Make Sendable setters synchronous (#1799)

Instead of being called asynchronously by NetworkTables, they are now called by updateValues() synchronously with the main loop, just like the getters.

wpilibj/src/main/java/edu/wpi/first/wpilibj/smartdashboard/ListenerExecutor.java

@@ -0,0 +1,50 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+package edu.wpi.first.wpilibj.smartdashboard;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.concurrent.Executor;
+
+/**
+ * An executor for running listener tasks posted by {@link edu.wpi.first.wpilibj.Sendable} listeners
+ * synchronously from the main application thread.
+ */
+class ListenerExecutor implements Executor {
+  private final Collection<Runnable> m_tasks = new ArrayList<>();
+  private final Object m_lock = new Object();
+
+  /**
+   * Posts a task to the executor to be run synchronously from the main thread.
+   *
+   * @param task The task to run synchronously from the main thread.
+   */
+  @Override
+  public void execute(Runnable task) {
+    synchronized (m_lock) {
+      m_tasks.add(task);
+    }
+  }
+
+  /**
+   * Runs all posted tasks.  Called periodically from main thread.
+   */
+  public void runListenerTasks() {
+    // Locally copy tasks from internal list; minimizes blocking time
+    Collection<Runnable> tasks = new ArrayList<>();
+    synchronized (m_lock) {
+      tasks.addAll(m_tasks);
+      m_tasks.clear();
+    }
+
+    // Run all tasks
+    for (Runnable task : tasks) {
+      task.run();
+    }
+  }
+}

wpilibj/src/main/java/edu/wpi/first/wpilibj/smartdashboard/SendableBuilderImpl.java

@@ -222,7 +222,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isBoolean()) {
-          setter.accept(event.value.getBoolean());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getBoolean()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -245,7 +245,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isDouble()) {
-          setter.accept(event.value.getDouble());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getDouble()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -268,7 +268,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isString()) {
-          setter.accept(event.value.getString());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getString()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -292,7 +292,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isBooleanArray()) {
-          setter.accept(event.value.getBooleanArray());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getBooleanArray()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -316,7 +316,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isDoubleArray()) {
-          setter.accept(event.value.getDoubleArray());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getDoubleArray()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -340,7 +340,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isStringArray()) {
-          setter.accept(event.value.getStringArray());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getStringArray()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -363,7 +363,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
         if (event.value.isRaw()) {
-          setter.accept(event.value.getRaw());
+          SmartDashboard.postListenerTask(() -> setter.accept(event.value.getRaw()));
         }
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
@@ -386,7 +386,7 @@ public class SendableBuilderImpl implements SendableBuilder {
     }
     if (setter != null) {
       property.m_createListener = entry -> entry.addListener(event -> {
-        setter.accept(event.value);
+        SmartDashboard.postListenerTask(() -> setter.accept(event.value));
       }, EntryListenerFlags.kImmediate | EntryListenerFlags.kNew | EntryListenerFlags.kUpdate);
     }
     m_properties.add(property);

wpilibj/src/main/java/edu/wpi/first/wpilibj/smartdashboard/SmartDashboard.java

@@ -50,6 +50,11 @@ public class SmartDashboard {
   @SuppressWarnings("PMD.UseConcurrentHashMap")
   private static final Map<String, Data> tablesToData = new HashMap<>();
 
+  /**
+   * The executor for listener tasks; calls listener tasks synchronously from main thread.
+   */
+  private static final ListenerExecutor listenerExecutor = new ListenerExecutor();
+
   static {
     HAL.report(tResourceType.kResourceType_SmartDashboard, 0);
   }
@@ -521,6 +526,16 @@ public class SmartDashboard {
     return getEntry(key).getRaw(defaultValue);
   }
 
+  /**
+   * Posts a task from a listener to the ListenerExecutor, so that it can be run synchronously
+   * from the main loop on the next call to {@link SmartDashboard#updateValues()}.
+   *
+   * @param task The task to run synchronously from the main thread.
+   */
+  public static void postListenerTask(Runnable task) {
+    listenerExecutor.execute(task);
+  }
+
   /**
    * Puts all sendable data to the dashboard.
    */
@@ -528,5 +543,7 @@ public class SmartDashboard {
     for (Data data : tablesToData.values()) {
       data.m_builder.updateTable();
     }
+    // Execute posted listener tasks
+    listenerExecutor.runListenerTasks();
   }
 }