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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
//! ```
//!
//! <pre class="ignore" style="white-space:normal;font:inherit;">
//! <strong>Note</strong>:the thread-local scoped dispatcher
//! (<a href="#fn.with_default"><code>with_default</code></a>) requires the
//! Rust standard library. <code>no_std</code> users should use
//! <a href="#fn.set_global_default"><code>set_global_default</code></a>
//! instead.
//! </pre>
//!
//! ## 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.
//!
use crate::{
callsite, span,
subscriber::{self, NoSubscriber, Subscriber},
Event, LevelFilter, Metadata,
};
use crate::stdlib::{
any::Any,
fmt,
sync::{
atomic::{AtomicBool, AtomicUsize, Ordering},
Arc, Weak,
},
};
#[cfg(feature = "std")]
use crate::stdlib::{
cell::{Cell, RefCell, RefMut},
error,
};
#[cfg(feature = "alloc")]
use alloc::sync::{Arc, Weak};
#[cfg(feature = "alloc")]
use core::ops::Deref;
/// `Dispatch` trace data to a [`Subscriber`].
#[derive(Clone)]
pub struct Dispatch {
subscriber: Arc<dyn Subscriber + Send + Sync>,
}
/// `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<Dispatch>`. 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
#[derive(Clone)]
pub struct WeakDispatch {
subscriber: Weak<dyn Subscriber + Send + Sync>,
}
#[cfg(feature = "alloc")]
#[derive(Clone)]
enum Kind<T> {
Global(&'static (dyn Collect + Send + Sync)),
Scoped(T),
}
#[cfg(feature = "std")]
thread_local! {
static CURRENT_STATE: State = State {
default: RefCell::new(None),
can_enter: Cell::new(true),
};
}
static EXISTS: AtomicBool = AtomicBool::new(false);
static GLOBAL_INIT: AtomicUsize = AtomicUsize::new(UNINITIALIZED);
const UNINITIALIZED: usize = 0;
const INITIALIZING: usize = 1;
const INITIALIZED: usize = 2;
static mut GLOBAL_DISPATCH: Option<Dispatch> = None;
/// The dispatch state of a thread.
#[cfg(feature = "std")]
struct State {
/// This thread's current default dispatcher.
default: RefCell<Option<Dispatch>>,
/// 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'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`.
can_enter: Cell<bool>,
}
/// 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.
#[cfg(feature = "std")]
struct Entered<'a>(&'a State);
/// A guard that resets the current default dispatcher to the prior
/// default dispatcher when dropped.
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
#[derive(Debug)]
pub struct DefaultGuard(Option<Dispatch>);
/// Sets this dispatch as the default for the duration of a closure.
///
/// The default dispatcher is used when creating a new [span] or
/// [`Event`].
///
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: This function required 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>
///
/// [span]: super::span
/// [`Subscriber`]: super::subscriber::Subscriber
/// [`Event`]: super::event::Event
/// [`set_global_default`]: super::set_global_default
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
pub fn with_default<T>(dispatcher: &Dispatch, f: impl FnOnce() -> T) -> T {
// 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.
let _guard = set_default(dispatcher);
f()
}
/// Sets the dispatch as the default dispatch for the duration of the lifetime
/// of the returned DefaultGuard
///
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: This function required 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>
///
/// [`set_global_default`]: super::set_global_default
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
#[must_use = "Dropping the guard unregisters the dispatcher."]
pub fn set_default(dispatcher: &Dispatch) -> DefaultGuard {
// 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.
State::set_default(dispatcher.clone())
}
/// 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.
///
/// <div class="example-wrap" style="display:inline-block"><pre class="compile_fail" style="white-space:normal;font:inherit;">
/// <strong>Warning</strong>: In general, libraries should <em>not</em> call
/// <code>set_global_default()</code>! Doing so will cause conflicts when
/// executables that depend on the library try to set the default later.
/// </pre></div>
///
/// [span]: super::span
/// [`Subscriber`]: super::subscriber::Subscriber
/// [`Event`]: super::event::Event
pub fn set_global_default(dispatcher: Dispatch) -> Result<(), SetGlobalDefaultError> {
// if `compare_exchange` returns Result::Ok(_), then `new` has been set and
// `current`—now the prior value—has been returned in the `Ok()` branch.
if GLOBAL_INIT
.compare_exchange(
UNINITIALIZED,
INITIALIZING,
Ordering::SeqCst,
Ordering::SeqCst,
)
.is_ok()
{
unsafe {
GLOBAL_DISPATCH = Some(dispatcher);
}
GLOBAL_INIT.store(INITIALIZED, Ordering::SeqCst);
EXISTS.store(true, Ordering::Release);
Ok(())
} else {
Err(SetGlobalDefaultError { _no_construct: () })
}
}
/// 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.
#[doc(hidden)]
#[inline(always)]
pub fn has_been_set() -> bool {
EXISTS.load(Ordering::Relaxed)
}
/// Returned if setting the global dispatcher fails.
pub struct SetGlobalDefaultError {
_no_construct: (),
}
impl fmt::Debug for SetGlobalDefaultError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("SetGlobalDefaultError")
.field(&Self::MESSAGE)
.finish()
}
}
impl fmt::Display for SetGlobalDefaultError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad(Self::MESSAGE)
}
}
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl error::Error for SetGlobalDefaultError {}
impl SetGlobalDefaultError {
const MESSAGE: &'static str = "a global default trace dispatcher has already been set";
}
/// Executes a closure with a reference to this thread'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
#[cfg(feature = "std")]
pub fn get_default<T, F>(mut f: F) -> T
where
F: FnMut(&Dispatch) -> T,
{
CURRENT_STATE
.try_with(|state| {
if let Some(entered) = state.enter() {
return f(&*entered.current());
}
f(&Dispatch::none())
})
.unwrap_or_else(|_| f(&Dispatch::none()))
}
/// Executes a closure with a reference to this thread'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
#[cfg(feature = "std")]
#[doc(hidden)]
#[inline(never)]
pub fn get_current<T>(f: impl FnOnce(&Dispatch) -> T) -> Option<T> {
CURRENT_STATE
.try_with(|state| {
let entered = state.enter()?;
Some(f(&*entered.current()))
})
.ok()?
}
/// Executes a closure with a reference to the current [dispatcher].
///
/// [dispatcher]: super::dispatcher::Dispatch
#[cfg(not(feature = "std"))]
#[doc(hidden)]
pub fn get_current<T>(f: impl FnOnce(&Dispatch) -> T) -> Option<T> {
let dispatch = get_global()?;
Some(f(&dispatch))
}
/// Executes a closure with a reference to the current [dispatcher].
///
/// [dispatcher]: super::dispatcher::Dispatch
#[cfg(not(feature = "std"))]
pub fn get_default<T, F>(mut f: F) -> T
where
F: FnMut(&Dispatch) -> T,
{
if let Some(d) = get_global() {
f(d)
} else {
f(&Dispatch::none())
}
}
fn get_global() -> Option<&'static Dispatch> {
if GLOBAL_INIT.load(Ordering::SeqCst) != INITIALIZED {
return None;
}
unsafe {
// This is safe given the invariant that setting the global dispatcher
// also sets `GLOBAL_INIT` to `INITIALIZED`.
Some(GLOBAL_DISPATCH.as_ref().expect(
"invariant violated: GLOBAL_DISPATCH must be initialized before GLOBAL_INIT is set",
))
}
}
#[cfg(feature = "std")]
pub(crate) struct Registrar(Weak<dyn Subscriber + Send + Sync>);
impl Dispatch {
/// Returns a new `Dispatch` that discards events and spans.
#[inline]
pub fn none() -> Self {
Dispatch {
subscriber: Arc::new(NoSubscriber::default()),
}
}
/// Returns a `Dispatch` that forwards to the given [`Subscriber`].
///
/// [`Subscriber`]: super::subscriber::Subscriber
pub fn new<S>(subscriber: S) -> Self
where
S: Subscriber + Send + Sync + 'static,
{
let me = Dispatch {
subscriber: Arc::new(subscriber),
};
callsite::register_dispatch(&me);
me
}
#[cfg(feature = "std")]
pub(crate) fn registrar(&self) -> Registrar {
Registrar(Arc::downgrade(&self.subscriber))
}
/// 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'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
pub fn downgrade(&self) -> WeakDispatch {
WeakDispatch {
subscriber: Arc::downgrade(&self.subscriber),
}
}
#[inline(always)]
#[cfg(not(feature = "alloc"))]
pub(crate) fn subscriber(&self) -> &(dyn Subscriber + Send + Sync) {
&self.subscriber
}
/// 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
#[inline]
pub fn register_callsite(&self, metadata: &'static Metadata<'static>) -> subscriber::Interest {
self.subscriber.register_callsite(metadata)
}
/// 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
// TODO(eliza): consider making this a public API?
#[inline]
pub(crate) fn max_level_hint(&self) -> Option<LevelFilter> {
self.subscriber.max_level_hint()
}
/// 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
#[inline]
pub fn new_span(&self, span: &span::Attributes<'_>) -> span::Id {
self.subscriber.new_span(span)
}
/// 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
#[inline]
pub fn record(&self, span: &span::Id, values: &span::Record<'_>) {
self.subscriber.record(span, values)
}
/// 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
#[inline]
pub fn record_follows_from(&self, span: &span::Id, follows: &span::Id) {
self.subscriber.record_follows_from(span, follows)
}
/// 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
#[inline]
pub fn enabled(&self, metadata: &Metadata<'_>) -> bool {
self.subscriber.enabled(metadata)
}
/// 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
#[inline]
pub fn event(&self, event: &Event<'_>) {
if self.subscriber.event_enabled(event) {
self.subscriber.event(event);
}
}
/// 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
pub fn enter(&self, span: &span::Id) {
self.subscriber.enter(span);
}
/// 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
pub fn exit(&self, span: &span::Id) {
self.subscriber.exit(span);
}
/// 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`'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
#[inline]
pub fn clone_span(&self, id: &span::Id) -> span::Id {
self.subscriber.clone_span(id)
}
/// 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`'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.
///
/// <pre class="compile_fail" style="white-space:normal;font:inherit;">
/// <strong>Deprecated</strong>: The <a href="#method.try_close"><code>
/// try_close</code></a> method is functionally identical, but returns
/// <code>true</code> if the span is now closed. It should be used
/// instead of this method.
/// </pre>
///
/// [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()
#[inline]
#[deprecated(since = "0.1.2", note = "use `Dispatch::try_close` instead")]
pub fn drop_span(&self, id: span::Id) {
#[allow(deprecated)]
self.subscriber.drop_span(id);
}
/// 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`'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
pub fn try_close(&self, id: span::Id) -> bool {
self.subscriber.try_close(id)
}
/// Returns a type representing this subscriber'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
#[inline]
pub fn current_span(&self) -> span::Current {
self.subscriber.current_span()
}
/// Returns `true` if this `Dispatch` forwards to a `Subscriber` of type
/// `T`.
#[inline]
pub fn is<T: Any>(&self) -> bool {
<dyn Subscriber>::is::<T>(&self.subscriber)
}
/// Returns some reference to the `Subscriber` this `Dispatch` forwards to
/// if it is of type `T`, or `None` if it isn't.
#[inline]
pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
<dyn Subscriber>::downcast_ref(&self.subscriber)
}
}
impl Default for Dispatch {
/// Returns the current default dispatcher
fn default() -> Self {
get_default(|default| default.clone())
}
}
impl fmt::Debug for Dispatch {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("Dispatch")
.field(&format_args!("{:p}", self.subscriber))
.finish()
}
}
impl<S> From<S> for Dispatch
where
S: Subscriber + Send + Sync + 'static,
{
#[inline]
fn from(subscriber: S) -> Self {
Dispatch::new(subscriber)
}
}
// === impl WeakDispatch ===
impl WeakDispatch {
/// 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());
/// ```
pub fn upgrade(&self) -> Option<Dispatch> {
self.subscriber
.upgrade()
.map(|subscriber| Dispatch { subscriber })
}
}
impl fmt::Debug for WeakDispatch {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut tuple = f.debug_tuple("WeakDispatch");
match self.subscriber.upgrade() {
Some(subscriber) => tuple.field(&format_args!("Some({:p})", subscriber)),
None => tuple.field(&format_args!("None")),
};
tuple.finish()
}
}
#[cfg(feature = "std")]
impl Registrar {
pub(crate) fn upgrade(&self) -> Option<Dispatch> {
self.0.upgrade().map(|subscriber| Dispatch { subscriber })
}
}
// ===== impl State =====
#[cfg(feature = "std")]
impl State {
/// 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.
#[inline]
fn set_default(new_dispatch: Dispatch) -> DefaultGuard {
let prior = CURRENT_STATE
.try_with(|state| {
state.can_enter.set(true);
state.default.replace(Some(new_dispatch))
})
.ok()
.flatten();
EXISTS.store(true, Ordering::Release);
DefaultGuard(prior)
}
#[inline]
fn enter(&self) -> Option<Entered<'_>> {
if self.can_enter.replace(false) {
Some(Entered(self))
} else {
None
}
}
}
// ===== impl Entered =====
#[cfg(feature = "std")]
impl<'a> Entered<'a> {
#[inline]
fn current(&self) -> RefMut<'a, Dispatch> {
let default = self.0.default.borrow_mut();
RefMut::map(default, |default| {
default.get_or_insert_with(|| get_global().cloned().unwrap_or_else(Dispatch::none))
})
}
}
#[cfg(feature = "std")]
impl<'a> Drop for Entered<'a> {
#[inline]
fn drop(&mut self) {
self.0.can_enter.set(true);
}
}
// ===== impl DefaultGuard =====
#[cfg(feature = "std")]
impl Drop for DefaultGuard {
#[inline]
fn drop(&mut self) {
// 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.
let prev = CURRENT_STATE.try_with(|state| state.default.replace(self.0.take()));
drop(prev)
}
}
#[cfg(test)]
mod test {
use super::*;
#[cfg(feature = "std")]
use crate::stdlib::sync::atomic::{AtomicUsize, Ordering};
use crate::{
callsite::Callsite,
metadata::{Kind, Level, Metadata},
subscriber::Interest,
};
#[test]
fn dispatch_is() {
let dispatcher = Dispatch::new(NoSubscriber::default());
assert!(dispatcher.is::<NoSubscriber>());
}
#[test]
fn dispatch_downcasts() {
let dispatcher = Dispatch::new(NoSubscriber::default());
assert!(dispatcher.downcast_ref::<NoSubscriber>().is_some());
}
struct TestCallsite;
static TEST_CALLSITE: TestCallsite = TestCallsite;
static TEST_META: Metadata<'static> = metadata! {
name: "test",
target: module_path!(),
level: Level::DEBUG,
fields: &[],
callsite: &TEST_CALLSITE,
kind: Kind::EVENT
};
impl Callsite for TestCallsite {
fn set_interest(&self, _: Interest) {}
fn metadata(&self) -> &Metadata<'_> {
&TEST_META
}
}
#[test]
#[cfg(feature = "std")]
fn events_dont_infinite_loop() {
// This test ensures that an event triggered within a subscriber
// won't cause an infinite loop of events.
struct TestSubscriber;
impl Subscriber for TestSubscriber {
fn enabled(&self, _: &Metadata<'_>) -> bool {
true
}
fn new_span(&self, _: &span::Attributes<'_>) -> span::Id {
span::Id::from_u64(0xAAAA)
}
fn record(&self, _: &span::Id, _: &span::Record<'_>) {}
fn record_follows_from(&self, _: &span::Id, _: &span::Id) {}
fn event(&self, _: &Event<'_>) {
static EVENTS: AtomicUsize = AtomicUsize::new(0);
assert_eq!(
EVENTS.fetch_add(1, Ordering::Relaxed),
0,
"event method called twice!"
);
Event::dispatch(&TEST_META, &TEST_META.fields().value_set(&[]))
}
fn enter(&self, _: &span::Id) {}
fn exit(&self, _: &span::Id) {}
}
with_default(&Dispatch::new(TestSubscriber), || {
Event::dispatch(&TEST_META, &TEST_META.fields().value_set(&[]))
})
}
#[test]
#[cfg(feature = "std")]
fn spans_dont_infinite_loop() {
// This test ensures that a span created within a subscriber
// won't cause an infinite loop of new spans.
fn mk_span() {
get_default(|current| {
current.new_span(&span::Attributes::new(
&TEST_META,
&TEST_META.fields().value_set(&[]),
))
});
}
struct TestSubscriber;
impl Subscriber for TestSubscriber {
fn enabled(&self, _: &Metadata<'_>) -> bool {
true
}
fn new_span(&self, _: &span::Attributes<'_>) -> span::Id {
static NEW_SPANS: AtomicUsize = AtomicUsize::new(0);
assert_eq!(
NEW_SPANS.fetch_add(1, Ordering::Relaxed),
0,
"new_span method called twice!"
);
mk_span();
span::Id::from_u64(0xAAAA)
}
fn record(&self, _: &span::Id, _: &span::Record<'_>) {}
fn record_follows_from(&self, _: &span::Id, _: &span::Id) {}
fn event(&self, _: &Event<'_>) {}
fn enter(&self, _: &span::Id) {}
fn exit(&self, _: &span::Id) {}
}
with_default(&Dispatch::new(TestSubscriber), mk_span)
}
#[test]
fn default_no_subscriber() {
let default_dispatcher = Dispatch::default();
assert!(default_dispatcher.is::<NoSubscriber>());
}
#[cfg(feature = "std")]
#[test]
fn default_dispatch() {
struct TestSubscriber;
impl Subscriber for TestSubscriber {
fn enabled(&self, _: &Metadata<'_>) -> bool {
true
}
fn new_span(&self, _: &span::Attributes<'_>) -> span::Id {
span::Id::from_u64(0xAAAA)
}
fn record(&self, _: &span::Id, _: &span::Record<'_>) {}
fn record_follows_from(&self, _: &span::Id, _: &span::Id) {}
fn event(&self, _: &Event<'_>) {}
fn enter(&self, _: &span::Id) {}
fn exit(&self, _: &span::Id) {}
}
let guard = set_default(&Dispatch::new(TestSubscriber));
let default_dispatcher = Dispatch::default();
assert!(default_dispatcher.is::<TestSubscriber>());
drop(guard);
let default_dispatcher = Dispatch::default();
assert!(default_dispatcher.is::<NoSubscriber>());
}
}