1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701
// Cadence - An extensible Statsd client for Rust!
//
// Copyright 2015-2021 Nick Pillitteri
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::sinks::core::MetricSink;
use crossbeam_channel::{self, Receiver, Sender, TrySendError};
use std::fmt;
use std::io::{self, ErrorKind};
use std::panic::RefUnwindSafe;
use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
use std::sync::Arc;
use std::thread;
/// Implementation of a `MetricSink` that wraps another implementation
/// and uses it to emit metrics asynchronously, in another thread.
///
/// Metrics submitted to this sink are queued and sent to the wrapped sink
/// that is running in a separate thread. The wrapped implementation can
/// be any thread (`Sync` + `Send`) and panic (`RefUnwindSafe`) safe
/// `MetricSink`. Results from the wrapped implementation will be discarded.
///
/// The thread used for network operations (actually sending the metrics
/// using the wrapped sink) is created and started when the `QueuingMetricSink`
/// is created. The dequeuing of metrics is stopped and the thread stopped
/// when `QueuingMetricSink` instance is destroyed (when `.drop()` is
/// called).
///
/// This sink may be created with either a bounded or unbounded queue
/// connecting the sink to the thread performning network operations. When an
/// unbounded queue is used, entries submitted to the sink will always be
/// accepted and queued until they can be drained by the network operation
/// thread. This means that if the network thread cannot drain entries off
/// the queue for some reason, it will grow without bound. Alternatively, if
/// created with a bounded queue, entries submitted to the sink will not be
/// accepted if the queue is full. This means that the network thread must
/// be able to keep up with the rate of entries submit to the queue or writes
/// to this sink will begin to fail.
///
/// Entries already queued are guaranteed to be sent to the wrapped sink
/// before the queuing sink is stopped. Meaning, the following code ends up
/// calling `wrapped.emit(metric)` on every metric submitted to the queuing
/// sink.
///
/// # Example
///
/// ```no_run
/// use cadence::{MetricSink, QueuingMetricSink, NopMetricSink};
///
/// let wrapped = NopMetricSink;
/// {
/// let queuing = QueuingMetricSink::from(wrapped);
/// queuing.emit("foo.counter:4|c");
/// queuing.emit("bar.counter:5|c");
/// queuing.emit("baz.gauge:6|g");
/// }
/// ```
///
/// At the end of this code block, all metrics are guaranteed to be sent to
/// the underlying wrapped metric sink before the thread used by the queuing
/// sink is stopped.
#[derive(Debug, Clone)]
pub struct QueuingMetricSink {
worker: Arc<Worker>,
}
impl QueuingMetricSink {
/// Construct a new `QueuingMetricSink` instance wrapping another sink
/// implementation with an unbounded queue connecting them.
///
/// The `.emit()` method of the wrapped sink will be executed in a
/// different thread after being passed to it via a queue. The wrapped
/// sink should be thread safe (`Send + Sync`) and panic safe
/// (`RefUnwindSafe`).
///
/// The thread in which the wrapped sink runs is created when the
/// `QueuingMetricSink` is created and stopped when the queuing sink
/// is destroyed.
///
/// The queuing sink communicates with the wrapped sink by an unbounded
/// queue. If entries cannot be drained from the queue for some reason, it
/// will grow without bound.
///
/// # Buffered UDP Sink Example
///
/// In this example we wrap a buffered UDP sink to execute it in a
/// different thread.
///
/// ```no_run
/// use std::net::UdpSocket;
/// use cadence::{BufferedUdpMetricSink, QueuingMetricSink, DEFAULT_PORT};
///
/// let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
/// let host = ("metrics.example.com", DEFAULT_PORT);
/// let udp_sink = BufferedUdpMetricSink::from(host, socket).unwrap();
/// let queuing_sink = QueuingMetricSink::from(udp_sink);
/// ```
pub fn from<T>(sink: T) -> Self
where
T: MetricSink + Sync + Send + RefUnwindSafe + 'static,
{
Self::with_optional_capacity(sink, None)
}
/// Construct a new `QueuingMetricSink` instance wrapping another sink
/// implementation with a queue of the given size connecting them.
///
/// The `.emit()` method of the wrapped sink will be executed in a
/// different thread after being passed to it via a queue. The wrapped
/// sink should be thread safe (`Send + Sync`) and panic safe
/// (`RefUnwindSafe`).
///
/// The thread in which the wrapped sink runs is created when the
/// `QueuingMetricSink` is created and stopped when the queuing sink
/// is destroyed.
///
/// The queuing sink communicates with the wrapped sink by a bounded
/// queue of the provided size. When the queue is full, writes to
/// this sink will fail until the queue is drained.
///
/// # Buffered UDP Sink Example
///
/// In this example we wrap a buffered UDP sink to execute it in a
/// different thread.
///
/// ```no_run
/// use std::net::UdpSocket;
/// use cadence::{BufferedUdpMetricSink, QueuingMetricSink, DEFAULT_PORT};
///
/// let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
/// let host = ("metrics.example.com", DEFAULT_PORT);
/// let udp_sink = BufferedUdpMetricSink::from(host, socket).unwrap();
/// let queuing_sink = QueuingMetricSink::with_capacity(udp_sink, 512 * 1024);
/// ```
pub fn with_capacity<T>(sink: T, capacity: usize) -> Self
where
T: MetricSink + Sync + Send + RefUnwindSafe + 'static,
{
Self::with_optional_capacity(sink, Some(capacity))
}
fn with_optional_capacity<T>(sink: T, capacity: Option<usize>) -> Self
where
T: MetricSink + Sync + Send + RefUnwindSafe + 'static,
{
let worker = Arc::new(Worker::new(capacity, move |v: String| {
let _r = sink.emit(&v);
}));
spawn_worker_in_thread(Arc::clone(&worker));
QueuingMetricSink { worker }
}
/// Return the number of times the wrapped sink or underlying worker thread
/// has panicked and needed to be restarted. In typical use this should always
/// be `0` but may be `> 0` for buggy `MetricSink` implementations.
pub fn panics(&self) -> u64 {
self.worker.stats.panics()
}
/// Return the number of currently queued metrics. Note that due to the way
/// this number is computed (submitted metrics - processed metrics), it is
/// necessarily approximate.
pub fn queued(&self) -> u64 {
self.worker.stats.queued()
}
/// Return the number of metrics successfully submitted to this sink.
pub fn submitted(&self) -> u64 {
self.worker.stats.submitted()
}
/// Return the number of metrics removed from the queue to be processed by
/// the wrapped sink. Note that this does not indicate that the metric has
/// been successfully sent to a backend, only that it has been passed to
/// the wrapped sink.
pub fn drained(&self) -> u64 {
self.worker.stats.drained()
}
}
impl MetricSink for QueuingMetricSink {
fn emit(&self, metric: &str) -> io::Result<usize> {
match self.worker.submit(metric.to_string()) {
Err(TrySendError::Disconnected(_)) => Err(io::Error::new(ErrorKind::Other, "channel disconnected")),
Err(TrySendError::Full(_)) => Err(io::Error::new(ErrorKind::Other, "channel full")),
Ok(_) => Ok(metric.len()),
}
}
}
impl Drop for QueuingMetricSink {
/// Send the worker a signal to stop processing metrics.
///
/// Note that this destructor only sends the worker thread a signal to
/// stop, it doesn't wait for it to stop.
fn drop(&mut self) {
self.worker.stop();
}
}
/// Statistics about the worker running.
///
/// These statistics are only used for unit testing to verify that our
/// sentinel can handle thread panics and restart the thread the worker
/// is running in.
#[derive(Debug)]
struct WorkerStats {
panics: AtomicU64,
submitted: AtomicU64,
drained: AtomicU64,
}
impl WorkerStats {
fn new() -> WorkerStats {
WorkerStats {
panics: AtomicU64::new(0),
submitted: AtomicU64::new(0),
drained: AtomicU64::new(0),
}
}
fn incr_panic(&self) {
self.panics.fetch_add(1, Ordering::Release);
}
fn panics(&self) -> u64 {
self.panics.load(Ordering::Acquire)
}
fn incr_submitted(&self) {
self.submitted.fetch_add(1, Ordering::Release);
}
fn submitted(&self) -> u64 {
self.submitted.load(Ordering::Acquire)
}
fn incr_drained(&self) {
self.drained.fetch_add(1, Ordering::Release);
}
fn drained(&self) -> u64 {
self.drained.load(Ordering::Acquire)
}
fn queued(&self) -> u64 {
let submitted = self.submitted.load(Ordering::Acquire);
let drained = self.drained.load(Ordering::Acquire);
if submitted > drained {
submitted - drained
} else {
0
}
}
}
/// Create a thread and run the worker in it to completion
///
/// This function uses a `Sentinel` struct to make sure that any panics from
/// running the worker result in another thread being spawned to start running
/// the worker again.
fn spawn_worker_in_thread(worker: Arc<Worker>) -> thread::JoinHandle<()> {
thread::spawn(move || {
let mut sentinel = Sentinel::new(&worker);
worker.run();
sentinel.cancel();
})
}
/// Struct for ensuring a worker runs to completion correctly, without
/// panicking.
///
/// The sentinel will spawn a new thread to continue running the worker
/// in its destructor unless the `.cancel()` method is called after the
/// worker completes (which won't happen if the worker panics).
#[derive(Debug)]
struct Sentinel<'a> {
worker: &'a Arc<Worker>,
active: bool,
}
impl<'a> Sentinel<'a> {
fn new(worker: &'a Arc<Worker>) -> Sentinel<'a> {
Sentinel { worker, active: true }
}
fn cancel(&mut self) {
self.active = false;
}
}
impl<'a> Drop for Sentinel<'a> {
fn drop(&mut self) {
if self.active {
// This sentinel didn't have its `.cancel()`method called so
// the thread must have panicked. Increment a counter indicating
// that this was a panic and spawn a new thread with an Arc of
// the worker.
self.worker.stats.incr_panic();
spawn_worker_in_thread(Arc::clone(self.worker));
}
}
}
/// Worker to repeatedly run a method consuming entries via a channel.
///
/// The `.run()` method of the worker is intended to be in a separate
/// thread (thread B). Meanwhile, the `.submit()`, `.stop()`,
/// `.stop_and_wait()`, and `.is_stopped()` methods are meant to be called
/// from the main thread (thread A).
///
/// This worker is stopped by receiving a "poison pill" message in the
/// channel that it is consuming messages from. Thus, calls to `.submit()`,
/// consuming messages in '.run()`, and `.stop()` typically involve no
/// locking.
///
/// However, in order to enable easier testing, after it stops receiving
/// messages the `.run()` method will use an atomic "stopped" flag to
/// allow callers waiting on a conditional variable (callers using
/// `.stop_and_wait()`) to wake up after the worker finally stops.
///
/// If you're just trying to make use of this worker you don't need to
/// worry about this, just call `.submit()`, `.run()`, and `.stop()`.
/// But, if you're wondering why the stopped flag and methods to wait
/// for it or inspect it even exist: testing is the reason.
struct Worker {
task: Box<dyn Fn(String) + Sync + Send + RefUnwindSafe + 'static>,
sender: Sender<Option<String>>,
receiver: Receiver<Option<String>>,
stopped: AtomicBool,
stats: WorkerStats,
}
impl Worker {
fn new<F>(capacity: Option<usize>, task: F) -> Self
where
F: Fn(String) + Sync + Send + RefUnwindSafe + 'static,
{
let (tx, rx) = Self::get_channels(capacity);
Worker {
task: Box::new(task),
sender: tx,
receiver: rx,
stopped: AtomicBool::new(false),
stats: WorkerStats::new(),
}
}
fn get_channels(capacity: Option<usize>) -> (Sender<Option<String>>, Receiver<Option<String>>) {
if let Some(v) = capacity {
crossbeam_channel::bounded(v)
} else {
crossbeam_channel::unbounded()
}
}
fn submit(&self, v: String) -> Result<(), TrySendError<Option<String>>> {
let res = self.sender.try_send(Some(v));
if res.is_ok() {
self.stats.incr_submitted();
}
res
}
fn run(&self) {
for opt in self.receiver.iter() {
if let Some(v) = opt {
self.stats.incr_drained();
(self.task)(v);
} else {
break;
}
}
// Set the "stopped" flag so that callers using the `stop_and_wait`
// method will see that we've stopped processing entries in the channel.
// This is only for the benefit of unit testing.
self.stopped.store(true, Ordering::Release);
}
fn stop(&self) {
// Send a `None` poison pill value to stop the run loop.
let _ = self.sender.try_send(None);
}
// Stop reading events from the channel and wait for the "stopped" flag
// to be set. Note that this repeatedly yields the current thread and is
// only intended for unit testing.
#[cfg(test)]
fn stop_and_wait(&self) {
self.stop();
while !self.stopped.load(Ordering::Acquire) {
thread::yield_now();
}
}
// Is the channel used between threads empty, i.e. are all values processed?
#[cfg(test)]
fn is_empty(&self) -> bool {
self.receiver.is_empty()
}
// Has this worker stopped running?
#[cfg(test)]
fn is_stopped(&self) -> bool {
self.stopped.load(Ordering::Acquire)
}
}
impl fmt::Debug for Worker {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Worker {{ ... }}")
}
}
#[cfg(test)]
mod tests {
use super::{QueuingMetricSink, Worker};
use crate::sinks::core::MetricSink;
use std::io;
use std::panic;
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use std::thread;
const QUEUE_SIZE: Option<usize> = Some(128);
#[test]
fn test_worker_submit_processes_event() {
let flag = Arc::new(AtomicBool::new(false));
let flag_ref = flag.clone();
let task = move |v: String| {
if v == "foo" {
flag_ref.store(true, Ordering::Release);
}
};
let worker = Arc::new(Worker::new(QUEUE_SIZE, task));
let worker_ref = worker.clone();
let t = thread::spawn(move || {
worker_ref.run();
});
worker.submit("bar".to_string()).unwrap();
worker.submit("foo".to_string()).unwrap();
worker.stop();
t.join().unwrap();
assert!(flag.load(Ordering::Acquire));
}
#[test]
fn test_worker_stop() {
let worker = Arc::new(Worker::new(QUEUE_SIZE, move |_: String| {}));
let worker_ref = worker.clone();
let t = thread::spawn(move || {
worker_ref.run();
});
worker.stop();
t.join().unwrap();
assert!(worker.is_stopped());
}
#[test]
fn test_worker_stop_and_wait() {
let worker = Arc::new(Worker::new(QUEUE_SIZE, move |_: String| {}));
let worker_ref = worker.clone();
let _t = thread::spawn(move || {
worker_ref.run();
});
worker.stop_and_wait();
assert!(worker.is_stopped());
}
// Make sure the worker and its channel are in the expected state
// when the producer size of the channel panics.
#[test]
fn test_worker_panic_on_submit_side() {
let worker = Arc::new(Worker::new(QUEUE_SIZE, move |_: String| {}));
let worker_ref1 = worker.clone();
let worker_ref2 = worker.clone();
#[allow(unreachable_code)]
let t1 = thread::spawn(move || {
worker_ref1.submit(panic!("This thread is supposed to panic")).unwrap();
});
let t2 = thread::spawn(move || {
worker_ref2.run();
});
worker.stop();
assert!(t1.join().is_err());
assert!(t2.join().is_ok());
assert!(worker.is_stopped());
assert!(worker.is_empty());
}
// Make sure the worker and its channel are in the expected state
// when the consumer side of the channel panics.
#[test]
fn test_worker_panic_on_run_side() {
let worker = Arc::new(Worker::new(QUEUE_SIZE, move |_: String| {
panic!("This thread is supposed to panic");
}));
let worker_ref1 = worker.clone();
let worker_ref2 = worker.clone();
let t1 = thread::spawn(move || {
worker_ref1.submit("foo".to_owned()).unwrap();
});
let t2 = thread::spawn(move || {
worker_ref2.run();
});
assert!(t1.join().is_ok());
assert!(t2.join().is_err());
assert!(!worker.is_stopped());
assert!(worker.is_empty());
}
#[test]
fn test_queuing_sink_emit() {
struct TestMetricSink {
metrics: Arc<Mutex<Vec<String>>>,
}
impl TestMetricSink {
fn new(metrics: Arc<Mutex<Vec<String>>>) -> TestMetricSink {
TestMetricSink { metrics }
}
}
impl MetricSink for TestMetricSink {
fn emit(&self, m: &str) -> io::Result<usize> {
let mut store = self.metrics.lock().unwrap();
store.push(m.to_string());
Ok(m.len())
}
}
let store = Arc::new(Mutex::new(vec![]));
let wrapped = TestMetricSink::new(store.clone());
let queuing = QueuingMetricSink::from(wrapped);
queuing.emit("foo.counter:1|c").unwrap();
queuing.emit("bar.counter:2|c").unwrap();
queuing.emit("baz.counter:3|c").unwrap();
queuing.worker.stop_and_wait();
assert_eq!("foo.counter:1|c".to_string(), store.lock().unwrap()[0]);
assert_eq!("bar.counter:2|c".to_string(), store.lock().unwrap()[1]);
assert_eq!("baz.counter:3|c".to_string(), store.lock().unwrap()[2]);
}
#[test]
fn test_queuing_sink_emit_panics() {
struct PanickingMetricSink;
impl MetricSink for PanickingMetricSink {
fn emit(&self, _m: &str) -> io::Result<usize> {
panic!("This thread is supposed to panic");
}
}
let queuing = QueuingMetricSink::from(PanickingMetricSink);
queuing.emit("foo.counter:4|c").unwrap();
queuing.emit("foo.counter:5|c").unwrap();
queuing.emit("foo.timer:34|ms").unwrap();
queuing.worker.stop_and_wait();
assert_eq!(3, queuing.panics());
}
// Make sure that subsequent metrics make it to the wrapped sink even when
// the wrapped sink panics. This ensures that the thread running the sink
// is restarted correctly and the worker and channel are in the correct state.
#[test]
fn test_queuing_sink_emit_recover_from_panics() {
struct SometimesPanickingMetricSink {
metrics: Arc<Mutex<Vec<String>>>,
counter: AtomicUsize,
}
impl SometimesPanickingMetricSink {
fn new(metrics: Arc<Mutex<Vec<String>>>) -> Self {
SometimesPanickingMetricSink {
metrics,
counter: AtomicUsize::new(0),
}
}
}
impl MetricSink for SometimesPanickingMetricSink {
fn emit(&self, m: &str) -> io::Result<usize> {
let val = self.counter.fetch_add(1, Ordering::Acquire);
if val == 0 {
panic!("This thread is supposed to panic");
}
let mut store = self.metrics.lock().unwrap();
store.push(m.to_string());
Ok(m.len())
}
}
let store = Arc::new(Mutex::new(vec![]));
let queuing = QueuingMetricSink::from(SometimesPanickingMetricSink::new(store.clone()));
queuing.emit("foo.counter:4|c").unwrap();
queuing.emit("foo.counter:5|c").unwrap();
queuing.emit("foo.timer:34|ms").unwrap();
queuing.worker.stop_and_wait();
assert_eq!(1, queuing.panics());
assert_eq!("foo.counter:5|c".to_string(), store.lock().unwrap()[0]);
assert_eq!("foo.timer:34|ms".to_string(), store.lock().unwrap()[1]);
}
// Make sure that our queuing sink is unwind safe (it has the auto trait) and
// that it handles any expected panics on its own, resulting in calling code not
// seeing any panics.
#[test]
fn test_queuing_sink_panic_handler() {
struct PanickingMetricSink;
impl MetricSink for PanickingMetricSink {
fn emit(&self, _m: &str) -> io::Result<usize> {
panic!("This thread is supposed to panic");
}
}
let queuing = QueuingMetricSink::from(PanickingMetricSink);
let res = panic::catch_unwind(move || {
queuing.emit("foo.counter:4|c").unwrap();
queuing.emit("foo.counter:5|c").unwrap();
queuing.emit("foo.timer:34|ms").unwrap();
queuing.worker.stop_and_wait();
});
assert!(res.is_ok());
}
// Make sure that attempts to write to the sink start to fail when none of the
// metrics have been drained by the wrapped sink. This is simulated by wrapping a
// sink that sleeps indefinitely. Since all threads in Rust are daemon threads we
// don't care that this thread won't stop, it'll be killed when the test process
// exits.
#[test]
fn test_queuing_metric_sink_blocking_sink_back_pressure() {
struct BlockingMetricSink;
impl MetricSink for BlockingMetricSink {
fn emit(&self, _m: &str) -> io::Result<usize> {
loop {
thread::park();
}
}
}
let queueing = QueuingMetricSink::with_capacity(BlockingMetricSink, 1);
let results = vec![
queueing.emit("foo.counter:1|c"),
queueing.emit("foo.counter:2|c"),
queueing.emit("foo.counter:3|c"),
];
let success = results.iter().map(|r| r.is_ok()).filter(|r| *r).count();
let failure = results.iter().map(|r| r.is_err()).filter(|r| *r).count();
// We've submitted three metrics to a queuing sink with a max capacity of one: at least
// one of the submissions should be successfully queued and one of them should have failed.
// Depending on how quickly the network thread of the sink started running, an entry may
// have been removed from the queue (meaning that two submissions would have succeeded).
assert!(
success >= 1,
"At least one submission to the queue should have succeeded"
);
assert!(failure >= 1, "At least one submission to the queue should have failed");
}
}