Add stress fd test

stress/stress_fd_leak.ml

@@ -0,0 +1,48 @@
+open Eio.Std
+
+(* Stress test to check for file descriptor (FD) leaks by repeatedly opening and closing files *)
+
+(* Number of iterations for the stress test *)
+let n_iters = 100_000
+
+(* File path to use for opening files. Using /dev/null as it doesn't create real files. *)
+let file_path = "/dev/null"
+
+(* Function to count the number of open file descriptors in the current process *)
+let count_open_fds () =
+  let proc_fd = "/proc/self/fd" in
+  Array.length (Sys.readdir proc_fd)  (* Read the directory containing open file descriptors *)
+
+(* Main function to run the stress test *)
+let main ~domain_mgr =
+  (* Count the initial number of open file descriptors *)
+  let initial_fds = count_open_fds () in
+
+  (* Create a new switch context for running fibers *)
+  Switch.run (fun sw ->
+      (* Fork a new fiber for the stress test *)
+      Fiber.fork ~sw (fun () ->
+          (* Run the stress test within the provided domain manager *)
+          Eio.Domain_manager.run domain_mgr (fun () ->
+              (* Perform the stress test iterations *)
+              for _ = 1 to n_iters do
+                let fd = Unix.openfile file_path [Unix.O_RDONLY] 0 in  (* Open the file descriptor *)
+                Unix.close fd  (* Close the file descriptor *)
+              done
+            )
+        )
+    );
+
+  (* Count the final number of open file descriptors *)
+  let final_fds = count_open_fds () in
+
+  (* Assert that the number of open file descriptors is unchanged *)
+  assert (initial_fds = final_fds);
+
+  (* Print the result of the FD leak test *)
+  print_endline "FD Leak Test Passed"
+
+(* Entry point of the program *)
+let () =
+  Eio_main.run @@ fun env ->
+  main ~domain_mgr:(Eio.Stdenv.domain_mgr env)  (* Pass the domain manager from the environment *)