memory pool

Memory pools中文意思為記憶體池，也叫動態記憶體分配，記憶體池(Memory Pool)是一種記憶體分配方式。 通常我們習慣直接使用new、malloc等API申請分配記憶體，這樣做的缺點在於：由於所申請記憶體塊的大小不定，當頻繁使用時會造成大量的記憶體碎片並進而降低性能。 記憶體池則是在真正使用記憶體之前，先申請分配一定數量的、大小相等（一般情況下）的記憶體塊留作備用。當有新的記憶體需求時，就從記憶體池中分出一部分記憶體塊，若記憶體塊不夠再繼續申請新的記憶體。這樣做的一個顯著優點是儘量避免了記憶體碎片，使得記憶體分配效率得到提升。

基本介紹

• 中文名：記憶體池
• 外文名：memory pool
• 別稱：動態記憶體分配
• 性質：記憶體分配方式

Memory pools

also called fixed-size-blocks allocation, allow dynamic memory allocationcomparable to mallocor C++'s operator new. As those implementations suffer from fragmentationbecause of variable block sizes, it can be impossible to use them in a real time systemdue to performance. A more efficient solution is preallocating a number of memory blocks with the same size called the memory pool. The application can allocate, access, and free blocks represented by handlesat runtime.

Many real-time operating systemsuse memory pools, such as the Transaction Processing Facility.

Contents[hide]1Sample memory pool implementationA simple memory pool module can allocate for example 3 pools at compile timewith block sizes optimized for the application, which deploys the module. The application can allocate, access and free memory with the following interface:

To allocate memory from the pools. The function will determine the pool, where the required block fits in. If all blocks of that pool are already reserved, the function tries to find one in the next bigger pool(s). An allocated memory block is represented with a handle.To get an access pointer to the allocated memory .To free the formerly allocated memory block.The handle can for example be implemented with an unsigned int. The module can interpret the handle internally by dividing it into pool index, memory block index and a version. The pool and memory block index allow fast access to the corresponding block with the handle, while the version, which is incremented at each new allocation, allows detection of handles whose memory block is already freed (caused by handles retained too long).

[edit]Memory pool vs malloc

Benefits

Memory pools allow memory allocation with constant execution time (nofragmentation). The memory release for thousands of objects in a pool is just one operation, not one by one if mallocis used to allocate memory for each object.Memory pools can be grouped in hierarchical tree structures, which is suitable for special programming structures like loopsand recursions.Fixed-size block memory pools do not need to store allocation metadata for each allocation, describing characteristics like the size of the allocated block. Particularly for small allocations, this provides a substantial space savings.Drawbacks

Memory pools may need to be tuned for the application which deploys them.