Limit Rayon threadpool threads (#5871)

rayon-threadlimit/.gitignore

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+/target/
+/farf/

rayon-threadlimit/Cargo.toml

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+[package]
+name = "solana-rayon-threadlimit"
+version = "0.19.0-pre0"
+homepage = "https://solana.com/"
+readme = "../README.md"
+repository = "https://github.com/solana-labs/solana"
+authors = ["Solana Maintainers <maintainers@solana.com>"]
+license = "Apache-2.0"
+edition = "2018"
+
+[dependencies]
+lazy_static = "1.4.0"
+sys-info = "0.5.7"

rayon-threadlimit/src/lib.rs

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+#[macro_use]
+extern crate lazy_static;
+
+use std::sync::RwLock;
+
+//TODO remove this hack when rayon fixes itself
+lazy_static! {
+    static ref MAX_RAYON_THREADS: RwLock<usize> =
+        RwLock::new(sys_info::cpu_num().unwrap() as usize);
+}
+
+pub fn get_thread_count() -> usize {
+    *MAX_RAYON_THREADS.read().unwrap()
+}
+
+pub fn set_thread_count(count: usize) {
+    *MAX_RAYON_THREADS.write().unwrap() = count;
+}