A Short Digression Stacks and Heaps

1 / 21

A Short Digression Stacks and Heaps - PowerPoint PPT Presentation

A Short Digression Stacks and Heaps. CS-502, Operating Systems Fall 2007 (Slides include materials from Operating System Concepts , 7 th ed., by Silbershatz, Galvin, & Gagne and from Modern Operating Systems , 2 nd ed., by Tanenbaum). Digression: the “Stack”.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

PowerPoint Slideshow about 'A Short Digression Stacks and Heaps' - keilah

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

A Short DigressionStacks and Heaps

CS-502, Operating SystemsFall 2007

(Slides include materials from Operating System Concepts, 7th ed., by Silbershatz, Galvin, & Gagne and from Modern Operating Systems, 2nd ed., by Tanenbaum)

Stacks and Heaps

Digression: the “Stack”
• Imagine the following program:–

int factorial(int n){

if (n <= 1)

return (1);

else

int y = factorial(n-1);

return (y * n);

}

• Imagine also the caller:–

int x = factorial(100);

• What does compiled code look like?

Stacks and Heaps

Compiled code: the caller

int x = factorial(100);

• Put the value “100” somewhere that factorial can find
• Put the current program counter somewhere so that factorial can return to the right place in caller
• Provide a place to put the result, so that caller can find it

Stacks and Heaps

Compiled code: factorial function
• Save the caller’s registers somewhere
• Get the argument n from the agreed-upon place
• Set aside some memory for local variables and intermediate results – i.e., y, n - 1
• Do whatever it was programmed to do
• Put the result where the caller can find it
• Restore the caller’s registers
• Transfer back to the program counter saved by the caller

Stacks and Heaps

Question: Where is “somewhere”?
• So that caller can provide as many arguments as needed (within reason)?
• So that called routine can decide at run-time how much temporary space is needed?
• So that called routine can call any other routine, potentially recursively?

Stacks and Heaps

• Stack – a linear data structure in which items are added and removed in last-in, first-out order.
• Calling program
• Push arguments & return address onto stack
• After return, pop result off stack

Stacks and Heaps

“Stack” (continued)
• Called routine
• Push registers and return address onto stack
• Push temporary storage space onto stack
• Do work of the routine
• Pop registers and temporary storage off stack
• Leave result on stack

Stacks and Heaps

Stack (continued)
• Definition: context – the region of the stack that provides the execution environment of a particular call to a function
• Implementation
• Usually, a linear piece of memory and a stack pointer contained in a (fixed) register
• Recursion
• Stack discipline allows multiple contexts for the same function in the stack at the same time

Stacks and Heaps

Stacks in Modern Systems
• All modern programming languages require a stack
• Fortran and Cobol did not (non-recursive)
• All modern processors provide a designated stack pointer register
• All modern process address spaces provide room for a stack
• Able to grow to a large size
• May grow upward or downward

Stacks and Heaps

0xFFFFFFFF

stack

(dynamically allocated)

SP

heap

(dynamically allocated)

Virtual

static data

program code

(text)

PC

0x00000000

Stacks and Heaps

• Every thread requires its own stack
• Separate from all other stacks
• Each stack may grow separately
• Address space must be big enough to accommodate stacks for all threads

Stacks and Heaps

SP (T1)

0xFFFFFFFF

SP

SP (T2)

SP (T3)

Virtual

heap

static data

0x00000000

PC

code

(text)

PC (T2)

PC (T1)

PC (T3)

Stacks and Heaps

• Every thread requires its own stack
• Separate from all other stacks
• Each stack may grow separately
• Address space must be big enough to accommodate stacks for all threads
• Some small or RT operating systems are equivalent to multi-threaded environments

Stacks and Heaps

Heap
• A place for allocating memory that is not part of last-in, first-out discipline
• I.e., dynamically allocated data structures that survive function calls
• E.g., strings in C
• new objects in C++, Java, etc.

Stacks and Heaps

0xFFFFFFFF

stack

(dynamically allocated)

SP

heap

(dynamically allocated)

Virtual

static data

program code

(text)

PC

0x00000000

Stacks and Heaps

Dynamically Allocating from Heap
• malloc() – POSIX standard function
• Allocates a chunk of memory of desired size
• Remembers size
• Returns pointer
• free () – POSIX standard function
• Returns previously allocated chunk to heap for reallocation
• Assumes that pointer is correct!

Stacks and Heaps

Dynamically Allocating from Heap
• malloc() – POSIX standard function
• Allocates a chunk of memory of desired size
• Remembers size
• Returns pointer
• free () – POSIX standard function
• Returns previously allocated chunk to heap for reallocation
• Assumes that pointer is correct!
• Storage leak – failure to free something

Stacks and Heaps

Heaps in Modern Systems
• Many modern programming languages require a heap
• C++, Java, etc.
• NOT Fortran
• Typical process environment
• Grows toward stack
• All threads share the same heap
• Data structures may be passed from one thread to another.

Stacks and Heaps

SP (T1)

0xFFFFFFFF

SP

SP (T2)

SP (T3)

Virtual

heap

static data

0x00000000

PC

code

(text)

PC (T2)

PC (T1)

PC (T3)

Stacks and Heaps

SP (T1)

0xFFFFFFFF

SP

SP (T2)

SP (T3)

Virtual

heap

static data

0x00000000

PC

code

(text)

PC (T2)

PC (T1)

PC (T3)

Stacks and Heaps

Stacks and Heaps