aws_smithy_runtime/client/http/body/minimum_throughput/throughput.rs
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/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0
*/
use std::fmt;
use std::time::{Duration, SystemTime};
/// Throughput representation for use when configuring [`super::MinimumThroughputBody`]
#[derive(Debug, Clone, Copy)]
#[cfg_attr(test, derive(Eq))]
pub struct Throughput {
pub(super) bytes_read: u64,
pub(super) per_time_elapsed: Duration,
}
impl Throughput {
/// Create a new throughput with the given bytes read and time elapsed.
pub fn new(bytes_read: u64, per_time_elapsed: Duration) -> Self {
debug_assert!(
!per_time_elapsed.is_zero(),
"cannot create a throughput if per_time_elapsed == 0"
);
Self {
bytes_read,
per_time_elapsed,
}
}
/// Create a new throughput in bytes per second.
pub const fn new_bytes_per_second(bytes: u64) -> Self {
Self {
bytes_read: bytes,
per_time_elapsed: Duration::from_secs(1),
}
}
/// Create a new throughput in kilobytes per second.
pub const fn new_kilobytes_per_second(kilobytes: u64) -> Self {
Self {
bytes_read: kilobytes * 1000,
per_time_elapsed: Duration::from_secs(1),
}
}
/// Create a new throughput in megabytes per second.
pub const fn new_megabytes_per_second(megabytes: u64) -> Self {
Self {
bytes_read: megabytes * 1000 * 1000,
per_time_elapsed: Duration::from_secs(1),
}
}
pub(super) fn bytes_per_second(&self) -> f64 {
let per_time_elapsed_secs = self.per_time_elapsed.as_secs_f64();
if per_time_elapsed_secs == 0.0 {
return 0.0; // Avoid dividing by zero.
};
self.bytes_read as f64 / per_time_elapsed_secs
}
}
impl PartialEq for Throughput {
fn eq(&self, other: &Self) -> bool {
self.bytes_per_second() == other.bytes_per_second()
}
}
impl PartialOrd for Throughput {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
self.bytes_per_second()
.partial_cmp(&other.bytes_per_second())
}
}
impl fmt::Display for Throughput {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// The default float formatting behavior will ensure the a number like 2.000 is rendered as 2
// while a number like 0.9982107441748642 will be rendered as 0.9982107441748642. This
// multiplication and division will truncate a float to have a precision of no greater than 3.
// For example, 0.9982107441748642 would become 0.999. This will fail for very large floats
// but should suffice for the numbers we're dealing with.
let pretty_bytes_per_second = (self.bytes_per_second() * 1000.0).round() / 1000.0;
write!(f, "{pretty_bytes_per_second} B/s")
}
}
impl From<(u64, Duration)> for Throughput {
fn from(value: (u64, Duration)) -> Self {
Self {
bytes_read: value.0,
per_time_elapsed: value.1,
}
}
}
/// Overall label for a given bin.
#[derive(Copy, Clone, Debug, Ord, PartialOrd, Eq, PartialEq)]
enum BinLabel {
// IMPORTANT: The order of these enums matters since it represents their priority:
// TransferredBytes > Pending > NoPolling > Empty
//
/// There is no data in this bin.
Empty,
/// No polling took place during this bin.
NoPolling,
/// The user/remote was not providing/consuming data fast enough during this bin.
Pending,
/// This many bytes were transferred during this bin.
TransferredBytes,
}
/// Represents a bin (or a cell) in a linear grid that represents a small chunk of time.
#[derive(Copy, Clone, Debug)]
struct Bin {
label: BinLabel,
bytes: u64,
}
impl Bin {
const fn new(label: BinLabel, bytes: u64) -> Self {
Self { label, bytes }
}
const fn empty() -> Self {
Self::new(BinLabel::Empty, 0)
}
fn is_empty(&self) -> bool {
matches!(self.label, BinLabel::Empty)
}
fn merge(&mut self, other: Bin) -> &mut Self {
// Assign values based on this priority order (highest priority higher up):
// 1. TransferredBytes
// 2. Pending
// 3. NoPolling
// 4. Empty
self.label = if other.label > self.label {
other.label
} else {
self.label
};
self.bytes += other.bytes;
self
}
/// Number of bytes transferred during this bin
fn bytes(&self) -> u64 {
self.bytes
}
}
#[derive(Copy, Clone, Debug, Default)]
struct BinCounts {
/// Number of bins with no data.
empty: usize,
/// Number of "no polling" bins.
no_polling: usize,
/// Number of "bytes transferred" bins.
transferred: usize,
/// Number of "pending" bins.
pending: usize,
}
/// Underlying stack-allocated linear grid buffer for tracking
/// throughput events for [`ThroughputLogs`].
#[derive(Copy, Clone, Debug)]
struct LogBuffer<const N: usize> {
entries: [Bin; N],
// The length only needs to exist so that the `fill_gaps` function
// can differentiate between `Empty` due to there not having been enough
// time to establish a full buffer worth of data vs. `Empty` due to a
// polling gap. Once the length reaches N, it will never change again.
length: usize,
}
impl<const N: usize> LogBuffer<N> {
fn new() -> Self {
Self {
entries: [Bin::empty(); N],
length: 0,
}
}
/// Mutably returns the tail of the buffer.
///
/// ## Panics
///
/// The buffer MUST have at least one bin in it before this is called.
fn tail_mut(&mut self) -> &mut Bin {
debug_assert!(self.length > 0);
&mut self.entries[self.length - 1]
}
/// Pushes a bin into the buffer. If the buffer is already full,
/// then this will rotate the entire buffer to the left.
fn push(&mut self, bin: Bin) {
if self.filled() {
self.entries.rotate_left(1);
self.entries[N - 1] = bin;
} else {
self.entries[self.length] = bin;
self.length += 1;
}
}
/// Returns the total number of bytes transferred within the time window.
fn bytes_transferred(&self) -> u64 {
self.entries.iter().take(self.length).map(Bin::bytes).sum()
}
#[inline]
fn filled(&self) -> bool {
self.length == N
}
/// Fills in missing NoData entries.
///
/// We want NoData entries to represent when a future hasn't been polled.
/// Since the future is in charge of logging in the first place, the only
/// way we can know about these is by examining gaps in time.
fn fill_gaps(&mut self) {
for entry in self.entries.iter_mut().take(self.length) {
if entry.is_empty() {
*entry = Bin::new(BinLabel::NoPolling, 0);
}
}
}
/// Returns the counts of each bin type in the buffer.
fn counts(&self) -> BinCounts {
let mut counts = BinCounts::default();
for entry in &self.entries {
match entry.label {
BinLabel::Empty => counts.empty += 1,
BinLabel::NoPolling => counts.no_polling += 1,
BinLabel::TransferredBytes => counts.transferred += 1,
BinLabel::Pending => counts.pending += 1,
}
}
counts
}
/// If this LogBuffer is empty, returns `true`. Else, returns `false`.
fn is_empty(&self) -> bool {
self.length == 0
}
}
/// Report/summary of all the events in a time window.
#[cfg_attr(test, derive(Debug, Eq, PartialEq))]
pub(crate) enum ThroughputReport {
/// Not enough data to draw any conclusions. This happens early in a request/response.
Incomplete,
/// The stream hasn't been polled for most of this time window.
NoPolling,
/// The stream has been waiting for most of the time window.
Pending,
/// The stream transferred this amount of throughput during the time window.
Transferred(Throughput),
/// The stream has completed, no more data is expected.
Complete,
}
const BIN_COUNT: usize = 10;
/// Log of throughput in a request or response stream.
///
/// Used to determine if a configured minimum throughput is being met or not
/// so that a request or response stream can be timed out in the event of a
/// stall.
///
/// Request/response streams push data transfer or pending events to this log
/// based on what's going on in their poll functions. The log tracks three kinds
/// of events despite only receiving two: the third is "no polling". The poll
/// functions cannot know when they're not being polled, so the log examines gaps
/// in the event history to know when no polling took place.
///
/// The event logging is simplified down to a linear grid consisting of 10 "bins",
/// with each bin representing 1/10th the total time window. When an event is pushed,
/// it is either merged into the current tail bin, or all the bins are rotated
/// left to create a new empty tail bin, and then it is merged into that one.
#[derive(Clone, Debug)]
pub(super) struct ThroughputLogs {
resolution: Duration,
current_tail: SystemTime,
buffer: LogBuffer<BIN_COUNT>,
stream_complete: bool,
}
impl ThroughputLogs {
/// Creates a new log starting at `now` with the given `time_window`.
///
/// Note: the `time_window` gets divided by 10 to create smaller sub-windows
/// to track throughput. The time window should be configured to be large enough
/// so that these sub-windows aren't too small for network-based events.
/// A time window of 10ms probably won't work, but 500ms might. The default
/// is one second.
pub(super) fn new(time_window: Duration, now: SystemTime) -> Self {
assert!(!time_window.is_zero());
let resolution = time_window.div_f64(BIN_COUNT as f64);
Self {
resolution,
current_tail: now,
buffer: LogBuffer::new(),
stream_complete: false,
}
}
/// Returns the resolution at which events are logged at.
///
/// The resolution is the number of bins in the time window.
pub(super) fn resolution(&self) -> Duration {
self.resolution
}
/// Pushes a "pending" event.
///
/// Pending indicates the streaming future is waiting for something.
/// In an upload, it is waiting for data from the user, and in a download,
/// it is waiting for data from the server.
pub(super) fn push_pending(&mut self, time: SystemTime) {
self.push(time, Bin::new(BinLabel::Pending, 0));
}
/// Pushes a data transferred event.
///
/// Indicates that this number of bytes were transferred at this time.
pub(super) fn push_bytes_transferred(&mut self, time: SystemTime, bytes: u64) {
self.push(time, Bin::new(BinLabel::TransferredBytes, bytes));
}
fn push(&mut self, now: SystemTime, value: Bin) {
self.catch_up(now);
if self.buffer.is_empty() {
self.buffer.push(value)
} else {
self.buffer.tail_mut().merge(value);
}
self.buffer.fill_gaps();
}
/// Pushes empty bins until `current_tail` is caught up to `now`.
fn catch_up(&mut self, now: SystemTime) {
while now >= self.current_tail {
self.current_tail += self.resolution;
self.buffer.push(Bin::empty());
}
assert!(self.current_tail >= now);
}
/// Mark the stream complete indicating no more data is expected. This is an
/// idempotent operation -- subsequent invocations of this function have no effect
/// and return false.
///
/// After marking a stream complete [report](#method.report) will forever more return
/// [ThroughputReport::Complete]
pub(super) fn mark_complete(&mut self) -> bool {
let prev = self.stream_complete;
self.stream_complete = true;
!prev
}
/// Generates an overall report of the time window.
pub(super) fn report(&mut self, now: SystemTime) -> ThroughputReport {
if self.stream_complete {
return ThroughputReport::Complete;
}
self.catch_up(now);
self.buffer.fill_gaps();
let BinCounts {
empty,
no_polling,
transferred,
pending,
} = self.buffer.counts();
// If there are any empty cells at all, then we haven't been tracking
// long enough to make any judgements about the stream's progress.
if empty > 0 {
return ThroughputReport::Incomplete;
}
let bytes = self.buffer.bytes_transferred();
let time = self.resolution * (BIN_COUNT - empty) as u32;
let throughput = Throughput::new(bytes, time);
let half = BIN_COUNT / 2;
match (transferred > 0, no_polling >= half, pending >= half) {
(true, _, _) => ThroughputReport::Transferred(throughput),
(_, true, _) => ThroughputReport::NoPolling,
(_, _, true) => ThroughputReport::Pending,
_ => ThroughputReport::Incomplete,
}
}
}
#[cfg(test)]
mod test {
use super::*;
use std::time::Duration;
#[test]
fn test_log_buffer_bin_label_priority() {
use BinLabel::*;
assert!(Empty < NoPolling);
assert!(NoPolling < Pending);
assert!(Pending < TransferredBytes);
}
#[test]
fn test_throughput_eq() {
let t1 = Throughput::new(1, Duration::from_secs(1));
let t2 = Throughput::new(25, Duration::from_secs(25));
let t3 = Throughput::new(100, Duration::from_secs(100));
assert_eq!(t1, t2);
assert_eq!(t2, t3);
}
#[test]
fn incomplete_no_entries() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
let report = logs.report(start);
assert_eq!(ThroughputReport::Incomplete, report);
}
#[test]
fn incomplete_with_entries() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
logs.push_pending(start);
let report = logs.report(start + Duration::from_millis(300));
assert_eq!(ThroughputReport::Incomplete, report);
}
#[test]
fn incomplete_with_transferred() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
logs.push_pending(start);
logs.push_bytes_transferred(start + Duration::from_millis(100), 10);
let report = logs.report(start + Duration::from_millis(300));
assert_eq!(ThroughputReport::Incomplete, report);
}
#[test]
fn push_pending_at_the_beginning_of_each_tick() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
let mut now = start;
for i in 1..=BIN_COUNT {
logs.push_pending(now);
now += logs.resolution();
assert_eq!(i, logs.buffer.counts().pending);
}
let report = dbg!(&mut logs).report(now);
assert_eq!(ThroughputReport::Pending, report);
}
#[test]
fn push_pending_at_the_end_of_each_tick() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
let mut now = start;
for i in 1..BIN_COUNT {
now += logs.resolution();
logs.push_pending(now);
assert_eq!(i, dbg!(&logs).buffer.counts().pending);
assert_eq!(0, logs.buffer.counts().transferred);
assert_eq!(1, logs.buffer.counts().no_polling);
}
// This should replace the initial "no polling" bin
now += logs.resolution();
logs.push_pending(now);
assert_eq!(0, logs.buffer.counts().no_polling);
let report = dbg!(&mut logs).report(now);
assert_eq!(ThroughputReport::Pending, report);
}
#[test]
fn push_transferred_at_the_beginning_of_each_tick() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
let mut now = start;
for i in 1..=BIN_COUNT {
logs.push_bytes_transferred(now, 10);
if i != BIN_COUNT {
now += logs.resolution();
}
assert_eq!(i, logs.buffer.counts().transferred);
assert_eq!(0, logs.buffer.counts().pending);
assert_eq!(0, logs.buffer.counts().no_polling);
}
let report = dbg!(&mut logs).report(now);
assert_eq!(
ThroughputReport::Transferred(Throughput::new(100, Duration::from_secs(1))),
report
);
}
#[test]
fn no_polling() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
let report = logs.report(start + Duration::from_secs(2));
assert_eq!(ThroughputReport::NoPolling, report);
}
// Transferred bytes MUST take priority over pending when reporting throughput
#[test]
fn mixed_bag_mostly_pending() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
logs.push_bytes_transferred(start + Duration::from_millis(50), 10);
logs.push_pending(start + Duration::from_millis(150));
logs.push_pending(start + Duration::from_millis(250));
logs.push_bytes_transferred(start + Duration::from_millis(350), 10);
logs.push_pending(start + Duration::from_millis(450));
// skip 550
logs.push_pending(start + Duration::from_millis(650));
logs.push_pending(start + Duration::from_millis(750));
logs.push_pending(start + Duration::from_millis(850));
let report = logs.report(start + Duration::from_millis(999));
assert_eq!(
ThroughputReport::Transferred(Throughput::new_bytes_per_second(20)),
report
);
}
#[test]
fn mixed_bag_mostly_pending_no_transferred() {
let start = SystemTime::UNIX_EPOCH;
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
logs.push_pending(start + Duration::from_millis(50));
logs.push_pending(start + Duration::from_millis(150));
logs.push_pending(start + Duration::from_millis(250));
// skip 350
logs.push_pending(start + Duration::from_millis(450));
// skip 550
logs.push_pending(start + Duration::from_millis(650));
logs.push_pending(start + Duration::from_millis(750));
logs.push_pending(start + Duration::from_millis(850));
let report = logs.report(start + Duration::from_millis(999));
assert_eq!(ThroughputReport::Pending, report);
}
#[test]
fn test_first_push_succeeds_although_time_window_has_not_elapsed() {
let t0 = SystemTime::UNIX_EPOCH;
let t1 = t0 + Duration::from_secs(1);
let mut tl = ThroughputLogs::new(Duration::from_secs(1), t1);
tl.push_pending(t0);
}
#[test]
fn test_label_transferred_bytes_should_not_be_overwritten_by_pending() {
let start = SystemTime::UNIX_EPOCH;
// Each `Bin`'s resolution is 100ms (1s / BIN_COUNT), where `BIN_COUNT` is 10
let mut logs = ThroughputLogs::new(Duration::from_secs(1), start);
// push `TransferredBytes` and then `Pending` in the same first `Bin`
logs.push_bytes_transferred(start + Duration::from_millis(10), 10);
logs.push_pending(start + Duration::from_millis(20));
let BinCounts {
empty,
no_polling,
transferred,
pending,
} = logs.buffer.counts();
assert_eq!(9, empty);
assert_eq!(0, no_polling);
assert_eq!(1, transferred); // `transferred` should still be there
assert_eq!(0, pending); // while `pending` should cease to exist, failing to overwrite `transferred`
}
}