[wpilib] Add EventLoop (#4104)

This is a generic expansion of the command-based Trigger framework.

wpilibj/src/test/java/edu/wpi/first/wpilibj/event/BooleanEventTest.java

@@ -0,0 +1,168 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.wpilibj.event;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.Test;
+
+class BooleanEventTest {
+  @Test
+  void testBinaryCompositions() {
+    var loop = new EventLoop();
+
+    var andCounter = new AtomicInteger(0);
+    var orCounter = new AtomicInteger(0);
+
+    assertEquals(0, andCounter.get());
+    assertEquals(0, orCounter.get());
+
+    new BooleanEvent(loop, () -> true).and(() -> false).ifHigh(andCounter::incrementAndGet);
+    new BooleanEvent(loop, () -> true).or(() -> false).ifHigh(orCounter::incrementAndGet);
+
+    loop.poll();
+
+    assertEquals(0, andCounter.get());
+    assertEquals(1, orCounter.get());
+  }
+
+  @Test
+  void testBinaryCompositionLoopSemantics() {
+    var loop1 = new EventLoop();
+    var loop2 = new EventLoop();
+
+    var counter1 = new AtomicInteger(0);
+    var counter2 = new AtomicInteger(0);
+
+    new BooleanEvent(loop1, () -> true)
+        .and(new BooleanEvent(loop2, () -> true))
+        .ifHigh(counter1::incrementAndGet);
+
+    new BooleanEvent(loop2, () -> true)
+        .and(new BooleanEvent(loop1, () -> true))
+        .ifHigh(counter2::incrementAndGet);
+
+    assertEquals(0, counter1.get());
+    assertEquals(0, counter2.get());
+
+    loop1.poll();
+
+    assertEquals(1, counter1.get());
+    assertEquals(0, counter2.get());
+
+    loop2.poll();
+
+    assertEquals(1, counter1.get());
+    assertEquals(1, counter2.get());
+  }
+
+  @Test
+  void testEdgeDecorators() {
+    var bool = new AtomicBoolean(false);
+    var counter = new AtomicInteger(0);
+
+    var loop = new EventLoop();
+
+    new BooleanEvent(loop, bool::get).falling().ifHigh(counter::decrementAndGet);
+    new BooleanEvent(loop, bool::get).rising().ifHigh(counter::incrementAndGet);
+
+    assertEquals(0, counter.get());
+
+    bool.set(false);
+    loop.poll();
+
+    assertEquals(0, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    assertEquals(1, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    assertEquals(1, counter.get());
+
+    bool.set(false);
+    loop.poll();
+
+    assertEquals(0, counter.get());
+  }
+
+  @Test
+  void testEdgeReuse() {
+    var loop = new EventLoop();
+    var bool = new AtomicBoolean(false);
+    var counter = new AtomicInteger(0);
+
+    var event = new BooleanEvent(loop, bool::get).rising();
+    event.ifHigh(counter::incrementAndGet);
+    event.ifHigh(counter::incrementAndGet);
+
+    assertEquals(0, counter.get());
+
+    loop.poll();
+
+    assertEquals(0, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    assertEquals(1, counter.get()); // FIXME?: natural sense dictates counter == 2!!
+
+    loop.poll();
+
+    assertEquals(1, counter.get());
+
+    bool.set(false);
+    loop.poll();
+
+    assertEquals(1, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    assertEquals(2, counter.get());
+  }
+
+  @Test
+  void testEdgeReconstruct() {
+    var loop = new EventLoop();
+    var bool = new AtomicBoolean(false);
+    var counter = new AtomicInteger(0);
+
+    var event = new BooleanEvent(loop, bool::get);
+    event.rising().ifHigh(counter::incrementAndGet);
+    event.rising().ifHigh(counter::incrementAndGet);
+
+    assertEquals(0, counter.get());
+
+    loop.poll();
+
+    assertEquals(0, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    // unlike the previous test ...
+    assertEquals(2, counter.get()); // as natural sense dictates, counter == 2
+
+    loop.poll();
+
+    assertEquals(2, counter.get());
+
+    bool.set(false);
+    loop.poll();
+
+    assertEquals(2, counter.get());
+
+    bool.set(true);
+    loop.poll();
+
+    assertEquals(4, counter.get());
+  }
+}

wpilibj/src/test/java/edu/wpi/first/wpilibj/event/EventLoopTest.java

@@ -0,0 +1,61 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.wpilibj.event;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.Test;
+
+class EventLoopTest {
+  @Test
+  void testConditions() {
+    var counterTrue = new AtomicInteger(0);
+    var counterFalse = new AtomicInteger(0);
+    var loop = new EventLoop();
+    loop.bind(() -> true, counterTrue::incrementAndGet);
+    loop.bind(() -> false, counterFalse::incrementAndGet);
+
+    assertEquals(0, counterTrue.get());
+    assertEquals(0, counterFalse.get());
+
+    loop.poll();
+
+    assertEquals(1, counterTrue.get());
+    assertEquals(0, counterFalse.get());
+
+    loop.poll();
+
+    assertEquals(2, counterTrue.get());
+    assertEquals(0, counterFalse.get());
+  }
+
+  @Test
+  void testClear() {
+    var condition = new AtomicBoolean(false);
+    var counter = new AtomicInteger(0);
+    var loop = new EventLoop();
+
+    // first ensure binding works
+    loop.bind(condition::get, counter::incrementAndGet);
+
+    condition.set(false);
+    loop.poll();
+    assertEquals(0, counter.get());
+
+    condition.set(true);
+    loop.poll();
+    assertEquals(1, counter.get());
+
+    // clear bindings
+    loop.clear();
+
+    condition.set(true);
+    loop.poll();
+    // shouldn't change
+    assertEquals(1, counter.get());
+  }
+}