🔬 Lab
CS 240 Lab 12
Learning Goals & Reflection
CS 240 Lab 12
- Lab slides
- Malloc assignment
- There is no notebook for today’s lab
Learning Goals
Core Goals
Students can:
- Explain how allocated memory blocks are tracked in the heap:
(
)
- Explain the minimum block size as well as the sizes of headers and footers.
- Explain what is stored in headers/footers and the purpose of storing this information in relation to the allocation algorithm.
- Explain how the requested size in bytes is related to the actually allocated block size.
- Explain how the free and previous-free flags are stored “on top of” the size, and why this is possible without corrupting the size information.
- Simulate the behavior of various heap allocation algorithms:
(
)
- Draw heap diagrams showing free/allocated blocks along with appropriate meta-information, given a description of the heap state.
- Draw heap diagrams that result from a specific sequence of allocate and/or free operations, for the provided starter code.
- Draw heap diagrams based on allocation sequences for the correct solution code (without having implemented that code yet).
- Read C code to understand what it does:
(
)
- Recognize code for rounding and alignment of values.
- Explain how the
|
operator in C can be used to combine multiple “flag bits” into a single value, what a “flag bit” can represent, and what numerical values “flag bits” have. - Explain how allocated bits and block sizes are combined into a single value, and how they can be split apart again.
- Explain the operation of helper functions that abstract common memory manipulation tasks.
- Explain the mechanics of allocating and freeing memory on the heap:
(
)
- Explain what changes are necessary to allocate part or all of a free block.
- Explain what changes are necessary to free an allocated block.
- Explain how fragmentation can occur and why different allocation strategies might affect how bad it gets.
Stretch goals
- Explain how allocated memory blocks are tracked in the heap:
(
)
- Explain why alignment requirements cause us to skip 8 bytes at the start of the heap.
- Explain how the restrictions on heap block sizes are related to the alignment requirement.
- Read C code to understand what it does:
(
)
- Explain why we did not use a C
struct
to describe a heap entry.
- Explain why we did not use a C
- Write pseudocode comments to design an algorithm before implementing
it:
(
)
- Concisely describe memory changes at an abstract level referring to heap blocks and allocated/free statuses.
- Plan out the steps needed to implement
malloc
,free
, and theallocate
&coalesce
helper functions.
Extra goals
- Understand how memory allocation connects to higher-level languages:
(
)
- Explain why writing Java code that uses primitive types instead of Object types can be faster in some cases.
- Explain why one creating one large object/array to store data and using math to compute offsets within it can be faster than creating many small objects (e.g., using a 1-D list in Python for 2- or 3D information rather than a list-of-lists).
- Explain the dangers of premature optimization in terms of both development time/effort and code correctness.
Reflection
Note: Make sure to use the ‘print’ dialog to save this page as a PDF when you’re done.
I’m most confident in (list a few):
I’m least confident in (list a few):
Questions (please take the time to ask at least one, thinking of a question will help you cement what you’ve learned):