glimmer 🔥

A tiny cpp23 flame graph profiling library

Motivation

• hot profiling, directly in code
• decide where and what you measure
• flamegraphs for regression testing via automated CI artifacts
• case study of std::stacktrace and other modern cpp23 features

Overview

• Frame - collection of scopes over time
• Scope - location and time of entry and exit
• Guard - lifetime-based scope

glimmer 🔥 is thread-safe, i.e. Frame::push, pop, close and in extension Guard can be used safely from anywhere, anytime.

Output

Folded stack collapse as .txt (LF) file. Can be used directly with FlameGraph or speedscope. Shoutout Brendan Gregg and Jamie Wong for building and sharing kool stuff.

Usage

Profile

#include <glimmer/glimmer.h>
#include <future>

void worker() {
    GLIMMER_GUARD;  //  automatic capture of function entry and exit
    std::this_thread::sleep_for( std::chrono::milliseconds( 10 ) );
}

int main( int argc, char* argv[] ) 
{
    GLIMMER_BEGIN;  //  manual scope

    worker();       //  sync call
    std::async( worker ).wait();    //  async call   
                    
    GLIMMER_END;    //  automatic close of latest active
    GLIMMER_DUMP;   //  write folded stack collapse to disk
}

# collapsed.txt
0aa4;main 39230
0aa4;main;worker 23121
2870;worker 15857

Visualize

View directly on https://speedscope.com, or convert using Brendan's FlameGraph.

flamegraph.pl --title minimal --colors java --inverted --width 480 --nametype "" --countname us --hash minimal.txt > minimal.svg

Options

• GLIMMER_DISABLE - Allows for zero-overhead production builds
• GLIMMER_INCLUDE_FUNCTION_OFFSET - Add function offset suffix, e.g. main+0x43
• GLIMMER_INCLUDE_SYSTEM_CALLS - Include system calls
  • Windows: MSVCP|ntdll|KERNEL32
  • Unix: libc|libpthread|libstdc++|libm|libdl|libgcc
• GLIMMER_INCLUDE_LIBRARY_ENTRIES - Include c/cpp standard library calls
  • Windows: Microsoft Visual Studio|vctools
  • Unix: /lib/|/usr/lib/|/opt/|/System/Library/`
• GLIMMER_BUILD_EXAMPLES

Defines

Convenience functions for quick access to a global frame instance.

• GLIMMER - global frame instance
• GLIMMER_BEGIN - generic scope; make sure to close it again
• GLIMMER_END - close latest active scope; make sure to match with begin
• GLIMMER_GUARD - generic guard; only one per cpp scope
• GLIMMER_DUMP - write global frame to YYYY-mm-dd_hhMMSS_collapsed.txt
• GLIMMER_NBEGIN - named scope; can be used to differentiate sections inside single function
• GLIMMER_NGUARD - named guard; can be used to add more readible name to guarded scope
• GLIMMER_NDUMP - named dump; write global frame to custom filename

Backlog

• left heavy and sandwich reductions
• imgui component