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Merged
Katacc merged 1 commit into from
Jan 2, 2026
Merged

reduce volume control latency #5

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190 changes: 154 additions & 36 deletions src/main/java/io/github/katacc/AudioController.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,28 +10,31 @@
import javax.sound.midi.MidiMessage;
import java.io.IOException;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;


public class AudioController {

private static AudioController single_instance = null;

private List<Integer> id0;
private List<Integer> id1;
private List<Integer> id2;
private List<Integer> id3;
private List<Integer> id4;
private List<Integer> id5;
private List<Integer> id6;
private List<Integer> id7;
private List<Integer> id16;
private List<Integer> id17;
private List<Integer> id18;
private List<Integer> id19;
private List<Integer> id20;
private List<Integer> id21;
private List<Integer> id22;
private List<Integer> id23;
private final List<Integer> id0;
private final List<Integer> id1;
private final List<Integer> id2;
private final List<Integer> id3;
private final List<Integer> id4;
private final List<Integer> id5;
private final List<Integer> id6;
private final List<Integer> id7;
private final List<Integer> id16;
private final List<Integer> id17;
private final List<Integer> id18;
private final List<Integer> id19;
private final List<Integer> id20;
private final List<Integer> id21;
private final List<Integer> id22;
private final List<Integer> id23;

private Vector<String> id7App;
private Vector<String> id16App;
Expand All @@ -55,6 +58,13 @@ public class AudioController {

private boolean debug = false;

// Throttling updates: capturing only the latest volume (not yet executed) per control
// https://medium.com/@anuragnitdgr/resolving-race-conditions-in-java-with-concurrenthashmap-and-atomicboolean-583d3e31b52c
private final ConcurrentHashMap<Integer, AtomicReference<Float>> pendingVolume = new ConcurrentHashMap<>();
private final AtomicBoolean volumeWorkerRunning = new AtomicBoolean(false);
// Protect ID/Config Updates
private final Object configLock = new Object();

private AudioController() {

id0 = new ArrayList<>();
Expand Down Expand Up @@ -130,21 +140,15 @@ public void changeVolume(MidiMessage msg) {
}
// Volume controls
if (isVolumeControl(control)) {
List<Integer> ids = getIdsForVolumeControl(control);
if (ids != null) {
if (ids.isEmpty()) {
System.out.println("id" + control + " is empty... refreshing config...");
getConfig();
}
for (int id : ids) {
runWpctlSetVolume(id, scaled_volume);
}
}
// Volume controls are high frequency and we like to skip non-applied, non-final volume changes for
// faster reaction). Therefore we queue them instead of executing them directly.
// Actual execution happens ansynchronously in volumeWorkerLoop() (applyVolumeToControl())
queueVolumeUpdate(control, scaled_volume);
}
}
audioSetTimer++;

// Media controls
// Media controls (keep synchronous; these are low frequency)
if (control == 41 && value == 127) {
runPlayerctl("play-pause");
}
Expand All @@ -158,7 +162,9 @@ public void changeVolume(MidiMessage msg) {
runPlayerctl("stop");
}
if (control == 46 && value == 127) {
getConfig();
synchronized (configLock) {
getConfigUnsafe();
}
System.out.println("Forced reconfig");
}
}
Expand All @@ -168,8 +174,84 @@ private boolean isVolumeControl(int control) {
return (control >= 0 && control <= 7) || (control >= 16 && control <= 23);
}

private void queueVolumeUpdate(int control, float scaled_volume) {
pendingVolume.computeIfAbsent(control, k -> new AtomicReference<>()).set(scaled_volume);

if (volumeWorkerRunning.compareAndSet(false, true)) {
new Thread(this::volumeWorkerLoop, "wpctl-volume-worker").start();
}
}

private void volumeWorkerLoop() {
try {
while (true) {
Integer nextControl = findAnyPendingControl();
if (nextControl == null) {
return;
}

AtomicReference<Float> ref = pendingVolume.get(nextControl);
if (ref == null) {
continue;
}

Float volume = ref.getAndSet(null);
if (volume == null) {
continue;
}

applyVolumeToControl(nextControl, volume);
}
} finally {
volumeWorkerRunning.set(false);

// If something arrived after we decided to stop, restart.
if (findAnyPendingControl() != null && volumeWorkerRunning.compareAndSet(false, true)) {
new Thread(this::volumeWorkerLoop, "wpctl-volume-worker").start();
}
}
}

private Integer findAnyPendingControl() {
for (Map.Entry<Integer, AtomicReference<Float>> entry : pendingVolume.entrySet()) {
if (entry.getValue().get() != null) {
return entry.getKey();
}
}
return null;
}

private void applyVolumeToControl(int control, float scaled_volume) {
List<Integer> idsSnapshot;

synchronized (configLock) {
List<Integer> ids = getIdsForVolumeControl(control);
if (ids == null) {
return;
}

if (ids.isEmpty()) {
if (debug) {
System.out.println("id" + control + " is empty... refreshing config...");
}
getConfigUnsafe();
ids = getIdsForVolumeControl(control);
if (ids == null) {
return;
}
}

idsSnapshot = new ArrayList<>(ids);
}

for (int id : idsSnapshot) {
runWpctlSetVolume(id, scaled_volume);
}
}

private List<Integer> getIdsForVolumeControl(int control) {
switch (control) {
// Faders
case 0: return id0;
case 1: return id1;
case 2: return id2;
Expand All @@ -178,6 +260,7 @@ private List<Integer> getIdsForVolumeControl(int control) {
case 5: return id5;
case 6: return id6;
case 7: return id7;
// Knobs
case 16: return id16;
case 17: return id17;
case 18: return id18;
Expand All @@ -186,31 +269,42 @@ private List<Integer> getIdsForVolumeControl(int control) {
case 21: return id21;
case 22: return id22;
case 23: return id23;
// Other controls are no volume controls
default: return null;
}
}

private void runWpctlSetVolume(int id, float scaled_volume) {
try {
String command = String.format("wpctl set-volume %s, %s", id, scaled_volume);
ProcessBuilder pb = new ProcessBuilder("wpctl", "set-volume", String.valueOf(id), String.valueOf(scaled_volume));
if (debug) {
System.out.println("Executing command: " + command);
System.out.println("Executing command: " + String.join(" ", pb.command()));
}
Process process = Runtime.getRuntime().exec(command);
} catch (IOException e) {
Process process = pb.start();
int returnCode = process.waitFor(); // prevent process pile-up
if (debug && returnCode != 0) {
System.out.println("wpctl exited with return code=" + returnCode);
}
} catch (IOException | InterruptedException e) {
System.out.println("Error: " + e.getMessage());
Thread.currentThread().interrupt();
}
}

private void runPlayerctl(String action) {
try {
String command = String.format("playerctl %s", action);
ProcessBuilder pb = new ProcessBuilder("playerctl", action);
if (debug) {
System.out.println("Executing command: " + command);
System.out.println("Executing command: " + String.join(" ", pb.command()));
}
Process process = Runtime.getRuntime().exec(command);
} catch (IOException e) {
Process process = pb.start();
int returnCode = process.waitFor();
if (debug && returnCode != 0) {
System.out.println("playerctl exited with return code=" + returnCode);
}
} catch (IOException | InterruptedException e) {
System.out.println("Error: " + e.getMessage());
Thread.currentThread().interrupt();
}
}

Expand Down Expand Up @@ -258,7 +352,19 @@ public List<Integer> getId(String name) {
return appId;
}

/**
* Thread-safe entry point: uses configLock.
*/
public void getConfig() {
synchronized (configLock) {
getConfigUnsafe();
}
}

/**
* Internal implementation; caller must hold configLock.
*/
private void getConfigUnsafe() {
// Path to config file
String userHome = System.getProperty("user.home");
String configPath = userHome + "/.config/midi-mixer/config.ini";
Expand Down Expand Up @@ -332,7 +438,19 @@ public void getConfig() {

}

/**
* Thread-safe entry point: uses configLock.
*/
public void constructConfig(int fader, Vector<String> applications) {
synchronized (configLock) {
constructConfigUnsafe(fader, applications);
}
}

/**
* Internal implementation; caller must hold configLock.
*/
private void constructConfigUnsafe(int fader, Vector<String> applications) {

// Set application id's for faders.
switch (fader) {
Expand Down