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diff --git a/src/subscriber.rs b/src/subscriber.rs new file mode 100644 index 0000000..e8f4441 --- /dev/null +++ b/src/subscriber.rs @@ -0,0 +1,870 @@ +//! 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<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) + } +} |