648db22b |
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 | } |