: Subscriber::register_callsite |
| /// [`enabled`]: Subscriber::enabled |
| /// [`clone_span`]: Subscriber::clone_span |
| /// [`try_close`]: Subscriber::try_close |
| /// [cs-reg]: crate::callsite#registering-callsites |
| /// [`event`]: Subscriber::event |
| /// [`event_enabled`]: Subscriber::event_enabled |
| pub trait Subscriber: 'static { |
| /// Invoked when this subscriber becomes a [`Dispatch`]. |
| /// |
| /// ## Avoiding Memory Leaks |
| /// |
| /// `Subscriber`s should not store their own [`Dispatch`]. Because the |
| /// `Dispatch` owns the `Subscriber`, storing the `Dispatch` within the |
| /// `Subscriber` will create a reference count cycle, preventing the `Dispatch` |
| /// from ever being dropped. |
| /// |
| /// Instead, when it is necessary to store a cyclical reference to the |
| /// `Dispatch` within a `Subscriber`, use [`Dispatch::downgrade`] to convert a |
| /// `Dispatch` into a [`WeakDispatch`]. This type is analogous to |
| /// [`std::sync::Weak`], and does not create a reference count cycle. A |
| /// [`WeakDispatch`] can be stored within a `Subscriber` without causing a |
| /// memory leak, and can be [upgraded] into a `Dispatch` temporarily when |
| /// the `Dispatch` must be accessed by the `Subscriber`. |
| /// |
| /// [`WeakDispatch`]: crate::dispatcher::WeakDispatch |
| /// [upgraded]: crate::dispatcher::WeakDispatch::upgrade |
| fn on_register_dispatch(&self, subscriber: &Dispatch) { |
| let _ = subscriber; |
| } |
| |
| /// Registers a new [callsite] with this subscriber, returning whether or not |
| /// the subscriber is interested in being notified about the callsite. |
| /// |
| /// By default, this function assumes that the subscriber's [filter] |
| /// represents an unchanging view of its interest in the callsite. However, |
| /// if this is not the case, subscribers may override this function to |
| /// indicate different interests, or to implement behaviour that should run |
| /// once for every callsite. |
| /// |
| /// This function is guaranteed to be called at least once per callsite on |
| /// every active subscriber. The subscriber may store the keys to fields it |
| /// cares about in order to reduce the cost of accessing fields by name, |
| /// preallocate storage for that callsite, or perform any other actions it |
| /// wishes to perform once for each callsite. |
| /// |
| /// The subscriber should then return an [`Interest`], indicating |
| /// whether it is interested in being notified about that callsite in the |
| /// future. This may be `Always` indicating that the subscriber always |
| /// wishes to be notified about the callsite, and its filter need not be |
| /// re-evaluated; `Sometimes`, indicating that the subscriber may sometimes |
| /// care about the callsite but not always (such as when sampling), or |
| /// `Never`, indicating that the subscriber never wishes to be notified about |
| /// that callsite. If all active subscribers return `Never`, a callsite will |
| /// never be enabled unless a new subscriber expresses interest in it. |
| /// |
| /// `Subscriber`s which require their filters to be run every time an event |
| /// occurs or a span is entered/exited should return `Interest::sometimes`. |
| /// If a subscriber returns `Interest::sometimes`, then its [`enabled`] method |
| /// will be called every time an event or span is created from that callsite. |
| /// |
| /// For example, suppose a sampling subscriber is implemented by |
| /// incrementing a counter every time `enabled` is called and only returning |
| /// `true` when the counter is divisible by a specified sampling rate. If |
| /// that subscriber returns `Interest::always` from `register_callsite`, then |
| /// the filter will not be re-evaluated once it has been applied to a given |
| /// set of metadata. Thus, the counter will not be incremented, and the span |
| /// or event that corresponds to the metadata will never be `enabled`. |
| /// |
| /// `Subscriber`s that need to change their filters occasionally should call |
| /// [`rebuild_interest_cache`] to re-evaluate `register_callsite` for all |
| /// callsites. |
| /// |
| /// Similarly, if a `Subscriber` has a filtering strategy that can be |
| /// changed dynamically at runtime, it would need to re-evaluate that filter |
| /// if the cached results have changed. |
| /// |
| /// A subscriber which manages fanout to multiple other subscribers |
| /// should proxy this decision to all of its child subscribers, |
| /// returning `Interest::never` only if _all_ such children return |
| /// `Interest::never`. If the set of subscribers to which spans are |
| /// broadcast may change dynamically, the subscriber should also never |
| /// return `Interest::Never`, as a new subscriber may be added that _is_ |
| /// interested. |
| /// |
| /// See the [documentation on the callsite registry][cs-reg] for more |
| /// details on how and when the `register_callsite` method is called. |
| /// |
| /// # Notes |
| /// This function may be called again when a new subscriber is created or |
| /// when the registry is invalidated. |
| /// |
| /// If a subscriber returns `Interest::never` for a particular callsite, it |
| /// _may_ still see spans and events originating from that callsite, if |
| /// another subscriber expressed interest in it. |
| /// |
| /// [callsite]: crate::callsite |
| /// [filter]: Self::enabled |
| /// [metadata]: super::metadata::Metadata |
| /// [`enabled`]: Subscriber::enabled() |
| /// [`rebuild_interest_cache`]: super::callsite::rebuild_interest_cache |
| /// [cs-reg]: crate::callsite#registering-callsites |
| fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
| if self.enabled(metadata) { |
| Interest::always() |
| } else { |
| Interest::never() |
| } |
| } |
| |
| /// Returns true if a span or event with the specified [metadata] would be |
| /// recorded. |
| /// |
| /// By default, it is assumed that this filter needs only be evaluated once |
| /// for each callsite, so it is called by [`register_callsite`] when each |
| /// callsite is registered. The result is used to determine if the subscriber |
| /// is always [interested] or never interested in that callsite. This is intended |
| /// primarily as an optimization, so that expensive filters (such as those |
| /// involving string search, et cetera) need not be re-evaluated. |
| /// |
| /// However, if the subscriber's interest in a particular span or event may |
| /// change, or depends on contexts only determined dynamically at runtime, |
| /// then the `register_callsite` method should be overridden to return |
| /// [`Interest::sometimes`]. In that case, this function will be called every |
| /// time that span or event occurs. |
| /// |
| /// [metadata]: super::metadata::Metadata |
| /// [interested]: Interest |
| /// [`Interest::sometimes`]: Interest::sometimes |
| /// [`register_callsite`]: Subscriber::register_callsite() |
| fn enabled(&self, metadata: &Metadata<'_>) -> bool; |
| |
| /// Returns the highest [verbosity level][level] that this `Subscriber` will |
| /// enable, or `None`, if the subscriber does not implement level-based |
| /// filtering or chooses not to implement this method. |
| /// |
| /// If this method returns a [`Level`][level], it will be used as a hint to |
| /// determine the most verbose level that will be enabled. This will allow |
| /// spans and events which are more verbose than that level to be skipped |
| /// more efficiently. Subscribers which perform filtering are strongly |
| /// encouraged to provide an implementation of this method. |
| /// |
| /// If the maximum level the subscriber will enable can change over the |
| /// course of its lifetime, it is free to return a different value from |
| /// multiple invocations of this method. However, note that changes in the |
| /// maximum level will **only** be reflected after the callsite [`Interest`] |
| /// cache is rebuilt, by calling the [`callsite::rebuild_interest_cache`][rebuild] |
| /// function. Therefore, if the subscriber will change the value returned by |
| /// this method, it is responsible for ensuring that |
| /// [`rebuild_interest_cache`][rebuild] is called after the value of the max |
| /// level changes. |
| /// |
| /// [level]: super::Level |
| /// [rebuild]: super::callsite::rebuild_interest_cache |
| fn max_level_hint(&self) -> Option<LevelFilter> { |
| None |
| } |
| |
| /// Visit the construction of a new span, returning a new [span ID] for the |
| /// span being constructed. |
| /// |
| /// The provided [`Attributes`] contains any field values that were provided |
| /// when the span was created. The subscriber may pass a [visitor] to the |
| /// `Attributes`' [`record` method] to record these values. |
| /// |
| /// IDs are used to uniquely identify spans and events within the context of a |
| /// subscriber, so span equality will be based on the returned ID. Thus, if |
| /// the subscriber wishes for all spans with the same metadata to be |
| /// considered equal, it should return the same ID every time it is given a |
| /// particular set of metadata. Similarly, if it wishes for two separate |
| /// instances of a span with the same metadata to *not* be equal, it should |
| /// return a distinct ID every time this function is called, regardless of |
| /// the metadata. |
| /// |
| /// Note that the subscriber is free to assign span IDs based on whatever |
| /// scheme it sees fit. Any guarantees about uniqueness, ordering, or ID |
| /// reuse are left up to the subscriber implementation to determine. |
| /// |
| /// [span ID]: super::span::Id |
| /// [`Attributes`]: super::span::Attributes |
| /// [visitor]: super::field::Visit |
| /// [`record` method]: super::span::Attributes::record |
| fn new_span(&self, span: &span::Attributes<'_>) -> span::Id; |
| |
| // === Notification methods =============================================== |
| |
| /// Record a set of values on a span. |
| /// |
| /// This method will be invoked when value is recorded on a span. |
| /// Recording multiple values for the same field is possible, |
| /// but the actual behaviour is defined by the subscriber implementation. |
| /// |
| /// Keep in mind that a span might not provide a value |
| /// for each field it declares. |
| /// |
| /// The subscriber is expected to provide a [visitor] to the `Record`'s |
| /// [`record` method] in order to record the added values. |
| /// |
| /// # Example |
| /// "foo = 3" will be recorded when [`record`] is called on the |
| /// `Attributes` passed to `new_span`. |
| /// Since values are not provided for the `bar` and `baz` fields, |
| /// the span's `Metadata` will indicate that it _has_ those fields, |
| /// but values for them won't be recorded at this time. |
| /// |
| /// ```rust,ignore |
| /// # use tracing::span; |
| /// |
| /// let mut span = span!("my_span", foo = 3, bar, baz); |
| /// |
| /// // `Subscriber::record` will be called with a `Record` |
| /// // containing "bar = false" |
| /// span.record("bar", &false); |
| /// |
| /// // `Subscriber::record` will be called with a `Record` |
| /// // containing "baz = "a string"" |
| /// span.record("baz", &"a string"); |
| /// ``` |
| /// |
| /// [visitor]: super::field::Visit |
| /// [`record`]: super::span::Attributes::record |
| /// [`record` method]: super::span::Record::record |
| fn record(&self, span: &span::Id, values: &span::Record<'_>); |
| |
| /// Adds an indication that `span` follows from the span with the id |
| /// `follows`. |
| /// |
| /// 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 the subscriber has spans corresponding to the given IDs, it should |
| /// record this relationship in whatever way it deems necessary. Otherwise, |
| /// if one or both of the given span IDs do not correspond to spans that the |
| /// subscriber knows about, or if a cyclical relationship would be created |
| /// (i.e., some span _a_ which proceeds some other span _b_ may not also |
| /// follow from _b_), it may silently do nothing. |
| fn record_follows_from(&self, span: &span::Id, follows: &span::Id); |
| |
| /// Determine if an [`Event`] should be recorded. |
| /// |
| /// By default, this returns `true` and `Subscriber`s can filter events in |
| /// [`event`][Self::event] without any penalty. However, when `event` is |
| /// more complicated, this can be used to determine if `event` should be |
| /// called at all, separating out the decision from the processing. |
| fn event_enabled(&self, event: &Event<'_>) -> bool { |
| let _ = event; |
| true |
| } |
| |
| /// Records that an [`Event`] has occurred. |
| /// |
| /// This method will be invoked when an Event is constructed by |
| /// the `Event`'s [`dispatch` method]. For example, this happens internally |
| /// when an event macro from `tracing` is called. |
| /// |
| /// The key difference between this method and `record` is that `record` is |
| /// called when a value is recorded for a field defined by a span, |
| /// while `event` is called when a new event occurs. |
| /// |
| /// The provided `Event` struct contains any field values attached to the |
| /// event. The subscriber may pass a [visitor] to the `Event`'s |
| /// [`record` method] to record these values. |
| /// |
| /// [`Event`]: super::event::Event |
| /// [visitor]: super::field::Visit |
| /// [`record` method]: super::event::Event::record |
| /// [`dispatch` method]: super::event::Event::dispatch |
| fn event(&self, event: &Event<'_>); |
| |
| /// Records that a span has been entered. |
| /// |
| /// When entering a span, this method is called to notify the subscriber |
| /// that the span has been entered. The subscriber is provided with the |
| /// [span ID] of the entered span, and should update any internal state |
| /// tracking the current span accordingly. |
| /// |
| /// [span ID]: super::span::Id |
| fn enter(&self, span: &span::Id); |
| |
| /// Records that a span has been exited. |
| /// |
| /// When exiting a span, this method is called to notify the subscriber |
| /// that the span has been exited. The subscriber is provided with the |
| /// [span ID] of the exited span, and should update any internal state |
| /// tracking the current span accordingly. |
| /// |
| /// Exiting a span does not imply that the span will not be re-entered. |
| /// |
| /// [span ID]: super::span::Id |
| fn exit(&self, span: &span::Id); |
| |
| /// Notifies the subscriber that a [span ID] has been cloned. |
| /// |
| /// This function is guaranteed to only be called with span IDs that were |
| /// returned by this subscriber's `new_span` function. |
| /// |
| /// Note that the default implementation of this function this is just the |
| /// identity function, passing through the identifier. However, it can be |
| /// used in conjunction with [`try_close`] to track the number of handles |
| /// capable of `enter`ing a span. When all the handles have been dropped |
| /// (i.e., `try_close` has been called one more time than `clone_span` for a |
| /// given ID), the subscriber may assume that the span will not be entered |
| /// again. It is then free to deallocate storage for data associated with |
| /// that span, write data from that span to IO, and so on. |
| /// |
| /// For more unsafe situations, however, if `id` is itself a pointer of some |
| /// kind this can be used as a hook to "clone" the pointer, depending on |
| /// what that means for the specified pointer. |
| /// |
| /// [span ID]: super::span::Id |
| /// [`try_close`]: Subscriber::try_close |
| fn clone_span(&self, id: &span::Id) -> span::Id { |
| id.clone() |
| } |
| |
| /// **This method is deprecated.** |
| /// |
| /// Using `drop_span` may result in subscribers composed using |
| /// `tracing-subscriber` crate's `Layer` trait from observing close events. |
| /// Use [`try_close`] instead. |
| /// |
| /// The default implementation of this function does nothing. |
| /// |
| /// [`try_close`]: Subscriber::try_close |
| #[deprecated(since = "0.1.2", note = "use `Subscriber::try_close` instead")] |
| fn drop_span(&self, _id: span::Id) {} |
| |
| /// Notifies the subscriber that a [span ID] has been dropped, and returns |
| /// `true` if there are now 0 IDs that refer to that span. |
| /// |
| /// Higher-level libraries providing functionality for composing multiple |
| /// subscriber implementations may use this return value to notify any |
| /// "layered" subscribers that this subscriber considers the span closed. |
| /// |
| /// The default implementation of this method calls the subscriber's |
| /// [`drop_span`] method and returns `false`. This means that, unless the |
| /// subscriber overrides the default implementation, close notifications |
| /// will never be sent to any layered subscribers. In general, if the |
| /// subscriber tracks reference counts, this method should be implemented, |
| /// rather than `drop_span`. |
| /// |
| /// This function is guaranteed to only be called with span IDs that were |
| /// returned by this subscriber's `new_span` function. |
| /// |
| /// It's guaranteed that if this function has been called once more than the |
| /// number of times `clone_span` was called with the same `id`, then no more |
| /// handles that can enter the span with that `id` exist. This means that it |
| /// can be used in conjunction with [`clone_span`] to track the number of |
| /// handles capable of `enter`ing a span. When all the handles have been |
| /// dropped (i.e., `try_close` has been called one more time than |
| /// `clone_span` for a given ID), the subscriber may assume that the span |
| /// will not be entered again, and should return `true`. It is then free to |
| /// deallocate storage for data associated with that span, write data from |
| /// that span to IO, and so on. |
| /// |
| /// **Note**: since this function is called when spans are dropped, |
| /// implementations should ensure that they are unwind-safe. Panicking from |
| /// inside of a `try_close` function may cause a double panic, if the span |
| /// was dropped due to a thread unwinding. |
| /// |
| /// [span ID]: super::span::Id |
| /// [`clone_span`]: Subscriber::clone_span |
| /// [`drop_span`]: Subscriber::drop_span |
| fn try_close(&self, id: span::Id) -> bool { |
| #[allow(deprecated)] |
| self.drop_span(id); |
| false |
| } |
| |
| /// Returns a type representing this subscriber's view of the current span. |
| /// |
| /// If subscribers track a current span, they should override this function |
| /// to return [`Current::new`] if the thread from which this method is |
| /// called is inside a span, or [`Current::none`] if the thread is not |
| /// inside a span. |
| /// |
| /// By default, this returns a value indicating that the subscriber |
| /// does **not** track what span is current. If the subscriber does not |
| /// implement a current span, it should not override this method. |
| /// |
| /// [`Current::new`]: super::span::Current#tymethod.new |
| /// [`Current::none`]: super::span::Current#tymethod.none |
| fn current_span(&self) -> span::Current { |
| span::Current::unknown() |
| } |
| |
| // === Downcasting methods ================================================ |
| |
| /// If `self` is the same type as the provided `TypeId`, returns an untyped |
| /// `*const` pointer to that type. Otherwise, returns `None`. |
| /// |
| /// If you wish to downcast a `Subscriber`, it is strongly advised to use |
| /// the safe API provided by [`downcast_ref`] instead. |
| /// |
| /// This API is required for `downcast_raw` to be a trait method; a method |
| /// signature like [`downcast_ref`] (with a generic type parameter) is not |
| /// object-safe, and thus cannot be a trait method for `Subscriber`. This |
| /// means that if we only exposed `downcast_ref`, `Subscriber` |
| /// implementations could not override the downcasting behavior |
| /// |
| /// This method may be overridden by "fan out" or "chained" subscriber |
| /// implementations which consist of multiple composed types. Such |
| /// subscribers might allow `downcast_raw` by returning references to those |
| /// component if they contain components with the given `TypeId`. |
| /// |
| /// # Safety |
| /// |
| /// The [`downcast_ref`] method expects that the pointer returned by |
| /// `downcast_raw` is non-null and points to a valid instance of the type |
| /// with the provided `TypeId`. Failure to ensure this will result in |
| /// undefined behaviour, so implementing `downcast_raw` is unsafe. |
| /// |
| /// [`downcast_ref`]: #method.downcast_ref |
| unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
| if id == TypeId::of::<Self>() { |
| Some(self as *const Self as *const ()) |
| } else { |
| None |
| } |
| } |
| } |
| |
| impl dyn Subscriber { |
| /// Returns `true` if this `Subscriber` is the same type as `T`. |
| pub fn is<T: Any>(&self) -> bool { |
| self.downcast_ref::<T>().is_some() |
| } |
| |
| /// Returns some reference to this `Subscriber` value if it is of type `T`, |
| /// or `None` if it isn't. |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| unsafe { |
| let raw = self.downcast_raw(TypeId::of::<T>())?; |
| if raw.is_null() { |
| None |
| } else { |
| Some(&*(raw as *const _)) |
| } |
| } |
| } |
| } |
| |
| impl dyn Subscriber + Send { |
| /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
| pub fn is<T: Any>(&self) -> bool { |
| self.downcast_ref::<T>().is_some() |
| } |
| |
| /// Returns some reference to this [`Subscriber`] value if it is of type `T`, |
| /// or `None` if it isn't. |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| unsafe { |
| let raw = self.downcast_raw(TypeId::of::<T>())?; |
| if raw.is_null() { |
| None |
| } else { |
| Some(&*(raw as *const _)) |
| } |
| } |
| } |
| } |
| |
| impl dyn Subscriber + Sync { |
| /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
| pub fn is<T: Any>(&self) -> bool { |
| self.downcast_ref::<T>().is_some() |
| } |
| |
| /// Returns some reference to this `[`Subscriber`] value if it is of type `T`, |
| /// or `None` if it isn't. |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| unsafe { |
| let raw = self.downcast_raw(TypeId::of::<T>())?; |
| if raw.is_null() { |
| None |
| } else { |
| Some(&*(raw as *const _)) |
| } |
| } |
| } |
| } |
| |
| impl dyn Subscriber + Send + Sync { |
| /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
| pub fn is<T: Any>(&self) -> bool { |
| self.downcast_ref::<T>().is_some() |
| } |
| |
| /// Returns some reference to this [`Subscriber`] value if it is of type `T`, |
| /// or `None` if it isn't. |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| unsafe { |
| let raw = self.downcast_raw(TypeId::of::<T>())?; |
| if raw.is_null() { |
| None |
| } else { |
| Some(&*(raw as *const _)) |
| } |
| } |
| } |
| } |
| |
| /// Indicates a [`Subscriber`]'s interest in a particular callsite. |
| /// |
| /// `Subscriber`s return an `Interest` from their [`register_callsite`] methods |
| /// in order to determine whether that span should be enabled or disabled. |
| /// |
| /// [`Subscriber`]: super::Subscriber |
| /// [`register_callsite`]: super::Subscriber::register_callsite |
| #[derive(Clone, Debug)] |
| pub struct Interest(InterestKind); |
| |
| #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)] |
| enum InterestKind { |
| Never = 0, |
| Sometimes = 1, |
| Always = 2, |
| } |
| |
| impl Interest { |
| /// Returns an `Interest` indicating that the subscriber is never interested |
| /// in being notified about a callsite. |
| /// |
| /// If all active subscribers are `never()` interested in a callsite, it will |
| /// be completely disabled unless a new subscriber becomes active. |
| #[inline] |
| pub fn never() -> Self { |
| Interest(InterestKind::Never) |
| } |
| |
| /// Returns an `Interest` indicating the subscriber is sometimes interested |
| /// in being notified about a callsite. |
| /// |
| /// If all active subscribers are `sometimes` or `never` interested in a |
| /// callsite, the currently active subscriber will be asked to filter that |
| /// callsite every time it creates a span. This will be the case until a new |
| /// subscriber expresses that it is `always` interested in the callsite. |
| #[inline] |
| pub fn sometimes() -> Self { |
| Interest(InterestKind::Sometimes) |
| } |
| |
| /// Returns an `Interest` indicating the subscriber is always interested in |
| /// being notified about a callsite. |
| /// |
| /// If any subscriber expresses that it is `always()` interested in a given |
| /// callsite, then the callsite will always be enabled. |
| #[inline] |
| pub fn always() -> Self { |
| Interest(InterestKind::Always) |
| } |
| |
| /// Returns `true` if the subscriber is never interested in being notified |
| /// about this callsite. |
| #[inline] |
| pub fn is_never(&self) -> bool { |
| matches!(self.0, InterestKind::Never) |
| } |
| |
| /// Returns `true` if the subscriber is sometimes interested in being notified |
| /// about this callsite. |
| #[inline] |
| pub fn is_sometimes(&self) -> bool { |
| matches!(self.0, InterestKind::Sometimes) |
| } |
| |
| /// Returns `true` if the subscriber is always interested in being notified |
| /// about this callsite. |
| #[inline] |
| pub fn is_always(&self) -> bool { |
| matches!(self.0, InterestKind::Always) |
| } |
| |
| /// Returns the common interest between these two Interests. |
| /// |
| /// If both interests are the same, this propagates that interest. |
| /// Otherwise, if they differ, the result must always be |
| /// `Interest::sometimes` --- if the two subscribers differ in opinion, we |
| /// will have to ask the current subscriber what it thinks, no matter what. |
| pub(crate) fn and(self, rhs: Interest) -> Self { |
| if self.0 == rhs.0 { |
| self |
| } else { |
| Interest::sometimes() |
| } |
| } |
| } |
| |
| /// A no-op [`Subscriber`]. |
| /// |
| /// [`NoSubscriber`] implements the [`Subscriber`] trait by never being enabled, |
| /// never being interested in any callsite, and dropping all spans and events. |
| #[derive(Copy, Clone, Debug, Default)] |
| pub struct NoSubscriber(()); |
| |
| impl Subscriber for NoSubscriber { |
| #[inline] |
| fn register_callsite(&self, _: &'static Metadata<'static>) -> Interest { |
| Interest::never() |
| } |
| |
| fn new_span(&self, _: &span::Attributes<'_>) -> span::Id { |
| span::Id::from_u64(0xDEAD) |
| } |
| |
| fn event(&self, _event: &Event<'_>) {} |
| |
| fn record(&self, _span: &span::Id, _values: &span::Record<'_>) {} |
| |
| fn record_follows_from(&self, _span: &span::Id, _follows: &span::Id) {} |
| |
| #[inline] |
| fn enabled(&self, _metadata: &Metadata<'_>) -> bool { |
| false |
| } |
| |
| fn enter(&self, _span: &span::Id) {} |
| fn exit(&self, _span: &span::Id) {} |
| } |
| |
| impl NoSubscriber { |
| /// Returns a new `NoSubscriber`. |
| #[must_use] |
| pub const fn new() -> Self { |
| Self(()) |
| } |
| } |
| |
| impl<S> Subscriber for Box<S> |
| where |
| S: Subscriber + ?Sized, |
| { |
| #[inline] |
| fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
| self.as_ref().register_callsite(metadata) |
| } |
| |
| #[inline] |
| fn enabled(&self, metadata: &Metadata<'_>) -> bool { |
| self.as_ref().enabled(metadata) |
| } |
| |
| #[inline] |
| fn max_level_hint(&self) -> Option<LevelFilter> { |
| self.as_ref().max_level_hint() |
| } |
| |
| #[inline] |
| fn new_span(&self, span: &span::Attributes<'_>) -> span::Id { |
| self.as_ref().new_span(span) |
| } |
| |
| #[inline] |
| fn record(&self, span: &span::Id, values: &span::Record<'_>) { |
| self.as_ref().record(span, values) |
| } |
| |
| #[inline] |
| fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { |
| self.as_ref().record_follows_from(span, follows) |
| } |
| |
| #[inline] |
| fn event_enabled(&self, event: &Event<'_>) -> bool { |
| self.as_ref().event_enabled(event) |
| } |
| |
| #[inline] |
| fn event(&self, event: &Event<'_>) { |
| self.as_ref().event(event) |
| } |
| |
| #[inline] |
| fn enter(&self, span: &span::Id) { |
| self.as_ref().enter(span) |
| } |
| |
| #[inline] |
| fn exit(&self, span: &span::Id) { |
| self.as_ref().exit(span) |
| } |
| |
| #[inline] |
| fn clone_span(&self, id: &span::Id) -> span::Id { |
| self.as_ref().clone_span(id) |
| } |
| |
| #[inline] |
| fn try_close(&self, id: span::Id) -> bool { |
| self.as_ref().try_close(id) |
| } |
| |
| #[inline] |
| #[allow(deprecated)] |
| fn drop_span(&self, id: span::Id) { |
| self.as_ref().try_close(id); |
| } |
| |
| #[inline] |
| fn current_span(&self) -> span::Current { |
| self.as_ref().current_span() |
| } |
| |
| #[inline] |
| unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
| if id == TypeId::of::<Self>() { |
| return Some(self as *const Self as *const _); |
| } |
| |
| self.as_ref().downcast_raw(id) |
| } |
| } |
| |
| impl<S> Subscriber for Arc<S> |
| where |
| S: Subscriber + ?Sized, |
| { |
| #[inline] |
| fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
| self.as_ref().register_callsite(metadata) |
| } |
| |
| #[inline] |
| fn enabled(&self, metadata: &Metadata<'_>) -> bool { |
| self.as_ref().enabled(metadata) |
| } |
| |
| #[inline] |
| fn max_level_hint(&self) -> Option<LevelFilter> { |
| self.as_ref().max_level_hint() |
| } |
| |
| #[inline] |
| fn new_span(&self, span: &span::Attributes<'_>) -> span::Id { |
| self.as_ref().new_span(span) |
| } |
| |
| #[inline] |
| fn record(&self, span: &span::Id, values: &span::Record<'_>) { |
| self.as_ref().record(span, values) |
| } |
| |
| #[inline] |
| fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { |
| self.as_ref().record_follows_from(span, follows) |
| } |
| |
| #[inline] |
| fn event_enabled(&self, event: &Event<'_>) -> bool { |
| self.as_ref().event_enabled(event) |
| } |
| |
| #[inline] |
| fn event(&self, event: &Event<'_>) { |
| self.as_ref().event(event) |
| } |
| |
| #[inline] |
| fn enter(&self, span: &span::Id) { |
| self.as_ref().enter(span) |
| } |
| |
| #[inline] |
| fn exit(&self, span: &span::Id) { |
| self.as_ref().exit(span) |
| } |
| |
| #[inline] |
| fn clone_span(&self, id: &span::Id) -> span::Id { |
| self.as_ref().clone_span(id) |
| } |
| |
| #[inline] |
| fn try_close(&self, id: span::Id) -> bool { |
| self.as_ref().try_close(id) |
| } |
| |
| #[inline] |
| #[allow(deprecated)] |
| fn drop_span(&self, id: span::Id) { |
| self.as_ref().try_close(id); |
| } |
| |
| #[inline] |
| fn current_span(&self) -> span::Current { |
| self.as_ref().current_span() |
| } |
| |
| #[inline] |
| unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
| if id == TypeId::of::<Self>() { |
| return Some(self as *const Self as *const _); |
| } |
| |
| self.as_ref().downcast_raw(id) |
| } |
| } |