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//===--- 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 consumed by implementations of the EventTracer interface.
// All APIs are no-ops unless a Session is active (created by ClangdMain).
#include "Context.h"
#include "Function.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/JSON.h"
#include "llvm/Support/raw_ostream.h"
namespace clang {
namespace clangd {
namespace trace {
/// A consumer of trace events. The events are produced by Spans and trace::log.
/// Implmentations of this interface must be thread-safe.
class EventTracer {
virtual ~EventTracer() = default;
/// Called when event that has a duration starts. \p Name describes the event.
/// Returns a derived context that will be destroyed when the event ends.
/// Usually implementations will store an object in the returned context
/// whose destructor records the end of the event.
/// The args are *Args, only complete when the event ends.
virtual Context beginSpan(llvm::StringRef Name, llvm::json::Object *Args) = 0;
// Called when a Span is destroyed (it may still be active on other threads).
// beginSpan() and endSpan() will always form a proper stack on each thread.
// The Context returned by beginSpan is active, but Args is not ready.
// Tracers should not override this unless they need to observe strict
// per-thread nesting. Instead they should observe context destruction.
virtual void endSpan(){};
/// Called for instant events.
virtual void instant(llvm::StringRef Name, llvm::json::Object &&Args) = 0;
/// 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 Session {
Session(EventTracer &Tracer);
/// 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:
std::unique_ptr<EventTracer> createJSONTracer(llvm::raw_ostream &OS,
bool Pretty = false);
/// Records a single instant event, associated with the current thread.
void log(const llvm::Twine &Name);
/// Records an event whose duration is the lifetime of the Span object.
/// This lifetime is extended when the span's context is reused.
/// 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 {
Span(llvm::Twine Name);
/// Mutable metadata, if this span is interested.
/// Prefer to use SPAN_ATTACH rather than accessing this directly.
llvm::json::Object *const Args;
WithContext RestoreCtx;
/// Attach a key-value pair to a Span event.
/// This is not threadsafe when used with the same Span.
#define SPAN_ATTACH(S, Name, Expr) \
do { \
if (auto *Args = (S).Args) \
(*Args)[Name] = Expr; \
} while (0)
} // namespace trace
} // namespace clangd
} // namespace clang