remove num_cpus dependency (#488)

actix-server/src/builder.rs

@@ -1,4 +1,4 @@
-use std::{io, time::Duration};
+use std::{io, num::NonZeroUsize, time::Duration};
 
 use actix_rt::net::TcpStream;
 use tokio::sync::mpsc::{unbounded_channel, UnboundedReceiver, UnboundedSender};
@@ -55,7 +55,7 @@ impl ServerBuilder {
         let (cmd_tx, cmd_rx) = unbounded_channel();
 
         ServerBuilder {
-            threads: num_cpus::get_physical(),
+            threads: std::thread::available_parallelism().map_or(2, NonZeroUsize::get),
             token: 0,
             factories: Vec::new(),
             sockets: Vec::new(),
@@ -76,6 +76,12 @@ impl ServerBuilder {
     /// The default worker count is the number of physical CPU cores available. If your benchmark
     /// testing indicates that simultaneous multi-threading is beneficial to your app, you can use
     /// the [`num_cpus`] crate to acquire the _logical_ core count instead.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `num` is 0.
+    ///
+    /// [`num_cpus`]: https://docs.rs/num_cpus
     pub fn workers(mut self, num: usize) -> Self {
         assert_ne!(num, 0, "workers must be greater than 0");
         self.threads = num;

actix-server/src/worker.rs

@@ -1,6 +1,7 @@
 use std::{
     future::Future,
     io, mem,
+    num::NonZeroUsize,
     pin::Pin,
     rc::Rc,
     sync::{
@@ -249,8 +250,11 @@ pub(crate) struct ServerWorkerConfig {
 
 impl Default for ServerWorkerConfig {
     fn default() -> Self {
-        // 512 is the default max blocking thread count of tokio runtime.
-        let max_blocking_threads = std::cmp::max(512 / num_cpus::get_physical(), 1);
+        let parallelism = std::thread::available_parallelism().map_or(2, NonZeroUsize::get);
+
+        // 512 is the default max blocking thread count of a Tokio runtime.
+        let max_blocking_threads = std::cmp::max(512 / parallelism, 1);
+
         Self {
             shutdown_timeout: Duration::from_secs(30),
             max_blocking_threads,