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wpilibj/src/main/java/org/wpilib/system/Tracer.java

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+// 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;
+
+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
+
+  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 final 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();
+    if (now - m_lastEpochsPrintTime > kMinPrintPeriod) {
+      StringBuilder sb = new StringBuilder();
+      m_lastEpochsPrintTime = now;
+      m_epochs.forEach(
+          (key, value) -> sb.append(String.format("\t%s: %.6fs\n", key, value / 1.0e6)));
+      if (sb.length() > 0) {
+        output.accept(sb.toString());
+      }
+    }
+  }
+}