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