| 1 | /* |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * All rights reserved. |
| 4 | * |
| 5 | * This source code is licensed under both the BSD-style license (found in the |
| 6 | * LICENSE file in the root directory of this source tree) and the GPLv2 (found |
| 7 | * in the COPYING file in the root directory of this source tree). |
| 8 | */ |
| 9 | #pragma once |
| 10 | |
| 11 | #include <cassert> |
| 12 | #include <functional> |
| 13 | #include <memory> |
| 14 | #include <mutex> |
| 15 | #include <vector> |
| 16 | |
| 17 | namespace pzstd { |
| 18 | |
| 19 | /** |
| 20 | * An unbounded pool of resources. |
| 21 | * A `ResourcePool<T>` requires a factory function that takes allocates `T*` and |
| 22 | * a free function that frees a `T*`. |
| 23 | * Calling `ResourcePool::get()` will give you a new `ResourcePool::UniquePtr` |
| 24 | * to a `T`, and when it goes out of scope the resource will be returned to the |
| 25 | * pool. |
| 26 | * The `ResourcePool<T>` *must* survive longer than any resources it hands out. |
| 27 | * Remember that `ResourcePool<T>` hands out mutable `T`s, so make sure to clean |
| 28 | * up the resource before or after every use. |
| 29 | */ |
| 30 | template <typename T> |
| 31 | class ResourcePool { |
| 32 | public: |
| 33 | class Deleter; |
| 34 | using Factory = std::function<T*()>; |
| 35 | using Free = std::function<void(T*)>; |
| 36 | using UniquePtr = std::unique_ptr<T, Deleter>; |
| 37 | |
| 38 | private: |
| 39 | std::mutex mutex_; |
| 40 | Factory factory_; |
| 41 | Free free_; |
| 42 | std::vector<T*> resources_; |
| 43 | unsigned inUse_; |
| 44 | |
| 45 | public: |
| 46 | /** |
| 47 | * Creates a `ResourcePool`. |
| 48 | * |
| 49 | * @param factory The function to use to create new resources. |
| 50 | * @param free The function to use to free resources created by `factory`. |
| 51 | */ |
| 52 | ResourcePool(Factory factory, Free free) |
| 53 | : factory_(std::move(factory)), free_(std::move(free)), inUse_(0) {} |
| 54 | |
| 55 | /** |
| 56 | * @returns A unique pointer to a resource. The resource is null iff |
| 57 | * there are no available resources and `factory()` returns null. |
| 58 | */ |
| 59 | UniquePtr get() { |
| 60 | std::lock_guard<std::mutex> lock(mutex_); |
| 61 | if (!resources_.empty()) { |
| 62 | UniquePtr resource{resources_.back(), Deleter{*this}}; |
| 63 | resources_.pop_back(); |
| 64 | ++inUse_; |
| 65 | return resource; |
| 66 | } |
| 67 | UniquePtr resource{factory_(), Deleter{*this}}; |
| 68 | ++inUse_; |
| 69 | return resource; |
| 70 | } |
| 71 | |
| 72 | ~ResourcePool() noexcept { |
| 73 | assert(inUse_ == 0); |
| 74 | for (const auto resource : resources_) { |
| 75 | free_(resource); |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | class Deleter { |
| 80 | ResourcePool *pool_; |
| 81 | public: |
| 82 | explicit Deleter(ResourcePool &pool) : pool_(&pool) {} |
| 83 | |
| 84 | void operator() (T *resource) { |
| 85 | std::lock_guard<std::mutex> lock(pool_->mutex_); |
| 86 | // Make sure we don't put null resources into the pool |
| 87 | if (resource) { |
| 88 | pool_->resources_.push_back(resource); |
| 89 | } |
| 90 | assert(pool_->inUse_ > 0); |
| 91 | --pool_->inUse_; |
| 92 | } |
| 93 | }; |
| 94 | }; |
| 95 | |
| 96 | } |