1. The role of the UnityECS memory allocator
In traditional object-oriented programming model, we usually use heap memory to store entity and component data. However, since the size of entity and component data is usually very large, using heap memory for allocation and management can lead to problems of memory fragmentation and performance degradation. To solve this problem, UnityECS introduces the concept of memory allocator.
The main function of the UnityECS memory allocator is to store entity and component data in continuous memory blocks to improve the efficiency of memory access. It uses a data structure called Chunk to store entity and component data, and each Chunk contains a certain amount of entity and component data, as well as some metadata for managing and accessing these data.
2. The principle of UnityECS memory allocator
- Chunk allocation and release
In UnityECS, the memory allocator dynamically allocates and manages Chunk according to the size and quantity of entity and component data. When a new Chunk needs to be allocated, the memory allocator will apply for a continuous memory space from the system memory and divide it into multiple Chunks of equal size. Each Chunk contains a certain amount of entity and component data, as well as some metadata for managing and accessing these data.
When a chunk needs to be freed, the memory allocator marks it as reusable and adds it to a free chunk list. In this way, when a Chunk needs to be allocated next time, the memory allocator will first look up the free Chunk list and try to reuse the Chunk in it, so as to reduce the number of application and release of system memory.
- Access to entity and component data
In UnityECS, access to entity and component data is implemented through Chunk and Archetype. Archetype is a data structure used to describe the data layout of entities and components, which contains a set of component types and corresponding memory offsets. Through Archetype, we can know which component types and their memory offsets are stored in each Chunk, so that we can directly access and modify these data.
When it is necessary to access entity and component data, UnityECS will determine the Chunk where it is based on the Archetype of the entity, and use the memory offset to locate and access the corresponding component data. Since entity and component data are stored in continuous memory blocks, they can be directly calculated through memory offsets when accessing, thereby improving the efficiency of memory access.
3. Advantages of UnityECS memory allocator
Compared with the traditional object-oriented programming model, the UnityECS memory allocator has the following advantages:
- Memory continuity: The UnityECS memory allocator stores entity and component data in continuous memory blocks, reducing the problem of memory fragmentation and improving the efficiency of memory access.
- Allocation and release efficiency: The UnityECS memory allocator reduces the number of application and release of system memory by reusing the allocated Chunk, improving the efficiency of allocation and release.
- Data locality: The UnityECS memory allocator stores component data of the same type in adjacent memory locations, improving data locality and reducing memory access latency.
- Batch processing: The UnityECS memory allocator accesses data in units of Chunk, and can batch process data of multiple entities and components, improving processing efficiency.