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'Main Toothpick implementation'

There is a newer version: 3.1.0

/*
 * Copyright 2019 Stephane Nicolas
 * Copyright 2019 Daniel Molinero Reguera
 *
 * 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 toothpick;

import java.lang.ref.WeakReference;
import javax.inject.Provider;

/**
 * A thread safe internal provider. It will be exposed outside of Toothpick.
 *
 * @param  the class of the instances provided by this provider.
 */
public class ThreadSafeProviderImpl implements Provider, Lazy {
  private volatile T instance;
  private WeakReference scope;
  private String scopeName;
  private Class clazz;
  private String name;
  private boolean isLazy;

  public ThreadSafeProviderImpl(Scope scope, Class clazz, String name, boolean isLazy) {
    this.scope = new WeakReference<>(scope);
    this.scopeName = scope.getName().toString();
    this.clazz = clazz;
    this.name = name;
    this.isLazy = isLazy;
  }

  @Override
  public T get() {
    // the first test avoids accessing a volatile when not needed
    if (isLazy && instance != null) {
      return instance;
    }

    // ensure both sync for DSL
    // and sync around provider
    // so that dev's providers don't deal with concurrency
    synchronized (this) {
      if (isLazy) {
        // DCL
        if (instance == null) {
          instance = getScope().getInstance(clazz, name);
          scope.clear();
        }
        return instance;
      }
      return getScope().getInstance(clazz, name);
    }
  }

  private Scope getScope() {
    final Scope scope = this.scope.get();
    if (scope == null) {
      throw new IllegalStateException(
          String.format(
              "The instance provided by the %s "
                  + "cannot be created when the associated scope: %s has been closed",
              isLazy ? "lazy" : "provider", scopeName));
    }
    return scope;
  }
}