use rand's SmallRng for random number generation

Cargo.toml

@@ -18,7 +18,7 @@ description = "A library for managing temporary files and directories."
 
 [dependencies]
 cfg-if = "1"
-rand = "0.8"
+rand = { version = "0.8", features = ["small_rng", "getrandom"], default_features = false }
 remove_dir_all = "0.5"
 
 [target.'cfg(any(unix, target_os = "wasi"))'.dependencies]

src/util.rs

@@ -1,20 +1,30 @@
-use rand::distributions::Alphanumeric;
-use rand::{self, Rng};
+use rand::{self, Rng, SeedableRng};
+use rand::{distributions::Alphanumeric, rngs::SmallRng};
 use std::ffi::{OsStr, OsString};
-use std::path::{Path, PathBuf};
+use std::thread_local;
+use std::{
+    cell::UnsafeCell,
+    path::{Path, PathBuf},
+    rc::Rc,
+};
 use std::{io, str};
 
 use crate::error::IoResultExt;
 
+thread_local! {
+    static THREAD_RNG_KEY: Rc<UnsafeCell<SmallRng>> = Rc::new(UnsafeCell::new(SmallRng::from_entropy()));
+}
+
 fn tmpname(prefix: &OsStr, suffix: &OsStr, rand_len: usize) -> OsString {
+    let rng = THREAD_RNG_KEY.with(|t| t.clone());
     let mut buf = OsString::with_capacity(prefix.len() + suffix.len() + rand_len);
     buf.push(prefix);
 
     // Push each character in one-by-one. Unfortunately, this is the only
     // safe(ish) simple way to do this without allocating a temporary
     // String/Vec.
     unsafe {
-        rand::thread_rng()
+        (&mut *rng.get())
             .sample_iter(&Alphanumeric)
             .take(rand_len)
             .for_each(|b| buf.push(str::from_utf8_unchecked(&[b as u8])))