Here is a coarse concept for the circular buffer event structure and usage example:

#include <fmt/format.h>

#include <string>
#include <vector>

enum class EventType {
    DurationBegin = 'B',  // Duration Event (begin).
    DurationEnd = 'E',    // Duration Event (end).
    Complete = 'X',       // Complete Event.
    Instant = 'I',        // Instant Event.
    Counter = 'C',        // Counter Event.
    AsyncStart = 'b',     // Async Event (start).
    AsyncStep = 'n',      // Async Event (step).
    AsyncEnd = 'e',       // Async Event (end).
    FlowStart = 's',      // Flow Event (start).
    FlowStep = 't',       // Flow Event (step).
    FlowEnd = 'f'         // Flow Event (end).
};

struct TraceEvent {
    int pid;           // Process ID.
    int tid;           // Thread ID.
    std::string name;  // Event name.
    EventType type;    // Event type.
    double ts;         // Timestamp in microseconds.
    int64_t dur;       // Duration of the event, for 'X' type.
    std::string id;    // ID for matching async or flow events.
    std::string cat;   // Event categories.
    std::string args;  // Event arguments.

    // Function to format a TraceEvent into JSON format.
    std::string toJSON() const {
        return fmt::format(
            R"({{"name": "{}", "ph": "{}", "ts": {}, "pid": {}, "tid": {}, "dur": {}, "id": "{}", "cat": "{}", "args": "{}"}})",
            name, static_cast<char>(type), ts, pid, tid, dur, id, cat, args);
    }
};

std::string export_trace_events(const std::vector<TraceEvent>& events) {
    std::string result = "[\n";
    for (const auto& event : events) {
        result += event.toJSON();
        result += ",\n";
    }
    // Remove the last comma and append the closing bracket.
    result = result.substr(0, result.size() - 2) + "\n]";
    return result;
}

void functionA(std::vector<TraceEvent>& events) {
    events.push_back(TraceEvent{1, 1, "functionA", EventType::DurationBegin, 0, 100, "1", "func", ""});
    events.push_back(TraceEvent{1, 1, "functionA", EventType::DurationEnd, 100, 0, "1", "func", ""});
}

void functionB(std::vector<TraceEvent>& events) {
    events.push_back(TraceEvent{1, 2, "functionB", EventType::DurationBegin, 50, 150, "2", "func", ""});
    events.push_back(TraceEvent{1, 2, "functionB", EventType::DurationEnd, 200, 0, "2", "func", ""});
}

void functionC(std::vector<TraceEvent>& events) {
    events.push_back(TraceEvent{1, 3, "functionC", EventType::DurationBegin, 100, 100, "3", "func", ""});
    events.push_back(TraceEvent{1, 3, "functionC", EventType::DurationEnd, 200, 0, "3", "func", ""});
}

int main() {
    std::vector<TraceEvent> events;

    functionA(events);
    functionB(events);
    functionC(events);

    // More events
    events.push_back(TraceEvent{1, 1, "CounterEvent", EventType::Counter, 250, 0, "0", "count", ""});
    events.push_back(TraceEvent{1, 1, "AsyncStart", EventType::AsyncStart, 300, 0, "4", "async", ""});
    events.push_back(TraceEvent{1, 1, "AsyncStep", EventType::AsyncStep, 350, 0, "4", "async", ""});
    events.push_back(TraceEvent{1, 1, "AsyncEnd", EventType::AsyncEnd, 400, 0, "4", "async", ""});

    events.push_back(TraceEvent{1, 1, "FlowScopeStart", EventType::DurationBegin, 450, 0, "5", "flow", ""});
    events.push_back(TraceEvent{1, 1, "FlowStart", EventType::FlowStart, 460, 0, "5", "flow", ""});
    events.push_back(TraceEvent{1, 1, "FlowStep", EventType::FlowStep, 470, 0, "5", "flow", ""});
    events.push_back(TraceEvent{1, 1, "FlowEnd", EventType::FlowEnd, 480, 0, "5", "flow", ""});
    events.push_back(TraceEvent{1, 1, "FlowScopeEnd", EventType::DurationEnd, 490, 0, "5", "flow", ""});

    events.push_back(TraceEvent{1, 1, "InstantEvent", EventType::Instant, 500, 0, "0", "inst", ""});


    std::string json = export_trace_events(events);
    fmt::print("open the following in https://ui.perfetto.dev/:\n{}", json);
    return 0;
}

Add the output to https://ui.perfetto.dev/ or google chrome's trace: yields:

This largely works (as shown above), needs some refactoring/constexpr wrapper to by-pass the profiling at compile-time if the user does not need this info and some nice/easy/performant (maybe fluent) API for the in-code usage.

[3pt, 3pt] graph/block profiling (enable/disable at compile-time) -- proposal: re-use chrome tracing format's & UI infrastructure (e.g. chrome://tracing/ and Perfetto) #71

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