CMPSCI 377 Operating Systems Fall 2005
Lecture 14: November 10
Lecturer: Emery Berger Scribe: Eric Hodge, Eric Patrick
Today:
•Memory Management
14.1 Memory Management
14.1.1 Introduction
- Not memory management in kernel, but memory management between app and
OS - the ”run time system.”
- Java runs in virtual machine (in run time system.)
- C/C++ runs in libraries (libc.so, libc++.so)
- Explicit memory management (c / c++)
- Garbage collection (Java, Python, Perl)
14.1.2 Explicit Memory Management
- One of the oldest fields in computer science
- Must say explicitly what you want to do with memory (ask for it.)
- Malloc (size) - returns a pointer to space big enough for size bytes.
- Calloc (size, times) - multiplies size * times, also fills memory with zeros.
- Realloc (old obj, size) - reallocates old object to a chunk of memory of size.
- realloc (null, sz) = malloc(sz)
- Realloc ( p, 0) = free(p)
- Min size returned by malloc = 8 bytes, sizeof (double) ==8 bytes
- Free(ptr) - dispose of object.
- Takes object at ptr and gives it back to runtime system.
- If you don’t free your objects, you get a memory leak.
- Things slow down due to paging.
realloc(NULL, size) == malloc(size)
realloc(p,0) == free(p)
14.1.3 Errors Involved in Memory Management
Dangling Pointer Error:
P = malloc()
x=p
14-1
