Flat Memory Pool (#572)

* Flat pool working on POSIX

* Flat pool working on POSIX

* Flat Pool working on Windows

* Apply clang-format

* Custom get_page_size()

* Fixing MacOS

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

modules/common/chowdsp_data_structures/Allocators/chowdsp_FlatMemoryPool.h

@@ -0,0 +1,150 @@
+#pragma once
+
+#if ! JUCE_TEENSY
+
+#if JUCE_WINDOWS
+#define NOMINMAX
+#define WIN32_LEAN_AND_MEAN 1
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#include <unistd.h>
+#endif
+
+namespace chowdsp
+{
+/**
+ * A "flat" memory pool that reserves a ton of virtual memory,
+ * and then commits pages of that memory as needed.
+ */
+struct FlatMemoryPool
+{
+    std::byte* current_pointer {};
+    std::byte* memory_base {};
+    std::byte* first_uncommitted_page {};
+    std::byte* address_limit {};
+    const size_t page_size { get_page_size() };
+
+    void* allocate_bytes (size_t num_bytes, size_t alignment = 8)
+    {
+        auto* p = juce::snapPointerToAlignment (current_pointer, alignment);
+        const auto end = p + num_bytes;
+
+        if (end > first_uncommitted_page)
+        {
+            if (end > address_limit)
+            {
+                // The memory pool is full!
+                jassertfalse;
+                return nullptr;
+            }
+            else
+            {
+                extend_committed_pages (end);
+            }
+        }
+
+        current_pointer = end;
+        return p;
+    }
+
+    [[nodiscard]] size_t get_bytes_used() const noexcept
+    {
+        return static_cast<size_t> (current_pointer - memory_base);
+    }
+
+    void clear()
+    {
+        if (memory_base == nullptr)
+            return;
+
+#if ARENA_ALLOCATOR_DEBUG
+        memset (memory_base, 0xcc, static_cast<size_t> (current_pointer - memory_base));
+#endif
+
+        current_pointer = memory_base;
+    }
+
+    struct Frame
+    {
+        FlatMemoryPool& pool;
+        std::byte* pointer_at_start;
+
+        explicit Frame (FlatMemoryPool& frame_pool)
+            : pool { frame_pool },
+              pointer_at_start { pool.current_pointer }
+        {
+        }
+
+        ~Frame()
+        {
+            pool.current_pointer = pointer_at_start;
+        }
+    };
+
+    /** Creates a frame for this allocator */
+    auto create_frame()
+    {
+        return Frame { *this };
+    }
+
+    void init (size_t reserve_bytes = 1 << 28)
+    {
+        const auto reserve_padded = page_size * ((reserve_bytes + page_size - 1) / page_size);
+
+#if JUCE_WINDOWS
+        memory_base = static_cast<std::byte*> (VirtualAlloc (nullptr, reserve_padded, MEM_RESERVE, PAGE_READWRITE));
+#else
+        memory_base = static_cast<std::byte*> (mmap (nullptr, reserve_padded, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0));
+        jassert (memory_base != nullptr);
+#endif
+
+        current_pointer = memory_base;
+        first_uncommitted_page = memory_base;
+        address_limit = memory_base + reserve_padded;
+    }
+
+    void deinit()
+    {
+        if (memory_base == nullptr)
+            return;
+
+#if JUCE_WINDOWS
+        VirtualFree (memory_base, 0, MEM_RELEASE);
+#else
+        munmap (memory_base, static_cast<size_t> (address_limit - memory_base));
+#endif
+
+        memory_base = nullptr;
+    }
+
+private:
+    void extend_committed_pages (std::byte* end)
+    {
+        jassert (end - first_uncommitted_page >= 0);
+#if JUCE_WINDOWS
+        const auto size = juce::snapPointerToAlignment (end, page_size) - first_uncommitted_page;
+        VirtualAlloc (first_uncommitted_page, static_cast<size_t> (size), MEM_COMMIT, PAGE_READWRITE);
+        first_uncommitted_page += size;
+#else
+        first_uncommitted_page = juce::snapPointerToAlignment (end, page_size);
+#endif
+    }
+
+#if JUCE_WINDOWS
+    static size_t get_page_size()
+    {
+        SYSTEM_INFO systemInfo;
+        GetNativeSystemInfo (&systemInfo);
+        return static_cast<size_t> (systemInfo.dwPageSize);
+    }
+#else
+    static size_t get_page_size()
+    {
+        return static_cast<size_t> (sysconf (_SC_PAGESIZE));
+    }
+#endif
+};
+} // namespace chowdsp
+
+#endif

modules/common/chowdsp_data_structures/Helpers/chowdsp_ArenaHelpers.h

@@ -2,10 +2,20 @@
 
 namespace chowdsp::arena
 {
+/**
+ * Allocates space for some number of objects of type T
+ * The returned memory will be un-initialized, so be sure to clear it manually if needed.
+ */
+template <typename T, typename IntType, typename Arena>
+T* allocate (Arena& arena, IntType num_Ts, size_t alignment = alignof (T)) noexcept
+{
+    return static_cast<T*> (arena.allocate_bytes ((size_t) num_Ts * sizeof (T), alignment));
+}
+
 template <typename T, typename I, typename Arena>
 nonstd::span<T> make_span (Arena& arena, I size, size_t alignment = alignof (T))
 {
-    return { arena.template allocate<T> (size, alignment), static_cast<size_t> (size) };
+    return { allocate<T> (arena, size, alignment), static_cast<size_t> (size) };
 }
 
 template <typename Arena>

modules/common/chowdsp_data_structures/chowdsp_data_structures.h

@@ -50,6 +50,7 @@ BEGIN_JUCE_MODULE_DECLARATION
 #include "Allocators/chowdsp_STLArenaAllocator.h"
 #include "Helpers/chowdsp_ArenaHelpers.h"
 
+#include "Allocators/chowdsp_FlatMemoryPool.h"
 #include "Allocators/chowdsp_PoolAllocator.h"
 
 #include "Structures/chowdsp_BucketArray.h"

tests/common_tests/chowdsp_data_structures_test/CMakeLists.txt

@@ -25,6 +25,7 @@ target_sources(chowdsp_data_structures_test
         PackedPointerTest.cpp
         ChunkListTest.cpp
         FixedSizeFunctionTest.cpp
+        FlatMemoryPoolTest.cpp
 )
 
 target_compile_features(chowdsp_data_structures_test PRIVATE cxx_std_20)

tests/common_tests/chowdsp_data_structures_test/FlatMemoryPoolTest.cpp

@@ -0,0 +1,70 @@
+#include <CatchUtils.h>
+#include <chowdsp_data_structures/chowdsp_data_structures.h>
+
+TEST_CASE ("Flat Memory Pool Test", "[common][data-structures]")
+{
+    chowdsp::FlatMemoryPool allocator {};
+    allocator.init();
+
+    SECTION ("Basic Usage")
+    {
+        // allocate doubles
+        double* some_doubles;
+        {
+            some_doubles = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_doubles != nullptr);
+            REQUIRE (allocator.get_bytes_used() == 80);
+
+            auto* some_more_doubles = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_more_doubles != nullptr);
+            REQUIRE (some_more_doubles == some_doubles + 10);
+            REQUIRE (allocator.get_bytes_used() == 160);
+        }
+
+        // clear allocator
+        allocator.clear();
+
+        // re-allocate doubles
+        {
+            auto* some_doubles2 = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_doubles2 != nullptr);
+            REQUIRE (some_doubles2 == some_doubles);
+            REQUIRE (allocator.get_bytes_used() == 80);
+
+            auto* some_more_doubles = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_more_doubles != nullptr);
+            REQUIRE (some_more_doubles == some_doubles + 10);
+            REQUIRE (allocator.get_bytes_used() == 160);
+        }
+    }
+
+    SECTION ("Overfull Allocation")
+    {
+        REQUIRE (chowdsp::arena::allocate<double> (allocator, 20'000) != nullptr);
+        REQUIRE (chowdsp::arena::allocate<double> (allocator, 200) != nullptr);
+        REQUIRE (chowdsp::arena::allocate<double> (allocator, 2'000'000) != nullptr);
+        REQUIRE (allocator.get_bytes_used() == 8 * 2'020'200);
+        allocator.clear();
+        REQUIRE (allocator.get_bytes_used() == 0);
+    }
+
+    SECTION ("Usage with Frame")
+    {
+        {
+            const auto frame = allocator.create_frame();
+
+            auto* some_doubles = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_doubles != nullptr);
+            REQUIRE (allocator.get_bytes_used() == 80);
+
+            auto* some_more_doubles = chowdsp::arena::allocate<double> (allocator, 10);
+            REQUIRE (some_more_doubles != nullptr);
+            REQUIRE (allocator.get_bytes_used() == 160);
+        }
+
+        REQUIRE (allocator.get_bytes_used() == 0);
+
+        allocator.deinit();
+        REQUIRE (allocator.memory_base == nullptr);
+    }
+}