src/utils/SkEventTracer.cpp

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/utils/SkEventTracer.h"

#include "include/private/base/SkMacros.h"

#include <stdlib.h>
#include <atomic>

class SkDefaultEventTracer : public SkEventTracer {
    SkEventTracer::Handle
        addTraceEvent(char phase,
                      const uint8_t* categoryEnabledFlag,
                      const char* name,
                      uint64_t id,
                      int numArgs,
                      const char** argNames,
                      const uint8_t* argTypes,
                      const uint64_t* argValues,
                      uint8_t flags) override { return 0; }

    void
        updateTraceEventDuration(const uint8_t* categoryEnabledFlag,
                                 const char* name,
                                 SkEventTracer::Handle handle) override {}

    const uint8_t* getCategoryGroupEnabled(const char* name) override {
        static uint8_t no = 0;
        return &no;
    }
    const char* getCategoryGroupName(
      const uint8_t* categoryEnabledFlag) override {
        static const char* stub = "stub";
        return stub;
    }

    // The default tracer does not yet support splitting up trace output into sections.
    void newTracingSection(const char* name) override {}
};

// We prefer gUserTracer if it's been set, otherwise we fall back on a default tracer;
static std::atomic<SkEventTracer*> gUserTracer{nullptr};

bool SkEventTracer::SetInstance(SkEventTracer* tracer) {
    SkEventTracer* expected = nullptr;
    if (!gUserTracer.compare_exchange_strong(expected, tracer)) {
        delete tracer;
        return false;
    }
    // Once set, `tracer` remains alive until the process is destroyed.
    SK_INTENTIONALLY_LEAKED(tracer);

    // GetInstance() will return `tracer` here, but allows us to avoid capturing anything in the
    // lambda. Even if it returned the SkDefaultEventTracer, calling onExit() on that is safe.
    // SkDefaultEventTracer::onExit() is a no-op, which is why we don't unconditionally add the
    // atexit() callback; it's only of interest if a custom tracer is installed.
    atexit([]() { GetInstance()->onExit(); });

    return true;
}

SkEventTracer* SkEventTracer::GetInstance() {
    if (auto tracer = gUserTracer.load(std::memory_order_acquire)) {
        return tracer;
    }
    static SkDefaultEventTracer* defaultTracer = new SkDefaultEventTracer;
    return defaultTracer;
}