diff --git a/src/worker/script.rs b/src/worker/script.rs
index bcd1ac8..18463a6 100644
--- a/src/worker/script.rs
+++ b/src/worker/script.rs
@@ -8,6 +8,7 @@ use std::{
     io::prelude::*,
     net::{Shutdown, TcpStream},
     process::Command,
+    sync::Arc,
     thread, time,
 };
 
@@ -22,6 +23,7 @@ use llvm::execution_engine::*;
 use llvm::target::*;
 use llvm_sys::LLVMType;
 use llvm_sys::prelude::*;
+use std::cell::RefCell;
 use std::ffi::{CStr, CString, c_void};
 use std::mem;
 
@@ -129,6 +131,11 @@ pub unsafe extern "C" fn task(name: *const i8, random: bool) -> u64 {
     0
 }
 
+thread_local! {
+    static LAST_RANDOM_PATH: RefCell<CString> =
+        RefCell::new(CString::new("").unwrap());
+}
+
 /// Return a randomly generated path.
 ///
 /// # Safety
@@ -144,7 +151,10 @@ pub unsafe extern "C" fn random_path(base: *const i8) -> *const i8 {
         .map(char::from)
         .collect();
 
-    CString::new(format!("{base}/{uniq}")).unwrap().into_raw()
+    LAST_RANDOM_PATH.with(|last| {
+        *last.borrow_mut() = CString::new(format!("{base}/{uniq}")).unwrap();
+        last.borrow().as_ptr()
+    })
 }
 
 #[derive(Debug, Clone)]
@@ -506,21 +516,43 @@ impl Worker for ScriptWorker {
                 debug!("Distribution {:?}", d);
                 let Dist::Exp { rate } = d else { todo!() };
 
-                loop {
-                    let worker = self.clone();
-                    thread::spawn(move || {
-                        (worker.jit)();
-                    });
-
-                    let interval: f64 =
-                        thread_rng().sample(Exp::new(*rate).unwrap());
-                    debug!("Interval {}", interval);
-                    thread::sleep(time::Duration::from_secs_f64(interval));
-                }
+                const MAX_CONCURRENT: usize = 16;
+                let semaphore = Arc::new((
+                    std::sync::Mutex::new(0usize),
+                    std::sync::Condvar::new(),
+                ));
+
+                thread::scope(|s| {
+                    loop {
+                        {
+                            let (lock, cvar) = &*semaphore;
+                            let mut count = cvar
+                                .wait_while(lock.lock().unwrap(), |c| {
+                                    *c >= MAX_CONCURRENT
+                                })
+                                .unwrap();
+                            *count += 1;
+                        }
+
+                        let worker = self.clone();
+                        let sem = Arc::clone(&semaphore);
+                        s.spawn(move || {
+                            (worker.jit)();
+                            let (lock, cvar) = &*sem;
+                            *lock.lock().unwrap() -= 1;
+                            cvar.notify_one();
+                        });
+
+                        let interval: f64 =
+                            thread_rng().sample(Exp::new(*rate).unwrap());
+                        debug!("Interval {}", interval);
+                        thread::sleep(time::Duration::from_secs_f64(interval));
+                    }
+                });
             }
             None => {
                 debug!("Single unit");
-                (self.jit)()
+                (self.jit)();
             }
         };