| // Copyright (C) 2022 The Android Open Source Project |
| // |
| // 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 com.google.gerrit.server.util.git; |
| |
| import com.google.common.flogger.FluentLogger; |
| import java.util.ArrayList; |
| import java.util.List; |
| import java.util.function.Supplier; |
| |
| /** |
| * Pool to manage resources that need to be closed but to whom we might lose the reference to or |
| * where closing resources individually is not always possible. |
| * |
| * <p>This pool can be used when we want to reuse closable resources in a multithreaded context. |
| * Example: |
| * |
| * <pre>{@code |
| * try (CloseablePool<T> pool = new CloseablePool(() -> new T())) { |
| * for (int i = 0; i < 100; i++) { |
| * executor.submit(() -> { |
| * try (CloseablePool<T>.Handle handle = pool.get()) { |
| * // Do work that might potentially take longer than the timeout. |
| * handle.get(); // pooled instance to be used |
| * } |
| * }).get(1000, MILLISECONDS); |
| * } |
| * } |
| * }</pre> |
| */ |
| public class CloseablePool<T extends AutoCloseable> implements AutoCloseable { |
| private static final FluentLogger logger = FluentLogger.forEnclosingClass(); |
| |
| private final Supplier<T> tCreator; |
| private List<T> ts; |
| |
| /** |
| * Instantiate a new pool. The {@link Supplier} must be capable of creating a new instance on |
| * every call. |
| */ |
| public CloseablePool(Supplier<T> tCreator) { |
| this.ts = new ArrayList<>(); |
| this.tCreator = tCreator; |
| } |
| |
| /** |
| * Get a shared instance or create a new instance. Close the returned handle to return it to the |
| * pool. |
| */ |
| public synchronized Handle get() { |
| if (ts.isEmpty()) { |
| return new Handle(tCreator.get()); |
| } |
| return new Handle(ts.remove(ts.size() - 1)); |
| } |
| |
| private synchronized boolean discard(T t) { |
| if (ts != null) { |
| ts.add(t); |
| return true; |
| } |
| return false; |
| } |
| |
| @Override |
| public synchronized void close() { |
| for (T t : ts) |
| try { |
| t.close(); |
| } catch (Exception e) { |
| logger.atWarning().withCause(e).log( |
| "Failed to close resource %s in CloseablePool %s", t, this); |
| } |
| ts = null; |
| } |
| |
| /** |
| * Wrapper around an {@link AutoCloseable}. Will try to return the resource to the pool and close |
| * it in case the pool was already closed. |
| */ |
| public class Handle implements AutoCloseable { |
| private final T t; |
| |
| private Handle(T t) { |
| this.t = t; |
| } |
| |
| /** Returns the managed instance. */ |
| public T get() { |
| return t; |
| } |
| |
| @Override |
| public void close() { |
| if (!discard(t)) { |
| try { |
| t.close(); |
| } catch (Exception e) { |
| logger.atWarning().withCause(e).log( |
| "Failed to close resource %s in CloseablePool %s", this, CloseablePool.this); |
| } |
| } |
| } |
| } |
| } |