[SOLVED] CS Java data structure python Carnegie Mellon

Carnegie Mellon
Dynamic Memory Allocation
Programmers use dynamic memory allocators (such as malloc) to acquire VM at run time.
For data structures whose size is only known at runtime.
Dynamic memory allocators manage an area of process virtual memory known as the heap.
Top of heap (brk ptr)
Application
Dynamic Memory Allocator
Heap
User stack
Heap (via malloc)
Uninitialized data (.bss)
Initialized data (.data)
Program text (.text)
0
1

Carnegie Mellon
Dynamic Memory Allocation
Allocator maintains heap as collection of variable sized
blocks, which are either allocated or free
Types of allocators
Explicit allocator: application allocates and frees space
E.g., malloc and free in C
Implicit allocator: application allocates, but does not free space
E.g. garbage collection in Python, Java, ML, and Lisp
Will discuss simple explicit memory allocation today
2

Carnegie Mellon
The malloc Package #include
void *malloc(size_t size)
Successful:
Returns a pointer to a memory block of at least size bytes
(typically) aligned to 8-byte boundary If size == 0, returns NULL
Unsuccessful: returns NULL (0) and sets errno
void free(void *p)
Returns the block pointed at by p to pool of available memory p must come from a previous call to malloc or realloc
Other functions
calloc: Version of malloc that initializes allocated block to zero. realloc: Changes the size of a previously allocated block.
sbrk: Used internally by allocators to grow or shrink the heap
3

Carnegie Mellon
malloc Example
void foo(int n, int m) {
int i, *p;
}
free(p);
/* Allocate a block of n ints */
p = (int *) malloc(n * sizeof(int));
if (p == NULL) {
}
perror(malloc);
exit(0);
/* Initialize allocated block */
for (i=0; i