set realtime priority for stream threads in alsa and wasapi

.github/workflows/cpal.yml

@@ -14,6 +14,8 @@ jobs:
       run: sudo apt-get install libasound2-dev
     - name: Install libjack
       run: sudo apt-get install libjack-jackd2-dev libjack-jackd2-0
+    - name: Install dbus
+      run: sudo apt-get install libdbus-1-dev
     - name: Install stable
       uses: dtolnay/rust-toolchain@stable
       with:
@@ -67,6 +69,8 @@ jobs:
       run: sudo apt-get install libasound2-dev
     - name: Install libjack
       run: sudo apt-get install libjack-jackd2-dev libjack-jackd2-0
+    - name: Install dbus
+      run: sudo apt-get install libdbus-1-dev
     - name: Install stable
       uses: dtolnay/rust-toolchain@stable
     - name: Run without features

Cargo.toml

@@ -35,12 +35,14 @@ windows = { version = "0.54.0", features = [
     "Win32_Media_Multimedia",
     "Win32_UI_Shell_PropertiesSystem"
 ]}
+audio_thread_priority = { version = "0.33.0", optional = true }
 asio-sys = { version = "0.2", path = "asio-sys", optional = true }
 num-traits = { version = "0.2.6", optional = true }
 
 [target.'cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd", target_os = "netbsd"))'.dependencies]
 alsa = "0.9"
 libc = "0.2"
+audio_thread_priority = { version = "0.33.0", optional = true }
 jack = { version = "0.13.0", optional = true }
 
 [target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies]

src/host/alsa/mod.rs

@@ -589,6 +589,8 @@ fn input_stream_worker(
     error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
     timeout: Option<Duration>,
 ) {
+    boost_current_thread_priority(stream.conf.buffer_size, stream.conf.sample_rate);
+
     let mut ctxt = StreamWorkerContext::new(&timeout);
     loop {
         let flow =
@@ -640,6 +642,8 @@ fn output_stream_worker(
     error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
     timeout: Option<Duration>,
 ) {
+    boost_current_thread_priority(stream.conf.buffer_size, stream.conf.sample_rate);
+
     let mut ctxt = StreamWorkerContext::new(&timeout);
     loop {
         let flow =
@@ -684,6 +688,25 @@ fn output_stream_worker(
     }
 }
 
+#[cfg(feature = "audio_thread_priority")]
+fn boost_current_thread_priority(buffer_size: BufferSize, sample_rate: SampleRate) {
+    use audio_thread_priority::promote_current_thread_to_real_time;
+
+    let buffer_size = if let BufferSize::Fixed(buffer_size) = buffer_size {
+        buffer_size
+    } else {
+        // if the buffer size isn't fixed, let audio_thread_priority choose a sensible default value
+        0
+    };
+
+    if let Err(err) = promote_current_thread_to_real_time(buffer_size, sample_rate.0) {
+        eprintln!("Failed to promote audio thread to real-time priority: {err}");
+    }
+}
+
+#[cfg(not(feature = "audio_thread_priority"))]
+fn boost_current_thread_priority(_: BufferSize, _: SampleRate) {}
+
 enum PollDescriptorsFlow {
     Continue,
     Return,

src/host/wasapi/stream.rs

@@ -1,15 +1,14 @@
 use super::windows_err_to_cpal_err;
 use crate::traits::StreamTrait;
 use crate::{
-    BackendSpecificError, Data, InputCallbackInfo, OutputCallbackInfo, PauseStreamError,
-    PlayStreamError, SampleFormat, StreamError,
+    BackendSpecificError, BufferSize, Data, InputCallbackInfo, OutputCallbackInfo,
+    PauseStreamError, PlayStreamError, SampleFormat, StreamError,
 };
 use std::mem;
 use std::ptr;
 use std::sync::mpsc::{channel, Receiver, SendError, Sender};
 use std::thread::{self, JoinHandle};
 use windows::Win32::Foundation;
-use windows::Win32::Foundation::HANDLE;
 use windows::Win32::Foundation::WAIT_OBJECT_0;
 use windows::Win32::Media::Audio;
 use windows::Win32::System::SystemServices;
@@ -269,7 +268,10 @@ fn run_input(
     data_callback: &mut dyn FnMut(&Data, &InputCallbackInfo),
     error_callback: &mut dyn FnMut(StreamError),
 ) {
-    boost_current_thread_priority();
+    boost_current_thread_priority(
+        run_ctxt.stream.config.buffer_size,
+        run_ctxt.stream.config.sample_rate,
+    );
 
     loop {
         match process_commands_and_await_signal(&mut run_ctxt, error_callback) {
@@ -298,7 +300,10 @@ fn run_output(
     data_callback: &mut dyn FnMut(&mut Data, &OutputCallbackInfo),
     error_callback: &mut dyn FnMut(StreamError),
 ) {
-    boost_current_thread_priority();
+    boost_current_thread_priority(
+        run_ctxt.stream.config.buffer_size,
+        run_ctxt.stream.config.sample_rate,
+    );
 
     loop {
         match process_commands_and_await_signal(&mut run_ctxt, error_callback) {
@@ -322,7 +327,26 @@ fn run_output(
     }
 }
 
-fn boost_current_thread_priority() {
+#[cfg(feature = "audio_thread_priority")]
+fn boost_current_thread_priority(buffer_size: BufferSize, sample_rate: crate::SampleRate) {
+    use audio_thread_priority::promote_current_thread_to_real_time;
+
+    let buffer_size = if let BufferSize::Fixed(buffer_size) = buffer_size {
+        buffer_size
+    } else {
+        // if the buffer size isn't fixed, let audio_thread_priority choose a sensible default value
+        0
+    };
+
+    if let Err(err) = promote_current_thread_to_real_time(buffer_size, sample_rate.0) {
+        eprintln!("Failed to promote audio thread to real-time priority: {err}");
+    }
+}
+
+#[cfg(not(feature = "audio_thread_priority"))]
+fn boost_current_thread_priority(_: BufferSize, _: crate::SampleRate) {
+    use windows::Win32::Foundation::HANDLE;
+
     unsafe {
         let thread_id = Threading::GetCurrentThreadId();