SWMM5 mempool.c Summary

 The mempool.c file implements a simple, fast memory allocation system using memory pools. It defines functions for managing memory blocks, pooling, and efficient allocation and deallocation of memory. This system is designed to minimize the overhead of frequent memory allocations by pre-allocating large memory blocks and managing them internally.

Key Components:

Memory Pool Management:

• AllocInit(): Initializes a new memory pool by creating a block and setting up a root pointer that tracks the pool's state.
• AllocSetPool(): Changes the current memory pool. This allows for managing multiple pools in the system.
• AllocReset(): Resets the current pool by moving the pointer back to the start of the first block. This enables the reuse of the memory without deallocating it.
• AllocFreePool(): Frees all memory used by the current pool, including all blocks within the pool.
• Alloc(): Allocates memory from the current pool. It ensures that memory is aligned to a 4-byte boundary and automatically handles moving to a new block when the current one is exhausted.

Helper Structures:

• alloc_hdr_t: Represents a header for each block of memory in the pool. It keeps track of the block's start, the next free memory location, and the block's end.
• alloc_root_t: Represents the root of the current memory pool, which includes a pointer to the first block and the current block being used for allocation.

Functions:

1. AllocHdr():

   • A helper function that allocates a new header and a memory block of size ALLOC_BLOCK_SIZE (defined as 64000 bytes). It initializes the block's memory pointers and returns the header for further use.

2. AllocInit():

   • Initializes a new memory pool by allocating an alloc_root_t structure and the first block. The pool is set as the current pool, and it returns a pointer to the pool.

3. Alloc():

   • Allocates a specified amount of memory from the current pool. It checks if the current block has enough free memory. If not, it allocates a new block. It also aligns memory to a 4-byte boundary and manages memory efficiently.

4. AllocSetPool():

   • Changes the current memory pool by updating the root pointer to a new pool. It returns the previous pool for potential future use.

5. AllocReset():

   • Resets the current pool by setting the free memory pointer back to the start of the first block. This allows reusing the memory pool without actually freeing the memory.

6. AllocFreePool():

   • Frees all memory used by the current pool, including the memory blocks and the root structure itself.

Memory Block Allocation:

The pool system allows memory to be allocated in large blocks (64000 bytes in this case). When a block is exhausted, a new block is created, and the pointer is moved to the new block. This reduces the overhead associated with frequent calls to malloc and free.

Allocation Flow:

• When memory is requested, the system checks the current block for available space. If the block is full, it allocates a new block and continues.
• The system uses block headers (alloc_hdr_t) to manage each block of memory and track the current free pointer (free), which points to the next available location in the block.
• The memory is aligned to a 4-byte boundary to ensure that it is suitable for typical machine architectures.

Memory Management Efficiency:

This memory pool system improves performance by reducing the overhead of repeatedly allocating and freeing small chunks of memory. Instead, it pre-allocates large blocks of memory and manages them internally.

Summary:

The mempool.c file is a simple and efficient memory management system designed to handle large memory allocations within the SWMM5 project. It uses a pooling mechanism to reduce allocation overhead, efficiently managing memory by allocating large blocks and dividing them as needed. This system helps improve performance in environments where frequent memory allocations and deallocations occur.