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11fdf7f2 | 1 | /* |
7c673cae FG |
2 | * Copyright (c) 2016-present, Facebook, Inc. |
3 | * All rights reserved. | |
4 | * | |
11fdf7f2 TL |
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). | |
7c673cae FG |
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 avaiable 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 | } |