Simple Pool Allocator implementation (#549)

modules/common/chowdsp_data_structures/Allocators/chowdsp_PoolAllocator.h

@@ -0,0 +1,135 @@
+#pragma once
+
+namespace chowdsp
+{
+/**
+ * A simple pool allocator.
+ *
+ * This implementation is based on GingerBill's blog post:
+ * https://www.gingerbill.org/article/2019/02/16/memory-allocation-strategies-004/
+ */
+template <size_t chunk_size, size_t alignment>
+struct PoolAllocator
+{
+private:
+    struct FreeListNode
+    {
+        FreeListNode* next = nullptr;
+    };
+    FreeListNode* free_list_head = nullptr;
+
+public:
+    static constexpr size_t chunk_size_padded = ((chunk_size + alignment - 1) / alignment) * alignment;
+    nonstd::span<std::byte> backing_buffer {};
+
+    PoolAllocator() = default;
+
+    /** Creates the allocator with some number of chunks pre-allocated. */
+    explicit PoolAllocator (size_t num_chunks)
+    {
+        resize (num_chunks);
+    }
+
+    ~PoolAllocator()
+    {
+        aligned_free (backing_buffer.data());
+    }
+
+    /** Re-allocates the allocator's backing buffer to fit some number of chunks. */
+    void resize (size_t num_chunks)
+    {
+        aligned_free (backing_buffer.data());
+
+        const auto allocator_bytes = chunk_size_padded * num_chunks;
+        backing_buffer = { static_cast<std::byte*> (aligned_alloc (alignment, allocator_bytes)), allocator_bytes };
+        free_all();
+    }
+
+    /** Resets the allocator free list. */
+    void free_all()
+    {
+        size_t chunk_count = backing_buffer.size() / chunk_size_padded;
+        // Set all chunks to be free
+        for (size_t i = 0; i < chunk_count; ++i)
+        {
+            auto* ptr = backing_buffer.data() + i * chunk_size_padded;
+            auto* node = reinterpret_cast<FreeListNode*> (ptr);
+
+            // Push free node onto the free list
+            node->next = free_list_head;
+            free_list_head = node;
+        }
+    }
+
+    /** Allocates a single chunk. */
+    void* allocate_chunk()
+    {
+        // Get latest free node
+        auto* node = free_list_head;
+
+        if (node == nullptr)
+        {
+            jassertfalse;
+            return nullptr;
+        }
+
+        // Pop free node
+        free_list_head = free_list_head->next;
+
+        // Zero memory by default
+        return memset (node, 0, chunk_size_padded);
+    }
+
+    /** Allocates a chunk and constructs an object in place. */
+    template <typename T, typename... Args>
+    T* allocate (Args&&... args)
+    {
+        static_assert (sizeof (T) <= chunk_size_padded);
+        static_assert (alignof (T) <= alignment);
+
+        auto* bytes = allocate_chunk();
+        return new (bytes) T { std::forward<Args> (args)... };
+    }
+
+    /** Frees a single chunk. */
+    void free_chunk (void* ptr)
+    {
+        if (ptr == nullptr)
+            return;
+
+        void* start = backing_buffer.data();
+        void* end = backing_buffer.data() + static_cast<int> (backing_buffer.size());
+        if (ptr < start || ptr >= end)
+        {
+            // this pointer was not allocated from this data!
+            jassertfalse;
+            return;
+        }
+
+        // Push free node
+        auto* node = static_cast<FreeListNode*> (ptr);
+        node->next = free_list_head;
+        free_list_head = node;
+    }
+
+    /** Calls an object's destructor and then frees the memory. */
+    template <typename T>
+    void free (T* ptr)
+    {
+        if (ptr == nullptr)
+            return;
+
+        void* start = backing_buffer.data();
+        void* end = backing_buffer.data() + static_cast<int> (backing_buffer.size());
+        if (ptr < start || ptr >= end)
+        {
+            // this pointer was not allocated from this data!
+            jassertfalse;
+            return;
+        }
+
+        ptr->~T();
+        free_chunk (ptr);
+    }
+};
+} // namespace chowdsp

modules/common/chowdsp_data_structures/chowdsp_data_structures.h

@@ -48,6 +48,8 @@ BEGIN_JUCE_MODULE_DECLARATION
 #include "Allocators/chowdsp_STLArenaAllocator.h"
 #include "Helpers/chowdsp_ArenaHelpers.h"
 
+#include "Allocators/chowdsp_PoolAllocator.h"
+
 #include "Structures/chowdsp_BucketArray.h"
 #include "Structures/chowdsp_AbstractTree.h"
 #include "Structures/chowdsp_SmallMap.h"

tests/common_tests/chowdsp_data_structures_test/CMakeLists.txt

@@ -21,6 +21,7 @@ target_sources(chowdsp_data_structures_test
         EnumMapTest.cpp
         OptionalRefTest.cpp
         OptionalArrayTest.cpp
+        PoolAllocatorTest.cpp
 )
 
 target_compile_features(chowdsp_data_structures_test PRIVATE cxx_std_20)

tests/common_tests/chowdsp_data_structures_test/PoolAllocatorTest.cpp

@@ -0,0 +1,57 @@
+#include <CatchUtils.h>
+#include <chowdsp_data_structures/chowdsp_data_structures.h>
+
+TEST_CASE ("Pool Allocator Test", "[common][data-structures]")
+{
+    SECTION ("Default")
+    {
+        chowdsp::PoolAllocator<32, 8> allocator {};
+        REQUIRE (allocator.backing_buffer.empty());
+    }
+
+    SECTION ("With Size")
+    {
+        chowdsp::PoolAllocator<32, 8> allocator { 4 };
+        REQUIRE (allocator.backing_buffer.size() == 128);
+    }
+
+    SECTION ("Allocate/Free")
+    {
+        chowdsp::PoolAllocator<32, 8> allocator { 4 };
+        std::array<void*, 6> pointers {};
+        for (size_t i = 0; i < 5; ++i)
+        {
+            pointers[i] = allocator.allocate_chunk();
+            if (i < 4)
+                REQUIRE (pointers[i] != nullptr);
+            else
+                REQUIRE (pointers[i] == nullptr);
+        }
+        pointers.back() = &allocator;
+        for (auto* pointer : pointers)
+            allocator.free_chunk (pointer);
+    }
+
+    SECTION ("Allocate/Free Object")
+    {
+        chowdsp::PoolAllocator<32, 8> allocator { 4 };
+
+        struct Thing
+        {
+            int64_t x {};
+            int64_t y {};
+            int64_t z {};
+        };
+        auto* thing = allocator.allocate<Thing> (0, 1, 2);
+        REQUIRE (thing != nullptr);
+        REQUIRE (thing->x == 0);
+        REQUIRE (thing->y == 1);
+        REQUIRE (thing->z == 2);
+        allocator.free (thing);
+
+        allocator.free<Thing> (nullptr);
+
+        Thing xx {};
+        allocator.free<Thing> (&xx);
+    }
+}