| // Copyright 2020 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef LIB_FIDL_LLCPP_BUFFER_THEN_HEAP_ALLOCATOR_H_ |
| #define LIB_FIDL_LLCPP_BUFFER_THEN_HEAP_ALLOCATOR_H_ |
| |
| #include "failover_allocator.h" |
| #include "unsafe_buffer_allocator.h" |
| |
| namespace fidl { |
| |
| // BufferThenHeapAllocator allocates objects from its internal contiguous region of memory, or if |
| // that internal memory is exhausted, from the heap. |
| // |
| // The NBytes template parameter specifies the size of the internal buffer. |
| // |
| // If BufferThenHeapAllocator is stored on the stack and objects all fit within NBytes including |
| // destructor tracking overhead, objects allocated with it will also be stored on the stack and |
| // heap allocations will not be made. |
| // |
| // When setting NBytes, please set a size that comfortably fits on the stack. Over-use of stack |
| // can lead to stack exhaustion which crashes the process. It's better to set a smaller NBytes |
| // and fail over to heap sometimes than to cause stack exhaustion. NBytes of 512 tends to be |
| // ok assuming very limited recursion. |
| // |
| // At NBytes > 2048, consider putting the whole BufferThenHeapAllocator<> on the heap (where it'll |
| // do one heap allocation instead of many, assuming everything fits). |
| // |
| // Consider using HeapAllocator for paths which aren't performance sensitive. |
| // |
| // If you need allocations to out-live the allocator that was used to make them, use HeapAllocator |
| // instead. |
| // |
| // Usage: |
| // BufferThenHeapAllocator<2048> allocator; |
| // tracking_ptr<MyObj> obj = allocator.make<MyObj>(arg1, arg2); |
| // tracking_ptr<int[]> arr = allocator.make<int[]>(10); |
| // // succeeds, but ends up in separate independent heap allocation: |
| // tracking_ptr<uint8_t[]> arr2 = allocator.make<uint8_t[]>(2 * 2048); |
| template <size_t NBytes> |
| using BufferThenHeapAllocator = FailoverHeapAllocator<::fidl::UnsafeBufferAllocator<NBytes>>; |
| |
| } // namespace fidl |
| |
| #endif // LIB_FIDL_LLCPP_BUFFER_THEN_HEAP_ALLOCATOR_H_ |
