Reapply "[llvm]Add a simple Telemetry framework" (llvm#120769) (llvm#121003)

This reverts commit 2ec6174.

New changes:
 - Use explicit overloads of write(<int types>)
 - Fix link error due to missing dependency (lib/Support)
 - Updated tests and docs

Author: oontvoo

llvm/docs/Telemetry.rst

@@ -0,0 +1,257 @@
+===========================
+Telemetry framework in LLVM
+===========================
+
+.. contents::
+   :local:
+
+.. toctree::
+   :hidden:
+
+Objective
+=========
+
+Provides a common framework in LLVM for collecting various usage and performance
+metrics.
+It is located at ``llvm/Telemetry/Telemetry.h``.
+
+Characteristics
+---------------
+* Configurable and extensible by:
+
+  * Tools: any tool that wants to use Telemetry can extend and customize it.
+  * Vendors: Toolchain vendors can also provide custom implementation of the
+    library, which could either override or extend the given tool's upstream
+    implementation, to best fit their organization's usage and privacy models.
+  * End users of such tool can also configure Telemetry (as allowed by their
+    vendor).
+
+Important notes
+---------------
+
+* There is no concrete implementation of a Telemetry library in upstream LLVM.
+  We only provide the abstract API here. Any tool that wants telemetry will
+  implement one.
+  
+  The rationale for this is that all the tools in LLVM are very different in
+  what they care about (what/where/when to instrument data). Hence, it might not
+  be practical to have a single implementation.
+  However, in the future, if we see enough common pattern, we can extract them
+  into a shared place. This is TBD - contributions are welcome.
+
+* No implementation of Telemetry in upstream LLVM shall store any of the
+  collected data due to privacy and security reasons:
+  
+  * Different organizations have different privacy models:
+  
+    * Which data is sensitive, which is not?
+    * Whether it is acceptable for instrumented data to be stored anywhere?
+      (to a local file, what not?)
+      
+  * Data ownership and data collection consents are hard to accommodate from
+    LLVM developers' point of view:
+  
+    * E.g., data collected by Telemetry is not necessarily owned by the user
+      of an LLVM tool with Telemetry enabled, hence the user's consent to data
+      collection is not meaningful. On the other hand, LLVM developers have no
+      reasonable ways to request consent from the "real" owners.
+
+
+High-level design
+=================
+
+Key components
+--------------
+
+The framework consists of four important classes:
+
+* ``llvm::telemetry::Manager``: The class responsible for collecting and
+  transmitting telemetry data. This is the main point of interaction between the
+  framework and any tool that wants to enable telemetry.
+* ``llvm::telemetry::TelemetryInfo``: Data courier
+* ``llvm::telemetry::Destination``: Data sink to which the Telemetry framework
+  sends data.
+  Its implementation is transparent to the framework.
+  It is up to the vendor to decide which pieces of data to forward and where
+  to forward them to for their final storage.
+* ``llvm::telemetry::Config``: Configurations for the ``Manager``.
+  
+.. image:: llvm_telemetry_design.png
+
+How to implement and interact with the API
+------------------------------------------
+
+To use Telemetry in your tool, you need to provide a concrete implementation of the ``Manager`` class and ``Destination``.
+
+1) Define a custom ``Serializer``, ``Manager``, ``Destination`` and optionally a subclass of ``TelemetryInfo``
+
+.. code-block:: c++
+
+  class JsonSerializer : public Serializer {
+  public:
+    json::Object *getOutputObject() { return Out.get(); }
+
+    Error init() override {
+      if (Started)
+        return createStringError("Serializer already in use");
+      started = true;
+      Out = std::make_unique<json::Object>();
+      return Error::success();
+    }
+
+    // Serialize the given value.
+    void write(StringRef KeyName, bool Value) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, int Value) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, long Value) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, long long Value ) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, unsigned int Value) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, unsigned long Value) override {
+      writeHelper(KeyName, Value);
+    }
+    
+    void write(StringRef KeyName, unsigned long long Value) override {
+      writeHelper(KeyName, Value);
+    }
+
+    void write(StringRef KeyName, StringRef Value) override {
+      writeHelper(KeyName, Value);
+    }
+ 
+    void beginObject(StringRef KeyName) override {
+      Children.push_back(json::Object());
+      ChildrenNames.push_back(KeyName.str());
+    }
+    
+    void endObject() override {
+      assert(!Children.empty() && !ChildrenNames.empty());
+      json::Value Val = json::Value(std::move(Children.back()));
+      std::string Name = ChildrenNames.back();
+
+      Children.pop_back();
+      ChildrenNames.pop_back();
+      writeHelper(Name, std::move(Val));
+    }
+    
+    Error finalize() override {
+      if (!Started)
+        return createStringError("Serializer not currently in use");
+      Started = false;
+      return Error::success();
+    }
+
+  private:
+    template <typename T> void writeHelper(StringRef Name, T Value) {
+      assert(Started && "serializer not started");
+      if (Children.empty())
+        Out->try_emplace(Name, Value);
+      else
+        Children.back().try_emplace(Name, Value);
+    }
+    bool Started = false;
+    std::unique_ptr<json::Object> Out;
+    std::vector<json::Object> Children;
+    std::vector<std::string> ChildrenNames;
+  };
+       
+  class MyManager : public telemery::Manager {
+  public:
+  static std::unique_ptr<MyManager> createInstatnce(telemetry::Config *Config) {
+    // If Telemetry is not enabled, then just return null;
+    if (!Config->EnableTelemetry)
+      return nullptr;
+    return std::make_unique<MyManager>();
+  }
+  MyManager() = default;
+
+  Error preDispatch(TelemetryInfo *Entry) override {
+    Entry->SessionId = SessionId;
+    return Error::success();
+  }
+  
+  // You can also define additional instrumentation points.
+  void logStartup(TelemetryInfo *Entry) {
+    // Add some additional data to entry.
+    Entry->Msg = "Some message";
+    dispatch(Entry);
+  }
+  
+  void logAdditionalPoint(TelemetryInfo *Entry) {
+    // .... code here
+  }
+  
+  private:    
+    const std::string SessionId;
+  };
+
+  class MyDestination : public telemetry::Destination {
+  public:
+    Error receiveEntry(const TelemetryInfo *Entry) override {
+      if (Error Err = Serializer.init())
+        return Err;
+      
+      Entry->serialize(Serializer);
+      if (Error Err = Serializer.finalize())
+        return Err;
+      
+      json::Object Copied = *Serializer.getOutputObject();
+      // Send the `Copied` object to wherever.
+      return Error::success();
+    }
+
+  private:
+    JsonSerializer Serializer;
+  };
+
+  // This defines a custom TelemetryInfo that has an additional Msg field.
+  struct MyTelemetryInfo : public telemetry::TelemetryInfo {
+    std::string Msg;
+    
+    Error serialize(Serializer &Serializer) const override {
+      TelemetryInfo::serialize(serializer);
+      Serializer.writeString("MyMsg", Msg);
+    }
+      
+    // Note: implement getKind() and classof() to support dyn_cast operations.
+  };
+
+    
+2) Use the library in your tool.
+
+Logging the tool init-process:
+
+.. code-block:: c++
+
+  // In tool's initialization code.
+  auto StartTime = std::chrono::time_point<std::chrono::steady_clock>::now();
+  telemetry::Config MyConfig = makeConfig(); // Build up the appropriate Config struct here.
+  auto Manager = MyManager::createInstance(&MyConfig);
+
+  
+  // Any other tool's init code can go here.
+  // ...
+  
+  // Finally, take a snapshot of the time now so we know how long it took the
+  // init process to finish.
+  auto EndTime = std::chrono::time_point<std::chrono::steady_clock>::now();
+  MyTelemetryInfo Entry;
+
+  Entry.Start = StartTime;
+  Entry.End = EndTime;
+  Manager->logStartup(&Entry);
+
+Similar code can be used for logging the tool's exit.

llvm/docs/UserGuides.rst

@@ -72,6 +72,7 @@ intermediate LLVM representation.
    SupportLibrary
    TableGen/index
    TableGenFundamentals
+   Telemetry
    Vectorizers
    WritingAnLLVMPass
    WritingAnLLVMNewPMPass
@@ -293,3 +294,6 @@ Additional Topics
 
 :doc:`Sandbox IR <SandboxIR>`
    This document describes the design and usage of Sandbox IR, a transactional layer over LLVM IR.
+
+:doc:`Telemetry`
+   This document describes the Telemetry framework in LLVM.

llvm/docs/llvm_telemetry_design.png

@@ -0,0 +1,154 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file provides the basic framework for Telemetry.
+/// Refer to its documentation at llvm/docs/Telemetry.rst for more details.
+//===---------------------------------------------------------------------===//
+
+#ifndef LLVM_TELEMETRY_TELEMETRY_H
+#define LLVM_TELEMETRY_TELEMETRY_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+#include <map>
+#include <memory>
+#include <optional>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+namespace llvm {
+namespace telemetry {
+
+class Serializer {
+public:
+  virtual Error init() = 0;
+  virtual void write(StringRef KeyName, bool Value) = 0;
+  virtual void write(StringRef KeyName, StringRef Value) = 0;
+  virtual void write(StringRef KeyName, int Value) = 0;
+  virtual void write(StringRef KeyName, long Value) = 0;
+  virtual void write(StringRef KeyName, long long Value) = 0;
+  virtual void write(StringRef KeyName, unsigned int Value) = 0;
+  virtual void write(StringRef KeyName, unsigned long Value) = 0;
+  virtual void write(StringRef KeyName, unsigned long long Value) = 0;
+  virtual void beginObject(StringRef KeyName) = 0;
+  virtual void endObject() = 0;
+  virtual Error finalize() = 0;
+
+  template <typename T, typename = typename T::mapped_type>
+  void write(StringRef KeyName, const T &Map) {
+    static_assert(std::is_convertible_v<typename T::key_type, StringRef>,
+                  "KeyType must be convertible to string");
+    beginObject(KeyName);
+    for (const auto &KeyVal : Map)
+      write(KeyVal.first, KeyVal.second);
+    endObject();
+  }
+};
+
+/// Configuration for the Manager class.
+/// This stores configurations from both users and vendors and is passed
+/// to the Manager upon construction. (Any changes to the config after
+/// the Manager's construction will not have any effect on it).
+///
+/// This struct can be extended as needed to add additional configuration
+/// points specific to a vendor's implementation.
+struct Config {
+  // If true, telemetry will be enabled.
+  const bool EnableTelemetry;
+  Config(bool E) : EnableTelemetry(E) {}
+
+  virtual std::optional<std::string> makeSessionId() { return std::nullopt; }
+};
+
+/// For isa, dyn_cast, etc operations on TelemetryInfo.
+typedef unsigned KindType;
+/// This struct is used by TelemetryInfo to support isa<>, dyn_cast<>
+/// operations.
+/// It is defined as a struct (rather than an enum) because it is
+/// expected to be extended by subclasses which may have
+/// additional TelemetryInfo types defined to describe different events.
+struct EntryKind {
+  static const KindType Base = 0;
+};
+
+/// TelemetryInfo is the data courier, used to move instrumented data
+/// from the tool being monitored to the Telemetry framework.
+///
+/// This base class contains only the basic set of telemetry data.
+/// Downstream implementations can define more subclasses with
+/// additional fields to describe different events and concepts.
+///
+/// For example, The LLDB debugger can define a DebugCommandInfo subclass
+/// which has additional fields about the debug-command being instrumented,
+/// such as `CommandArguments` or `CommandName`.
+struct TelemetryInfo {
+  // This represents a unique-id, conventionally corresponding to
+  // a tool's session - i.e., every time the tool starts until it exits.
+  //
+  // Note: a tool could have multiple sessions running at once, in which
+  // case, these shall be multiple sets of TelemetryInfo with multiple unique
+  // IDs.
+  //
+  // Different usages can assign different types of IDs to this field.
+  std::string SessionId;
+
+  TelemetryInfo() = default;
+  virtual ~TelemetryInfo() = default;
+
+  virtual void serialize(Serializer &serializer) const;
+
+  // For isa, dyn_cast, etc, operations.
+  virtual KindType getKind() const { return EntryKind::Base; }
+  static bool classof(const TelemetryInfo *T) {
+    return T->getKind() == EntryKind::Base;
+  }
+};
+
+/// This class presents a data sink to which the Telemetry framework
+/// sends data.
+///
+/// Its implementation is transparent to the framework.
+/// It is up to the vendor to decide which pieces of data to forward
+/// and where to forward them.
+class Destination {
+public:
+  virtual ~Destination() = default;
+  virtual Error receiveEntry(const TelemetryInfo *Entry) = 0;
+  virtual StringLiteral name() const = 0;
+};
+
+/// This class is the main interaction point between any LLVM tool
+/// and this framework.
+/// It is responsible for collecting telemetry data from the tool being
+/// monitored and transmitting the data elsewhere.
+class Manager {
+public:
+  // Optional callback for subclasses to perform additional tasks before
+  // dispatching to Destinations.
+  virtual Error preDispatch(TelemetryInfo *Entry) = 0;
+
+  // Dispatch Telemetry data to the Destination(s).
+  // The argument is non-const because the Manager may add or remove
+  // data from the entry.
+  virtual Error dispatch(TelemetryInfo *Entry);
+
+  // Register a Destination.
+  void addDestination(std::unique_ptr<Destination> Destination);
+
+private:
+  std::vector<std::unique_ptr<Destination>> Destinations;
+};
+
+} // namespace telemetry
+} // namespace llvm
+
+#endif // LLVM_TELEMETRY_TELEMETRY_H

llvm/include/llvm/Telemetry/Telemetry.h

@@ -41,6 +41,7 @@ add_subdirectory(ProfileData)
 add_subdirectory(Passes)
 add_subdirectory(TargetParser)
 add_subdirectory(TextAPI)
+add_subdirectory(Telemetry)
 add_subdirectory(ToolDrivers)
 add_subdirectory(XRay)
 if (LLVM_INCLUDE_TESTS)

llvm/lib/CMakeLists.txt

@@ -0,0 +1,9 @@
+add_llvm_component_library(LLVMTelemetry
+  Telemetry.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  "${LLVM_MAIN_INCLUDE_DIR}/llvm/Telemetry"
+
+  LINK_COMPONENTS
+    Support
+)

llvm/lib/Telemetry/CMakeLists.txt

@@ -0,0 +1,26 @@
+#include "llvm/Telemetry/Telemetry.h"
+
+namespace llvm {
+namespace telemetry {
+
+void TelemetryInfo::serialize(Serializer &serializer) const {
+  serializer.write("SessionId", SessionId);
+}
+
+Error Manager::dispatch(TelemetryInfo *Entry) {
+  if (Error Err = preDispatch(Entry))
+    return Err;
+
+  Error AllErrs = Error::success();
+  for (auto &Dest : Destinations) {
+    AllErrs = joinErrors(std::move(AllErrs), Dest->receiveEntry(Entry));
+  }
+  return AllErrs;
+}
+
+void Manager::addDestination(std::unique_ptr<Destination> Dest) {
+  Destinations.push_back(std::move(Dest));
+}
+
+} // namespace telemetry
+} // namespace llvm

llvm/lib/Telemetry/Telemetry.cpp

@@ -63,6 +63,7 @@ add_subdirectory(Support)
 add_subdirectory(TableGen)
 add_subdirectory(Target)
 add_subdirectory(TargetParser)
+add_subdirectory(Telemetry)
 add_subdirectory(Testing)
 add_subdirectory(TextAPI)
 add_subdirectory(Transforms)

llvm/unittests/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+  Telemetry
+  Core
+  Support
+  )
+
+add_llvm_unittest(TelemetryTests
+  TelemetryTest.cpp
+  )

llvm/unittests/Telemetry/CMakeLists.txt

@@ -0,0 +1,258 @@
+//===- llvm/unittest/Telemetry/TelemetryTest.cpp - Telemetry unittests ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Telemetry/Telemetry.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Error.h"
+#include "gtest/gtest.h"
+#include <optional>
+#include <vector>
+
+namespace llvm {
+namespace telemetry {
+// Testing parameters.
+//
+// These are set by each test to force certain outcomes.
+struct TestContext {
+  // Controlling whether there is vendor plugin.  In "real" implementation, the
+  // plugin-registration framework will handle the overrides but for tests, we
+  // just use a bool flag to decide which function to call.
+  bool HasVendorPlugin = false;
+
+  // This field contains data emitted by the framework for later
+  // verification by the tests.
+  std::string Buffer = "";
+
+  // The expected Uuid generated by the fake tool.
+  std::string ExpectedUuid = "";
+};
+
+class StringSerializer : public Serializer {
+public:
+  const std::string &getString() { return Buffer; }
+
+  Error init() override {
+    if (Started)
+      return createStringError("Serializer already in use");
+    Started = true;
+    Buffer.clear();
+    return Error::success();
+  }
+
+  void write(StringRef KeyName, bool Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, StringRef Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, int Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, long Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, long long Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, unsigned int Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, unsigned long Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void write(StringRef KeyName, unsigned long long Value) override {
+    writeHelper(KeyName, Value);
+  }
+
+  void beginObject(StringRef KeyName) override {
+    Children.push_back(std::string("\n"));
+    ChildrenNames.push_back(KeyName.str());
+  }
+
+  void endObject() override {
+    assert(!Children.empty() && !ChildrenNames.empty());
+    std::string ChildBuff = Children.back();
+    std::string Name = ChildrenNames.back();
+    Children.pop_back();
+    ChildrenNames.pop_back();
+    writeHelper(Name, ChildBuff);
+  }
+
+  Error finalize() override {
+    assert(Children.empty() && ChildrenNames.empty());
+    if (!Started)
+      return createStringError("Serializer not currently in use");
+    Started = false;
+    return Error::success();
+  }
+
+private:
+  template <typename T> void writeHelper(StringRef Name, T Value) {
+    assert(Started && "serializer not started");
+    if (Children.empty())
+      Buffer.append((Name + ":" + Twine(Value) + "\n").str());
+    else
+      Children.back().append((Name + ":" + Twine(Value) + "\n").str());
+  }
+
+  bool Started = false;
+  std::string Buffer;
+  std::vector<std::string> Children;
+  std::vector<std::string> ChildrenNames;
+};
+
+namespace vendor {
+struct VendorConfig : public Config {
+  VendorConfig(bool Enable) : Config(Enable) {}
+  std::optional<std::string> makeSessionId() override {
+    static int seed = 0;
+    return std::to_string(seed++);
+  }
+};
+
+std::shared_ptr<Config> getTelemetryConfig(const TestContext &Ctxt) {
+  return std::make_shared<VendorConfig>(/*EnableTelemetry=*/true);
+}
+
+class TestStorageDestination : public Destination {
+public:
+  TestStorageDestination(TestContext *Ctxt) : CurrentContext(Ctxt) {}
+
+  Error receiveEntry(const TelemetryInfo *Entry) override {
+    if (Error Err = serializer.init())
+      return Err;
+
+    Entry->serialize(serializer);
+    if (Error Err = serializer.finalize())
+      return Err;
+
+    CurrentContext->Buffer.append(serializer.getString());
+    return Error::success();
+  }
+
+  StringLiteral name() const override { return "TestDestination"; }
+
+private:
+  TestContext *CurrentContext;
+  StringSerializer serializer;
+};
+
+struct StartupInfo : public TelemetryInfo {
+  std::string ToolName;
+  std::map<std::string, std::string> MetaData;
+
+  void serialize(Serializer &serializer) const override {
+    TelemetryInfo::serialize(serializer);
+    serializer.write("ToolName", ToolName);
+    serializer.write("MetaData", MetaData);
+  }
+};
+
+struct ExitInfo : public TelemetryInfo {
+  int ExitCode;
+  std::string ExitDesc;
+  void serialize(Serializer &serializer) const override {
+    TelemetryInfo::serialize(serializer);
+    serializer.write("ExitCode", ExitCode);
+    serializer.write("ExitDesc", ExitDesc);
+  }
+};
+
+class TestManager : public Manager {
+public:
+  static std::unique_ptr<TestManager>
+  createInstance(Config *Config, TestContext *CurrentContext) {
+    if (!Config->EnableTelemetry)
+      return nullptr;
+    CurrentContext->ExpectedUuid = *(Config->makeSessionId());
+    std::unique_ptr<TestManager> Ret = std::make_unique<TestManager>(
+        CurrentContext, CurrentContext->ExpectedUuid);
+
+    // Add a destination.
+    Ret->addDestination(
+        std::make_unique<TestStorageDestination>(CurrentContext));
+
+    return Ret;
+  }
+
+  TestManager(TestContext *Ctxt, std::string Id)
+      : CurrentContext(Ctxt), SessionId(Id) {}
+
+  Error preDispatch(TelemetryInfo *Entry) override {
+    Entry->SessionId = SessionId;
+    return Error::success();
+  }
+
+  std::string getSessionId() { return SessionId; }
+
+private:
+  TestContext *CurrentContext;
+  const std::string SessionId;
+};
+} // namespace vendor
+
+std::shared_ptr<Config> getTelemetryConfig(const TestContext &Ctxt) {
+  if (Ctxt.HasVendorPlugin)
+    return vendor::getTelemetryConfig(Ctxt);
+
+  return std::make_shared<Config>(false);
+}
+
+TEST(TelemetryTest, TelemetryDisabled) {
+  TestContext Context;
+  Context.HasVendorPlugin = false;
+
+  std::shared_ptr<Config> Config = getTelemetryConfig(Context);
+  auto Manager = vendor::TestManager::createInstance(Config.get(), &Context);
+  EXPECT_EQ(nullptr, Manager);
+}
+
+TEST(TelemetryTest, TelemetryEnabled) {
+  const std::string ToolName = "TelemetryTestTool";
+
+  // Preset some params.
+  TestContext Context;
+  Context.HasVendorPlugin = true;
+  Context.Buffer.clear();
+
+  std::shared_ptr<Config> Config = getTelemetryConfig(Context);
+  auto Manager = vendor::TestManager::createInstance(Config.get(), &Context);
+
+  EXPECT_STREQ(Manager->getSessionId().c_str(), Context.ExpectedUuid.c_str());
+
+  vendor::StartupInfo S;
+  S.ToolName = ToolName;
+  S.MetaData["a"] = "A";
+  S.MetaData["b"] = "B";
+
+  Error startupEmitStatus = Manager->dispatch(&S);
+  EXPECT_FALSE(startupEmitStatus);
+  std::string ExpectedBuffer =
+      "SessionId:0\nToolName:TelemetryTestTool\nMetaData:\na:A\nb:B\n\n";
+  EXPECT_EQ(ExpectedBuffer, Context.Buffer);
+  Context.Buffer.clear();
+
+  vendor::ExitInfo E;
+  E.ExitCode = 0;
+  E.ExitDesc = "success";
+  Error exitEmitStatus = Manager->dispatch(&E);
+  EXPECT_FALSE(exitEmitStatus);
+  ExpectedBuffer = "SessionId:0\nExitCode:0\nExitDesc:success\n";
+  EXPECT_EQ(ExpectedBuffer, Context.Buffer);
+}
+
+} // namespace telemetry
+} // namespace llvm