forked from OSchip/llvm-project
109 lines
4.0 KiB
C++
109 lines
4.0 KiB
C++
//===--- Trace.h - Performance tracing facilities ---------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Supports writing performance traces describing clangd's behavior.
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// Traces are consumed by implementations of the EventTracer interface.
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//
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//
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// All APIs are no-ops unless a Session is active (created by ClangdMain).
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
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#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
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#include "Context.h"
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#include "Function.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/Support/JSON.h"
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#include "llvm/Support/raw_ostream.h"
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namespace clang {
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namespace clangd {
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namespace trace {
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/// A consumer of trace events. The events are produced by Spans and trace::log.
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/// Implmentations of this interface must be thread-safe.
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class EventTracer {
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public:
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virtual ~EventTracer() = default;
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/// Called when event that has a duration starts. \p Name describes the event.
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/// Returns a derived context that will be destroyed when the event ends.
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/// Usually implementations will store an object in the returned context
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/// whose destructor records the end of the event.
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/// The args are *Args, only complete when the event ends.
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virtual Context beginSpan(llvm::StringRef Name, llvm::json::Object *Args) = 0;
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// Called when a Span is destroyed (it may still be active on other threads).
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// beginSpan() and endSpan() will always form a proper stack on each thread.
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// The Context returned by beginSpan is active, but Args is not ready.
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// Tracers should not override this unless they need to observe strict
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// per-thread nesting. Instead they should observe context destruction.
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virtual void endSpan(){};
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/// Called for instant events.
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virtual void instant(llvm::StringRef Name, llvm::json::Object &&Args) = 0;
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};
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/// Sets up a global EventTracer that consumes events produced by Span and
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/// trace::log. Only one TracingSession can be active at a time and it should be
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/// set up before calling any clangd-specific functions.
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class Session {
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public:
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Session(EventTracer &Tracer);
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~Session();
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};
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/// Create an instance of EventTracer that produces an output in the Trace Event
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/// format supported by Chrome's trace viewer (chrome://tracing).
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///
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/// The format is documented here:
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/// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
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std::unique_ptr<EventTracer> createJSONTracer(llvm::raw_ostream &OS,
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bool Pretty = false);
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/// Records a single instant event, associated with the current thread.
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void log(const llvm::Twine &Name);
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/// Records an event whose duration is the lifetime of the Span object.
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/// This lifetime is extended when the span's context is reused.
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///
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/// This is the main public interface for producing tracing events.
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///
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/// Arbitrary JSON metadata can be attached while this span is active:
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/// SPAN_ATTACH(MySpan, "Payload", SomeJSONExpr);
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///
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/// SomeJSONExpr is evaluated and copied only if actually needed.
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class Span {
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public:
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Span(llvm::Twine Name);
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~Span();
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/// Mutable metadata, if this span is interested.
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/// Prefer to use SPAN_ATTACH rather than accessing this directly.
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llvm::json::Object *const Args;
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private:
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WithContext RestoreCtx;
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};
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/// Attach a key-value pair to a Span event.
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/// This is not threadsafe when used with the same Span.
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#define SPAN_ATTACH(S, Name, Expr) \
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do { \
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if (auto *Args = (S).Args) \
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(*Args)[Name] = Expr; \
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} while (0)
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} // namespace trace
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} // namespace clangd
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} // namespace clang
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#endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
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