Avoid using rand::thread_rng in the stdlib benchmarks.

Cargo.lock

@@ -827,6 +827,7 @@ name = "core"
 version = "0.0.0"
 dependencies = [
  "rand 0.7.3",
+ "rand_xorshift",
 ]
 
 [[package]]

library/alloc/benches/binary_heap.rs

@@ -1,11 +1,11 @@
 use std::collections::BinaryHeap;
 
-use rand::{seq::SliceRandom, thread_rng};
+use rand::seq::SliceRandom;
 use test::{black_box, Bencher};
 
 #[bench]
 fn bench_find_smallest_1000(b: &mut Bencher) {
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     let mut vec: Vec<u32> = (0..100_000).collect();
     vec.shuffle(&mut rng);
 
@@ -47,7 +47,7 @@ fn bench_peek_mut_deref_mut(b: &mut Bencher) {
 
 #[bench]
 fn bench_from_vec(b: &mut Bencher) {
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     let mut vec: Vec<u32> = (0..100_000).collect();
     vec.shuffle(&mut rng);
 
@@ -64,7 +64,7 @@ fn bench_into_sorted_vec(b: &mut Bencher) {
 #[bench]
 fn bench_push(b: &mut Bencher) {
     let mut bheap = BinaryHeap::with_capacity(50_000);
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     let mut vec: Vec<u32> = (0..50_000).collect();
     vec.shuffle(&mut rng);
 

library/alloc/benches/btree/map.rs

@@ -3,7 +3,7 @@ use std::iter::Iterator;
 use std::ops::RangeBounds;
 use std::vec::Vec;
 
-use rand::{seq::SliceRandom, thread_rng, Rng};
+use rand::{seq::SliceRandom, Rng};
 use test::{black_box, Bencher};
 
 macro_rules! map_insert_rand_bench {
@@ -13,7 +13,7 @@ macro_rules! map_insert_rand_bench {
             let n: usize = $n;
             let mut map = $map::new();
             // setup
-            let mut rng = thread_rng();
+            let mut rng = crate::bench_rng();
 
             for _ in 0..n {
                 let i = rng.gen::<usize>() % n;
@@ -60,7 +60,7 @@ macro_rules! map_from_iter_rand_bench {
         pub fn $name(b: &mut Bencher) {
             let n: usize = $n;
             // setup
-            let mut rng = thread_rng();
+            let mut rng = crate::bench_rng();
             let mut vec = Vec::with_capacity(n);
 
             for _ in 0..n {
@@ -106,7 +106,7 @@ macro_rules! map_find_rand_bench {
             let n: usize = $n;
 
             // setup
-            let mut rng = thread_rng();
+            let mut rng = crate::bench_rng();
             let mut keys: Vec<_> = (0..n).map(|_| rng.gen::<usize>() % n).collect();
 
             for &k in &keys {
@@ -169,7 +169,7 @@ map_find_seq_bench! {find_seq_10_000, 10_000, BTreeMap}
 
 fn bench_iteration(b: &mut Bencher, size: i32) {
     let mut map = BTreeMap::<i32, i32>::new();
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
 
     for _ in 0..size {
         map.insert(rng.gen(), rng.gen());
@@ -199,7 +199,7 @@ pub fn iteration_100000(b: &mut Bencher) {
 
 fn bench_iteration_mut(b: &mut Bencher, size: i32) {
     let mut map = BTreeMap::<i32, i32>::new();
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
 
     for _ in 0..size {
         map.insert(rng.gen(), rng.gen());

library/alloc/benches/btree/set.rs

@@ -1,10 +1,10 @@
 use std::collections::BTreeSet;
 
-use rand::{thread_rng, Rng};
+use rand::Rng;
 use test::Bencher;
 
 fn random(n: usize) -> BTreeSet<usize> {
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     let mut set = BTreeSet::new();
     while set.len() < n {
         set.insert(rng.gen());

library/alloc/benches/lib.rs

@@ -17,3 +17,11 @@ mod str;
 mod string;
 mod vec;
 mod vec_deque;
+
+/// Returns a `rand::Rng` seeded with a consistent seed.
+///
+/// This is done to avoid introducing nondeterminism in benchmark results.
+fn bench_rng() -> rand_xorshift::XorShiftRng {
+    const SEED: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
+    rand::SeedableRng::from_seed(SEED)
+}

library/alloc/benches/slice.rs

@@ -1,8 +1,7 @@
 use std::{mem, ptr};
 
 use rand::distributions::{Alphanumeric, Standard};
-use rand::{thread_rng, Rng, SeedableRng};
-use rand_xorshift::XorShiftRng;
+use rand::Rng;
 use test::{black_box, Bencher};
 
 #[bench]
@@ -152,7 +151,7 @@ fn zero_1kb_mut_iter(b: &mut Bencher) {
 
 #[bench]
 fn random_inserts(b: &mut Bencher) {
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     b.iter(|| {
         let mut v = vec![(0, 0); 30];
         for _ in 0..100 {
@@ -164,7 +163,7 @@ fn random_inserts(b: &mut Bencher) {
 
 #[bench]
 fn random_removes(b: &mut Bencher) {
-    let mut rng = thread_rng();
+    let mut rng = crate::bench_rng();
     b.iter(|| {
         let mut v = vec![(0, 0); 130];
         for _ in 0..100 {
@@ -182,20 +181,18 @@ fn gen_descending(len: usize) -> Vec<u64> {
     (0..len as u64).rev().collect()
 }
 
-const SEED: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
-
 fn gen_random(len: usize) -> Vec<u64> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     (&mut rng).sample_iter(&Standard).take(len).collect()
 }
 
 fn gen_random_bytes(len: usize) -> Vec<u8> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     (&mut rng).sample_iter(&Standard).take(len).collect()
 }
 
 fn gen_mostly_ascending(len: usize) -> Vec<u64> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     let mut v = gen_ascending(len);
     for _ in (0usize..).take_while(|x| x * x <= len) {
         let x = rng.gen::<usize>() % len;
@@ -206,7 +203,7 @@ fn gen_mostly_ascending(len: usize) -> Vec<u64> {
 }
 
 fn gen_mostly_descending(len: usize) -> Vec<u64> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     let mut v = gen_descending(len);
     for _ in (0usize..).take_while(|x| x * x <= len) {
         let x = rng.gen::<usize>() % len;
@@ -217,7 +214,7 @@ fn gen_mostly_descending(len: usize) -> Vec<u64> {
 }
 
 fn gen_strings(len: usize) -> Vec<String> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     let mut v = vec![];
     for _ in 0..len {
         let n = rng.gen::<usize>() % 20 + 1;
@@ -227,7 +224,7 @@ fn gen_strings(len: usize) -> Vec<String> {
 }
 
 fn gen_big_random(len: usize) -> Vec<[u64; 16]> {
-    let mut rng = XorShiftRng::from_seed(SEED);
+    let mut rng = crate::bench_rng();
     (&mut rng).sample_iter(&Standard).map(|x| [x; 16]).take(len).collect()
 }
 

library/alloc/benches/vec.rs

@@ -476,7 +476,7 @@ fn bench_in_place_recycle(b: &mut Bencher) {
 #[bench]
 fn bench_in_place_zip_recycle(b: &mut Bencher) {
     let mut data = vec![0u8; 1000];
-    let mut rng = rand::thread_rng();
+    let mut rng = crate::bench_rng();
     let mut subst = vec![0u8; 1000];
     rng.fill_bytes(&mut subst[..]);
 
@@ -495,7 +495,7 @@ fn bench_in_place_zip_recycle(b: &mut Bencher) {
 #[bench]
 fn bench_in_place_zip_iter_mut(b: &mut Bencher) {
     let mut data = vec![0u8; 256];
-    let mut rng = rand::thread_rng();
+    let mut rng = crate::bench_rng();
     let mut subst = vec![0u8; 1000];
     rng.fill_bytes(&mut subst[..]);
 

library/core/Cargo.toml

@@ -25,6 +25,7 @@ test = true
 
 [dev-dependencies]
 rand = "0.7"
+rand_xorshift = "0.2"
 
 [features]
 # Make panics and failed asserts immediately abort without formatting any message

library/core/benches/lib.rs

@@ -17,3 +17,11 @@ mod ops;
 mod pattern;
 mod slice;
 mod str;
+
+/// Returns a `rand::Rng` seeded with a consistent seed.
+///
+/// This is done to avoid introducing nondeterminism in benchmark results.
+fn bench_rng() -> rand_xorshift::XorShiftRng {
+    const SEED: [u8; 16] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
+    rand::SeedableRng::from_seed(SEED)
+}

library/core/benches/num/int_log/mod.rs

@@ -17,7 +17,7 @@ macro_rules! int_log_bench {
 
         #[bench]
         fn $random(bench: &mut Bencher) {
-            let mut rng = rand::thread_rng();
+            let mut rng = crate::bench_rng();
             /* Exponentially distributed random numbers from the whole range of the type.  */
             let numbers: Vec<$t> = (0..256)
                 .map(|_| {
@@ -34,7 +34,7 @@ macro_rules! int_log_bench {
 
         #[bench]
         fn $random_small(bench: &mut Bencher) {
-            let mut rng = rand::thread_rng();
+            let mut rng = crate::bench_rng();
             /* Exponentially distributed random numbers from the range 0..256.  */
             let numbers: Vec<$t> = (0..256)
                 .map(|_| {