I am a student of a system software faculty. Now I\'m developing a memory manager for Windows. Here\'s my simple implementation of malloc()
and free()
:
This is a good link that elaborates on why you may need multiple heap: https://caligari.dartmouth.edu/doc/ibmcxx/en_US/doc/libref/concepts/cumemmng.htm
"Why Use Multiple Heaps?
Using a single runtime heap is fine for most programs. However, using multiple
heaps can be more efficient and can help you improve your program's performance
and reduce wasted memory for a number of reasons:
1- When you allocate from a single heap, you may end up with memory blocks on
different pages of memory. For example, you might have a linked list that
allocates memory each time you add a node to the list. If you allocate memory for
other data in between adding nodes, the memory blocks for the nodes could end up
on many different pages. To access the data in the list, the system may have to
swap many pages, which can significantly slow your program.
With multiple heaps, you can specify which heap you allocate from. For example,
you might create a heap specifically for the linked list. The list's memory blocks
and the data they contain would remain close together on fewer pages, reducing the
amount of swapping required.
2- In multithread applications, only one thread can access the heap at a time to
ensure memory is safely allocated and freed. For example, say thread 1 is
allocating memory, and thread 2 has a call to free. Thread 2 must wait until
thread 1 has finished its allocation before it can access the heap. Again, this
can slow down performance, especially if your program does a lot of memory
operations.
If you create a separate heap for each thread, you can allocate from them
concurrently, eliminating both the waiting period and the overhead required to
serialize access to the heap.
3- With a single heap, you must explicitly free each block that you allocate. If you
have a linked list that allocates memory for each node, you have to traverse the
entire list and free each block individually, which can take some time.
If you create a separate heap for that linked list, you can destroy it with a
single call and free all the memory at once.
4- When you have only one heap, all components share it (including the IBM C and
C++ Compilers runtime library, vendor libraries, and your own code). If one
component corrupts the heap, another component might fail. You may have trouble
discovering the cause of the problem and where the heap was damaged.
With multiple heaps, you can create a separate heap for each component, so if
one damages the heap (for example, by using a freed pointer), the others can
continue unaffected. You also know where to look to correct the problem."