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A StackAllocator performs fast allocation and deallocation of memory by implementing a bump-pointer allocation strategy. In contrast to a pure bump-pointer allocator, it's possible to free memory. Allocations and deallocations must follow a strict stack discipline. In general, slabs which become unused are _not_ freed, but reused for subsequent allocations. The first slab can be placed into pre-allocated memory.
117 lines
3.9 KiB
C++
117 lines
3.9 KiB
C++
//===--- StackAllocator.cpp - Unit tests for the StackAllocator -----------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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#include "../../stdlib/public/runtime/StackAllocator.h"
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#include "gtest/gtest.h"
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using namespace swift;
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static constexpr size_t slabCapacity = 256;
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static constexpr size_t firstSlabBufferCapacity = 140;
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static constexpr size_t fitsIntoFirstSlab = 16;
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static constexpr size_t fitsIntoSlab = slabCapacity - 16;
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static constexpr size_t twoFitIntoSlab = slabCapacity / 2 - 32;
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static constexpr size_t exceedsSlab = slabCapacity + 16;
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TEST(StackAllocatorTest, withPreallocatedSlab) {
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char firstSlab[firstSlabBufferCapacity];
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StackAllocator<slabCapacity> allocator(firstSlab, firstSlabBufferCapacity);
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char *mem1 = (char *)allocator.alloc(fitsIntoFirstSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 0);
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char *mem1a = (char *)allocator.alloc(fitsIntoFirstSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 0);
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char *mem2 = (char *)allocator.alloc(exceedsSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 1);
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char *mem3 = (char *)allocator.alloc(fitsIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 2);
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char *mem4 = (char *)allocator.alloc(fitsIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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allocator.dealloc(mem4);
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allocator.dealloc(mem3);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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char *mem5 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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char *mem6 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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char *mem7 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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allocator.dealloc(mem7);
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allocator.dealloc(mem6);
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allocator.dealloc(mem5);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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char *mem8 = (char *)allocator.alloc(exceedsSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 2);
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allocator.dealloc(mem8);
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allocator.dealloc(mem2);
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allocator.dealloc(mem1a);
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allocator.dealloc(mem1);
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}
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TEST(StackAllocatorTest, withoutPreallocatedSlab) {
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constexpr size_t slabCapacity = 256;
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StackAllocator<slabCapacity> allocator;
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size_t fitsIntoSlab = slabCapacity - 16;
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size_t twoFitIntoSlab = slabCapacity / 2 - 32;
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size_t exceedsSlab = slabCapacity + 16;
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char *mem1 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 1);
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char *mem1a = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 1);
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char *mem2 = (char *)allocator.alloc(exceedsSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 2);
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char *mem3 = (char *)allocator.alloc(fitsIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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char *mem4 = (char *)allocator.alloc(fitsIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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allocator.dealloc(mem4);
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allocator.dealloc(mem3);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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char *mem5 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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char *mem6 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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char *mem7 = (char *)allocator.alloc(twoFitIntoSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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allocator.dealloc(mem7);
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allocator.dealloc(mem6);
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allocator.dealloc(mem5);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 4);
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char *mem8 = (char *)allocator.alloc(exceedsSlab);
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EXPECT_EQ(allocator.getNumAllocatedSlabs(), 3);
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allocator.dealloc(mem8);
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allocator.dealloc(mem2);
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allocator.dealloc(mem1a);
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allocator.dealloc(mem1);
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}
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