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rt: remove rng_seed+mt test and update docs (#5142)

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While setting the random number generator seed with the multi-threaded
scheduler does result in deterministic behavior related to the random
number generator, threads still introduce non-determinism, making it
hard (impossible?) to test this. There also is little value in doing so.

This patch also updates the docs to remove mention of work stealing.
This commit is contained in:
Carl Lerche
2022-10-28 11:55:34 -07:00
committed by GitHub
parent b749013a54
commit 121f839b4b
2 changed files with 11 additions and 59 deletions
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tokio/src/runtime/builder.rs
+11 -14
View File
@@ -836,22 +836,19 @@ impl Builder {
self
}
/// Specifies the random number generation seed to use within all threads associated
/// with the runtime being built.
/// Specifies the random number generation seed to use within all
/// threads associated with the runtime being built.
///
/// This option is intended to make certain parts of the runtime deterministic.
/// Specifically, it affects the [`tokio::select!`] macro and the work stealing
/// algorithm. In the case of [`tokio::select!`] it will ensure that the order that
/// branches are polled is deterministic.
/// This option is intended to make certain parts of the runtime
/// deterministic (e.g. the [`tokio::select!`] macro). In the case of
/// [`tokio::select!`] it will ensure that the order that branches are
/// polled is deterministic.
///
/// In the case of work stealing, it's a little more complicated. Each worker will
/// be given a deterministic seed so that the starting peer for each work stealing
/// search will be deterministic.
///
/// In addition to the code specifying `rng_seed` and interacting with the runtime,
/// the internals of Tokio and the Rust compiler may affect the sequences of random
/// numbers. In order to ensure repeatable results, the version of Tokio, the versions
/// of all other dependencies that interact with Tokio, and the Rust compiler version
/// In addition to the code specifying `rng_seed` and interacting with
/// the runtime, the internals of Tokio and the Rust compiler may affect
/// the sequences of random numbers. In order to ensure repeatable
/// results, the version of Tokio, the versions of all other
/// dependencies that interact with Tokio, and the Rust compiler version
/// should also all remain constant.
///
/// # Examples
tokio/tests/rt_threaded.rs
-45
View File
@@ -542,7 +542,6 @@ fn rt() -> runtime::Runtime {
#[cfg(tokio_unstable)]
mod unstable {
use super::*;
use tokio::runtime::RngSeed;
#[test]
fn test_disable_lifo_slot() {
@@ -562,48 +561,4 @@ mod unstable {
.unwrap();
})
}
#[test]
fn rng_seed() {
let seed = b"bytes used to generate seed";
let rt1 = tokio::runtime::Builder::new_multi_thread()
.worker_threads(1)
.rng_seed(RngSeed::from_bytes(seed))
.build()
.unwrap();
let rt1_values = rt1.block_on(async {
let rand_1 = tokio::macros::support::thread_rng_n(100);
let rand_2 = tokio::spawn(async {
// Because we only have a single worker thread, the
// RNG will be deterministic here as well.
tokio::macros::support::thread_rng_n(100)
})
.await
.unwrap();
(rand_1, rand_2)
});
let rt2 = tokio::runtime::Builder::new_multi_thread()
.worker_threads(1)
.rng_seed(RngSeed::from_bytes(seed))
.build()
.unwrap();
let rt2_values = rt2.block_on(async {
let rand_1 = tokio::macros::support::thread_rng_n(100);
let rand_2 = tokio::spawn(async {
// Because we only have a single worker thread, the
// RNG will be deterministic here as well.
tokio::macros::support::thread_rng_n(100)
})
.await
.unwrap();
(rand_1, rand_2)
});
assert_eq!(rt1_values, rt2_values);
}
}