[wpilibj] Refactor Tracer functionality out of Watchdog class (#2452)

wpilibj/src/main/java/edu/wpi/first/wpilibj/Tracer.java

@@ -0,0 +1,95 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018-2020 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;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Consumer;
+
+/**
+ * A class for keeping track of how much time it takes for different parts of code to execute.
+ * This is done with epochs, that are added by calls to {@link #addEpoch(String)},
+ * and can be printed with a call to {@link #printEpochs()}.
+ *
+ * <p>Epochs are a way to partition the time elapsed so that when overruns occur, one can
+ * determine which parts of an operation consumed the most time.
+ */
+public class Tracer {
+  private static final long kMinPrintPeriod = 1000000; // microseconds
+
+  private long m_lastEpochsPrintTime; // microseconds
+  private long m_startTime; // microseconds
+
+  @SuppressWarnings("PMD.UseConcurrentHashMap")
+  private final Map<String, Long> m_epochs = new HashMap<>(); // microseconds
+
+  /**
+   * Tracer constructor.
+   */
+  public Tracer() {
+    resetTimer();
+  }
+
+  /**
+   * Clears all epochs.
+   */
+  public void clearEpochs() {
+    m_epochs.clear();
+    resetTimer();
+  }
+
+  /**
+   * Restarts the epoch timer.
+   */
+  public void resetTimer() {
+    m_startTime = RobotController.getFPGATime();
+  }
+
+  /**
+   * Adds time since last epoch to the list printed by printEpochs().
+   *
+   * <p>Epochs are a way to partition the time elapsed so that when overruns occur, one can
+   * determine which parts of an operation consumed the most time.
+   *
+   * <p>This should be called immediately after execution has finished,
+   * with a call to this method or {@link #resetTimer()} before execution.
+   *
+   * @param epochName The name to associate with the epoch.
+   */
+  public void addEpoch(String epochName) {
+    long currentTime = RobotController.getFPGATime();
+    m_epochs.put(epochName, currentTime - m_startTime);
+    m_startTime = currentTime;
+  }
+
+  /**
+   * Prints list of epochs added so far and their times to the DriverStation.
+   */
+  public void printEpochs() {
+    printEpochs(out -> DriverStation.reportWarning(out, false));
+  }
+
+  /**
+   * Prints list of epochs added so far and their times to the entered String consumer.
+   *
+   * <p>This overload can be useful for logging to a file, etc.
+   *
+   * @param output the stream that the output is sent to
+   */
+  public void printEpochs(Consumer<String> output) {
+    long now = RobotController.getFPGATime();
+    StringBuilder sb = new StringBuilder();
+    if (now  - m_lastEpochsPrintTime > kMinPrintPeriod) {
+      m_lastEpochsPrintTime = now;
+      m_epochs.forEach((key, value) -> {
+        sb.append(String.format("\t%s: %.6fs\n", key, value / 1.0e6));
+      });
+    }
+    output.accept(sb.toString());
+  }
+}

wpilibj/src/main/java/edu/wpi/first/wpilibj/Watchdog.java

@@ -8,8 +8,6 @@
 package edu.wpi.first.wpilibj;
 
 import java.io.Closeable;
-import java.util.HashMap;
-import java.util.Map;
 import java.util.PriorityQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.Condition;
@@ -33,14 +31,13 @@ public class Watchdog implements Closeable, Comparable<Watchdog> {
   private long m_expirationTime; // microseconds
   private final Runnable m_callback;
   private long m_lastTimeoutPrintTime; // microseconds
-  private long m_lastEpochsPrintTime; // microseconds
 
-  @SuppressWarnings("PMD.UseConcurrentHashMap")
-  private final Map<String, Long> m_epochs = new HashMap<>(); // microseconds
   boolean m_isExpired;
 
   boolean m_suppressTimeoutMessage;
 
+  private final Tracer m_tracer;
+
   static {
     startDaemonThread(Watchdog::schedulerFunc);
   }
@@ -58,6 +55,7 @@ public class Watchdog implements Closeable, Comparable<Watchdog> {
   public Watchdog(double timeout, Runnable callback) {
     m_timeout = (long) (timeout * 1.0e6);
     m_callback = callback;
+    m_tracer = new Tracer();
   }
 
   @Override
@@ -87,7 +85,7 @@ public class Watchdog implements Closeable, Comparable<Watchdog> {
    */
   public void setTimeout(double timeout) {
     m_startTime = RobotController.getFPGATime();
-    m_epochs.clear();
+    m_tracer.clearEpochs();
 
     m_queueMutex.lock();
     try {
@@ -130,26 +128,20 @@ public class Watchdog implements Closeable, Comparable<Watchdog> {
   /**
    * Adds time since last epoch to the list printed by printEpochs().
    *
-   * <p>Epochs are a way to partition the time elapsed so that when overruns occur, one can
-   * determine which parts of an operation consumed the most time.
+   * @see Tracer#addEpoch(String)
    *
    * @param epochName The name to associate with the epoch.
    */
   public void addEpoch(String epochName) {
-    long currentTime = RobotController.getFPGATime();
-    m_epochs.put(epochName, currentTime - m_startTime);
-    m_startTime = currentTime;
+    m_tracer.addEpoch(epochName);
   }
 
   /**
    * Prints list of epochs added so far and their times.
+   * @see Tracer#printEpochs()
    */
   public void printEpochs() {
-    long now = RobotController.getFPGATime();
-    if (now  - m_lastEpochsPrintTime > kMinPrintPeriod) {
-      m_lastEpochsPrintTime = now;
-      m_epochs.forEach((key, value) -> System.out.format("\t%s: %.6fs\n", key, value / 1.0e6));
-    }
+    m_tracer.printEpochs();
   }
 
   /**
@@ -166,7 +158,7 @@ public class Watchdog implements Closeable, Comparable<Watchdog> {
    */
   public void enable() {
     m_startTime = RobotController.getFPGATime();
-    m_epochs.clear();
+    m_tracer.clearEpochs();
 
     m_queueMutex.lock();
     try {