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 </pre><pre class="rust"><code><span class="doccomment">//! Dispatches trace events to [`Subscriber`]s.
 //!
 //! The _dispatcher_ is the component of the tracing system which is responsible
 //! for forwarding trace data from the instrumentation points that generate it
 //! to the subscriber that collects it.
 //!
 //! # Using the Trace Dispatcher
 //!
 //! Every thread in a program using `tracing` has a _default subscriber_. When
 //! events occur, or spans are created, they are dispatched to the thread&#39;s
 //! current subscriber.
 //!
 //! ## Setting the Default Subscriber
 //!
 //! By default, the current subscriber is an empty implementation that does
 //! nothing. To use a subscriber implementation, it must be set as the default.
 //! There are two methods for doing so: [`with_default`] and
 //! [`set_global_default`]. `with_default` sets the default subscriber for the
 //! duration of a scope, while `set_global_default` sets a default subscriber
 //! for the entire process.
 //!
 //! To use either of these functions, we must first wrap our subscriber in a
 //! [`Dispatch`], a cloneable, type-erased reference to a subscriber. For
 //! example:
 //! ```rust
 //! # pub struct FooSubscriber;
 //! # use tracing_core::{
 //! #   dispatcher, Event, Metadata,
 //! #   span::{Attributes, Id, Record}
 //! # };
 //! # impl tracing_core::Subscriber for FooSubscriber {
 //! #   fn new_span(&amp;self, _: &amp;Attributes) -&gt; Id { Id::from_u64(0) }
 //! #   fn record(&amp;self, _: &amp;Id, _: &amp;Record) {}
 //! #   fn event(&amp;self, _: &amp;Event) {}
 //! #   fn record_follows_from(&amp;self, _: &amp;Id, _: &amp;Id) {}
 //! #   fn enabled(&amp;self, _: &amp;Metadata) -&gt; bool { false }
 //! #   fn enter(&amp;self, _: &amp;Id) {}
 //! #   fn exit(&amp;self, _: &amp;Id) {}
 //! # }
 //! # impl FooSubscriber { fn new() -&gt; Self { FooSubscriber } }
 //! use dispatcher::Dispatch;
 //!
 //! let my_subscriber = FooSubscriber::new();
 //! let my_dispatch = Dispatch::new(my_subscriber);
 //! ```
 //! Then, we can use [`with_default`] to set our `Dispatch` as the default for
 //! the duration of a block:
 //! ```rust
 //! # pub struct FooSubscriber;
 //! # use tracing_core::{
 //! #   dispatcher, Event, Metadata,
 //! #   span::{Attributes, Id, Record}
 //! # };
 //! # impl tracing_core::Subscriber for FooSubscriber {
 //! #   fn new_span(&amp;self, _: &amp;Attributes) -&gt; Id { Id::from_u64(0) }
 //! #   fn record(&amp;self, _: &amp;Id, _: &amp;Record) {}
 //! #   fn event(&amp;self, _: &amp;Event) {}
 //! #   fn record_follows_from(&amp;self, _: &amp;Id, _: &amp;Id) {}
 //! #   fn enabled(&amp;self, _: &amp;Metadata) -&gt; bool { false }
 //! #   fn enter(&amp;self, _: &amp;Id) {}
 //! #   fn exit(&amp;self, _: &amp;Id) {}
 //! # }
 //! # impl FooSubscriber { fn new() -&gt; Self { FooSubscriber } }
 //! # let my_subscriber = FooSubscriber::new();
 //! # let my_dispatch = dispatcher::Dispatch::new(my_subscriber);
 //! // no default subscriber
 //!
 //! # #[cfg(feature = &quot;std&quot;)]
 //! dispatcher::with_default(&amp;my_dispatch, || {
 //!     // my_subscriber is the default
 //! });
 //!
 //! // no default subscriber again
 //! ```
 //! It&#39;s important to note that `with_default` will not propagate the current
 //! thread&#39;s default subscriber to any threads spawned within the `with_default`
 //! block. To propagate the default subscriber to new threads, either use
 //! `with_default` from the new thread, or use `set_global_default`.
 //!
 //! As an alternative to `with_default`, we can use [`set_global_default`] to
 //! set a `Dispatch` as the default for all threads, for the lifetime of the
 //! program. For example:
 //! ```rust
 //! # pub struct FooSubscriber;
 //! # use tracing_core::{
 //! #   dispatcher, Event, Metadata,
 //! #   span::{Attributes, Id, Record}
 //! # };
 //! # impl tracing_core::Subscriber for FooSubscriber {
 //! #   fn new_span(&amp;self, _: &amp;Attributes) -&gt; Id { Id::from_u64(0) }
 //! #   fn record(&amp;self, _: &amp;Id, _: &amp;Record) {}
 //! #   fn event(&amp;self, _: &amp;Event) {}
 //! #   fn record_follows_from(&amp;self, _: &amp;Id, _: &amp;Id) {}
 //! #   fn enabled(&amp;self, _: &amp;Metadata) -&gt; bool { false }
 //! #   fn enter(&amp;self, _: &amp;Id) {}
 //! #   fn exit(&amp;self, _: &amp;Id) {}
 //! # }
 //! # impl FooSubscriber { fn new() -&gt; Self { FooSubscriber } }
 //! # let my_subscriber = FooSubscriber::new();
 //! # let my_dispatch = dispatcher::Dispatch::new(my_subscriber);
 //! // no default subscriber
 //!
 //! dispatcher::set_global_default(my_dispatch)
 //!     // `set_global_default` will return an error if the global default
 //!     // subscriber has already been set.
 //!     .expect(&quot;global default was already set!&quot;);
 //!
 //! // `my_subscriber` is now the default
 //! ```
 //!
 //! &lt;pre class=&quot;ignore&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 //!     &lt;strong&gt;Note&lt;/strong&gt;:the thread-local scoped dispatcher
 //!     (&lt;a href=&quot;#fn.with_default&quot;&gt;&lt;code&gt;with_default&lt;/code&gt;&lt;/a&gt;) requires the
 //!     Rust standard library. &lt;code&gt;no_std&lt;/code&gt; users should use
 //!     &lt;a href=&quot;#fn.set_global_default&quot;&gt;&lt;code&gt;set_global_default&lt;/code&gt;&lt;/a&gt;
 //!     instead.
 //! &lt;/pre&gt;
 //!
 //! ## Accessing the Default Subscriber
 //!
 //! A thread&#39;s current default subscriber can be accessed using the
 //! [`get_default`] function, which executes a closure with a reference to the
 //! currently default `Dispatch`. This is used primarily by `tracing`
 //! instrumentation.
 //!
 </span><span class="kw">use crate</span>::{
     callsite, span,
     subscriber::{<span class="self">self</span>, NoSubscriber, Subscriber},
     Event, LevelFilter, Metadata,
 };

 <span class="kw">use </span><span class="kw">crate</span>::stdlib::{
     any::Any,
     fmt,
     sync::{
         atomic::{AtomicBool, AtomicUsize, Ordering},
         Arc, Weak,
     },
 };

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">use </span><span class="kw">crate</span>::stdlib::{
     cell::{Cell, Ref, RefCell},
     error,
 };

 <span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
 </span><span class="kw">use </span>alloc::sync::{Arc, Weak};

 <span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
 </span><span class="kw">use </span>core::ops::Deref;

 <span class="doccomment">/// `Dispatch` trace data to a [`Subscriber`].
 </span><span class="attribute">#[derive(Clone)]
 </span><span class="kw">pub struct </span>Dispatch {
     subscriber: Kind&lt;Arc&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt;,
 }

 <span class="doccomment">/// `WeakDispatch` is a version of [`Dispatch`] that holds a non-owning reference
 /// to a [`Subscriber`].
 ///
 /// The Subscriber` may be accessed by calling [`WeakDispatch::upgrade`],
 /// which returns an `Option&lt;Dispatch&gt;`. If all [`Dispatch`] clones that point
 /// at the `Subscriber` have been dropped, [`WeakDispatch::upgrade`] will return
 /// `None`. Otherwise, it will return `Some(Dispatch)`.
 ///
 /// A `WeakDispatch` may be created from a [`Dispatch`] by calling the
 /// [`Dispatch::downgrade`] method. The primary use for creating a
 /// [`WeakDispatch`] is to allow a Subscriber` to hold a cyclical reference to
 /// itself without creating a memory leak. See [here] for details.
 ///
 /// This type is analogous to the [`std::sync::Weak`] type, but for a
 /// [`Dispatch`] rather than an [`Arc`].
 ///
 /// [`Arc`]: std::sync::Arc
 /// [here]: Subscriber#avoiding-memory-leaks
 </span><span class="attribute">#[derive(Clone)]
 </span><span class="kw">pub struct </span>WeakDispatch {
     subscriber: Kind&lt;Weak&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt;,
 }

 <span class="attribute">#[derive(Clone)]
 </span><span class="kw">enum </span>Kind&lt;T&gt; {
     Global(<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>(<span class="kw">dyn </span>Subscriber + Send + Sync)),
     Scoped(T),
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="macro">thread_local! </span>{
     <span class="kw">static </span>CURRENT_STATE: State = State {
         default: RefCell::new(<span class="prelude-val">None</span>),
         can_enter: Cell::new(<span class="bool-val">true</span>),
     };
 }

 <span class="kw">static </span>EXISTS: AtomicBool = AtomicBool::new(<span class="bool-val">false</span>);
 <span class="kw">static </span>GLOBAL_INIT: AtomicUsize = AtomicUsize::new(UNINITIALIZED);

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">static </span>SCOPED_COUNT: AtomicUsize = AtomicUsize::new(<span class="number">0</span>);

 <span class="kw">const </span>UNINITIALIZED: usize = <span class="number">0</span>;
 <span class="kw">const </span>INITIALIZING: usize = <span class="number">1</span>;
 <span class="kw">const </span>INITIALIZED: usize = <span class="number">2</span>;

 <span class="kw">static </span><span class="kw-2">mut </span>GLOBAL_DISPATCH: Dispatch = Dispatch {
     subscriber: Kind::Global(<span class="kw-2">&amp;</span>NO_SUBSCRIBER),
 };
 <span class="kw">static </span>NONE: Dispatch = Dispatch {
     subscriber: Kind::Global(<span class="kw-2">&amp;</span>NO_SUBSCRIBER),
 };
 <span class="kw">static </span>NO_SUBSCRIBER: NoSubscriber = NoSubscriber::new();

 <span class="doccomment">/// The dispatch state of a thread.
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">struct </span>State {
     <span class="doccomment">/// This thread&#39;s current default dispatcher.
     </span>default: RefCell&lt;<span class="prelude-ty">Option</span>&lt;Dispatch&gt;&gt;,
     <span class="doccomment">/// Whether or not we can currently begin dispatching a trace event.
     ///
     /// This is set to `false` when functions such as `enter`, `exit`, `event`,
     /// and `new_span` are called on this thread&#39;s default dispatcher, to
     /// prevent further trace events triggered inside those functions from
     /// creating an infinite recursion. When we finish handling a dispatch, this
     /// is set back to `true`.
     </span>can_enter: Cell&lt;bool&gt;,
 }

 <span class="doccomment">/// While this guard is active, additional calls to subscriber functions on
 /// the default dispatcher will not be able to access the dispatch context.
 /// Dropping the guard will allow the dispatch context to be re-entered.
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">struct </span>Entered&lt;<span class="lifetime">&#39;a</span>&gt;(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>State);

 <span class="doccomment">/// A guard that resets the current default dispatcher to the prior
 /// default dispatcher when dropped.
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">&quot;std&quot;</span>)))]
 #[derive(Debug)]
 </span><span class="kw">pub struct </span>DefaultGuard(<span class="prelude-ty">Option</span>&lt;Dispatch&gt;);

 <span class="doccomment">/// Sets this dispatch as the default for the duration of a closure.
 ///
 /// The default dispatcher is used when creating a new [span] or
 /// [`Event`].
 ///
 /// &lt;pre class=&quot;ignore&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 ///     &lt;strong&gt;Note&lt;/strong&gt;: This function required the Rust standard library.
 ///     &lt;code&gt;no_std&lt;/code&gt; users should use &lt;a href=&quot;../fn.set_global_default.html&quot;&gt;
 ///     &lt;code&gt;set_global_default&lt;/code&gt;&lt;/a&gt; instead.
 /// &lt;/pre&gt;
 ///
 /// [span]: super::span
 /// [`Subscriber`]: super::subscriber::Subscriber
 /// [`Event`]: super::event::Event
 /// [`set_global_default`]: super::set_global_default
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">&quot;std&quot;</span>)))]
 </span><span class="kw">pub fn </span>with_default&lt;T&gt;(dispatcher: <span class="kw-2">&amp;</span>Dispatch, f: <span class="kw">impl </span>FnOnce() -&gt; T) -&gt; T {
     <span class="comment">// When this guard is dropped, the default dispatcher will be reset to the
     // prior default. Using this (rather than simply resetting after calling
     // `f`) ensures that we always reset to the prior dispatcher even if `f`
     // panics.
     </span><span class="kw">let </span>_guard = set_default(dispatcher);
     f()
 }

 <span class="doccomment">/// Sets the dispatch as the default dispatch for the duration of the lifetime
 /// of the returned DefaultGuard
 ///
 /// &lt;pre class=&quot;ignore&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 ///     &lt;strong&gt;Note&lt;/strong&gt;: This function required the Rust standard library.
 ///     &lt;code&gt;no_std&lt;/code&gt; users should use &lt;a href=&quot;../fn.set_global_default.html&quot;&gt;
 ///     &lt;code&gt;set_global_default&lt;/code&gt;&lt;/a&gt; instead.
 /// &lt;/pre&gt;
 ///
 /// [`set_global_default`]: super::set_global_default
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">&quot;std&quot;</span>)))]
 #[must_use = <span class="string">&quot;Dropping the guard unregisters the dispatcher.&quot;</span>]
 </span><span class="kw">pub fn </span>set_default(dispatcher: <span class="kw-2">&amp;</span>Dispatch) -&gt; DefaultGuard {
     <span class="comment">// When this guard is dropped, the default dispatcher will be reset to the
     // prior default. Using this ensures that we always reset to the prior
     // dispatcher even if the thread calling this function panics.
     </span>State::set_default(dispatcher.clone())
 }

 <span class="doccomment">/// Sets this dispatch as the global default for the duration of the entire program.
 /// Will be used as a fallback if no thread-local dispatch has been set in a thread
 /// (using `with_default`.)
 ///
 /// Can only be set once; subsequent attempts to set the global default will fail.
 /// Returns `Err` if the global default has already been set.
 ///
 /// &lt;div class=&quot;example-wrap&quot; style=&quot;display:inline-block&quot;&gt;&lt;pre class=&quot;compile_fail&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 ///     &lt;strong&gt;Warning&lt;/strong&gt;: In general, libraries should &lt;em&gt;not&lt;/em&gt; call
 ///     &lt;code&gt;set_global_default()&lt;/code&gt;! Doing so will cause conflicts when
 ///     executables that depend on the library try to set the default later.
 /// &lt;/pre&gt;&lt;/div&gt;
 ///
 /// [span]: super::span
 /// [`Subscriber`]: super::subscriber::Subscriber
 /// [`Event`]: super::event::Event
 </span><span class="kw">pub fn </span>set_global_default(dispatcher: Dispatch) -&gt; <span class="prelude-ty">Result</span>&lt;(), SetGlobalDefaultError&gt; {
     <span class="comment">// if `compare_exchange` returns Result::Ok(_), then `new` has been set and
     // `current`—now the prior value—has been returned in the `Ok()` branch.
     </span><span class="kw">if </span>GLOBAL_INIT
         .compare_exchange(
             UNINITIALIZED,
             INITIALIZING,
             Ordering::SeqCst,
             Ordering::SeqCst,
         )
         .is_ok()
     {
         <span class="kw">let </span>subscriber = {
             <span class="kw">let </span>subscriber = <span class="kw">match </span>dispatcher.subscriber {
                 Kind::Global(s) =&gt; s,
                 Kind::Scoped(s) =&gt; <span class="kw">unsafe </span>{
                     <span class="comment">// safety: this leaks the subscriber onto the heap. the
                     // reference count will always be at least 1, because the
                     // global default will never be dropped.
                     </span><span class="kw-2">&amp;*</span>Arc::into_raw(s)
                 },
             };
             Kind::Global(subscriber)
         };
         <span class="kw">unsafe </span>{
             GLOBAL_DISPATCH = Dispatch { subscriber };
         }
         GLOBAL_INIT.store(INITIALIZED, Ordering::SeqCst);
         EXISTS.store(<span class="bool-val">true</span>, Ordering::Release);
         <span class="prelude-val">Ok</span>(())
     } <span class="kw">else </span>{
         <span class="prelude-val">Err</span>(SetGlobalDefaultError { _no_construct: () })
     }
 }

 <span class="doccomment">/// Returns true if a `tracing` dispatcher has ever been set.
 ///
 /// This may be used to completely elide trace points if tracing is not in use
 /// at all or has yet to be initialized.
 </span><span class="attribute">#[doc(hidden)]
 #[inline(always)]
 </span><span class="kw">pub fn </span>has_been_set() -&gt; bool {
     EXISTS.load(Ordering::Relaxed)
 }

 <span class="doccomment">/// Returned if setting the global dispatcher fails.
 </span><span class="kw">pub struct </span>SetGlobalDefaultError {
     _no_construct: (),
 }

 <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>SetGlobalDefaultError {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         f.debug_tuple(<span class="string">&quot;SetGlobalDefaultError&quot;</span>)
             .field(<span class="kw-2">&amp;</span><span class="self">Self</span>::MESSAGE)
             .finish()
     }
 }

 <span class="kw">impl </span>fmt::Display <span class="kw">for </span>SetGlobalDefaultError {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         f.pad(<span class="self">Self</span>::MESSAGE)
     }
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">&quot;std&quot;</span>)))]
 </span><span class="kw">impl </span>error::Error <span class="kw">for </span>SetGlobalDefaultError {}

 <span class="kw">impl </span>SetGlobalDefaultError {
     <span class="kw">const </span>MESSAGE: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>str = <span class="string">&quot;a global default trace dispatcher has already been set&quot;</span>;
 }

 <span class="doccomment">/// Executes a closure with a reference to this thread&#39;s current [dispatcher].
 ///
 /// Note that calls to `get_default` should not be nested; if this function is
 /// called while inside of another `get_default`, that closure will be provided
 /// with `Dispatch::none` rather than the previously set dispatcher.
 ///
 /// [dispatcher]: super::dispatcher::Dispatch
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">pub fn </span>get_default&lt;T, F&gt;(<span class="kw-2">mut </span>f: F) -&gt; T
 <span class="kw">where
     </span>F: FnMut(<span class="kw-2">&amp;</span>Dispatch) -&gt; T,
 {
     <span class="kw">if </span>SCOPED_COUNT.load(Ordering::Acquire) == <span class="number">0 </span>{
         <span class="comment">// fast path if no scoped dispatcher has been set; just use the global
         // default.
         </span><span class="kw">return </span>f(get_global());
     }

     CURRENT_STATE
         .try_with(|state| {
             <span class="kw">if let </span><span class="prelude-val">Some</span>(entered) = state.enter() {
                 <span class="kw">return </span>f(<span class="kw-2">&amp;</span>entered.current());
             }

             f(<span class="kw-2">&amp;</span>NONE)
         })
         .unwrap_or_else(|<span class="kw">_</span>| f(<span class="kw-2">&amp;</span>NONE))
 }

 <span class="doccomment">/// Executes a closure with a reference to this thread&#39;s current [dispatcher].
 ///
 /// Note that calls to `get_default` should not be nested; if this function is
 /// called while inside of another `get_default`, that closure will be provided
 /// with `Dispatch::none` rather than the previously set dispatcher.
 ///
 /// [dispatcher]: super::dispatcher::Dispatch
 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 #[doc(hidden)]
 #[inline(never)]
 </span><span class="kw">pub fn </span>get_current&lt;T&gt;(f: <span class="kw">impl </span>FnOnce(<span class="kw-2">&amp;</span>Dispatch) -&gt; T) -&gt; <span class="prelude-ty">Option</span>&lt;T&gt; {
     <span class="kw">if </span>SCOPED_COUNT.load(Ordering::Acquire) == <span class="number">0 </span>{
         <span class="comment">// fast path if no scoped dispatcher has been set; just use the global
         // default.
         </span><span class="kw">return </span><span class="prelude-val">Some</span>(f(get_global()));
     }

     CURRENT_STATE
         .try_with(|state| {
             <span class="kw">let </span>entered = state.enter()<span class="question-mark">?</span>;
             <span class="prelude-val">Some</span>(f(<span class="kw-2">&amp;</span>entered.current()))
         })
         .ok()<span class="question-mark">?
 </span>}

 <span class="doccomment">/// Executes a closure with a reference to the current [dispatcher].
 ///
 /// [dispatcher]: super::dispatcher::Dispatch
 </span><span class="attribute">#[cfg(not(feature = <span class="string">&quot;std&quot;</span>))]
 #[doc(hidden)]
 </span><span class="kw">pub fn </span>get_current&lt;T&gt;(f: <span class="kw">impl </span>FnOnce(<span class="kw-2">&amp;</span>Dispatch) -&gt; T) -&gt; <span class="prelude-ty">Option</span>&lt;T&gt; {
     <span class="prelude-val">Some</span>(f(get_global()))
 }

 <span class="doccomment">/// Executes a closure with a reference to the current [dispatcher].
 ///
 /// [dispatcher]: super::dispatcher::Dispatch
 </span><span class="attribute">#[cfg(not(feature = <span class="string">&quot;std&quot;</span>))]
 </span><span class="kw">pub fn </span>get_default&lt;T, F&gt;(<span class="kw-2">mut </span>f: F) -&gt; T
 <span class="kw">where
     </span>F: FnMut(<span class="kw-2">&amp;</span>Dispatch) -&gt; T,
 {
     f(<span class="kw-2">&amp;</span>get_global())
 }

 <span class="attribute">#[inline]
 </span><span class="kw">fn </span>get_global() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Dispatch {
     <span class="kw">if </span>GLOBAL_INIT.load(Ordering::SeqCst) != INITIALIZED {
         <span class="kw">return </span><span class="kw-2">&amp;</span>NONE;
     }
     <span class="kw">unsafe </span>{
         <span class="comment">// This is safe given the invariant that setting the global dispatcher
         // also sets `GLOBAL_INIT` to `INITIALIZED`.
         </span><span class="kw-2">&amp;</span>GLOBAL_DISPATCH
     }
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Registrar(Kind&lt;Weak&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt;);

 <span class="kw">impl </span>Dispatch {
     <span class="doccomment">/// Returns a new `Dispatch` that discards events and spans.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>none() -&gt; <span class="self">Self </span>{
         Dispatch {
             subscriber: Kind::Global(<span class="kw-2">&amp;</span>NO_SUBSCRIBER),
         }
     }

     <span class="doccomment">/// Returns a `Dispatch` that forwards to the given [`Subscriber`].
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     </span><span class="kw">pub fn </span>new&lt;S&gt;(subscriber: S) -&gt; <span class="self">Self
     </span><span class="kw">where
         </span>S: Subscriber + Send + Sync + <span class="lifetime">&#39;static</span>,
     {
         <span class="kw">let </span>me = Dispatch {
             subscriber: Kind::Scoped(Arc::new(subscriber)),
         };
         callsite::register_dispatch(<span class="kw-2">&amp;</span>me);
         me
     }

     <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>registrar(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; Registrar {
         Registrar(<span class="self">self</span>.subscriber.downgrade())
     }

     <span class="doccomment">/// Creates a [`WeakDispatch`] from this `Dispatch`.
     ///
     /// A [`WeakDispatch`] is similar to a [`Dispatch`], but it does not prevent
     /// the underlying [`Subscriber`] from being dropped. Instead, it only permits
     /// access while other references to the `Subscriber` exist. This is equivalent
     /// to the standard library&#39;s [`Arc::downgrade`] method, but for `Dispatch`
     /// rather than `Arc`.
     ///
     /// The primary use for creating a [`WeakDispatch`] is to allow a `Subscriber`
     /// to hold a cyclical reference to itself without creating a memory leak.
     /// See [here] for details.
     ///
     /// [`Arc::downgrade`]: std::sync::Arc::downgrade
     /// [here]: Subscriber#avoiding-memory-leaks
     </span><span class="kw">pub fn </span>downgrade(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; WeakDispatch {
         WeakDispatch {
             subscriber: <span class="self">self</span>.subscriber.downgrade(),
         }
     }

     <span class="attribute">#[inline(always)]
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>subscriber(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>(<span class="kw">dyn </span>Subscriber + Send + Sync) {
         <span class="kw">match </span><span class="self">self</span>.subscriber {
             Kind::Global(s) =&gt; s,
             Kind::Scoped(<span class="kw-2">ref </span>s) =&gt; s.as_ref(),
         }
     }

     <span class="doccomment">/// Registers a new callsite with this collector, returning whether or not
     /// the collector is interested in being notified about the callsite.
     ///
     /// This calls the [`register_callsite`] function on the [`Subscriber`]
     /// that this `Dispatch` forwards to.
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`register_callsite`]: super::subscriber::Subscriber::register_callsite
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>register_callsite(<span class="kw-2">&amp;</span><span class="self">self</span>, metadata: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Metadata&lt;<span class="lifetime">&#39;static</span>&gt;) -&gt; subscriber::Interest {
         <span class="self">self</span>.subscriber().register_callsite(metadata)
     }

     <span class="doccomment">/// 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.
     ///
     /// This calls the [`max_level_hint`] function on the [`Subscriber`]
     /// that this `Dispatch` forwards to.
     ///
     /// [level]: super::Level
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`register_callsite`]: super::subscriber::Subscriber::max_level_hint
     </span><span class="comment">// TODO(eliza): consider making this a public API?
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>max_level_hint(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;LevelFilter&gt; {
         <span class="self">self</span>.subscriber().max_level_hint()
     }

     <span class="doccomment">/// Record the construction of a new span, returning a new [ID] for the
     /// span being constructed.
     ///
     /// This calls the [`new_span`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [ID]: super::span::Id
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`new_span`]: super::subscriber::Subscriber::new_span
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>new_span(<span class="kw-2">&amp;</span><span class="self">self</span>, span: <span class="kw-2">&amp;</span>span::Attributes&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; span::Id {
         <span class="self">self</span>.subscriber().new_span(span)
     }

     <span class="doccomment">/// Record a set of values on a span.
     ///
     /// This calls the [`record`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`record`]: super::subscriber::Subscriber::record
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>record(<span class="kw-2">&amp;</span><span class="self">self</span>, span: <span class="kw-2">&amp;</span>span::Id, values: <span class="kw-2">&amp;</span>span::Record&lt;<span class="lifetime">&#39;_</span>&gt;) {
         <span class="self">self</span>.subscriber().record(span, values)
     }

     <span class="doccomment">/// Adds an indication that `span` follows from the span with the id
     /// `follows`.
     ///
     /// This calls the [`record_follows_from`] function on the [`Subscriber`]
     /// that this `Dispatch` forwards to.
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`record_follows_from`]: super::subscriber::Subscriber::record_follows_from
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>record_follows_from(<span class="kw-2">&amp;</span><span class="self">self</span>, span: <span class="kw-2">&amp;</span>span::Id, follows: <span class="kw-2">&amp;</span>span::Id) {
         <span class="self">self</span>.subscriber().record_follows_from(span, follows)
     }

     <span class="doccomment">/// Returns true if a span with the specified [metadata] would be
     /// recorded.
     ///
     /// This calls the [`enabled`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [metadata]: super::metadata::Metadata
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`enabled`]: super::subscriber::Subscriber::enabled
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>enabled(<span class="kw-2">&amp;</span><span class="self">self</span>, metadata: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; bool {
         <span class="self">self</span>.subscriber().enabled(metadata)
     }

     <span class="doccomment">/// Records that an [`Event`] has occurred.
     ///
     /// This calls the [`event`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [`Event`]: super::event::Event
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`event`]: super::subscriber::Subscriber::event
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>event(<span class="kw-2">&amp;</span><span class="self">self</span>, event: <span class="kw-2">&amp;</span>Event&lt;<span class="lifetime">&#39;_</span>&gt;) {
         <span class="kw">let </span>subscriber = <span class="self">self</span>.subscriber();
         <span class="kw">if </span>subscriber.event_enabled(event) {
             subscriber.event(event);
         }
     }

     <span class="doccomment">/// Records that a span has been can_enter.
     ///
     /// This calls the [`enter`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`enter`]: super::subscriber::Subscriber::enter
     </span><span class="kw">pub fn </span>enter(<span class="kw-2">&amp;</span><span class="self">self</span>, span: <span class="kw-2">&amp;</span>span::Id) {
         <span class="self">self</span>.subscriber().enter(span);
     }

     <span class="doccomment">/// Records that a span has been exited.
     ///
     /// This calls the [`exit`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`exit`]: super::subscriber::Subscriber::exit
     </span><span class="kw">pub fn </span>exit(<span class="kw-2">&amp;</span><span class="self">self</span>, span: <span class="kw-2">&amp;</span>span::Id) {
         <span class="self">self</span>.subscriber().exit(span);
     }

     <span class="doccomment">/// Notifies the subscriber that a [span ID] has been cloned.
     ///
     /// This function must only be called with span IDs that were returned by
     /// this `Dispatch`&#39;s [`new_span`] function. The `tracing` crate upholds
     /// this guarantee and any other libraries implementing instrumentation APIs
     /// must as well.
     ///
     /// This calls the [`clone_span`] function on the `Subscriber` that this
     /// `Dispatch` forwards to.
     ///
     /// [span ID]: super::span::Id
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`clone_span`]: super::subscriber::Subscriber::clone_span
     /// [`new_span`]: super::subscriber::Subscriber::new_span
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>clone_span(<span class="kw-2">&amp;</span><span class="self">self</span>, id: <span class="kw-2">&amp;</span>span::Id) -&gt; span::Id {
         <span class="self">self</span>.subscriber().clone_span(id)
     }

     <span class="doccomment">/// Notifies the subscriber that a [span ID] has been dropped.
     ///
     /// This function must only be called with span IDs that were returned by
     /// this `Dispatch`&#39;s [`new_span`] function. The `tracing` crate upholds
     /// this guarantee and any other libraries implementing instrumentation APIs
     /// must as well.
     ///
     /// This calls the [`drop_span`] function on the [`Subscriber`] that this
     /// `Dispatch` forwards to.
     ///
     /// &lt;pre class=&quot;compile_fail&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
     ///     &lt;strong&gt;Deprecated&lt;/strong&gt;: The &lt;a href=&quot;#method.try_close&quot;&gt;&lt;code&gt;
     ///     try_close&lt;/code&gt;&lt;/a&gt; method is functionally identical, but returns
     ///     &lt;code&gt;true&lt;/code&gt; if the span is now closed. It should be used
     ///     instead of this method.
     /// &lt;/pre&gt;
     ///
     /// [span ID]: super::span::Id
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`drop_span`]: super::subscriber::Subscriber::drop_span
     /// [`new_span`]: super::subscriber::Subscriber::new_span
     /// [`try_close`]: Entered::try_close()
     </span><span class="attribute">#[inline]
     #[deprecated(since = <span class="string">&quot;0.1.2&quot;</span>, note = <span class="string">&quot;use `Dispatch::try_close` instead&quot;</span>)]
     </span><span class="kw">pub fn </span>drop_span(<span class="kw-2">&amp;</span><span class="self">self</span>, id: span::Id) {
         <span class="attribute">#[allow(deprecated)]
         </span><span class="self">self</span>.subscriber().drop_span(id);
     }

     <span class="doccomment">/// Notifies the subscriber that a [span ID] has been dropped, and returns
     /// `true` if there are now 0 IDs referring to that span.
     ///
     /// This function must only be called with span IDs that were returned by
     /// this `Dispatch`&#39;s [`new_span`] function. The `tracing` crate upholds
     /// this guarantee and any other libraries implementing instrumentation APIs
     /// must as well.
     ///
     /// This calls the [`try_close`] function on the [`Subscriber`] that this
     ///  `Dispatch` forwards to.
     ///
     /// [span ID]: super::span::Id
     /// [`Subscriber`]: super::subscriber::Subscriber
     /// [`try_close`]: super::subscriber::Subscriber::try_close
     /// [`new_span`]: super::subscriber::Subscriber::new_span
     </span><span class="kw">pub fn </span>try_close(<span class="kw-2">&amp;</span><span class="self">self</span>, id: span::Id) -&gt; bool {
         <span class="self">self</span>.subscriber().try_close(id)
     }

     <span class="doccomment">/// Returns a type representing this subscriber&#39;s view of the current span.
     ///
     /// This calls the [`current`] function on the `Subscriber` that this
     /// `Dispatch` forwards to.
     ///
     /// [`current`]: super::subscriber::Subscriber::current_span
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>current_span(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; span::Current {
         <span class="self">self</span>.subscriber().current_span()
     }

     <span class="doccomment">/// Returns `true` if this `Dispatch` forwards to a `Subscriber` of type
     /// `T`.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>is&lt;T: Any&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
         &lt;<span class="kw">dyn </span>Subscriber&gt;::is::&lt;T&gt;(<span class="self">self</span>.subscriber())
     }

     <span class="doccomment">/// Returns some reference to the `Subscriber` this `Dispatch` forwards to
     /// if it is of type `T`, or `None` if it isn&#39;t.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>downcast_ref&lt;T: Any&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span>T&gt; {
         &lt;<span class="kw">dyn </span>Subscriber&gt;::downcast_ref(<span class="self">self</span>.subscriber())
     }
 }

 <span class="kw">impl </span>Default <span class="kw">for </span>Dispatch {
     <span class="doccomment">/// Returns the current default dispatcher
     </span><span class="kw">fn </span>default() -&gt; <span class="self">Self </span>{
         get_default(|default| default.clone())
     }
 }

 <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>Dispatch {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         <span class="kw">match </span><span class="self">self</span>.subscriber {
             Kind::Scoped(<span class="kw-2">ref </span>s) =&gt; f
                 .debug_tuple(<span class="string">&quot;Dispatch::Scoped&quot;</span>)
                 .field(<span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{:p}&quot;</span>, s))
                 .finish(),
             Kind::Global(s) =&gt; f
                 .debug_tuple(<span class="string">&quot;Dispatch::Global&quot;</span>)
                 .field(<span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{:p}&quot;</span>, s))
                 .finish(),
         }
     }
 }

 <span class="kw">impl</span>&lt;S&gt; From&lt;S&gt; <span class="kw">for </span>Dispatch
 <span class="kw">where
     </span>S: Subscriber + Send + Sync + <span class="lifetime">&#39;static</span>,
 {
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>from(subscriber: S) -&gt; <span class="self">Self </span>{
         Dispatch::new(subscriber)
     }
 }

 <span class="comment">// === impl WeakDispatch ===

 </span><span class="kw">impl </span>WeakDispatch {
     <span class="doccomment">/// Attempts to upgrade this `WeakDispatch` to a [`Dispatch`].
     ///
     /// Returns `None` if the referenced `Dispatch` has already been dropped.
     ///
     /// ## Examples
     ///
     /// ```
     /// # use tracing_core::subscriber::NoSubscriber;
     /// # use tracing_core::dispatcher::Dispatch;
     /// let strong = Dispatch::new(NoSubscriber::default());
     /// let weak = strong.downgrade();
     ///
     /// // The strong here keeps it alive, so we can still access the object.
     /// assert!(weak.upgrade().is_some());
     ///
     /// drop(strong); // But not any more.
     /// assert!(weak.upgrade().is_none());
     /// ```
     </span><span class="kw">pub fn </span>upgrade(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;Dispatch&gt; {
         <span class="self">self</span>.subscriber
             .upgrade()
             .map(|subscriber| Dispatch { subscriber })
     }
 }

 <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>WeakDispatch {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         <span class="kw">match </span><span class="self">self</span>.subscriber {
             Kind::Scoped(<span class="kw-2">ref </span>s) =&gt; f
                 .debug_tuple(<span class="string">&quot;WeakDispatch::Scoped&quot;</span>)
                 .field(<span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{:p}&quot;</span>, s))
                 .finish(),
             Kind::Global(s) =&gt; f
                 .debug_tuple(<span class="string">&quot;WeakDispatch::Global&quot;</span>)
                 .field(<span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{:p}&quot;</span>, s))
                 .finish(),
         }
     }
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">impl </span>Registrar {
     <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>upgrade(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;Dispatch&gt; {
         <span class="self">self</span>.<span class="number">0</span>.upgrade().map(|subscriber| Dispatch { subscriber })
     }
 }

 <span class="comment">// ===== impl State =====

 </span><span class="kw">impl </span>Kind&lt;Arc&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt; {
     <span class="kw">fn </span>downgrade(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; Kind&lt;Weak&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt; {
         <span class="kw">match </span><span class="self">self </span>{
             Kind::Global(s) =&gt; Kind::Global(<span class="kw-2">*</span>s),
             Kind::Scoped(<span class="kw-2">ref </span>s) =&gt; Kind::Scoped(Arc::downgrade(s)),
         }
     }
 }

 <span class="kw">impl </span>Kind&lt;Weak&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt; {
     <span class="kw">fn </span>upgrade(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;Kind&lt;Arc&lt;<span class="kw">dyn </span>Subscriber + Send + Sync&gt;&gt;&gt; {
         <span class="kw">match </span><span class="self">self </span>{
             Kind::Global(s) =&gt; <span class="prelude-val">Some</span>(Kind::Global(<span class="kw-2">*</span>s)),
             Kind::Scoped(<span class="kw-2">ref </span>s) =&gt; <span class="prelude-val">Some</span>(Kind::Scoped(s.upgrade()<span class="question-mark">?</span>)),
         }
     }
 }

 <span class="comment">// ===== impl State =====

 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">impl </span>State {
     <span class="doccomment">/// Replaces the current default dispatcher on this thread with the provided
     /// dispatcher.Any
     ///
     /// Dropping the returned `ResetGuard` will reset the default dispatcher to
     /// the previous value.
     </span><span class="attribute">#[inline]
     </span><span class="kw">fn </span>set_default(new_dispatch: Dispatch) -&gt; DefaultGuard {
         <span class="kw">let </span>prior = CURRENT_STATE
             .try_with(|state| {
                 state.can_enter.set(<span class="bool-val">true</span>);
                 state.default.replace(<span class="prelude-val">Some</span>(new_dispatch))
             })
             .ok()
             .flatten();
         EXISTS.store(<span class="bool-val">true</span>, Ordering::Release);
         SCOPED_COUNT.fetch_add(<span class="number">1</span>, Ordering::Release);
         DefaultGuard(prior)
     }

     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>enter(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;Entered&lt;<span class="lifetime">&#39;_</span>&gt;&gt; {
         <span class="kw">if </span><span class="self">self</span>.can_enter.replace(<span class="bool-val">false</span>) {
             <span class="prelude-val">Some</span>(Entered(<span class="self">self</span>))
         } <span class="kw">else </span>{
             <span class="prelude-val">None
         </span>}
     }
 }

 <span class="comment">// ===== impl Entered =====

 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Entered&lt;<span class="lifetime">&#39;a</span>&gt; {
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>current(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; Ref&lt;<span class="lifetime">&#39;a</span>, Dispatch&gt; {
         <span class="kw">let </span>default = <span class="self">self</span>.<span class="number">0</span>.default.borrow();
         Ref::map(default, |default| <span class="kw">match </span>default {
             <span class="prelude-val">Some</span>(default) =&gt; default,
             <span class="prelude-val">None </span>=&gt; get_global(),
         })
     }
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Drop <span class="kw">for </span>Entered&lt;<span class="lifetime">&#39;a</span>&gt; {
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="self">self</span>.<span class="number">0</span>.can_enter.set(<span class="bool-val">true</span>);
     }
 }

 <span class="comment">// ===== impl DefaultGuard =====

 </span><span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">impl </span>Drop <span class="kw">for </span>DefaultGuard {
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="comment">// Replace the dispatcher and then drop the old one outside
         // of the thread-local context. Dropping the dispatch may
         // lead to the drop of a subscriber which, in the process,
         // could then also attempt to access the same thread local
         // state -- causing a clash.
         </span><span class="kw">let </span>prev = CURRENT_STATE.try_with(|state| state.default.replace(<span class="self">self</span>.<span class="number">0</span>.take()));
         SCOPED_COUNT.fetch_sub(<span class="number">1</span>, Ordering::Release);
         drop(prev)
     }
 }

 <span class="attribute">#[cfg(test)]
 </span><span class="kw">mod </span>test {
     <span class="kw">use super</span>::<span class="kw-2">*</span>;
     <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
     </span><span class="kw">use </span><span class="kw">crate</span>::stdlib::sync::atomic::{AtomicUsize, Ordering};
     <span class="kw">use crate</span>::{
         callsite::Callsite,
         metadata::{Kind, Level, Metadata},
         subscriber::Interest,
     };

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>dispatch_is() {
         <span class="kw">let </span>dispatcher = Dispatch::new(NoSubscriber::default());
         <span class="macro">assert!</span>(dispatcher.is::&lt;NoSubscriber&gt;());
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>dispatch_downcasts() {
         <span class="kw">let </span>dispatcher = Dispatch::new(NoSubscriber::default());
         <span class="macro">assert!</span>(dispatcher.downcast_ref::&lt;NoSubscriber&gt;().is_some());
     }

     <span class="kw">struct </span>TestCallsite;
     <span class="kw">static </span>TEST_CALLSITE: TestCallsite = TestCallsite;
     <span class="kw">static </span>TEST_META: Metadata&lt;<span class="lifetime">&#39;static</span>&gt; = <span class="macro">metadata! </span>{
         name: <span class="string">&quot;test&quot;</span>,
         target: <span class="macro">module_path!</span>(),
         level: Level::DEBUG,
         fields: <span class="kw-2">&amp;</span>[],
         callsite: <span class="kw-2">&amp;</span>TEST_CALLSITE,
         kind: Kind::EVENT
     };

     <span class="kw">impl </span>Callsite <span class="kw">for </span>TestCallsite {
         <span class="kw">fn </span>set_interest(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: Interest) {}
         <span class="kw">fn </span>metadata(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;_</span>&gt; {
             <span class="kw-2">&amp;</span>TEST_META
         }
     }

     <span class="attribute">#[test]
     #[cfg(feature = <span class="string">&quot;std&quot;</span>)]
     </span><span class="kw">fn </span>events_dont_infinite_loop() {
         <span class="comment">// This test ensures that an event triggered within a subscriber
         // won&#39;t cause an infinite loop of events.
         </span><span class="kw">struct </span>TestSubscriber;
         <span class="kw">impl </span>Subscriber <span class="kw">for </span>TestSubscriber {
             <span class="kw">fn </span>enabled(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; bool {
                 <span class="bool-val">true
             </span>}

             <span class="kw">fn </span>new_span(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Attributes&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; span::Id {
                 span::Id::from_u64(<span class="number">0xAAAA</span>)
             }

             <span class="kw">fn </span>record(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Record&lt;<span class="lifetime">&#39;_</span>&gt;) {}

             <span class="kw">fn </span>record_follows_from(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>event(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Event&lt;<span class="lifetime">&#39;_</span>&gt;) {
                 <span class="kw">static </span>EVENTS: AtomicUsize = AtomicUsize::new(<span class="number">0</span>);
                 <span class="macro">assert_eq!</span>(
                     EVENTS.fetch_add(<span class="number">1</span>, Ordering::Relaxed),
                     <span class="number">0</span>,
                     <span class="string">&quot;event method called twice!&quot;
                 </span>);
                 Event::dispatch(<span class="kw-2">&amp;</span>TEST_META, <span class="kw-2">&amp;</span>TEST_META.fields().value_set(<span class="kw-2">&amp;</span>[]))
             }

             <span class="kw">fn </span>enter(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>exit(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}
         }

         with_default(<span class="kw-2">&amp;</span>Dispatch::new(TestSubscriber), || {
             Event::dispatch(<span class="kw-2">&amp;</span>TEST_META, <span class="kw-2">&amp;</span>TEST_META.fields().value_set(<span class="kw-2">&amp;</span>[]))
         })
     }

     <span class="attribute">#[test]
     #[cfg(feature = <span class="string">&quot;std&quot;</span>)]
     </span><span class="kw">fn </span>spans_dont_infinite_loop() {
         <span class="comment">// This test ensures that a span created within a subscriber
         // won&#39;t cause an infinite loop of new spans.

         </span><span class="kw">fn </span>mk_span() {
             get_default(|current| {
                 current.new_span(<span class="kw-2">&amp;</span>span::Attributes::new(
                     <span class="kw-2">&amp;</span>TEST_META,
                     <span class="kw-2">&amp;</span>TEST_META.fields().value_set(<span class="kw-2">&amp;</span>[]),
                 ))
             });
         }

         <span class="kw">struct </span>TestSubscriber;
         <span class="kw">impl </span>Subscriber <span class="kw">for </span>TestSubscriber {
             <span class="kw">fn </span>enabled(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; bool {
                 <span class="bool-val">true
             </span>}

             <span class="kw">fn </span>new_span(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Attributes&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; span::Id {
                 <span class="kw">static </span>NEW_SPANS: AtomicUsize = AtomicUsize::new(<span class="number">0</span>);
                 <span class="macro">assert_eq!</span>(
                     NEW_SPANS.fetch_add(<span class="number">1</span>, Ordering::Relaxed),
                     <span class="number">0</span>,
                     <span class="string">&quot;new_span method called twice!&quot;
                 </span>);
                 mk_span();
                 span::Id::from_u64(<span class="number">0xAAAA</span>)
             }

             <span class="kw">fn </span>record(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Record&lt;<span class="lifetime">&#39;_</span>&gt;) {}

             <span class="kw">fn </span>record_follows_from(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>event(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Event&lt;<span class="lifetime">&#39;_</span>&gt;) {}

             <span class="kw">fn </span>enter(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>exit(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}
         }

         with_default(<span class="kw-2">&amp;</span>Dispatch::new(TestSubscriber), mk_span)
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>default_no_subscriber() {
         <span class="kw">let </span>default_dispatcher = Dispatch::default();
         <span class="macro">assert!</span>(default_dispatcher.is::&lt;NoSubscriber&gt;());
     }

     <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
     #[test]
     </span><span class="kw">fn </span>default_dispatch() {
         <span class="kw">struct </span>TestSubscriber;
         <span class="kw">impl </span>Subscriber <span class="kw">for </span>TestSubscriber {
             <span class="kw">fn </span>enabled(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; bool {
                 <span class="bool-val">true
             </span>}

             <span class="kw">fn </span>new_span(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Attributes&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; span::Id {
                 span::Id::from_u64(<span class="number">0xAAAA</span>)
             }

             <span class="kw">fn </span>record(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Record&lt;<span class="lifetime">&#39;_</span>&gt;) {}

             <span class="kw">fn </span>record_follows_from(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>event(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>Event&lt;<span class="lifetime">&#39;_</span>&gt;) {}

             <span class="kw">fn </span>enter(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}

             <span class="kw">fn </span>exit(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;</span>span::Id) {}
         }
         <span class="kw">let </span>guard = set_default(<span class="kw-2">&amp;</span>Dispatch::new(TestSubscriber));
         <span class="kw">let </span>default_dispatcher = Dispatch::default();
         <span class="macro">assert!</span>(default_dispatcher.is::&lt;TestSubscriber&gt;());

         drop(guard);
         <span class="kw">let </span>default_dispatcher = Dispatch::default();
         <span class="macro">assert!</span>(default_dispatcher.is::&lt;NoSubscriber&gt;());
     }
 }
 </code></pre></div>
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