rt: implement initial set of task hooks

tokio/src/runtime/blocking/schedule.rs

@@ -1,6 +1,6 @@
 #[cfg(feature = "test-util")]
 use crate::runtime::scheduler;
-use crate::runtime::task::{self, Task};
+use crate::runtime::task::{self, Task, TaskHarnessScheduleHooks};
 use crate::runtime::Handle;
 
 /// `task::Schedule` implementation that does nothing (except some bookkeeping
@@ -12,6 +12,7 @@ use crate::runtime::Handle;
 pub(crate) struct BlockingSchedule {
     #[cfg(feature = "test-util")]
     handle: Handle,
+    hooks: TaskHarnessScheduleHooks,
 }
 
 impl BlockingSchedule {
@@ -32,6 +33,9 @@ impl BlockingSchedule {
         BlockingSchedule {
             #[cfg(feature = "test-util")]
             handle: handle.clone(),
+            hooks: TaskHarnessScheduleHooks {
+                task_terminate_callback: handle.inner.hooks().task_terminate_callback.clone(),
+            },
         }
     }
 }
@@ -57,4 +61,10 @@ impl task::Schedule for BlockingSchedule {
     fn schedule(&self, _task: task::Notified<Self>) {
         unreachable!();
     }
+
+    fn hooks(&self) -> TaskHarnessScheduleHooks {
+        TaskHarnessScheduleHooks {
+            task_terminate_callback: self.hooks.task_terminate_callback.clone(),
+        }
+    }
 }

tokio/src/runtime/builder.rs

@@ -1,5 +1,9 @@
+#![cfg_attr(loom, allow(unused_imports))]
+
 use crate::runtime::handle::Handle;
-use crate::runtime::{blocking, driver, Callback, HistogramBuilder, Runtime};
+#[cfg(tokio_unstable)]
+use crate::runtime::TaskMeta;
+use crate::runtime::{blocking, driver, Callback, HistogramBuilder, Runtime, TaskCallback};
 use crate::util::rand::{RngSeed, RngSeedGenerator};
 
 use std::fmt;
@@ -78,6 +82,12 @@ pub struct Builder {
     /// To run after each thread is unparked.
     pub(super) after_unpark: Option<Callback>,
 
+    /// To run before each task is spawned.
+    pub(super) before_spawn: Option<TaskCallback>,
+
+    /// To run after each task is terminated.
+    pub(super) after_termination: Option<TaskCallback>,
+
     /// Customizable keep alive timeout for `BlockingPool`
     pub(super) keep_alive: Option<Duration>,
 
@@ -290,6 +300,9 @@ impl Builder {
             before_park: None,
             after_unpark: None,
 
+            before_spawn: None,
+            after_termination: None,
+
             keep_alive: None,
 
             // Defaults for these values depend on the scheduler kind, so we get them
@@ -677,6 +690,91 @@ impl Builder {
         self
     }
 
+    /// Executes function `f` just before a task is spawned.
+    ///
+    /// `f` is called within the Tokio context, so functions like
+    /// [`tokio::spawn`](crate::spawn) can be called, and may result in this callback being
+    /// invoked immediately.
+    ///
+    /// This can be used for bookkeeping or monitoring purposes.
+    ///
+    /// Note: There can only be one spawn callback for a runtime; calling this function more
+    /// than once replaces the last callback defined, rather than adding to it.
+    ///
+    /// This *does not* support [`LocalSet`](crate::task::LocalSet) at this time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    /// # pub fn main() {
+    /// let runtime = runtime::Builder::new_current_thread()
+    ///     .on_task_spawn(|_| {
+    ///         println!("spawning task");
+    ///     })
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// runtime.block_on(async {
+    ///     tokio::task::spawn(std::future::ready(()));
+    ///
+    ///     for _ in 0..64 {
+    ///         tokio::task::yield_now().await;
+    ///     }
+    /// })
+    /// # }
+    /// ```
+    #[cfg(all(not(loom), tokio_unstable))]
+    pub fn on_task_spawn<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn(&TaskMeta<'_>) + Send + Sync + 'static,
+    {
+        self.before_spawn = Some(std::sync::Arc::new(f));
+        self
+    }
+
+    /// Executes function `f` just after a task is terminated.
+    ///
+    /// `f` is called within the Tokio context, so functions like
+    /// [`tokio::spawn`](crate::spawn) can be called.
+    ///
+    /// This can be used for bookkeeping or monitoring purposes.
+    ///
+    /// Note: There can only be one task termination callback for a runtime; calling this
+    /// function more than once replaces the last callback defined, rather than adding to it.
+    ///
+    /// This *does not* support [`LocalSet`](crate::task::LocalSet) at this time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    /// # pub fn main() {
+    /// let runtime = runtime::Builder::new_current_thread()
+    ///     .on_task_terminate(|_| {
+    ///         println!("killing task");
+    ///     })
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// runtime.block_on(async {
+    ///     tokio::task::spawn(std::future::ready(()));
+    ///
+    ///     for _ in 0..64 {
+    ///         tokio::task::yield_now().await;
+    ///     }
+    /// })
+    /// # }
+    /// ```
+    #[cfg(all(not(loom), tokio_unstable))]
+    pub fn on_task_terminate<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn(&TaskMeta<'_>) + Send + Sync + 'static,
+    {
+        self.after_termination = Some(std::sync::Arc::new(f));
+        self
+    }
+
     /// Creates the configured `Runtime`.
     ///
     /// The returned `Runtime` instance is ready to spawn tasks.
@@ -1118,6 +1216,8 @@ impl Builder {
             Config {
                 before_park: self.before_park.clone(),
                 after_unpark: self.after_unpark.clone(),
+                before_spawn: self.before_spawn.clone(),
+                after_termination: self.after_termination.clone(),
                 global_queue_interval: self.global_queue_interval,
                 event_interval: self.event_interval,
                 local_queue_capacity: self.local_queue_capacity,
@@ -1269,6 +1369,8 @@ cfg_rt_multi_thread! {
                 Config {
                     before_park: self.before_park.clone(),
                     after_unpark: self.after_unpark.clone(),
+                    before_spawn: self.before_spawn.clone(),
+                    after_termination: self.after_termination.clone(),
                     global_queue_interval: self.global_queue_interval,
                     event_interval: self.event_interval,
                     local_queue_capacity: self.local_queue_capacity,
@@ -1316,6 +1418,8 @@ cfg_rt_multi_thread! {
                     Config {
                         before_park: self.before_park.clone(),
                         after_unpark: self.after_unpark.clone(),
+                        before_spawn: self.before_spawn.clone(),
+                        after_termination: self.after_termination.clone(),
                         global_queue_interval: self.global_queue_interval,
                         event_interval: self.event_interval,
                         local_queue_capacity: self.local_queue_capacity,

tokio/src/runtime/config.rs

@@ -2,7 +2,7 @@
     any(not(all(tokio_unstable, feature = "full")), target_family = "wasm"),
     allow(dead_code)
 )]
-use crate::runtime::Callback;
+use crate::runtime::{Callback, TaskCallback};
 use crate::util::RngSeedGenerator;
 
 pub(crate) struct Config {
@@ -21,6 +21,12 @@ pub(crate) struct Config {
     /// Callback for a worker unparking itself
     pub(crate) after_unpark: Option<Callback>,
 
+    /// To run before each task is spawned.
+    pub(crate) before_spawn: Option<TaskCallback>,
+
+    /// To run after each task is terminated.
+    pub(crate) after_termination: Option<TaskCallback>,
+
     /// The multi-threaded scheduler includes a per-worker LIFO slot used to
     /// store the last scheduled task. This can improve certain usage patterns,
     /// especially message passing between tasks. However, this LIFO slot is not

tokio/src/runtime/mod.rs

@@ -379,6 +379,13 @@ cfg_rt! {
         pub use dump::Dump;
     }
 
+    mod task_hooks;
+    pub(crate) use task_hooks::{TaskHooks, TaskCallback};
+    #[cfg(tokio_unstable)]
+    pub use task_hooks::TaskMeta;
+    #[cfg(not(tokio_unstable))]
+    pub(crate) use task_hooks::TaskMeta;
+
     mod handle;
     pub use handle::{EnterGuard, Handle, TryCurrentError};
 

tokio/src/runtime/scheduler/current_thread/mod.rs

@@ -3,8 +3,12 @@ use crate::loom::sync::atomic::AtomicBool;
 use crate::loom::sync::Arc;
 use crate::runtime::driver::{self, Driver};
 use crate::runtime::scheduler::{self, Defer, Inject};
-use crate::runtime::task::{self, JoinHandle, OwnedTasks, Schedule, Task};
-use crate::runtime::{blocking, context, Config, MetricsBatch, SchedulerMetrics, WorkerMetrics};
+use crate::runtime::task::{
+    self, JoinHandle, OwnedTasks, Schedule, Task, TaskHarnessScheduleHooks,
+};
+use crate::runtime::{
+    blocking, context, Config, MetricsBatch, SchedulerMetrics, TaskHooks, TaskMeta, WorkerMetrics,
+};
 use crate::sync::notify::Notify;
 use crate::util::atomic_cell::AtomicCell;
 use crate::util::{waker_ref, RngSeedGenerator, Wake, WakerRef};
@@ -41,6 +45,9 @@ pub(crate) struct Handle {
 
     /// Current random number generator seed
     pub(crate) seed_generator: RngSeedGenerator,
+
+    /// User-supplied hooks to invoke for things
+    pub(crate) task_hooks: TaskHooks,
 }
 
 /// Data required for executing the scheduler. The struct is passed around to
@@ -131,6 +138,10 @@ impl CurrentThread {
             .unwrap_or(DEFAULT_GLOBAL_QUEUE_INTERVAL);
 
         let handle = Arc::new(Handle {
+            task_hooks: TaskHooks {
+                task_spawn_callback: config.before_spawn.clone(),
+                task_terminate_callback: config.after_termination.clone(),
+            },
             shared: Shared {
                 inject: Inject::new(),
                 owned: OwnedTasks::new(1),
@@ -436,6 +447,12 @@ impl Handle {
     {
         let (handle, notified) = me.shared.owned.bind(future, me.clone(), id);
 
+        me.task_hooks.spawn(&TaskMeta {
+            #[cfg(tokio_unstable)]
+            id,
+            _phantom: Default::default(),
+        });
+
         if let Some(notified) = notified {
             me.schedule(notified);
         }
@@ -600,6 +617,12 @@ impl Schedule for Arc<Handle> {
         });
     }
 
+    fn hooks(&self) -> TaskHarnessScheduleHooks {
+        TaskHarnessScheduleHooks {
+            task_terminate_callback: self.task_hooks.task_terminate_callback.clone(),
+        }
+    }
+
     cfg_unstable! {
         fn unhandled_panic(&self) {
             use crate::runtime::UnhandledPanic;

tokio/src/runtime/scheduler/mod.rs

@@ -7,6 +7,8 @@ cfg_rt! {
 
     pub(crate) mod inject;
     pub(crate) use inject::Inject;
+
+    use crate::runtime::TaskHooks;
 }
 
 cfg_rt_multi_thread! {
@@ -151,6 +153,16 @@ cfg_rt! {
             }
         }
 
+        pub(crate) fn hooks(&self) -> &TaskHooks {
+            match self {
+                Handle::CurrentThread(h) => &h.task_hooks,
+                #[cfg(feature = "rt-multi-thread")]
+                Handle::MultiThread(h) => &h.task_hooks,
+                #[cfg(all(tokio_unstable, feature = "rt-multi-thread"))]
+                Handle::MultiThreadAlt(h) => &h.task_hooks,
+            }
+        }
+
         cfg_rt_multi_thread! {
             cfg_unstable! {
                 pub(crate) fn expect_multi_thread_alt(&self) -> &Arc<multi_thread_alt::Handle> {

tokio/src/runtime/scheduler/multi_thread/handle.rs

@@ -4,6 +4,7 @@ use crate::runtime::scheduler::multi_thread::worker;
 use crate::runtime::{
     blocking, driver,
     task::{self, JoinHandle},
+    TaskHooks, TaskMeta,
 };
 use crate::util::RngSeedGenerator;
 
@@ -28,6 +29,9 @@ pub(crate) struct Handle {
 
     /// Current random number generator seed
     pub(crate) seed_generator: RngSeedGenerator,
+
+    /// User-supplied hooks to invoke for things
+    pub(crate) task_hooks: TaskHooks,
 }
 
 impl Handle {
@@ -51,6 +55,12 @@ impl Handle {
     {
         let (handle, notified) = me.shared.owned.bind(future, me.clone(), id);
 
+        me.task_hooks.spawn(&TaskMeta {
+            #[cfg(tokio_unstable)]
+            id,
+            _phantom: Default::default(),
+        });
+
         me.schedule_option_task_without_yield(notified);
 
         handle

tokio/src/runtime/scheduler/multi_thread/worker.rs

@@ -58,15 +58,15 @@
 
 use crate::loom::sync::{Arc, Mutex};
 use crate::runtime;
-use crate::runtime::context;
 use crate::runtime::scheduler::multi_thread::{
     idle, queue, Counters, Handle, Idle, Overflow, Parker, Stats, TraceStatus, Unparker,
 };
 use crate::runtime::scheduler::{inject, Defer, Lock};
-use crate::runtime::task::OwnedTasks;
+use crate::runtime::task::{OwnedTasks, TaskHarnessScheduleHooks};
 use crate::runtime::{
     blocking, coop, driver, scheduler, task, Config, SchedulerMetrics, WorkerMetrics,
 };
+use crate::runtime::{context, TaskHooks};
 use crate::util::atomic_cell::AtomicCell;
 use crate::util::rand::{FastRand, RngSeedGenerator};
 
@@ -284,6 +284,10 @@ pub(super) fn create(
 
     let remotes_len = remotes.len();
     let handle = Arc::new(Handle {
+        task_hooks: TaskHooks {
+            task_spawn_callback: config.before_spawn.clone(),
+            task_terminate_callback: config.after_termination.clone(),
+        },
         shared: Shared {
             remotes: remotes.into_boxed_slice(),
             inject,
@@ -1037,6 +1041,12 @@ impl task::Schedule for Arc<Handle> {
         self.schedule_task(task, false);
     }
 
+    fn hooks(&self) -> TaskHarnessScheduleHooks {
+        TaskHarnessScheduleHooks {
+            task_terminate_callback: self.task_hooks.task_terminate_callback.clone(),
+        }
+    }
+
     fn yield_now(&self, task: Notified) {
         self.schedule_task(task, true);
     }