diff --git a/benches/benchmarks/deepcopy.py b/benches/benchmarks/deepcopy.py
index bcae0d1567d..24f512e6977 100644
--- a/benches/benchmarks/deepcopy.py
+++ b/benches/benchmarks/deepcopy.py
@@ -66,6 +66,7 @@ def benchmark(n):
                     dc.boolean = b
                     _ = copy.deepcopy(dc)
 
-benchmark(1)
-benchmark_reduce(5)
-benchmark_memo(1)
+N = 10
+benchmark(N)
+benchmark_reduce(5 * N)
+benchmark_memo(N)
diff --git a/crates/host_env/src/posix.rs b/crates/host_env/src/posix.rs
index 928f8df3963..4eb52aa6825 100644
--- a/crates/host_env/src/posix.rs
+++ b/crates/host_env/src/posix.rs
@@ -1113,6 +1113,34 @@ pub fn openpty() -> std::io::Result<(OwnedFd, OwnedFd)> {
     Ok((pty.master, pty.slave))
 }
 
+/// `forkpty(3)`. The child is a session leader with the slave as its
+/// controlling terminal. The parent receives the master fd. The child may
+/// see `master_fd == -1` (Apple's `forkpty`); that is returned as `-1`.
+///
+/// rustix has no `forkpty`. `nix::pty::forkpty` wraps the master in
+/// `OwnedFd`, which panics on Apple's child `-1`, and its `Child` arm
+/// drops the master fd the caller returns as the second item.
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
+pub fn forkpty() -> std::io::Result<(pid_t, i32)> {
+    let mut master_fd: libc::c_int = -1;
+    let pid = unsafe {
+        libc::forkpty(
+            &mut master_fd,
+            core::ptr::null_mut(),
+            core::ptr::null_mut(),
+            core::ptr::null_mut(),
+        )
+    };
+    if pid < 0 {
+        return Err(std::io::Error::last_os_error());
+    }
+    if pid != 0 && master_fd >= 0 {
+        let fd = unsafe { BorrowedFd::borrow_raw(master_fd) };
+        set_inheritable(fd, false)?;
+    }
+    Ok((pid, master_fd))
+}
+
 pub fn ttyname(fd: BorrowedFd<'_>) -> std::io::Result<OsString> {
     nix::unistd::ttyname(fd)
         .map(std::path::PathBuf::into_os_string)
diff --git a/crates/stdlib/src/select.rs b/crates/stdlib/src/select.rs
index dd4d484e03c..9de8bafc27b 100644
--- a/crates/stdlib/src/select.rs
+++ b/crates/stdlib/src/select.rs
@@ -112,27 +112,55 @@ mod decl {
             Ok((v, fds))
         };
 
-        let (rlist, mut r) = seq2set(&rlist)?;
-        let (wlist, mut w) = seq2set(&wlist)?;
-        let (xlist, mut x) = seq2set(&xlist)?;
+        let (rlist, _) = seq2set(&rlist)?;
+        let (wlist, _) = seq2set(&wlist)?;
+        let (xlist, _) = seq2set(&xlist)?;
 
         let nfds = cfg_select! {
             windows => 0, // value is ignored on windows
 
-            _ => [&mut r, &mut w, &mut x]
-                .iter_mut()
-                .filter_map(|set| set.highest())
+            _ => rlist
+                .iter()
+                .chain(&wlist)
+                .chain(&xlist)
+                .map(|fd| fd.fno)
                 .max()
                 .map_or(0, |n| n + 1) as _,
         };
 
+        let fill = |list: &[Selectable]| {
+            let mut fds = FdSet::new();
+            for fd in list {
+                fds.insert(fd.fno);
+            }
+            fds
+        };
+
+        let set2list = |list: Vec<Selectable>, mut set: FdSet| {
+            vm.ctx.new_list(
+                list.into_iter()
+                    .filter(|fd| set.contains(fd.fno))
+                    .map(|fd| fd.obj)
+                    .collect(),
+            )
+        };
+
         loop {
+            // `select(2)` updates the fd sets in place. Rebuild them on every
+            // attempt, including EINTR retries; otherwise an interrupted call
+            // can leave empty sets and a NULL timeout, which blocks forever.
+            let mut r = fill(&rlist);
+            let mut w = fill(&wlist);
+            let mut x = fill(&xlist);
+
             let mut tv = timeout.map(host_select::sec_to_timeval);
             let res =
                 vm.allow_threads(|| host_select::select(nfds, &mut r, &mut w, &mut x, tv.as_mut()));
 
             match res {
-                Ok(_) => break,
+                Ok(_) => {
+                    return Ok((set2list(rlist, r), set2list(wlist, w), set2list(xlist, x)));
+                }
                 Err(err) if err.kind() == io::ErrorKind::Interrupted => {}
                 Err(err) => return Err(err.to_pyexception(vm)),
             }
@@ -142,29 +170,14 @@ mod decl {
             if let Some(ref mut timeout) = timeout {
                 *timeout = deadline.unwrap() - time::time(vm).unwrap();
                 if *timeout < 0.0 {
-                    r.clear();
-                    w.clear();
-                    x.clear();
-                    break;
+                    return Ok((
+                        vm.ctx.new_list(Vec::new()),
+                        vm.ctx.new_list(Vec::new()),
+                        vm.ctx.new_list(Vec::new()),
+                    ));
                 }
-                // retry select() if we haven't reached the deadline yet
             }
         }
-
-        let set2list = |list: Vec<Selectable>, mut set: FdSet| {
-            vm.ctx.new_list(
-                list.into_iter()
-                    .filter(|fd| set.contains(fd.fno))
-                    .map(|fd| fd.obj)
-                    .collect(),
-            )
-        };
-
-        let rlist = set2list(rlist, r);
-        let wlist = set2list(wlist, w);
-        let xlist = set2list(xlist, x);
-
-        Ok((rlist, wlist, xlist))
     }
 
     #[cfg(unix)]
diff --git a/crates/vm/src/stdlib/posix.rs b/crates/vm/src/stdlib/posix.rs
index 6ad0df60310..4076523c8fd 100644
--- a/crates/vm/src/stdlib/posix.rs
+++ b/crates/vm/src/stdlib/posix.rs
@@ -832,6 +832,50 @@ pub mod module {
         }
     }
 
+    #[cfg(not(any(target_os = "redox", target_os = "wasi")))]
+    #[pyfunction]
+    fn forkpty(vm: &VirtualMachine) -> PyResult<(i32, i32)> {
+        if vm
+            .state
+            .finalizing
+            .load(core::sync::atomic::Ordering::Acquire)
+        {
+            return Err(vm.new_exception_msg(
+                vm.ctx.exceptions.python_finalization_error.to_owned(),
+                "can't fork at interpreter shutdown".into(),
+            ));
+        }
+        if !vm.state.allow_fork() {
+            return Err(
+                vm.new_runtime_error("fork not supported for isolated subinterpreters".to_owned())
+            );
+        }
+
+        vm.sys_module
+            .get_attr("audit", vm)?
+            .call(("os.forkpty",), vm)?;
+
+        py_os_before_fork(vm);
+        let result = rustpython_host_env::posix::forkpty();
+
+        match result {
+            Ok((0, master)) => {
+                py_os_after_fork_child(vm);
+                Ok((0, master))
+            }
+            Ok((pid, master)) => {
+                let num_os_threads = get_number_of_os_threads();
+                py_os_after_fork_parent(vm);
+                warn_if_multi_threaded("forkpty", num_os_threads, vm);
+                Ok((pid, master))
+            }
+            Err(err) => {
+                py_os_after_fork_parent(vm);
+                Err(err.into_pyexception(vm))
+            }
+        }
+    }
+
     #[cfg(not(target_os = "redox"))]
     const MKNOD_DIR_FD: bool = cfg!(not(target_vendor = "apple"));