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std.experimental.allocator.building_blocks.fallback_allocator
- struct
FallbackAllocator(Primary, Fallback); FallbackAllocatoris the allocator equivalent of an "or" operator in algebra. An allocation request is first attempted with the Primary allocator. If that returns null, the request is forwarded to the Fallback allocator. All other requests are dispatched appropriately to one of the two allocators.In order to work,FallbackAllocatorrequires that Primary defines the owns method. This is needed in order to decide which allocator was responsible for a given allocation.FallbackAllocatoris useful for fast, special-purpose allocators backed up by general-purpose allocators. The example below features a stack region backed up by the GCAllocator.- Primary
primary; - The primary allocator.
- Fallback
fallback; - The fallback allocator.
- static FallbackAllocator
instance; - If both Primary and Fallback are stateless, FallbackAllocator defines a static instance called
instance. - enum uint
alignment; - The alignment offered is the minimum of the two allocators' alignment.
- void[]
allocate(size_ts); - Allocates memory trying the primary allocator first. If it returns null, the fallback allocator is tried.
- void[]
alignedAllocate(size_ts, uinta); - FallbackAllocator offers
alignedAllocateiff at least one of the allocators also offers it. It attempts to allocate using either or both. - bool
expand(ref void[]b, size_tdelta); expandis defined if and only if at least one of the allocators definesexpand. It works as follows. If primary.owns(b), then the request is forwarded to primary.expandif it is defined, or fails (returning false) otherwise. If primary does not ownb, then the request is forwarded to fallback.expandif it is defined, or fails (returning false) otherwise.- bool
reallocate(ref void[]b, size_tnewSize); reallocateworks as follows. If primary.owns(b), then primary.reallocate(b, newSize) is attempted. If it fails, an attempt is made to move the allocation from primary to fallback.If primary does not ownb, then fallback.reallocate(b, newSize) is attempted. If that fails, an attempt is made to move the allocation from fallback to primary.- Ternary
owns(void[]b); ownsis defined if and only if both allocators defineowns. Returns primary.owns(b) | fallback.owns(b).- Ternary
resolveInternalPointer(const void*p, ref void[]result); resolveInternalPointeris defined if and only if both allocators define it.- bool
deallocate(void[]b); deallocateis defined if and only if at least one of the allocators definedeallocate. It works as follows. If primary.owns(b), then the request is forwarded to primary.deallocateif it is defined, or is a no-op otherwise. If primary does not ownb, then the request is forwarded to fallback.deallocateif it is defined, or is a no-op otherwise.- Ternary
empty(); emptyis defined if both allocators also define it.Returns:primary.empty & fallback.empty
- FallbackAllocator!(Primary, Fallback)
fallbackAllocator(Primary, Fallback)(auto ref Primaryp, auto ref Fallbackf); - Convenience function that uses type deduction to return the appropriate FallbackAllocator instance. To initialize with allocators that don't have state, use their it static member.Examples:
import std.experimental.allocator.building_blocks.region : Region; import std.experimental.allocator.gc_allocator : GCAllocator; import std.typecons : Ternary; auto a = fallbackAllocator(Region!GCAllocator(1024), GCAllocator.instance); auto b1 = a.allocate(1020); writeln(b1.length); // 1020 writeln(a.primary.owns(b1)); // Ternary.yes auto b2 = a.allocate(10); writeln(b2.length); // 10 writeln(a.primary.owns(b2)); // Ternary.no
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Ddoc on Sun Sep 1 19:49:55 2019