From da365a2d23139bd255046ef08fe13a441059835a Mon Sep 17 00:00:00 2001
From: Harold Dost <h.dost@criteo.com>
Date: Fri, 9 Jun 2023 10:36:50 +0200
Subject: [PATCH] Use faster Rng in RandomIdGenerator

Represents a minimum a 11%-22% improvement in relevant benchmarks.

Fixes #808
---
 opentelemetry-sdk/Cargo.toml                    | 3 ++-
 opentelemetry-sdk/src/trace/id_generator/mod.rs | 5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/opentelemetry-sdk/Cargo.toml b/opentelemetry-sdk/Cargo.toml
index 70e9961b5cb..63aaf573acf 100644
--- a/opentelemetry-sdk/Cargo.toml
+++ b/opentelemetry-sdk/Cargo.toml
@@ -22,6 +22,7 @@ once_cell = "1.10"
 ordered-float = "3.4.0"
 percent-encoding = { version = "2.0", optional = true }
 rand = { version = "0.8", default-features = false, features = ["std", "std_rng"], optional = true }
+rand_pcg = { version = "0.3", default-features = false, optional = true }
 regex = { version = "1.0", optional = true }
 serde = { version = "1.0", features = ["derive", "rc"], optional = true }
 serde_json = { version = "1", optional = true }
@@ -41,7 +42,7 @@ pprof = { version = "0.11.1", features = ["flamegraph", "criterion"] }
 
 [features]
 default = ["trace"]
-trace = ["opentelemetry_api/trace", "crossbeam-channel", "rand", "async-trait", "percent-encoding"]
+trace = ["opentelemetry_api/trace", "crossbeam-channel", "rand", "rand_pcg", "async-trait", "percent-encoding"]
 jaeger_remote_sampler = ["trace", "opentelemetry-http", "http", "serde", "serde_json", "url"]
 logs = ["opentelemetry_api/logs", "crossbeam-channel", "async-trait", "serde_json"]
 metrics = ["opentelemetry_api/metrics", "regex", "async-trait"]
diff --git a/opentelemetry-sdk/src/trace/id_generator/mod.rs b/opentelemetry-sdk/src/trace/id_generator/mod.rs
index cf99b197cf8..5a788837eb7 100644
--- a/opentelemetry-sdk/src/trace/id_generator/mod.rs
+++ b/opentelemetry-sdk/src/trace/id_generator/mod.rs
@@ -2,7 +2,8 @@
 pub(super) mod aws;
 
 use opentelemetry_api::trace::{SpanId, TraceId};
-use rand::{rngs, Rng};
+use rand::{thread_rng, Rng, SeedableRng};
+use rand_pcg::Pcg64Mcg;
 use std::cell::RefCell;
 use std::fmt;
 
@@ -35,5 +36,5 @@ impl IdGenerator for RandomIdGenerator {
 
 thread_local! {
     /// Store random number generator for each thread
-    static CURRENT_RNG: RefCell<rngs::ThreadRng> = RefCell::new(rngs::ThreadRng::default());
+    static CURRENT_RNG: RefCell<Pcg64Mcg> = RefCell::new(Pcg64Mcg::from_rng(thread_rng()).unwrap());
 }