Limit Rayon threadpool threads (#5871)

rayon-threadlimit/src/lib.rs

@@ -0,0 +1,18 @@
+#[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;
+}