tokio: Add initial io driver metrics

.gitignore

@@ -1,2 +1,4 @@
 target
 Cargo.lock
+
+.cargo/config.toml

tests-integration/Cargo.toml

@@ -20,7 +20,7 @@ required-features = ["rt-process-signal"]
 # For mem check
 rt-net = ["tokio/rt", "tokio/rt-multi-thread", "tokio/net"]
 # For test-process-signal
-rt-process-signal = ["rt", "tokio/process", "tokio/signal"]
+rt-process-signal = ["rt-net", "tokio/process", "tokio/signal"]
 
 full = [
     "macros",

tokio/src/io/driver/metrics.rs

@@ -0,0 +1,22 @@
+//! This file contains mocks of the metrics types used in the I/O driver.
+//!
+//! The reason these mocks don't live in `src/runtime/mock.rs` is because
+//! these need to be available in the case when `net` is enabled but
+//! `rt` is not.
+
+cfg_not_rt_and_metrics! {
+    #[derive(Default)]
+    pub(crate) struct IoDriverMetrics {}
+
+    impl IoDriverMetrics {
+        pub(crate) fn incr_fd_count(&self) {}
+        pub(crate) fn dec_fd_count(&self) {}
+        pub(crate) fn incr_ready_count_by(&self, _amt: u64) {}
+    }
+}
+
+cfg_rt! {
+    cfg_metrics! {
+        pub(crate) use crate::runtime::IoDriverMetrics;
+    }
+}

tokio/src/io/driver/mod.rs

@@ -14,10 +14,14 @@ pub(crate) use registration::Registration;
 mod scheduled_io;
 use scheduled_io::ScheduledIo;
 
+mod metrics;
+
 use crate::park::{Park, Unpark};
 use crate::util::slab::{self, Slab};
 use crate::{loom::sync::Mutex, util::bit};
 
+use metrics::IoDriverMetrics;
+
 use std::fmt;
 use std::io;
 use std::sync::{Arc, Weak};
@@ -74,6 +78,8 @@ pub(super) struct Inner {
 
     /// Used to wake up the reactor from a call to `turn`.
     waker: mio::Waker,
+
+    metrics: IoDriverMetrics,
 }
 
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
@@ -130,6 +136,7 @@ impl Driver {
                 registry,
                 io_dispatch: allocator,
                 waker,
+                metrics: IoDriverMetrics::default(),
             }),
         })
     }
@@ -167,14 +174,18 @@ impl Driver {
         }
 
         // Process all the events that came in, dispatching appropriately
+        let mut ready_count = 0;
         for event in events.iter() {
             let token = event.token();
 
             if token != TOKEN_WAKEUP {
                 self.dispatch(token, Ready::from_mio(event));
+                ready_count += 1;
             }
         }
 
+        self.inner.metrics.incr_ready_count_by(ready_count);
+
         self.events = Some(events);
 
         Ok(())
@@ -279,6 +290,25 @@ cfg_not_rt! {
     }
 }
 
+cfg_metrics! {
+   impl Handle {
+        // TODO: Remove this when handle contains `Arc<Inner>` so that we can return
+        // &IoDriverMetrics instead of using a closure.
+        //
+        // Related issue: https://github.com/tokio-rs/tokio/issues/4509
+        pub(crate) fn with_io_driver_metrics<F, R>(&self, f: F) -> Option<R>
+        where
+            F: Fn(&IoDriverMetrics) -> R,
+        {
+            if let Some(inner) = self.inner() {
+                Some(f(&inner.metrics))
+            } else {
+                None
+            }
+        }
+   }
+}
+
 impl Handle {
     /// Forces a reactor blocked in a call to `turn` to wakeup, or otherwise
     /// makes the next call to `turn` return immediately.
@@ -335,12 +365,18 @@ impl Inner {
         self.registry
             .register(source, mio::Token(token), interest.to_mio())?;
 
+        self.metrics.incr_fd_count();
+
         Ok(shared)
     }
 
     /// Deregisters an I/O resource from the reactor.
     pub(super) fn deregister_source(&self, source: &mut impl mio::event::Source) -> io::Result<()> {
-        self.registry.deregister(source)
+        self.registry.deregister(source)?;
+
+        self.metrics.dec_fd_count();
+
+        Ok(())
     }
 }
 

tokio/src/lib.rs

@@ -483,7 +483,7 @@ pub(crate) use self::doc::winapi;
 
 #[cfg(all(not(docsrs), windows, feature = "net"))]
 #[allow(unused)]
-pub(crate) use ::winapi;
+pub(crate) use winapi;
 
 cfg_macros! {
     /// Implementation detail of the `select!` macro. This macro is **not**

tokio/src/macros/cfg.rs

@@ -195,6 +195,12 @@ macro_rules! cfg_not_metrics {
     }
 }
 
+macro_rules! cfg_not_rt_and_metrics {
+    ($($item:item)*) => {
+        $( #[cfg(not(all(feature = "rt", all(tokio_unstable, not(loom)))))] $item )*
+    }
+}
+
 macro_rules! cfg_net {
     ($($item:item)*) => {
         $(

tokio/src/runtime/metrics/io.rs

@@ -0,0 +1,30 @@
+#![cfg_attr(not(feature = "net"), allow(dead_code))]
+
+use std::sync::atomic::{AtomicU64, Ordering::Relaxed};
+
+#[derive(Default)]
+pub(crate) struct IoDriverMetrics {
+    pub(super) fd_registered_count: AtomicU64,
+    pub(super) fd_deregistered_count: AtomicU64,
+    pub(super) ready_count: AtomicU64,
+}
+
+impl IoDriverMetrics {
+    pub(crate) fn incr_fd_count(&self) {
+        let prev = self.fd_registered_count.load(Relaxed);
+        let new = prev.wrapping_add(1);
+        self.fd_registered_count.store(new, Relaxed);
+    }
+
+    pub(crate) fn dec_fd_count(&self) {
+        let prev = self.fd_deregistered_count.load(Relaxed);
+        let new = prev.wrapping_add(1);
+        self.fd_deregistered_count.store(new, Relaxed);
+    }
+
+    pub(crate) fn incr_ready_count_by(&self, amt: u64) {
+        let prev = self.ready_count.load(Relaxed);
+        let new = prev.wrapping_add(amt);
+        self.ready_count.store(new, Relaxed);
+    }
+}

tokio/src/runtime/metrics/mod.rs

@@ -21,6 +21,11 @@ cfg_metrics! {
 
     mod worker;
     pub(crate) use worker::WorkerMetrics;
+
+    cfg_net! {
+        mod io;
+        pub(crate) use io::IoDriverMetrics;
+    }
 }
 
 cfg_not_metrics! {

tokio/src/runtime/metrics/runtime.rs

@@ -447,3 +447,65 @@ impl RuntimeMetrics {
         self.handle.spawner.worker_local_queue_depth(worker)
     }
 }
+
+cfg_net! {
+    impl RuntimeMetrics {
+        /// Returns the number of file descriptors currently registered with the
+        /// runtime's I/O driver.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Handle;
+        ///
+        /// #[tokio::main]
+        /// async fn main() {
+        ///     let metrics = Handle::current().metrics();
+        ///
+        ///     let n = metrics.io_driver_fd_count();
+        ///     println!("{} fds currently registered with the runtime's I/O driver.", n);
+        /// }
+        /// ```
+        pub fn io_driver_fd_count(&self) -> u64 {
+            self.with_io_driver_metrics(|m| {
+                let registered = m.fd_registered_count.load(Relaxed);
+                let deregistered = m.fd_deregistered_count.load(Relaxed);
+                registered.wrapping_sub(deregistered)
+            })
+        }
+
+        /// Returns the number of ready events processed by the runtime's
+        /// I/O driver.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Handle;
+        ///
+        /// #[tokio::main]
+        /// async fn main() {
+        ///     let metrics = Handle::current().metrics();
+        ///
+        ///     let n = metrics.io_driver_ready_count();
+        ///     println!("{} ready events procssed by the runtime's I/O driver.", n);
+        /// }
+        /// ```
+        pub fn io_driver_ready_count(&self) -> u64 {
+            self.with_io_driver_metrics(|m| m.ready_count.load(Relaxed))
+        }
+
+        fn with_io_driver_metrics<F>(&self, f: F) -> u64
+        where
+            F: Fn(&super::IoDriverMetrics) -> u64,
+        {
+            // TODO: Investigate if this should return 0, most of our metrics always increase
+            // thus this breaks that guarantee.
+            self.handle
+                .io_handle
+                .as_ref()
+                .map(|h| h.with_io_driver_metrics(f))
+                .flatten()
+                .unwrap_or(0)
+        }
+    }
+}

tokio/src/runtime/mod.rs

@@ -187,6 +187,10 @@ cfg_metrics! {
     pub use metrics::RuntimeMetrics;
 
     pub(crate) use metrics::{MetricsBatch, SchedulerMetrics, WorkerMetrics};
+
+    cfg_net! {
+       pub(crate) use metrics::IoDriverMetrics;
+    }
 }
 
 cfg_not_metrics! {

tokio/tests/rt_metrics.rs

@@ -369,6 +369,34 @@ fn worker_local_queue_depth() {
     });
 }
 
+#[cfg(any(target_os = "linux", target_os = "macos"))]
+#[test]
+fn io_driver_fd_count() {
+    let rt = basic();
+    let metrics = rt.metrics();
+
+    let stream = tokio::net::TcpStream::connect("google.com:80");
+    let stream = rt.block_on(async move { stream.await.unwrap() });
+
+    assert_eq!(metrics.io_driver_fd_count(), 2);
+
+    drop(stream);
+
+    assert_eq!(metrics.io_driver_fd_count(), 1);
+}
+
+#[cfg(any(target_os = "linux", target_os = "macos"))]
+#[test]
+fn io_driver_ready_count() {
+    let rt = basic();
+    let metrics = rt.metrics();
+
+    let stream = tokio::net::TcpStream::connect("google.com:80");
+    let _stream = rt.block_on(async move { stream.await.unwrap() });
+
+    assert_eq!(metrics.io_driver_ready_count(), 2);
+}
+
 fn basic() -> Runtime {
     tokio::runtime::Builder::new_current_thread()
         .enable_all()