48 lines
1.9 KiB
Markdown
48 lines
1.9 KiB
Markdown
# allocPool - A simple & high performance object pool using modern C++
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This is allocPool, a pool of objects in a single header file that allow you to
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avoid expensive allocations during runtime. This preallocates objects in the
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constructor (with threads) then offers you two functions: `getPtr()` and `returnPtr(ptr)`.
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Using C++ concepts, we can use templates and require the class given to have a
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default constructor and to have a `.reset()` function. It will be used to clean the
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objects before giving them to another caller.
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We avoid false sharing by keeping a high amount of work per thread. This should
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lead to cache lines not being shared between threads. While this pool uses a hashmap
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and a pivot to make `returnPtr(ptr)` extremely fast, the construction's main bottleneck is
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in the locking and unlocking of the hashmap's mutex. We need to do this since we cannot
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write in a `std::unordered_map` at different hashes concurrently.
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It will automatically grow when the max capacity is reached, though there will
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be a performance penalty.
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## Performance
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With a simple stub class and a pool of 10000 objects, using the pool to take a pointer
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and give it back for each element is significantly faster than doing it by hand.
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```
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class stub {
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public:
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stub() {
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for (int j{}; j < 1000; j++) { i++; }
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};
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void reset() {}
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private:
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int i = 15;
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};
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```
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```
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Time (milliseconds) required for allocations without pool: 21
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Time (milliseconds) required for allocations with pool: 3
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Time (milliseconds) required for real allocations when constructing pool: 9
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```
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This trivial example shows some performance improvements that would be much more
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important should the allocation and construction/destruction of the objects be more
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complex.
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## Safety
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AddressSanitizer, LeakSanitizer and ThreadSanitizer have been used to ensure the safety
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of the class. Tests have been added to ensure the correct behavior in all cases. |