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Support for distributed tracing.

There is a newer version: 4.1.1

/*
 * Copyright (c) 2019, 2022 Oracle and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.helidon.tracing;

import java.util.List;
import java.util.Optional;
import java.util.ServiceLoader;

import io.helidon.common.serviceloader.HelidonServiceLoader;
import io.helidon.tracing.spi.TracerProvider;

/**
 * Tracer provider helper to find implementation to use.
 */
final class TracerProviderHelper {
    private static final System.Logger LOGGER = System.getLogger(TracerProviderHelper.class.getName());
    private static final TracerProvider TRACER_PROVIDER;

    static {
        TracerProvider provider = null;
        try {
            List allProviders = HelidonServiceLoader.builder(ServiceLoader.load(TracerProvider.class))
                    .addService(new NoOpTracerProvider(), 100000)
                    .build()
                    .asList();

            if (allProviders.size() == 1 || allProviders.size() == 2) {
                // only noop or one and noop
                provider = allProviders.get(0);
            }
            for (TracerProvider aProvider : allProviders) {
                if (aProvider.available()) {
                    provider = aProvider;
                    break;
                }
            }
        } catch (Throwable e) {
            LOGGER.log(System.Logger.Level.WARNING, "Failed to set up tracer provider, using no-op", e);
        }

        TRACER_PROVIDER = provider == null ? new NoOpTracerProvider() : provider;
    }

    private TracerProviderHelper() {
    }

    public static Optional currentSpan() {
        return TRACER_PROVIDER.currentSpan();
    }

    static Tracer global() {
        return TRACER_PROVIDER.global();
    }

    static void global(Tracer tracer) {
        TRACER_PROVIDER.global(tracer);
    }

    static TracerBuilder findTracerBuilder() {
        return TRACER_PROVIDER.createBuilder();
    }
}