1// Written in the D programming language. 2/** 3Collection of typical and useful prebuilt allocators using the given 4components. User code would typically import this module and use its 5facilities, or import individual heap building blocks and assemble them. 6 7Source: $(PHOBOSSRC std/experimental/allocator/_showcase.d) 8*/ 9module std.experimental.allocator.showcase; 10 11import std.experimental.allocator.building_blocks.fallback_allocator, 12 std.experimental.allocator.gc_allocator, 13 std.experimental.allocator.building_blocks.region; 14import std.traits : hasMember; 15 16/** 17 18Allocator that uses stack allocation for up to `stackSize` bytes and 19then falls back to `Allocator`. Defined as: 20 21---- 22alias StackFront(size_t stackSize, Allocator) = 23 FallbackAllocator!( 24 InSituRegion!(stackSize, Allocator.alignment, 25 hasMember!(Allocator, "deallocate") 26 ? Yes.defineDeallocate 27 : No.defineDeallocate), 28 Allocator); 29---- 30 31Choosing `stackSize` is as always a compromise. Too small a size exhausts the 32stack storage after a few allocations, after which there are no gains over the 33backup allocator. Too large a size increases the stack consumed by the thread 34and may end up worse off because it explores cold portions of the stack. 35 36*/ 37alias StackFront(size_t stackSize, Allocator = GCAllocator) = 38 FallbackAllocator!( 39 InSituRegion!(stackSize, Allocator.alignment), 40 Allocator); 41 42/// 43@system unittest 44{ 45 StackFront!4096 a; 46 auto b = a.allocate(4000); 47 assert(b.length == 4000); 48 auto c = a.allocate(4000); 49 assert(c.length == 4000); 50 a.deallocate(b); 51 a.deallocate(c); 52} 53 54/** 55Creates a scalable `AllocatorList` of `Regions`, each having at least 56`bytesPerRegion` bytes. Allocation is very fast. This allocator does not offer 57`deallocate` but does free all regions in its destructor. It is recommended for 58short-lived batch applications that count on never running out of memory. 59*/ 60auto mmapRegionList(size_t bytesPerRegion) 61{ 62 static struct Factory 63 { 64 size_t bytesPerRegion; 65 import std.algorithm.comparison : max; 66 import std.experimental.allocator.building_blocks.region 67 : Region; 68 import std.experimental.allocator.mmap_allocator 69 : MmapAllocator; 70 this(size_t n) 71 { 72 bytesPerRegion = n; 73 } 74 auto opCall(size_t n) 75 { 76 return Region!MmapAllocator(max(n, bytesPerRegion)); 77 } 78 } 79 import std.experimental.allocator.building_blocks.allocator_list 80 : AllocatorList; 81 import std.experimental.allocator.building_blocks.null_allocator 82 : NullAllocator; 83 auto shop = Factory(bytesPerRegion); 84 return AllocatorList!(Factory, NullAllocator)(shop); 85} 86 87/// 88@system unittest 89{ 90 auto alloc = mmapRegionList(1024 * 1024); 91 const b = alloc.allocate(100); 92 assert(b.length == 100); 93} 94