1 | //! Collectors collect and record trace data. |
2 | use crate::{span, Dispatch, Event, LevelFilter, Metadata}; |
3 | |
4 | use crate::stdlib::{ |
5 | any::{Any, TypeId}, |
6 | boxed::Box, |
7 | sync::Arc, |
8 | }; |
9 | |
10 | /// Trait representing the functions required to collect trace data. |
11 | /// |
12 | /// Crates that provide implementations of methods for collecting or recording |
13 | /// trace data should implement the `Subscriber` interface. This trait is |
14 | /// intended to represent fundamental primitives for collecting trace events and |
15 | /// spans — other libraries may offer utility functions and types to make |
16 | /// subscriber implementations more modular or improve the ergonomics of writing |
17 | /// subscribers. |
18 | /// |
19 | /// A subscriber is responsible for the following: |
20 | /// - Registering new spans as they are created, and providing them with span |
21 | /// IDs. Implicitly, this means the subscriber may determine the strategy for |
22 | /// determining span equality. |
23 | /// - Recording the attachment of field values and follows-from annotations to |
24 | /// spans. |
25 | /// - Filtering spans and events, and determining when those filters must be |
26 | /// invalidated. |
27 | /// - Observing spans as they are entered, exited, and closed, and events as |
28 | /// they occur. |
29 | /// |
30 | /// When a span is entered or exited, the subscriber is provided only with the |
31 | /// [ID] with which it tagged that span when it was created. This means |
32 | /// that it is up to the subscriber to determine whether and how span _data_ — |
33 | /// the fields and metadata describing the span — should be stored. The |
34 | /// [`new_span`] function is called when a new span is created, and at that |
35 | /// point, the subscriber _may_ choose to store the associated data if it will |
36 | /// be referenced again. However, if the data has already been recorded and will |
37 | /// not be needed by the implementations of `enter` and `exit`, the subscriber |
38 | /// may freely discard that data without allocating space to store it. |
39 | /// |
40 | /// ## Overriding default impls |
41 | /// |
42 | /// Some trait methods on `Subscriber` have default implementations, either in |
43 | /// order to reduce the surface area of implementing `Subscriber`, or for |
44 | /// backward-compatibility reasons. However, many subscribers will likely want |
45 | /// to override these default implementations. |
46 | /// |
47 | /// The following methods are likely of interest: |
48 | /// |
49 | /// - [`register_callsite`] is called once for each callsite from which a span |
50 | /// event may originate, and returns an [`Interest`] value describing whether or |
51 | /// not the subscriber wishes to see events or spans from that callsite. By |
52 | /// default, it calls [`enabled`], and returns `Interest::always()` if |
53 | /// `enabled` returns true, or `Interest::never()` if enabled returns false. |
54 | /// However, if the subscriber's interest can change dynamically at runtime, |
55 | /// it may want to override this function to return `Interest::sometimes()`. |
56 | /// Additionally, subscribers which wish to perform a behaviour once for each |
57 | /// callsite, such as allocating storage for data related to that callsite, |
58 | /// can perform it in `register_callsite`. |
59 | /// |
60 | /// See also the [documentation on the callsite registry][cs-reg] for details |
61 | /// on [`register_callsite`]. |
62 | /// |
63 | /// - [`event_enabled`] is called once before every call to the [`event`] |
64 | /// method. This can be used to implement filtering on events once their field |
65 | /// values are known, but before any processing is done in the `event` method. |
66 | /// - [`clone_span`] is called every time a span ID is cloned, and [`try_close`] |
67 | /// is called when a span ID is dropped. By default, these functions do |
68 | /// nothing. However, they can be used to implement reference counting for |
69 | /// spans, allowing subscribers to free storage for span data and to determine |
70 | /// when a span has _closed_ permanently (rather than being exited). |
71 | /// Subscribers which store per-span data or which need to track span closures |
72 | /// should override these functions together. |
73 | /// |
74 | /// [ID]: super::span::Id |
75 | /// [`new_span`]: Subscriber::new_span |
76 | /// [`register_callsite`]: Subscriber::register_callsite |
77 | /// [`enabled`]: Subscriber::enabled |
78 | /// [`clone_span`]: Subscriber::clone_span |
79 | /// [`try_close`]: Subscriber::try_close |
80 | /// [cs-reg]: crate::callsite#registering-callsites |
81 | /// [`event`]: Subscriber::event |
82 | /// [`event_enabled`]: Subscriber::event_enabled |
83 | pub trait Subscriber: 'static { |
84 | /// Invoked when this subscriber becomes a [`Dispatch`]. |
85 | /// |
86 | /// ## Avoiding Memory Leaks |
87 | /// |
88 | /// `Subscriber`s should not store their own [`Dispatch`]. Because the |
89 | /// `Dispatch` owns the `Subscriber`, storing the `Dispatch` within the |
90 | /// `Subscriber` will create a reference count cycle, preventing the `Dispatch` |
91 | /// from ever being dropped. |
92 | /// |
93 | /// Instead, when it is necessary to store a cyclical reference to the |
94 | /// `Dispatch` within a `Subscriber`, use [`Dispatch::downgrade`] to convert a |
95 | /// `Dispatch` into a [`WeakDispatch`]. This type is analogous to |
96 | /// [`std::sync::Weak`], and does not create a reference count cycle. A |
97 | /// [`WeakDispatch`] can be stored within a `Subscriber` without causing a |
98 | /// memory leak, and can be [upgraded] into a `Dispatch` temporarily when |
99 | /// the `Dispatch` must be accessed by the `Subscriber`. |
100 | /// |
101 | /// [`WeakDispatch`]: crate::dispatcher::WeakDispatch |
102 | /// [upgraded]: crate::dispatcher::WeakDispatch::upgrade |
103 | fn on_register_dispatch(&self, subscriber: &Dispatch) { |
104 | let _ = subscriber; |
105 | } |
106 | |
107 | /// Registers a new [callsite] with this subscriber, returning whether or not |
108 | /// the subscriber is interested in being notified about the callsite. |
109 | /// |
110 | /// By default, this function assumes that the subscriber's [filter] |
111 | /// represents an unchanging view of its interest in the callsite. However, |
112 | /// if this is not the case, subscribers may override this function to |
113 | /// indicate different interests, or to implement behaviour that should run |
114 | /// once for every callsite. |
115 | /// |
116 | /// This function is guaranteed to be called at least once per callsite on |
117 | /// every active subscriber. The subscriber may store the keys to fields it |
118 | /// cares about in order to reduce the cost of accessing fields by name, |
119 | /// preallocate storage for that callsite, or perform any other actions it |
120 | /// wishes to perform once for each callsite. |
121 | /// |
122 | /// The subscriber should then return an [`Interest`], indicating |
123 | /// whether it is interested in being notified about that callsite in the |
124 | /// future. This may be `Always` indicating that the subscriber always |
125 | /// wishes to be notified about the callsite, and its filter need not be |
126 | /// re-evaluated; `Sometimes`, indicating that the subscriber may sometimes |
127 | /// care about the callsite but not always (such as when sampling), or |
128 | /// `Never`, indicating that the subscriber never wishes to be notified about |
129 | /// that callsite. If all active subscribers return `Never`, a callsite will |
130 | /// never be enabled unless a new subscriber expresses interest in it. |
131 | /// |
132 | /// `Subscriber`s which require their filters to be run every time an event |
133 | /// occurs or a span is entered/exited should return `Interest::sometimes`. |
134 | /// If a subscriber returns `Interest::sometimes`, then its [`enabled`] method |
135 | /// will be called every time an event or span is created from that callsite. |
136 | /// |
137 | /// For example, suppose a sampling subscriber is implemented by |
138 | /// incrementing a counter every time `enabled` is called and only returning |
139 | /// `true` when the counter is divisible by a specified sampling rate. If |
140 | /// that subscriber returns `Interest::always` from `register_callsite`, then |
141 | /// the filter will not be re-evaluated once it has been applied to a given |
142 | /// set of metadata. Thus, the counter will not be incremented, and the span |
143 | /// or event that corresponds to the metadata will never be `enabled`. |
144 | /// |
145 | /// `Subscriber`s that need to change their filters occasionally should call |
146 | /// [`rebuild_interest_cache`] to re-evaluate `register_callsite` for all |
147 | /// callsites. |
148 | /// |
149 | /// Similarly, if a `Subscriber` has a filtering strategy that can be |
150 | /// changed dynamically at runtime, it would need to re-evaluate that filter |
151 | /// if the cached results have changed. |
152 | /// |
153 | /// A subscriber which manages fanout to multiple other subscribers |
154 | /// should proxy this decision to all of its child subscribers, |
155 | /// returning `Interest::never` only if _all_ such children return |
156 | /// `Interest::never`. If the set of subscribers to which spans are |
157 | /// broadcast may change dynamically, the subscriber should also never |
158 | /// return `Interest::Never`, as a new subscriber may be added that _is_ |
159 | /// interested. |
160 | /// |
161 | /// See the [documentation on the callsite registry][cs-reg] for more |
162 | /// details on how and when the `register_callsite` method is called. |
163 | /// |
164 | /// # Notes |
165 | /// This function may be called again when a new subscriber is created or |
166 | /// when the registry is invalidated. |
167 | /// |
168 | /// If a subscriber returns `Interest::never` for a particular callsite, it |
169 | /// _may_ still see spans and events originating from that callsite, if |
170 | /// another subscriber expressed interest in it. |
171 | /// |
172 | /// [callsite]: crate::callsite |
173 | /// [filter]: Self::enabled |
174 | /// [metadata]: super::metadata::Metadata |
175 | /// [`enabled`]: Subscriber::enabled() |
176 | /// [`rebuild_interest_cache`]: super::callsite::rebuild_interest_cache |
177 | /// [cs-reg]: crate::callsite#registering-callsites |
178 | fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
179 | if self.enabled(metadata) { |
180 | Interest::always() |
181 | } else { |
182 | Interest::never() |
183 | } |
184 | } |
185 | |
186 | /// Returns true if a span or event with the specified [metadata] would be |
187 | /// recorded. |
188 | /// |
189 | /// By default, it is assumed that this filter needs only be evaluated once |
190 | /// for each callsite, so it is called by [`register_callsite`] when each |
191 | /// callsite is registered. The result is used to determine if the subscriber |
192 | /// is always [interested] or never interested in that callsite. This is intended |
193 | /// primarily as an optimization, so that expensive filters (such as those |
194 | /// involving string search, et cetera) need not be re-evaluated. |
195 | /// |
196 | /// However, if the subscriber's interest in a particular span or event may |
197 | /// change, or depends on contexts only determined dynamically at runtime, |
198 | /// then the `register_callsite` method should be overridden to return |
199 | /// [`Interest::sometimes`]. In that case, this function will be called every |
200 | /// time that span or event occurs. |
201 | /// |
202 | /// [metadata]: super::metadata::Metadata |
203 | /// [interested]: Interest |
204 | /// [`Interest::sometimes`]: Interest::sometimes |
205 | /// [`register_callsite`]: Subscriber::register_callsite() |
206 | fn enabled(&self, metadata: &Metadata<'_>) -> bool; |
207 | |
208 | /// Returns the highest [verbosity level][level] that this `Subscriber` will |
209 | /// enable, or `None`, if the subscriber does not implement level-based |
210 | /// filtering or chooses not to implement this method. |
211 | /// |
212 | /// If this method returns a [`Level`][level], it will be used as a hint to |
213 | /// determine the most verbose level that will be enabled. This will allow |
214 | /// spans and events which are more verbose than that level to be skipped |
215 | /// more efficiently. Subscribers which perform filtering are strongly |
216 | /// encouraged to provide an implementation of this method. |
217 | /// |
218 | /// If the maximum level the subscriber will enable can change over the |
219 | /// course of its lifetime, it is free to return a different value from |
220 | /// multiple invocations of this method. However, note that changes in the |
221 | /// maximum level will **only** be reflected after the callsite [`Interest`] |
222 | /// cache is rebuilt, by calling the [`callsite::rebuild_interest_cache`][rebuild] |
223 | /// function. Therefore, if the subscriber will change the value returned by |
224 | /// this method, it is responsible for ensuring that |
225 | /// [`rebuild_interest_cache`][rebuild] is called after the value of the max |
226 | /// level changes. |
227 | /// |
228 | /// [level]: super::Level |
229 | /// [rebuild]: super::callsite::rebuild_interest_cache |
230 | fn max_level_hint(&self) -> Option<LevelFilter> { |
231 | None |
232 | } |
233 | |
234 | /// Visit the construction of a new span, returning a new [span ID] for the |
235 | /// span being constructed. |
236 | /// |
237 | /// The provided [`Attributes`] contains any field values that were provided |
238 | /// when the span was created. The subscriber may pass a [visitor] to the |
239 | /// `Attributes`' [`record` method] to record these values. |
240 | /// |
241 | /// IDs are used to uniquely identify spans and events within the context of a |
242 | /// subscriber, so span equality will be based on the returned ID. Thus, if |
243 | /// the subscriber wishes for all spans with the same metadata to be |
244 | /// considered equal, it should return the same ID every time it is given a |
245 | /// particular set of metadata. Similarly, if it wishes for two separate |
246 | /// instances of a span with the same metadata to *not* be equal, it should |
247 | /// return a distinct ID every time this function is called, regardless of |
248 | /// the metadata. |
249 | /// |
250 | /// Note that the subscriber is free to assign span IDs based on whatever |
251 | /// scheme it sees fit. Any guarantees about uniqueness, ordering, or ID |
252 | /// reuse are left up to the subscriber implementation to determine. |
253 | /// |
254 | /// [span ID]: super::span::Id |
255 | /// [`Attributes`]: super::span::Attributes |
256 | /// [visitor]: super::field::Visit |
257 | /// [`record` method]: super::span::Attributes::record |
258 | fn new_span(&self, span: &span::Attributes<'_>) -> span::Id; |
259 | |
260 | // === Notification methods =============================================== |
261 | |
262 | /// Record a set of values on a span. |
263 | /// |
264 | /// This method will be invoked when value is recorded on a span. |
265 | /// Recording multiple values for the same field is possible, |
266 | /// but the actual behaviour is defined by the subscriber implementation. |
267 | /// |
268 | /// Keep in mind that a span might not provide a value |
269 | /// for each field it declares. |
270 | /// |
271 | /// The subscriber is expected to provide a [visitor] to the `Record`'s |
272 | /// [`record` method] in order to record the added values. |
273 | /// |
274 | /// # Example |
275 | /// "foo = 3" will be recorded when [`record`] is called on the |
276 | /// `Attributes` passed to `new_span`. |
277 | /// Since values are not provided for the `bar` and `baz` fields, |
278 | /// the span's `Metadata` will indicate that it _has_ those fields, |
279 | /// but values for them won't be recorded at this time. |
280 | /// |
281 | /// ```rust,ignore |
282 | /// # use tracing::span; |
283 | /// |
284 | /// let mut span = span!("my_span" , foo = 3, bar, baz); |
285 | /// |
286 | /// // `Subscriber::record` will be called with a `Record` |
287 | /// // containing "bar = false" |
288 | /// span.record("bar" , &false); |
289 | /// |
290 | /// // `Subscriber::record` will be called with a `Record` |
291 | /// // containing "baz = "a string"" |
292 | /// span.record("baz" , &"a string" ); |
293 | /// ``` |
294 | /// |
295 | /// [visitor]: super::field::Visit |
296 | /// [`record`]: super::span::Attributes::record |
297 | /// [`record` method]: super::span::Record::record |
298 | fn record(&self, span: &span::Id, values: &span::Record<'_>); |
299 | |
300 | /// Adds an indication that `span` follows from the span with the id |
301 | /// `follows`. |
302 | /// |
303 | /// This relationship differs somewhat from the parent-child relationship: a |
304 | /// span may have any number of prior spans, rather than a single one; and |
305 | /// spans are not considered to be executing _inside_ of the spans they |
306 | /// follow from. This means that a span may close even if subsequent spans |
307 | /// that follow from it are still open, and time spent inside of a |
308 | /// subsequent span should not be included in the time its precedents were |
309 | /// executing. This is used to model causal relationships such as when a |
310 | /// single future spawns several related background tasks, et cetera. |
311 | /// |
312 | /// If the subscriber has spans corresponding to the given IDs, it should |
313 | /// record this relationship in whatever way it deems necessary. Otherwise, |
314 | /// if one or both of the given span IDs do not correspond to spans that the |
315 | /// subscriber knows about, or if a cyclical relationship would be created |
316 | /// (i.e., some span _a_ which proceeds some other span _b_ may not also |
317 | /// follow from _b_), it may silently do nothing. |
318 | fn record_follows_from(&self, span: &span::Id, follows: &span::Id); |
319 | |
320 | /// Determine if an [`Event`] should be recorded. |
321 | /// |
322 | /// By default, this returns `true` and `Subscriber`s can filter events in |
323 | /// [`event`][Self::event] without any penalty. However, when `event` is |
324 | /// more complicated, this can be used to determine if `event` should be |
325 | /// called at all, separating out the decision from the processing. |
326 | fn event_enabled(&self, event: &Event<'_>) -> bool { |
327 | let _ = event; |
328 | true |
329 | } |
330 | |
331 | /// Records that an [`Event`] has occurred. |
332 | /// |
333 | /// This method will be invoked when an Event is constructed by |
334 | /// the `Event`'s [`dispatch` method]. For example, this happens internally |
335 | /// when an event macro from `tracing` is called. |
336 | /// |
337 | /// The key difference between this method and `record` is that `record` is |
338 | /// called when a value is recorded for a field defined by a span, |
339 | /// while `event` is called when a new event occurs. |
340 | /// |
341 | /// The provided `Event` struct contains any field values attached to the |
342 | /// event. The subscriber may pass a [visitor] to the `Event`'s |
343 | /// [`record` method] to record these values. |
344 | /// |
345 | /// [`Event`]: super::event::Event |
346 | /// [visitor]: super::field::Visit |
347 | /// [`record` method]: super::event::Event::record |
348 | /// [`dispatch` method]: super::event::Event::dispatch |
349 | fn event(&self, event: &Event<'_>); |
350 | |
351 | /// Records that a span has been entered. |
352 | /// |
353 | /// When entering a span, this method is called to notify the subscriber |
354 | /// that the span has been entered. The subscriber is provided with the |
355 | /// [span ID] of the entered span, and should update any internal state |
356 | /// tracking the current span accordingly. |
357 | /// |
358 | /// [span ID]: super::span::Id |
359 | fn enter(&self, span: &span::Id); |
360 | |
361 | /// Records that a span has been exited. |
362 | /// |
363 | /// When exiting a span, this method is called to notify the subscriber |
364 | /// that the span has been exited. The subscriber is provided with the |
365 | /// [span ID] of the exited span, and should update any internal state |
366 | /// tracking the current span accordingly. |
367 | /// |
368 | /// Exiting a span does not imply that the span will not be re-entered. |
369 | /// |
370 | /// [span ID]: super::span::Id |
371 | fn exit(&self, span: &span::Id); |
372 | |
373 | /// Notifies the subscriber that a [span ID] has been cloned. |
374 | /// |
375 | /// This function is guaranteed to only be called with span IDs that were |
376 | /// returned by this subscriber's `new_span` function. |
377 | /// |
378 | /// Note that the default implementation of this function this is just the |
379 | /// identity function, passing through the identifier. However, it can be |
380 | /// used in conjunction with [`try_close`] to track the number of handles |
381 | /// capable of `enter`ing a span. When all the handles have been dropped |
382 | /// (i.e., `try_close` has been called one more time than `clone_span` for a |
383 | /// given ID), the subscriber may assume that the span will not be entered |
384 | /// again. It is then free to deallocate storage for data associated with |
385 | /// that span, write data from that span to IO, and so on. |
386 | /// |
387 | /// For more unsafe situations, however, if `id` is itself a pointer of some |
388 | /// kind this can be used as a hook to "clone" the pointer, depending on |
389 | /// what that means for the specified pointer. |
390 | /// |
391 | /// [span ID]: super::span::Id |
392 | /// [`try_close`]: Subscriber::try_close |
393 | fn clone_span(&self, id: &span::Id) -> span::Id { |
394 | id.clone() |
395 | } |
396 | |
397 | /// **This method is deprecated.** |
398 | /// |
399 | /// Using `drop_span` may result in subscribers composed using |
400 | /// `tracing-subscriber` crate's `Layer` trait from observing close events. |
401 | /// Use [`try_close`] instead. |
402 | /// |
403 | /// The default implementation of this function does nothing. |
404 | /// |
405 | /// [`try_close`]: Subscriber::try_close |
406 | #[deprecated (since = "0.1.2" , note = "use `Subscriber::try_close` instead" )] |
407 | fn drop_span(&self, _id: span::Id) {} |
408 | |
409 | /// Notifies the subscriber that a [span ID] has been dropped, and returns |
410 | /// `true` if there are now 0 IDs that refer to that span. |
411 | /// |
412 | /// Higher-level libraries providing functionality for composing multiple |
413 | /// subscriber implementations may use this return value to notify any |
414 | /// "layered" subscribers that this subscriber considers the span closed. |
415 | /// |
416 | /// The default implementation of this method calls the subscriber's |
417 | /// [`drop_span`] method and returns `false`. This means that, unless the |
418 | /// subscriber overrides the default implementation, close notifications |
419 | /// will never be sent to any layered subscribers. In general, if the |
420 | /// subscriber tracks reference counts, this method should be implemented, |
421 | /// rather than `drop_span`. |
422 | /// |
423 | /// This function is guaranteed to only be called with span IDs that were |
424 | /// returned by this subscriber's `new_span` function. |
425 | /// |
426 | /// It's guaranteed that if this function has been called once more than the |
427 | /// number of times `clone_span` was called with the same `id`, then no more |
428 | /// handles that can enter the span with that `id` exist. This means that it |
429 | /// can be used in conjunction with [`clone_span`] to track the number of |
430 | /// handles capable of `enter`ing a span. When all the handles have been |
431 | /// dropped (i.e., `try_close` has been called one more time than |
432 | /// `clone_span` for a given ID), the subscriber may assume that the span |
433 | /// will not be entered again, and should return `true`. It is then free to |
434 | /// deallocate storage for data associated with that span, write data from |
435 | /// that span to IO, and so on. |
436 | /// |
437 | /// **Note**: since this function is called when spans are dropped, |
438 | /// implementations should ensure that they are unwind-safe. Panicking from |
439 | /// inside of a `try_close` function may cause a double panic, if the span |
440 | /// was dropped due to a thread unwinding. |
441 | /// |
442 | /// [span ID]: super::span::Id |
443 | /// [`clone_span`]: Subscriber::clone_span |
444 | /// [`drop_span`]: Subscriber::drop_span |
445 | fn try_close(&self, id: span::Id) -> bool { |
446 | #[allow (deprecated)] |
447 | self.drop_span(id); |
448 | false |
449 | } |
450 | |
451 | /// Returns a type representing this subscriber's view of the current span. |
452 | /// |
453 | /// If subscribers track a current span, they should override this function |
454 | /// to return [`Current::new`] if the thread from which this method is |
455 | /// called is inside a span, or [`Current::none`] if the thread is not |
456 | /// inside a span. |
457 | /// |
458 | /// By default, this returns a value indicating that the subscriber |
459 | /// does **not** track what span is current. If the subscriber does not |
460 | /// implement a current span, it should not override this method. |
461 | /// |
462 | /// [`Current::new`]: super::span::Current#tymethod.new |
463 | /// [`Current::none`]: super::span::Current#tymethod.none |
464 | fn current_span(&self) -> span::Current { |
465 | span::Current::unknown() |
466 | } |
467 | |
468 | // === Downcasting methods ================================================ |
469 | |
470 | /// If `self` is the same type as the provided `TypeId`, returns an untyped |
471 | /// `*const` pointer to that type. Otherwise, returns `None`. |
472 | /// |
473 | /// If you wish to downcast a `Subscriber`, it is strongly advised to use |
474 | /// the safe API provided by [`downcast_ref`] instead. |
475 | /// |
476 | /// This API is required for `downcast_raw` to be a trait method; a method |
477 | /// signature like [`downcast_ref`] (with a generic type parameter) is not |
478 | /// object-safe, and thus cannot be a trait method for `Subscriber`. This |
479 | /// means that if we only exposed `downcast_ref`, `Subscriber` |
480 | /// implementations could not override the downcasting behavior |
481 | /// |
482 | /// This method may be overridden by "fan out" or "chained" subscriber |
483 | /// implementations which consist of multiple composed types. Such |
484 | /// subscribers might allow `downcast_raw` by returning references to those |
485 | /// component if they contain components with the given `TypeId`. |
486 | /// |
487 | /// # Safety |
488 | /// |
489 | /// The [`downcast_ref`] method expects that the pointer returned by |
490 | /// `downcast_raw` is non-null and points to a valid instance of the type |
491 | /// with the provided `TypeId`. Failure to ensure this will result in |
492 | /// undefined behaviour, so implementing `downcast_raw` is unsafe. |
493 | /// |
494 | /// [`downcast_ref`]: #method.downcast_ref |
495 | unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
496 | if id == TypeId::of::<Self>() { |
497 | Some(self as *const Self as *const ()) |
498 | } else { |
499 | None |
500 | } |
501 | } |
502 | } |
503 | |
504 | impl dyn Subscriber { |
505 | /// Returns `true` if this `Subscriber` is the same type as `T`. |
506 | pub fn is<T: Any>(&self) -> bool { |
507 | self.downcast_ref::<T>().is_some() |
508 | } |
509 | |
510 | /// Returns some reference to this `Subscriber` value if it is of type `T`, |
511 | /// or `None` if it isn't. |
512 | pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
513 | unsafe { |
514 | let raw: *const () = self.downcast_raw(id:TypeId::of::<T>())?; |
515 | if raw.is_null() { |
516 | None |
517 | } else { |
518 | Some(&*(raw as *const _)) |
519 | } |
520 | } |
521 | } |
522 | } |
523 | |
524 | impl dyn Subscriber + Send { |
525 | /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
526 | pub fn is<T: Any>(&self) -> bool { |
527 | self.downcast_ref::<T>().is_some() |
528 | } |
529 | |
530 | /// Returns some reference to this [`Subscriber`] value if it is of type `T`, |
531 | /// or `None` if it isn't. |
532 | pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
533 | unsafe { |
534 | let raw: *const () = self.downcast_raw(id:TypeId::of::<T>())?; |
535 | if raw.is_null() { |
536 | None |
537 | } else { |
538 | Some(&*(raw as *const _)) |
539 | } |
540 | } |
541 | } |
542 | } |
543 | |
544 | impl dyn Subscriber + Sync { |
545 | /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
546 | pub fn is<T: Any>(&self) -> bool { |
547 | self.downcast_ref::<T>().is_some() |
548 | } |
549 | |
550 | /// Returns some reference to this `[`Subscriber`] value if it is of type `T`, |
551 | /// or `None` if it isn't. |
552 | pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
553 | unsafe { |
554 | let raw: *const () = self.downcast_raw(id:TypeId::of::<T>())?; |
555 | if raw.is_null() { |
556 | None |
557 | } else { |
558 | Some(&*(raw as *const _)) |
559 | } |
560 | } |
561 | } |
562 | } |
563 | |
564 | impl dyn Subscriber + Send + Sync { |
565 | /// Returns `true` if this [`Subscriber`] is the same type as `T`. |
566 | pub fn is<T: Any>(&self) -> bool { |
567 | self.downcast_ref::<T>().is_some() |
568 | } |
569 | |
570 | /// Returns some reference to this [`Subscriber`] value if it is of type `T`, |
571 | /// or `None` if it isn't. |
572 | pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
573 | unsafe { |
574 | let raw: *const () = self.downcast_raw(id:TypeId::of::<T>())?; |
575 | if raw.is_null() { |
576 | None |
577 | } else { |
578 | Some(&*(raw as *const _)) |
579 | } |
580 | } |
581 | } |
582 | } |
583 | |
584 | /// Indicates a [`Subscriber`]'s interest in a particular callsite. |
585 | /// |
586 | /// `Subscriber`s return an `Interest` from their [`register_callsite`] methods |
587 | /// in order to determine whether that span should be enabled or disabled. |
588 | /// |
589 | /// [`Subscriber`]: super::Subscriber |
590 | /// [`register_callsite`]: super::Subscriber::register_callsite |
591 | #[derive (Clone, Debug)] |
592 | pub struct Interest(InterestKind); |
593 | |
594 | #[derive (Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)] |
595 | enum InterestKind { |
596 | Never = 0, |
597 | Sometimes = 1, |
598 | Always = 2, |
599 | } |
600 | |
601 | impl Interest { |
602 | /// Returns an `Interest` indicating that the subscriber is never interested |
603 | /// in being notified about a callsite. |
604 | /// |
605 | /// If all active subscribers are `never()` interested in a callsite, it will |
606 | /// be completely disabled unless a new subscriber becomes active. |
607 | #[inline ] |
608 | pub fn never() -> Self { |
609 | Interest(InterestKind::Never) |
610 | } |
611 | |
612 | /// Returns an `Interest` indicating the subscriber is sometimes interested |
613 | /// in being notified about a callsite. |
614 | /// |
615 | /// If all active subscribers are `sometimes` or `never` interested in a |
616 | /// callsite, the currently active subscriber will be asked to filter that |
617 | /// callsite every time it creates a span. This will be the case until a new |
618 | /// subscriber expresses that it is `always` interested in the callsite. |
619 | #[inline ] |
620 | pub fn sometimes() -> Self { |
621 | Interest(InterestKind::Sometimes) |
622 | } |
623 | |
624 | /// Returns an `Interest` indicating the subscriber is always interested in |
625 | /// being notified about a callsite. |
626 | /// |
627 | /// If any subscriber expresses that it is `always()` interested in a given |
628 | /// callsite, then the callsite will always be enabled. |
629 | #[inline ] |
630 | pub fn always() -> Self { |
631 | Interest(InterestKind::Always) |
632 | } |
633 | |
634 | /// Returns `true` if the subscriber is never interested in being notified |
635 | /// about this callsite. |
636 | #[inline ] |
637 | pub fn is_never(&self) -> bool { |
638 | matches!(self.0, InterestKind::Never) |
639 | } |
640 | |
641 | /// Returns `true` if the subscriber is sometimes interested in being notified |
642 | /// about this callsite. |
643 | #[inline ] |
644 | pub fn is_sometimes(&self) -> bool { |
645 | matches!(self.0, InterestKind::Sometimes) |
646 | } |
647 | |
648 | /// Returns `true` if the subscriber is always interested in being notified |
649 | /// about this callsite. |
650 | #[inline ] |
651 | pub fn is_always(&self) -> bool { |
652 | matches!(self.0, InterestKind::Always) |
653 | } |
654 | |
655 | /// Returns the common interest between these two Interests. |
656 | /// |
657 | /// If both interests are the same, this propagates that interest. |
658 | /// Otherwise, if they differ, the result must always be |
659 | /// `Interest::sometimes` --- if the two subscribers differ in opinion, we |
660 | /// will have to ask the current subscriber what it thinks, no matter what. |
661 | pub(crate) fn and(self, rhs: Interest) -> Self { |
662 | if self.0 == rhs.0 { |
663 | self |
664 | } else { |
665 | Interest::sometimes() |
666 | } |
667 | } |
668 | } |
669 | |
670 | /// A no-op [`Subscriber`]. |
671 | /// |
672 | /// [`NoSubscriber`] implements the [`Subscriber`] trait by never being enabled, |
673 | /// never being interested in any callsite, and dropping all spans and events. |
674 | #[derive (Copy, Clone, Debug, Default)] |
675 | pub struct NoSubscriber(()); |
676 | |
677 | impl Subscriber for NoSubscriber { |
678 | #[inline ] |
679 | fn register_callsite(&self, _: &'static Metadata<'static>) -> Interest { |
680 | Interest::never() |
681 | } |
682 | |
683 | fn new_span(&self, _: &span::Attributes<'_>) -> span::Id { |
684 | span::Id::from_u64(0xDEAD) |
685 | } |
686 | |
687 | fn event(&self, _event: &Event<'_>) {} |
688 | |
689 | fn record(&self, _span: &span::Id, _values: &span::Record<'_>) {} |
690 | |
691 | fn record_follows_from(&self, _span: &span::Id, _follows: &span::Id) {} |
692 | |
693 | #[inline ] |
694 | fn enabled(&self, _metadata: &Metadata<'_>) -> bool { |
695 | false |
696 | } |
697 | |
698 | fn enter(&self, _span: &span::Id) {} |
699 | fn exit(&self, _span: &span::Id) {} |
700 | } |
701 | |
702 | impl<S> Subscriber for Box<S> |
703 | where |
704 | S: Subscriber + ?Sized, |
705 | { |
706 | #[inline ] |
707 | fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
708 | self.as_ref().register_callsite(metadata) |
709 | } |
710 | |
711 | #[inline ] |
712 | fn enabled(&self, metadata: &Metadata<'_>) -> bool { |
713 | self.as_ref().enabled(metadata) |
714 | } |
715 | |
716 | #[inline ] |
717 | fn max_level_hint(&self) -> Option<LevelFilter> { |
718 | self.as_ref().max_level_hint() |
719 | } |
720 | |
721 | #[inline ] |
722 | fn new_span(&self, span: &span::Attributes<'_>) -> span::Id { |
723 | self.as_ref().new_span(span) |
724 | } |
725 | |
726 | #[inline ] |
727 | fn record(&self, span: &span::Id, values: &span::Record<'_>) { |
728 | self.as_ref().record(span, values) |
729 | } |
730 | |
731 | #[inline ] |
732 | fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { |
733 | self.as_ref().record_follows_from(span, follows) |
734 | } |
735 | |
736 | #[inline ] |
737 | fn event_enabled(&self, event: &Event<'_>) -> bool { |
738 | self.as_ref().event_enabled(event) |
739 | } |
740 | |
741 | #[inline ] |
742 | fn event(&self, event: &Event<'_>) { |
743 | self.as_ref().event(event) |
744 | } |
745 | |
746 | #[inline ] |
747 | fn enter(&self, span: &span::Id) { |
748 | self.as_ref().enter(span) |
749 | } |
750 | |
751 | #[inline ] |
752 | fn exit(&self, span: &span::Id) { |
753 | self.as_ref().exit(span) |
754 | } |
755 | |
756 | #[inline ] |
757 | fn clone_span(&self, id: &span::Id) -> span::Id { |
758 | self.as_ref().clone_span(id) |
759 | } |
760 | |
761 | #[inline ] |
762 | fn try_close(&self, id: span::Id) -> bool { |
763 | self.as_ref().try_close(id) |
764 | } |
765 | |
766 | #[inline ] |
767 | #[allow (deprecated)] |
768 | fn drop_span(&self, id: span::Id) { |
769 | self.as_ref().try_close(id); |
770 | } |
771 | |
772 | #[inline ] |
773 | fn current_span(&self) -> span::Current { |
774 | self.as_ref().current_span() |
775 | } |
776 | |
777 | #[inline ] |
778 | unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
779 | if id == TypeId::of::<Self>() { |
780 | return Some(self as *const Self as *const _); |
781 | } |
782 | |
783 | self.as_ref().downcast_raw(id) |
784 | } |
785 | } |
786 | |
787 | impl<S> Subscriber for Arc<S> |
788 | where |
789 | S: Subscriber + ?Sized, |
790 | { |
791 | #[inline ] |
792 | fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { |
793 | self.as_ref().register_callsite(metadata) |
794 | } |
795 | |
796 | #[inline ] |
797 | fn enabled(&self, metadata: &Metadata<'_>) -> bool { |
798 | self.as_ref().enabled(metadata) |
799 | } |
800 | |
801 | #[inline ] |
802 | fn max_level_hint(&self) -> Option<LevelFilter> { |
803 | self.as_ref().max_level_hint() |
804 | } |
805 | |
806 | #[inline ] |
807 | fn new_span(&self, span: &span::Attributes<'_>) -> span::Id { |
808 | self.as_ref().new_span(span) |
809 | } |
810 | |
811 | #[inline ] |
812 | fn record(&self, span: &span::Id, values: &span::Record<'_>) { |
813 | self.as_ref().record(span, values) |
814 | } |
815 | |
816 | #[inline ] |
817 | fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { |
818 | self.as_ref().record_follows_from(span, follows) |
819 | } |
820 | |
821 | #[inline ] |
822 | fn event_enabled(&self, event: &Event<'_>) -> bool { |
823 | self.as_ref().event_enabled(event) |
824 | } |
825 | |
826 | #[inline ] |
827 | fn event(&self, event: &Event<'_>) { |
828 | self.as_ref().event(event) |
829 | } |
830 | |
831 | #[inline ] |
832 | fn enter(&self, span: &span::Id) { |
833 | self.as_ref().enter(span) |
834 | } |
835 | |
836 | #[inline ] |
837 | fn exit(&self, span: &span::Id) { |
838 | self.as_ref().exit(span) |
839 | } |
840 | |
841 | #[inline ] |
842 | fn clone_span(&self, id: &span::Id) -> span::Id { |
843 | self.as_ref().clone_span(id) |
844 | } |
845 | |
846 | #[inline ] |
847 | fn try_close(&self, id: span::Id) -> bool { |
848 | self.as_ref().try_close(id) |
849 | } |
850 | |
851 | #[inline ] |
852 | #[allow (deprecated)] |
853 | fn drop_span(&self, id: span::Id) { |
854 | self.as_ref().try_close(id); |
855 | } |
856 | |
857 | #[inline ] |
858 | fn current_span(&self) -> span::Current { |
859 | self.as_ref().current_span() |
860 | } |
861 | |
862 | #[inline ] |
863 | unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { |
864 | if id == TypeId::of::<Self>() { |
865 | return Some(self as *const Self as *const _); |
866 | } |
867 | |
868 | self.as_ref().downcast_raw(id) |
869 | } |
870 | } |
871 | |