[wpilibc] Add ScopedTracer class (#2724)

This makes it easier for C++ teams to log a certain piece of code using RAII.

wpilibc/src/main/native/cpp/ScopedTracer.cpp

@@ -0,0 +1,22 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/ScopedTracer.h"
+
+#include <wpi/raw_ostream.h>
+
+using namespace frc;
+
+ScopedTracer::ScopedTracer(wpi::Twine name, wpi::raw_ostream& os)
+    : m_name(name.str()), m_os(os) {
+  m_tracer.ResetTimer();
+}
+
+ScopedTracer::~ScopedTracer() {
+  m_tracer.AddEpoch(m_name);
+  m_tracer.PrintEpochs(m_os);
+}

wpilibc/src/main/native/include/frc/ScopedTracer.h

@@ -0,0 +1,48 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <string>
+
+#include <wpi/StringRef.h>
+#include <wpi/Twine.h>
+
+#include "frc/Tracer.h"
+
+namespace wpi {
+class raw_ostream;
+}  // namespace wpi
+
+namespace frc {
+/**
+ * A class for keeping track of how much time it takes for different
+ * parts of code to execute. This class uses RAII, meaning you simply
+ * need to create an instance at the top of the block you are timing. After the
+ * block finishes execution (i.e. when the ScopedTracer instance gets
+ * destroyed), the epoch is printed to the provided raw_ostream.
+ */
+class ScopedTracer {
+ public:
+  /**
+   * Constructs a ScopedTracer instance.
+   *
+   * @param name The name of the epoch.
+   * @param os A reference to the raw_ostream to print data to.
+   */
+  ScopedTracer(wpi::Twine name, wpi::raw_ostream& os);
+  ~ScopedTracer();
+
+  ScopedTracer(const ScopedTracer&) = delete;
+  ScopedTracer& operator=(const ScopedTracer&) = delete;
+
+ private:
+  Tracer m_tracer;
+  std::string m_name;
+  wpi::raw_ostream& m_os;
+};
+}  // namespace frc

wpilibc/src/test/native/cpp/ScopedTracerTest.cpp

@@ -0,0 +1,33 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <string>
+#include <thread>
+
+#include <wpi/SmallString.h>
+#include <wpi/StringRef.h>
+#include <wpi/raw_ostream.h>
+
+#include "frc/ScopedTracer.h"
+#include "gtest/gtest.h"
+
+wpi::SmallString<128> buf;
+wpi::raw_svector_ostream os(buf);
+
+#ifdef __APPLE__
+TEST(ScopedTracerTest, DISABLED_Timing) {
+#else
+TEST(ScopedTracerTest, Timing) {
+#endif
+  {
+    frc::ScopedTracer tracer("timing_test", os);
+    std::this_thread::sleep_for(std::chrono::milliseconds(1500));
+  }
+
+  wpi::StringRef out = os.str();
+  EXPECT_TRUE(out.startswith("	timing_test: 1.5"));
+}