[clangd] Implemented tracing using Context

[ilya-biryukov]

clangd/JSONRPCDispatcher.h

80 ↗

(On Diff #124357)

This is still wrong, Context is used by Tracer internally and should not be moved.

[ilya-biryukov]

• Updated tracing to use the new Context implementation.
• Restored global tracer.

[ilya-biryukov]

• Use getExistingKey instead of getPtr in JSONRPCDispatcher.

[ilya-biryukov]

Updated the patch after changes to Context

[ilya-biryukov]

• Use derive(key, value) instead of derive().add(key, value).

[ilya-biryukov]

Merged with head

[sammccall]

clangd/Trace.cpp

123

This is a little unfortunate. Oh, well.

clangd/Trace.h

42

hmm, trace::TracingSession seems redundant? Up to you

[ilya-biryukov]

• Renamed TracingSession to Session (it is always used qualified via trace::Session anyway)

clangd/ClangdUnit.cpp

auto DoRebuildPreamble =
       if (OldPreamble && OldPreamble->Preamble.CanReuse(
                              *CI, ContentsBuffer.get(), Bounds, VFS.get())) {
         return OldPreamble;
       }
       // We won't need the OldPreamble anymore, release it so it can be deleted
       // (if there are no other references to it).
       OldPreamble.reset();
 
-      trace::Span Tracer("Preamble");
+      trace::Span Tracer(Ctx, "Preamble");
       SPAN_ATTACH(Tracer, "File", That->FileName);
       std::vector<DiagWithFixIts> PreambleDiags;
       StoreDiagsConsumer PreambleDiagnosticsConsumer(/*ref*/ PreambleDiags);
       IntrusiveRefCntPtr<DiagnosticsEngine> PreambleDiagsEngine =
           CompilerInstance::createDiagnostics(
               &CI->getDiagnosticOpts(), &PreambleDiagnosticsConsumer, false);
       CppFilePreambleCallbacks SerializedDeclsCollector;
       auto BuiltPreamble = PrecompiledPreamble::Build(
auto FinishRebuild = [OldPreamble, VFS, RequestRebuildCounter, PCHs,
     if (NewPreamble) {
       Diagnostics.insert(Diagnostics.begin(), NewPreamble->Diags.begin(),
                          NewPreamble->Diags.end());
     }
 
     // Compute updated AST.
     llvm::Optional<ParsedAST> NewAST;
     {
-      trace::Span Tracer("Build");
+      trace::Span Tracer(Ctx, "Build");
       SPAN_ATTACH(Tracer, "File", That->FileName);
       NewAST = ParsedAST::Build(std::move(CI), std::move(NewPreamble),
                                 std::move(ContentsBuffer), PCHs, VFS, Ctx);
     }
 
     if (NewAST) {
       Diagnostics.insert(Diagnostics.end(), NewAST->getDiagnostics().begin(),
                          NewAST->getDiagnostics().end());

clangd/JSONRPCDispatcher.cpp

void JSONOutput::writeMessage(const json::Expr &Message) {
   Logs.flush();
 
   // Emit message with header.
   Outs << "Content-Length: " << S.size() << "\r\n\r\n" << S;
   Outs.flush();
 }
 
 void JSONOutput::log(const Context &Ctx, const Twine &Message) {
-  // FIXME(ibiryukov): get rid of trace::log here.
-  trace::log(Message);
+  trace::log(Ctx, Message);
   std::lock_guard<std::mutex> Guard(StreamMutex);
   Logs << Message << '\n';
   Logs.flush();
 }
 
 void JSONOutput::mirrorInput(const Twine &Message) {
   if (!InputMirror)
     return;
bool JSONRPCDispatcher::call(const json::Expr &Message, JSONOutput &Out) const {
   // Params should be given, use null if not.
   json::Expr Params = nullptr;
   if (auto *P = Object->get("params"))
     Params = std::move(*P);
 
   auto I = Handlers.find(*Method);
   auto &Handler = I != Handlers.end() ? I->second : UnknownHandler;
 
-  auto Tracer = llvm::make_unique<trace::Span>(*Method);
+  // Create a Context that contains request information.
+  Context Ctx = buildCtx().addOpt(IDKey, ID).add(OutKey, &Out);
+
+  // Create a tracing Span covering the whole request lifetime.
+  auto Tracer = llvm::make_unique<trace::Span>(Ctx, *Method);
   if (ID)
     SPAN_ATTACH(*Tracer, "ID", *ID);
   SPAN_ATTACH(*Tracer, "Params", Params);
 
-  auto Ctx = buildCtx()
-                 .addOpt(IDKey, ID)
-                 .add(OutKey, &Out)
-                 .add(TracerKey, std::move(Tracer));
+  // Update Ctx to include Tracer.
+  Ctx = Ctx.derive().add(TracerKey, std::move(Tracer));
 
   Handler(std::move(Ctx), std::move(Params));
   return true;
 }
 
 void clangd::runLanguageServerLoop(std::istream &In, JSONOutput &Out,
                                    JSONRPCDispatcher &Dispatcher,
                                    bool &IsDone) {

clangd/Trace.h

 //===--- Trace.h - Performance tracing facilities ---------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Supports writing performance traces describing clangd's behavior.
-// Traces are written in the Trace Event format supported by chrome's trace
-// viewer (chrome://tracing).
+// Traces are consumed by implementations of the EventTracer interface.
 //
-// The format is documented here:
-// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
 //
 // All APIs are no-ops unless a Session is active (created by ClangdMain).
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
 
+#include "Context.h"
 #include "JSONExpr.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/raw_ostream.h"
 
 namespace clang {
 namespace clangd {
 namespace trace {
 
-// A session directs the output of trace events. Only one Session can exist.
-// It should be created before clangd threads are spawned, and destroyed after
-// they exit.
-// TODO: we may want to add pluggable support for other tracing backends.
-class Session {
+/// A consumer of trace events. The events are produced by Spans and trace::log.
+class EventTracer {
 public:
-  // Starts a sessions capturing trace events and writing Trace Event JSON.
-  static std::unique_ptr<Session> create(llvm::raw_ostream &OS,
-                                         bool Pretty = false);
-  ~Session();
+  virtual ~EventTracer() = default;
+  /// Consume a trace event.
+  virtual void event(const Context &Ctx, llvm::StringRef Phase,
+                     json::obj &&Contents) = 0;
+};
 
-private:
-  Session() = default;
+/// Sets up a global EventTracer that consumes events produced by Span and
+/// trace::log. Only one TracingSession can be active at a time and it should be
+/// set up before calling any clangd-specific functions.
+class TracingSession {
+public:
+  TracingSession(EventTracer &Tracer);
+  ~TracingSession();
 };
 
-// Records a single instant event, associated with the current thread.
-void log(const llvm::Twine &Name);
+/// Create an instance of EventTracer that produces an output in the Trace Event
+/// format supported by Chrome's trace viewer (chrome://tracing).
+///
+/// The format is documented here:
+/// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
+///
+/// The implementation supports concurrent calls and can be used as a global
+/// tracer (i.e., can be put into a global Context).
+std::unique_ptr<EventTracer> createJSONTracer(llvm::raw_ostream &OS,
+                                              bool Pretty = false);
 
-// Records an event whose duration is the lifetime of the Span object.
-//
-// Arbitrary JSON metadata can be attached while this span is active:
-//   SPAN_ATTACH(MySpan, "Payload", SomeJSONExpr);
-// SomeJSONExpr is evaluated and copied only if actually needed.
+/// Records a single instant event, associated with the current thread.
+void log(const Context &Ctx, const llvm::Twine &Name);
+
+/// Records an event whose duration is the lifetime of the Span object.
+/// This is the main public interface for producing tracing events.
+///
+/// Arbitrary JSON metadata can be attached while this span is active:
+///   SPAN_ATTACH(MySpan, "Payload", SomeJSONExpr);
+/// SomeJSONExpr is evaluated and copied only if actually needed.
 class Span {
 public:
-  Span(std::string Name);
+  Span(const Context &Ctx, std::string Name);
   ~Span();
 
-  // Returns mutable span metadata if this span is interested.
-  // Prefer to use SPAN_ATTACH rather than accessing this directly.
+  /// Returns mutable span metadata if this span is interested.
+  /// Prefer to use SPAN_ATTACH rather than accessing this directly.
   json::obj *args() { return Args.get(); }
 
 private:
+  llvm::Optional<Context> Ctx;
   std::unique_ptr<json::obj> Args;
 };
 
 #define SPAN_ATTACH(S, Name, Expr)                                             \
   do {                                                                         \
     if ((S).args() != nullptr) {                                               \
       (*((S).args()))[(Name)] = (Expr);                                        \
     }                                                                          \
   } while (0)
 
 } // namespace trace
 } // namespace clangd
 } // namespace clang
 
 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_

clangd/Trace.cpp

 namespace clang {
 namespace clangd {
 namespace trace {
 using namespace llvm;
 
 namespace {
 // The current implementation is naive: each thread writes to Out guarded by Mu.
 // Perhaps we should replace this by something that disturbs performance less.
-class Tracer {
+class JSONTracer : public EventTracer {
 public:
-  Tracer(raw_ostream &Out, bool Pretty)
+  JSONTracer(raw_ostream &Out, bool Pretty)
       : Out(Out), Sep(""), Start(std::chrono::system_clock::now()),
         JSONFormat(Pretty ? "{0:2}" : "{0}") {
     // The displayTimeUnit must be ns to avoid low-precision overlap
     // calculations!
     Out << R"({"displayTimeUnit":"ns","traceEvents":[)"
         << "\n";
     rawEvent("M", json::obj{
                       {"name", "process_name"},
                       {"args", json::obj{{"name", "clangd"}}},
                   });
   }
 
-  ~Tracer() {
+  ~JSONTracer() {
     Out << "\n]}";
     Out.flush();
   }
 
   // Record an event on the current thread. ph, pid, tid, ts are set.
   // Contents must be a list of the other JSON key/values.
-  void event(StringRef Phase, json::obj &&Contents) {
+  void event(const Context &Ctx, StringRef Phase,
+             json::obj &&Contents) override {
     uint64_t TID = get_threadid();
     std::lock_guard<std::mutex> Lock(Mu);
     // If we haven't already, emit metadata describing this thread.
     if (ThreadsWithMD.insert(TID).second) {
       SmallString<32> Name;
       get_thread_name(Name);
       if (!Name.empty()) {
         rawEvent("M", json::obj{
private:
   std::mutex Mu;
   raw_ostream &Out /*GUARDED_BY(Mu)*/;
   const char *Sep /*GUARDED_BY(Mu)*/;
   DenseSet<uint64_t> ThreadsWithMD /*GUARDED_BY(Mu)*/;
   const sys::TimePoint<> Start;
   const char *JSONFormat;
 };
 
-static Tracer *T = nullptr;
+EventTracer *T = nullptr;
 } // namespace
 
-std::unique_ptr<Session> Session::create(raw_ostream &OS, bool Pretty) {
-  assert(!T && "A session is already active");
-  T = new Tracer(OS, Pretty);
-  return std::unique_ptr<Session>(new Session());
+TracingSession::TracingSession(EventTracer &Tracer) {
+  assert(!T && "Resetting global tracer is not allowed.");
+  T = &Tracer;
 }
 
-Session::~Session() {
-  delete T;
-  T = nullptr;
+TracingSession::~TracingSession() { T = nullptr; }
+
+std::unique_ptr<EventTracer> createJSONTracer(llvm::raw_ostream &OS,
+                                              bool Pretty) {
+  return llvm::make_unique<JSONTracer>(OS, Pretty);
 }
 
-void log(const Twine &Message) {
+void log(const Context &Ctx, const Twine &Message) {
   if (!T)
     return;
-  T->event("i", json::obj{
-                    {"name", "Log"},
-                    {"args", json::obj{{"Message", Message.str()}}},
-                });
+  T->event(Ctx, "i",
+           json::obj{
 }
 
-Span::Span(std::string Name) {
+Span::Span(const Context &Ctx, std::string Name) {
   if (!T)
     return;
-  T->event("B", json::obj{{"name", std::move(Name)}});
+  // Clone the context, so that the original Context can be moved.
+  this->Ctx.emplace(Ctx.clone());
+
+  T->event(*this->Ctx, "B", json::obj{{"name", std::move(Name)}});
   Args = llvm::make_unique<json::obj>();
 }
 
 Span::~Span() {
   if (!T)
     return;
   if (!Args)
     Args = llvm::make_unique<json::obj>();
-  T->event("E", Args ? json::obj{{"args", std::move(*Args)}} : json::obj{});
+  T->event(*Ctx, "E",
+           Args ? json::obj{{"args", std::move(*Args)}} : json::obj{});
 }
 
 } // namespace trace
 } // namespace clangd
 } // namespace clang

clangd/tool/ClangdMain.cpp

if (!InputMirrorFile.empty()) {
     std::error_code EC;
     InputMirrorStream.emplace(InputMirrorFile, /*ref*/ EC, llvm::sys::fs::F_RW);
     if (EC) {
       InputMirrorStream.reset();
       llvm::errs() << "Error while opening an input mirror file: "
                    << EC.message();
     }
   }
+
+  // Setup tracing facilities.
   llvm::Optional<llvm::raw_fd_ostream> TraceStream;
-  std::unique_ptr<trace::Session> TraceSession;
+  std::unique_ptr<trace::EventTracer> Tracer;
   if (!TraceFile.empty()) {
     std::error_code EC;
     TraceStream.emplace(TraceFile, /*ref*/ EC, llvm::sys::fs::F_RW);
     if (EC) {
       TraceFile.reset();
       llvm::errs() << "Error while opening trace file: " << EC.message();
     } else {
-      TraceSession = trace::Session::create(*TraceStream, PrettyPrint);
+      Tracer = trace::createJSONTracer(*TraceStream, PrettyPrint);
     }
   }
 
+  llvm::Optional<trace::TracingSession> TracingSession;
+  if (Tracer)
+    TracingSession.emplace(*Tracer);
+
   llvm::raw_ostream &Outs = llvm::outs();
   llvm::raw_ostream &Logs = llvm::errs();
   JSONOutput Out(Outs, Logs,
                  InputMirrorStream ? InputMirrorStream.getPointer() : nullptr,
                  PrettyPrint);
 
   clangd::LoggingSession LoggingSession(Out);
 

unittests/clangd/TraceTests.cpp

 //===-- TraceTests.cpp - Tracing unit tests ---------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
+#include "Context.h"
 #include "Trace.h"
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/YAMLParser.h"
 #include "gmock/gmock.h"
bool VerifyObject(yaml::Node &N, std::map<std::string, std::string> Expected) {
   return Match;
 }
 
 TEST(TraceTest, SmokeTest) {
   // Capture some events.
   std::string JSON;
   {
     raw_string_ostream OS(JSON);
-    auto Session = trace::Session::create(OS);
+    auto JSONTracer = trace::createJSONTracer(OS);
+    trace::TracingSession Session(*JSONTracer);
     {
-      trace::Span S("A");
-      trace::log("B");
+      trace::Span S(Context::empty(), "A");
+      trace::log(Context::empty(), "B");
     }
   }
 
   // Get the root JSON object using the YAML parser.
   SourceMgr SM;
   yaml::Stream Stream(JSON, SM);
   auto Doc = Stream.begin();
   ASSERT_NE(Doc, Stream.end());