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Make test-util paused time fully deterministic #3492

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Feb 5, 2021
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31 changes: 31 additions & 0 deletions tokio/src/runtime/builder.rs
Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,9 @@ pub struct Builder {
/// Whether or not to enable the time driver
enable_time: bool,

/// Whether or not the clock should start paused.
start_paused: bool,

/// The number of worker threads, used by Runtime.
///
/// Only used when not using the current-thread executor.
Expand Down Expand Up @@ -110,6 +113,9 @@ impl Builder {
// Time defaults to "off"
enable_time: false,

// The clock starts not-paused
start_paused: false,

// Default to lazy auto-detection (one thread per CPU core)
worker_threads: None,

Expand Down Expand Up @@ -386,6 +392,7 @@ impl Builder {
},
enable_io: self.enable_io,
enable_time: self.enable_time,
start_paused: self.start_paused,
}
}

Expand Down Expand Up @@ -489,6 +496,30 @@ cfg_time! {
}
}

cfg_test_util! {
impl Builder {
/// Controls if the runtime's clock starts paused or advancing.
///
/// Pausing time requires the current-thread runtime; construction of
/// the runtime will panic otherwise.
Comment on lines +503 to +504
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Where is this panic?

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The call to clock.pause in Clock::new will panic when running on a multi threaded runtime.

///
/// # Examples
///
/// ```
/// use tokio::runtime;
///
/// let rt = runtime::Builder::new_current_thread()
/// .enable_time()
/// .start_paused(true)
/// .unwrap();
/// ```
pub fn start_paused(&mut self, start_paused: bool) -> &mut Self {
self.start_paused = start_paused;
self
}
}
}

cfg_rt_multi_thread! {
impl Builder {
fn build_threaded_runtime(&mut self) -> io::Result<Runtime> {
Expand Down
5 changes: 5 additions & 0 deletions tokio/src/runtime/driver.rs
Original file line number Diff line number Diff line change
Expand Up @@ -162,13 +162,18 @@ pub(crate) struct Cfg {
pub(crate) enable_io: bool,
pub(crate) enable_time: bool,
pub(crate) enable_pause_time: bool,
pub(crate) start_paused: bool,
}

impl Driver {
pub(crate) fn new(cfg: Cfg) -> io::Result<(Self, Resources)> {
let (io_stack, io_handle, signal_handle) = create_io_stack(cfg.enable_io)?;

let clock = create_clock(cfg.enable_pause_time);
if cfg.start_paused {
clock.pause();
}

let (time_driver, time_handle) =
create_time_driver(cfg.enable_time, io_stack, clock.clone());
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So this makes it deterministic because pause is called before create_time_driver sets the start time?

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That, along with changing the ClockTime constructor to pull start_time out of the clock passed to it rather than going for the global clock (which isn't installed at that point so it falls back to the system clock).


Expand Down
2 changes: 1 addition & 1 deletion tokio/src/time/driver/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -102,8 +102,8 @@ pub(self) struct ClockTime {
impl ClockTime {
pub(self) fn new(clock: Clock) -> Self {
Self {
start_time: clock.now(),
clock,
start_time: super::clock::now(),
}
}

Expand Down