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docs: Fix rendering issue with misaligned tooltips. (tokio-rs#1435)
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| Original file line number | Diff line number | Diff line change |
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| //! 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'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(&self, _: &Attributes) -> Id { Id::from_u64(0) } | ||
| //! # fn record(&self, _: &Id, _: &Record) {} | ||
| //! # fn event(&self, _: &Event) {} | ||
| //! # fn record_follows_from(&self, _: &Id, _: &Id) {} | ||
| //! # fn enabled(&self, _: &Metadata) -> bool { false } | ||
| //! # fn enter(&self, _: &Id) {} | ||
| //! # fn exit(&self, _: &Id) {} | ||
| //! # } | ||
| //! # impl FooSubscriber { fn new() -> 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(&self, _: &Attributes) -> Id { Id::from_u64(0) } | ||
| //! # fn record(&self, _: &Id, _: &Record) {} | ||
| //! # fn event(&self, _: &Event) {} | ||
| //! # fn record_follows_from(&self, _: &Id, _: &Id) {} | ||
| //! # fn enabled(&self, _: &Metadata) -> bool { false } | ||
| //! # fn enter(&self, _: &Id) {} | ||
| //! # fn exit(&self, _: &Id) {} | ||
| //! # } | ||
| //! # impl FooSubscriber { fn new() -> Self { FooSubscriber } } | ||
| //! # let my_subscriber = FooSubscriber::new(); | ||
| //! # let my_dispatch = dispatcher::Dispatch::new(my_subscriber); | ||
| //! // no default subscriber | ||
| //! | ||
| //! # #[cfg(feature = "std")] | ||
| //! dispatcher::with_default(&my_dispatch, || { | ||
| //! // my_subscriber is the default | ||
| //! }); | ||
| //! | ||
| //! // no default subscriber again | ||
| //! ``` | ||
| //! It's important to note that `with_default` will not propagate the current | ||
| //! thread'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(&self, _: &Attributes) -> Id { Id::from_u64(0) } | ||
| //! # fn record(&self, _: &Id, _: &Record) {} | ||
| //! # fn event(&self, _: &Event) {} | ||
| //! # fn record_follows_from(&self, _: &Id, _: &Id) {} | ||
| //! # fn enabled(&self, _: &Metadata) -> bool { false } | ||
| //! # fn enter(&self, _: &Id) {} | ||
| //! # fn exit(&self, _: &Id) {} | ||
| //! # } | ||
| //! # impl FooSubscriber { fn new() -> 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("global default was already set!"); | ||
| //! | ||
| //! // `my_subscriber` is now the default | ||
| //! ``` | ||
| //! <div class="example-wrap" style="display:inline-block"> | ||
| //! <pre class="ignore" style="white-space:normal;font:inherit;"> | ||
| //! <strong>Note</strong>: The thread-local scoped dispatcher (<code>with_default</code>) | ||
| //! requires the Rust standard library. <code>no_std</code> users should | ||
| //! use <a href="fn.set_global_default.html"><code>set_global_default</code></a> | ||
| //! instead. | ||
| //! </pre></div> | ||
| //! | ||
| //! ## Accessing the Default Subscriber | ||
| //! | ||
| //! A thread'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. | ||
| //! | ||
| //! [`Subscriber`]: struct.Subscriber.html | ||
| //! [`with_default`]: fn.with_default.html | ||
| //! [`set_global_default`]: fn.set_global_default.html | ||
| //! [`get_default`]: fn.get_default.html | ||
| //! [`Dispatch`]: struct.Dispatch.html | ||
| #[cfg(feature = "std")] | ||
| #[cfg_attr(docsrs, doc(cfg(feature = "std")))] | ||
| pub use tracing_core::dispatcher::set_default; | ||
| #[cfg(feature = "std")] | ||
| #[cfg_attr(docsrs, doc(cfg(feature = "std")))] | ||
| pub use tracing_core::dispatcher::with_default; | ||
| #[cfg(feature = "std")] | ||
| #[cfg_attr(docsrs, doc(cfg(feature = "std")))] | ||
| pub use tracing_core::dispatcher::DefaultGuard; | ||
| pub use tracing_core::dispatcher::{ | ||
| get_default, set_global_default, Dispatch, SetGlobalDefaultError, | ||
| }; | ||
|
|
||
| /// Private API for internal use by tracing's macros. | ||
| /// | ||
| /// This function is *not* considered part of `tracing`'s public API, and has no | ||
| /// stability guarantees. If you use it, and it breaks or disappears entirely, | ||
| /// don't say we didn;'t warn you. | ||
| #[doc(hidden)] | ||
| pub use tracing_core::dispatcher::has_been_set; |