1 | //! Callsites represent the source locations from which spans or events |
2 | //! originate. |
3 | //! |
4 | //! # What Are Callsites? |
5 | //! |
6 | //! Every span or event in `tracing` is associated with a [`Callsite`]. A |
7 | //! callsite is a small `static` value that is responsible for the following: |
8 | //! |
9 | //! * Storing the span or event's [`Metadata`], |
10 | //! * Uniquely [identifying](Identifier) the span or event definition, |
11 | //! * Caching the subscriber's [`Interest`][^1] in that span or event, to avoid |
12 | //! re-evaluating filters, |
13 | //! * Storing a [`Registration`] that allows the callsite to be part of a global |
14 | //! list of all callsites in the program. |
15 | //! |
16 | //! # Registering Callsites |
17 | //! |
18 | //! When a span or event is recorded for the first time, its callsite |
19 | //! [`register`]s itself with the global callsite registry. Registering a |
20 | //! callsite calls the [`Subscriber::register_callsite`][`register_callsite`] |
21 | //! method with that callsite's [`Metadata`] on every currently active |
22 | //! subscriber. This serves two primary purposes: informing subscribers of the |
23 | //! callsite's existence, and performing static filtering. |
24 | //! |
25 | //! ## Callsite Existence |
26 | //! |
27 | //! If a [`Subscriber`] implementation wishes to allocate storage for each |
28 | //! unique span/event location in the program, or pre-compute some value |
29 | //! that will be used to record that span or event in the future, it can |
30 | //! do so in its [`register_callsite`] method. |
31 | //! |
32 | //! ## Performing Static Filtering |
33 | //! |
34 | //! The [`register_callsite`] method returns an [`Interest`] value, |
35 | //! which indicates that the subscriber either [always] wishes to record |
36 | //! that span or event, [sometimes] wishes to record it based on a |
37 | //! dynamic filter evaluation, or [never] wishes to record it. |
38 | //! |
39 | //! When registering a new callsite, the [`Interest`]s returned by every |
40 | //! currently active subscriber are combined, and the result is stored at |
41 | //! each callsite. This way, when the span or event occurs in the |
42 | //! future, the cached [`Interest`] value can be checked efficiently |
43 | //! to determine if the span or event should be recorded, without |
44 | //! needing to perform expensive filtering (i.e. calling the |
45 | //! [`Subscriber::enabled`] method every time a span or event occurs). |
46 | //! |
47 | //! ### Rebuilding Cached Interest |
48 | //! |
49 | //! When a new [`Dispatch`] is created (i.e. a new subscriber becomes |
50 | //! active), any previously cached [`Interest`] values are re-evaluated |
51 | //! for all callsites in the program. This way, if the new subscriber |
52 | //! will enable a callsite that was not previously enabled, the |
53 | //! [`Interest`] in that callsite is updated. Similarly, when a |
54 | //! subscriber is dropped, the interest cache is also re-evaluated, so |
55 | //! that any callsites enabled only by that subscriber are disabled. |
56 | //! |
57 | //! In addition, the [`rebuild_interest_cache`] function in this module can be |
58 | //! used to manually invalidate all cached interest and re-register those |
59 | //! callsites. This function is useful in situations where a subscriber's |
60 | //! interest can change, but it does so relatively infrequently. The subscriber |
61 | //! may wish for its interest to be cached most of the time, and return |
62 | //! [`Interest::always`][always] or [`Interest::never`][never] in its |
63 | //! [`register_callsite`] method, so that its [`Subscriber::enabled`] method |
64 | //! doesn't need to be evaluated every time a span or event is recorded. |
65 | //! However, when the configuration changes, the subscriber can call |
66 | //! [`rebuild_interest_cache`] to re-evaluate the entire interest cache with its |
67 | //! new configuration. This is a relatively costly operation, but if the |
68 | //! configuration changes infrequently, it may be more efficient than calling |
69 | //! [`Subscriber::enabled`] frequently. |
70 | //! |
71 | //! # Implementing Callsites |
72 | //! |
73 | //! In most cases, instrumenting code using `tracing` should *not* require |
74 | //! implementing the [`Callsite`] trait directly. When using the [`tracing` |
75 | //! crate's macros][macros] or the [`#[instrument]` attribute][instrument], a |
76 | //! `Callsite` is automatically generated. |
77 | //! |
78 | //! However, code which provides alternative forms of `tracing` instrumentation |
79 | //! may need to interact with the callsite system directly. If |
80 | //! instrumentation-side code needs to produce a `Callsite` to emit spans or |
81 | //! events, the [`DefaultCallsite`] struct provided in this module is a |
82 | //! ready-made `Callsite` implementation that is suitable for most uses. When |
83 | //! possible, the use of `DefaultCallsite` should be preferred over implementing |
84 | //! [`Callsite`] for user types, as `DefaultCallsite` may benefit from |
85 | //! additional performance optimizations. |
86 | //! |
87 | //! [^1]: Returned by the [`Subscriber::register_callsite`][`register_callsite`] |
88 | //! method. |
89 | //! |
90 | //! [`Metadata`]: crate::metadata::Metadata |
91 | //! [`Interest`]: crate::subscriber::Interest |
92 | //! [`Subscriber`]: crate::subscriber::Subscriber |
93 | //! [`register_callsite`]: crate::subscriber::Subscriber::register_callsite |
94 | //! [`Subscriber::enabled`]: crate::subscriber::Subscriber::enabled |
95 | //! [always]: crate::subscriber::Interest::always |
96 | //! [sometimes]: crate::subscriber::Interest::sometimes |
97 | //! [never]: crate::subscriber::Interest::never |
98 | //! [`Dispatch`]: crate::dispatch::Dispatch |
99 | //! [macros]: https://docs.rs/tracing/latest/tracing/#macros |
100 | //! [instrument]: https://docs.rs/tracing/latest/tracing/attr.instrument.html |
101 | use crate::stdlib::{ |
102 | any::TypeId, |
103 | fmt, |
104 | hash::{Hash, Hasher}, |
105 | ptr, |
106 | sync::{ |
107 | atomic::{AtomicBool, AtomicPtr, AtomicU8, Ordering}, |
108 | Mutex, |
109 | }, |
110 | vec::Vec, |
111 | }; |
112 | use crate::{ |
113 | dispatcher::Dispatch, |
114 | lazy::Lazy, |
115 | metadata::{LevelFilter, Metadata}, |
116 | subscriber::Interest, |
117 | }; |
118 | |
119 | use self::dispatchers::Dispatchers; |
120 | |
121 | /// Trait implemented by callsites. |
122 | /// |
123 | /// These functions are only intended to be called by the callsite registry, which |
124 | /// correctly handles determining the common interest between all subscribers. |
125 | /// |
126 | /// See the [module-level documentation](crate::callsite) for details on |
127 | /// callsites. |
128 | pub trait Callsite: Sync { |
129 | /// Sets the [`Interest`] for this callsite. |
130 | /// |
131 | /// See the [documentation on callsite interest caching][cache-docs] for |
132 | /// details. |
133 | /// |
134 | /// [`Interest`]: super::subscriber::Interest |
135 | /// [cache-docs]: crate::callsite#performing-static-filtering |
136 | fn set_interest(&self, interest: Interest); |
137 | |
138 | /// Returns the [metadata] associated with the callsite. |
139 | /// |
140 | /// <div class="example-wrap" style="display:inline-block"> |
141 | /// <pre class="ignore" style="white-space:normal;font:inherit;"> |
142 | /// |
143 | /// **Note:** Implementations of this method should not produce [`Metadata`] |
144 | /// that share the same callsite [`Identifier`] but otherwise differ in any |
145 | /// way (e.g., have different `name`s). |
146 | /// |
147 | /// </pre></div> |
148 | /// |
149 | /// [metadata]: super::metadata::Metadata |
150 | fn metadata(&self) -> &Metadata<'_>; |
151 | |
152 | /// This method is an *internal implementation detail* of `tracing-core`. It |
153 | /// is *not* intended to be called or overridden from downstream code. |
154 | /// |
155 | /// The `Private` type can only be constructed from within `tracing-core`. |
156 | /// Because this method takes a `Private` as an argument, it cannot be |
157 | /// called from (safe) code external to `tracing-core`. Because it must |
158 | /// *return* a `Private`, the only valid implementation possible outside of |
159 | /// `tracing-core` would have to always unconditionally panic. |
160 | /// |
161 | /// THIS IS BY DESIGN. There is currently no valid reason for code outside |
162 | /// of `tracing-core` to override this method. |
163 | // TODO(eliza): this could be used to implement a public downcasting API |
164 | // for `&dyn Callsite`s in the future. |
165 | #[doc (hidden)] |
166 | #[inline ] |
167 | fn private_type_id(&self, _: private::Private<()>) -> private::Private<TypeId> |
168 | where |
169 | Self: 'static, |
170 | { |
171 | private::Private(TypeId::of::<Self>()) |
172 | } |
173 | } |
174 | |
175 | /// Uniquely identifies a [`Callsite`] |
176 | /// |
177 | /// Two `Identifier`s are equal if they both refer to the same callsite. |
178 | /// |
179 | /// [`Callsite`]: super::callsite::Callsite |
180 | #[derive (Clone)] |
181 | pub struct Identifier( |
182 | /// **Warning**: The fields on this type are currently `pub` because it must |
183 | /// be able to be constructed statically by macros. However, when `const |
184 | /// fn`s are available on stable Rust, this will no longer be necessary. |
185 | /// Thus, these fields are *not* considered stable public API, and they may |
186 | /// change warning. Do not rely on any fields on `Identifier`. When |
187 | /// constructing new `Identifier`s, use the `identify_callsite!` macro |
188 | /// instead. |
189 | #[doc (hidden)] |
190 | pub &'static dyn Callsite, |
191 | ); |
192 | |
193 | /// A default [`Callsite`] implementation. |
194 | #[derive (Debug)] |
195 | pub struct DefaultCallsite { |
196 | interest: AtomicU8, |
197 | registration: AtomicU8, |
198 | meta: &'static Metadata<'static>, |
199 | next: AtomicPtr<Self>, |
200 | } |
201 | |
202 | /// Clear and reregister interest on every [`Callsite`] |
203 | /// |
204 | /// This function is intended for runtime reconfiguration of filters on traces |
205 | /// when the filter recalculation is much less frequent than trace events are. |
206 | /// The alternative is to have the [`Subscriber`] that supports runtime |
207 | /// reconfiguration of filters always return [`Interest::sometimes()`] so that |
208 | /// [`enabled`] is evaluated for every event. |
209 | /// |
210 | /// This function will also re-compute the global maximum level as determined by |
211 | /// the [`max_level_hint`] method. If a [`Subscriber`] |
212 | /// implementation changes the value returned by its `max_level_hint` |
213 | /// implementation at runtime, then it **must** call this function after that |
214 | /// value changes, in order for the change to be reflected. |
215 | /// |
216 | /// See the [documentation on callsite interest caching][cache-docs] for |
217 | /// additional information on this function's usage. |
218 | /// |
219 | /// [`max_level_hint`]: super::subscriber::Subscriber::max_level_hint |
220 | /// [`Callsite`]: super::callsite::Callsite |
221 | /// [`enabled`]: super::subscriber::Subscriber#tymethod.enabled |
222 | /// [`Interest::sometimes()`]: super::subscriber::Interest::sometimes |
223 | /// [`Subscriber`]: super::subscriber::Subscriber |
224 | /// [cache-docs]: crate::callsite#rebuilding-cached-interest |
225 | pub fn rebuild_interest_cache() { |
226 | CALLSITES.rebuild_interest(dispatchers:DISPATCHERS.rebuilder()); |
227 | } |
228 | |
229 | /// Register a new [`Callsite`] with the global registry. |
230 | /// |
231 | /// This should be called once per callsite after the callsite has been |
232 | /// constructed. |
233 | /// |
234 | /// See the [documentation on callsite registration][reg-docs] for details |
235 | /// on the global callsite registry. |
236 | /// |
237 | /// [`Callsite`]: crate::callsite::Callsite |
238 | /// [reg-docs]: crate::callsite#registering-callsites |
239 | pub fn register(callsite: &'static dyn Callsite) { |
240 | rebuild_callsite_interest(callsite, &DISPATCHERS.rebuilder()); |
241 | |
242 | // Is this a `DefaultCallsite`? If so, use the fancy linked list! |
243 | if callsite.private_type_id(private::Private(())).0 == TypeId::of::<DefaultCallsite>() { |
244 | let callsite: &DefaultCallsite = unsafe { |
245 | // Safety: the pointer cast is safe because the type id of the |
246 | // provided callsite matches that of the target type for the cast |
247 | // (`DefaultCallsite`). Because user implementations of `Callsite` |
248 | // cannot override `private_type_id`, we can trust that the callsite |
249 | // is not lying about its type ID. |
250 | &*(callsite as *const dyn Callsite as *const DefaultCallsite) |
251 | }; |
252 | CALLSITES.push_default(callsite); |
253 | return; |
254 | } |
255 | |
256 | CALLSITES.push_dyn(callsite); |
257 | } |
258 | |
259 | static CALLSITES: Callsites = Callsites { |
260 | list_head: AtomicPtr::new(ptr::null_mut()), |
261 | has_locked_callsites: AtomicBool::new(false), |
262 | }; |
263 | |
264 | static DISPATCHERS: Dispatchers = Dispatchers::new(); |
265 | |
266 | static LOCKED_CALLSITES: Lazy<Mutex<Vec<&'static dyn Callsite>>> = Lazy::new(Default::default); |
267 | |
268 | struct Callsites { |
269 | list_head: AtomicPtr<DefaultCallsite>, |
270 | has_locked_callsites: AtomicBool, |
271 | } |
272 | |
273 | // === impl DefaultCallsite === |
274 | |
275 | impl DefaultCallsite { |
276 | const UNREGISTERED: u8 = 0; |
277 | const REGISTERING: u8 = 1; |
278 | const REGISTERED: u8 = 2; |
279 | |
280 | const INTEREST_NEVER: u8 = 0; |
281 | const INTEREST_SOMETIMES: u8 = 1; |
282 | const INTEREST_ALWAYS: u8 = 2; |
283 | |
284 | /// Returns a new `DefaultCallsite` with the specified `Metadata`. |
285 | pub const fn new(meta: &'static Metadata<'static>) -> Self { |
286 | Self { |
287 | interest: AtomicU8::new(0xFF), |
288 | meta, |
289 | next: AtomicPtr::new(ptr::null_mut()), |
290 | registration: AtomicU8::new(Self::UNREGISTERED), |
291 | } |
292 | } |
293 | |
294 | /// Registers this callsite with the global callsite registry. |
295 | /// |
296 | /// If the callsite is already registered, this does nothing. When using |
297 | /// [`DefaultCallsite`], this method should be preferred over |
298 | /// [`tracing_core::callsite::register`], as it ensures that the callsite is |
299 | /// only registered a single time. |
300 | /// |
301 | /// Other callsite implementations will generally ensure that |
302 | /// callsites are not re-registered through another mechanism. |
303 | /// |
304 | /// See the [documentation on callsite registration][reg-docs] for details |
305 | /// on the global callsite registry. |
306 | /// |
307 | /// [`Callsite`]: crate::callsite::Callsite |
308 | /// [reg-docs]: crate::callsite#registering-callsites |
309 | #[inline (never)] |
310 | // This only happens once (or if the cached interest value was corrupted). |
311 | #[cold ] |
312 | pub fn register(&'static self) -> Interest { |
313 | // Attempt to advance the registration state to `REGISTERING`... |
314 | match self.registration.compare_exchange( |
315 | Self::UNREGISTERED, |
316 | Self::REGISTERING, |
317 | Ordering::AcqRel, |
318 | Ordering::Acquire, |
319 | ) { |
320 | Ok(_) => { |
321 | // Okay, we advanced the state, try to register the callsite. |
322 | rebuild_callsite_interest(self, &DISPATCHERS.rebuilder()); |
323 | CALLSITES.push_default(self); |
324 | self.registration.store(Self::REGISTERED, Ordering::Release); |
325 | } |
326 | // Great, the callsite is already registered! Just load its |
327 | // previous cached interest. |
328 | Err(Self::REGISTERED) => {} |
329 | // Someone else is registering... |
330 | Err(_state) => { |
331 | debug_assert_eq!( |
332 | _state, |
333 | Self::REGISTERING, |
334 | "weird callsite registration state" |
335 | ); |
336 | // Just hit `enabled` this time. |
337 | return Interest::sometimes(); |
338 | } |
339 | } |
340 | |
341 | match self.interest.load(Ordering::Relaxed) { |
342 | Self::INTEREST_NEVER => Interest::never(), |
343 | Self::INTEREST_ALWAYS => Interest::always(), |
344 | _ => Interest::sometimes(), |
345 | } |
346 | } |
347 | |
348 | /// Returns the callsite's cached `Interest`, or registers it for the |
349 | /// first time if it has not yet been registered. |
350 | #[inline ] |
351 | pub fn interest(&'static self) -> Interest { |
352 | match self.interest.load(Ordering::Relaxed) { |
353 | Self::INTEREST_NEVER => Interest::never(), |
354 | Self::INTEREST_SOMETIMES => Interest::sometimes(), |
355 | Self::INTEREST_ALWAYS => Interest::always(), |
356 | _ => self.register(), |
357 | } |
358 | } |
359 | } |
360 | |
361 | impl Callsite for DefaultCallsite { |
362 | fn set_interest(&self, interest: Interest) { |
363 | let interest: u8 = match () { |
364 | _ if interest.is_never() => Self::INTEREST_NEVER, |
365 | _ if interest.is_always() => Self::INTEREST_ALWAYS, |
366 | _ => Self::INTEREST_SOMETIMES, |
367 | }; |
368 | self.interest.store(val:interest, order:Ordering::SeqCst); |
369 | } |
370 | |
371 | #[inline (always)] |
372 | fn metadata(&self) -> &Metadata<'static> { |
373 | self.meta |
374 | } |
375 | } |
376 | |
377 | // ===== impl Identifier ===== |
378 | |
379 | impl PartialEq for Identifier { |
380 | fn eq(&self, other: &Identifier) -> bool { |
381 | core::ptr::eq( |
382 | self.0 as *const _ as *const (), |
383 | b:other.0 as *const _ as *const (), |
384 | ) |
385 | } |
386 | } |
387 | |
388 | impl Eq for Identifier {} |
389 | |
390 | impl fmt::Debug for Identifier { |
391 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
392 | write!(f, "Identifier( {:p})" , self.0) |
393 | } |
394 | } |
395 | |
396 | impl Hash for Identifier { |
397 | fn hash<H>(&self, state: &mut H) |
398 | where |
399 | H: Hasher, |
400 | { |
401 | (self.0 as *const dyn Callsite).hash(state) |
402 | } |
403 | } |
404 | |
405 | // === impl Callsites === |
406 | |
407 | impl Callsites { |
408 | /// Rebuild `Interest`s for all callsites in the registry. |
409 | /// |
410 | /// This also re-computes the max level hint. |
411 | fn rebuild_interest(&self, dispatchers: dispatchers::Rebuilder<'_>) { |
412 | let mut max_level = LevelFilter::OFF; |
413 | dispatchers.for_each(|dispatch| { |
414 | // If the subscriber did not provide a max level hint, assume |
415 | // that it may enable every level. |
416 | let level_hint = dispatch.max_level_hint().unwrap_or(LevelFilter::TRACE); |
417 | if level_hint > max_level { |
418 | max_level = level_hint; |
419 | } |
420 | }); |
421 | |
422 | self.for_each(|callsite| { |
423 | rebuild_callsite_interest(callsite, &dispatchers); |
424 | }); |
425 | LevelFilter::set_max(max_level); |
426 | } |
427 | |
428 | /// Push a `dyn Callsite` trait object to the callsite registry. |
429 | /// |
430 | /// This will attempt to lock the callsites vector. |
431 | fn push_dyn(&self, callsite: &'static dyn Callsite) { |
432 | let mut lock = LOCKED_CALLSITES.lock().unwrap(); |
433 | self.has_locked_callsites.store(true, Ordering::Release); |
434 | lock.push(callsite); |
435 | } |
436 | |
437 | /// Push a `DefaultCallsite` to the callsite registry. |
438 | /// |
439 | /// If we know the callsite being pushed is a `DefaultCallsite`, we can push |
440 | /// it to the linked list without having to acquire a lock. |
441 | fn push_default(&self, callsite: &'static DefaultCallsite) { |
442 | let mut head = self.list_head.load(Ordering::Acquire); |
443 | |
444 | loop { |
445 | callsite.next.store(head, Ordering::Release); |
446 | |
447 | assert_ne!( |
448 | callsite as *const _, head, |
449 | "Attempted to register a `DefaultCallsite` that already exists! \ |
450 | This will cause an infinite loop when attempting to read from the \ |
451 | callsite cache. This is likely a bug! You should only need to call \ |
452 | `DefaultCallsite::register` once per `DefaultCallsite`." |
453 | ); |
454 | |
455 | match self.list_head.compare_exchange( |
456 | head, |
457 | callsite as *const _ as *mut _, |
458 | Ordering::AcqRel, |
459 | Ordering::Acquire, |
460 | ) { |
461 | Ok(_) => { |
462 | break; |
463 | } |
464 | Err(current) => head = current, |
465 | } |
466 | } |
467 | } |
468 | |
469 | /// Invokes the provided closure `f` with each callsite in the registry. |
470 | fn for_each(&self, mut f: impl FnMut(&'static dyn Callsite)) { |
471 | let mut head = self.list_head.load(Ordering::Acquire); |
472 | |
473 | while let Some(cs) = unsafe { head.as_ref() } { |
474 | f(cs); |
475 | |
476 | head = cs.next.load(Ordering::Acquire); |
477 | } |
478 | |
479 | if self.has_locked_callsites.load(Ordering::Acquire) { |
480 | let locked = LOCKED_CALLSITES.lock().unwrap(); |
481 | for &cs in locked.iter() { |
482 | f(cs); |
483 | } |
484 | } |
485 | } |
486 | } |
487 | |
488 | pub(crate) fn register_dispatch(dispatch: &Dispatch) { |
489 | let dispatchers: Rebuilder<'_> = DISPATCHERS.register_dispatch(dispatch); |
490 | dispatch.subscriber().on_register_dispatch(subscriber:dispatch); |
491 | CALLSITES.rebuild_interest(dispatchers); |
492 | } |
493 | |
494 | fn rebuild_callsite_interest( |
495 | callsite: &'static dyn Callsite, |
496 | dispatchers: &dispatchers::Rebuilder<'_>, |
497 | ) { |
498 | let meta: &Metadata<'_> = callsite.metadata(); |
499 | |
500 | let mut interest: Option = None; |
501 | dispatchers.for_each(|dispatch: &Dispatch| { |
502 | let this_interest: Interest = dispatch.register_callsite(metadata:meta); |
503 | interest = match interest.take() { |
504 | None => Some(this_interest), |
505 | Some(that_interest: Interest) => Some(that_interest.and(this_interest)), |
506 | } |
507 | }); |
508 | |
509 | let interest: Interest = interest.unwrap_or_else(Interest::never); |
510 | callsite.set_interest(interest) |
511 | } |
512 | |
513 | mod private { |
514 | /// Don't call this function, it's private. |
515 | #[allow (missing_debug_implementations)] |
516 | pub struct Private<T>(pub(crate) T); |
517 | } |
518 | |
519 | #[cfg (feature = "std" )] |
520 | mod dispatchers { |
521 | use crate::{dispatcher, lazy::Lazy}; |
522 | use std::sync::{ |
523 | atomic::{AtomicBool, Ordering}, |
524 | RwLock, RwLockReadGuard, RwLockWriteGuard, |
525 | }; |
526 | |
527 | pub(super) struct Dispatchers { |
528 | has_just_one: AtomicBool, |
529 | } |
530 | |
531 | static LOCKED_DISPATCHERS: Lazy<RwLock<Vec<dispatcher::Registrar>>> = |
532 | Lazy::new(Default::default); |
533 | |
534 | pub(super) enum Rebuilder<'a> { |
535 | JustOne, |
536 | Read(RwLockReadGuard<'a, Vec<dispatcher::Registrar>>), |
537 | Write(RwLockWriteGuard<'a, Vec<dispatcher::Registrar>>), |
538 | } |
539 | |
540 | impl Dispatchers { |
541 | pub(super) const fn new() -> Self { |
542 | Self { |
543 | has_just_one: AtomicBool::new(true), |
544 | } |
545 | } |
546 | |
547 | pub(super) fn rebuilder(&self) -> Rebuilder<'_> { |
548 | if self.has_just_one.load(Ordering::SeqCst) { |
549 | return Rebuilder::JustOne; |
550 | } |
551 | Rebuilder::Read(LOCKED_DISPATCHERS.read().unwrap()) |
552 | } |
553 | |
554 | pub(super) fn register_dispatch(&self, dispatch: &dispatcher::Dispatch) -> Rebuilder<'_> { |
555 | let mut dispatchers = LOCKED_DISPATCHERS.write().unwrap(); |
556 | dispatchers.retain(|d| d.upgrade().is_some()); |
557 | dispatchers.push(dispatch.registrar()); |
558 | self.has_just_one |
559 | .store(dispatchers.len() <= 1, Ordering::SeqCst); |
560 | Rebuilder::Write(dispatchers) |
561 | } |
562 | } |
563 | |
564 | impl Rebuilder<'_> { |
565 | pub(super) fn for_each(&self, mut f: impl FnMut(&dispatcher::Dispatch)) { |
566 | let iter = match self { |
567 | Rebuilder::JustOne => { |
568 | dispatcher::get_default(f); |
569 | return; |
570 | } |
571 | Rebuilder::Read(vec) => vec.iter(), |
572 | Rebuilder::Write(vec) => vec.iter(), |
573 | }; |
574 | iter.filter_map(dispatcher::Registrar::upgrade) |
575 | .for_each(|dispatch| f(&dispatch)) |
576 | } |
577 | } |
578 | } |
579 | |
580 | #[cfg (not(feature = "std" ))] |
581 | mod dispatchers { |
582 | use crate::dispatcher; |
583 | |
584 | pub(super) struct Dispatchers(()); |
585 | pub(super) struct Rebuilder<'a>(Option<&'a dispatcher::Dispatch>); |
586 | |
587 | impl Dispatchers { |
588 | pub(super) const fn new() -> Self { |
589 | Self(()) |
590 | } |
591 | |
592 | pub(super) fn rebuilder(&self) -> Rebuilder<'_> { |
593 | Rebuilder(None) |
594 | } |
595 | |
596 | pub(super) fn register_dispatch<'dispatch>( |
597 | &self, |
598 | dispatch: &'dispatch dispatcher::Dispatch, |
599 | ) -> Rebuilder<'dispatch> { |
600 | // nop; on no_std, there can only ever be one dispatcher |
601 | Rebuilder(Some(dispatch)) |
602 | } |
603 | } |
604 | |
605 | impl Rebuilder<'_> { |
606 | #[inline ] |
607 | pub(super) fn for_each(&self, mut f: impl FnMut(&dispatcher::Dispatch)) { |
608 | if let Some(dispatch) = self.0 { |
609 | // we are rebuilding the interest cache because a new dispatcher |
610 | // is about to be set. on `no_std`, this should only happen |
611 | // once, because the new dispatcher will be the global default. |
612 | f(dispatch) |
613 | } else { |
614 | // otherwise, we are rebuilding the cache because the subscriber |
615 | // configuration changed, so use the global default. |
616 | // on no_std, there can only ever be one dispatcher |
617 | dispatcher::get_default(f) |
618 | } |
619 | } |
620 | } |
621 | } |
622 | |