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CSCE-313

Fall 2016

Machine Problem 1: A High Performance Linked List
(Due: Before lab meeting in week 2)

Introduction:
In a traditional implementation of a linked list, memory is allocated for each newly
inserted item. When an item on this list is deleted, the memory allocated for it is freed
and given back to the operating system. Consequently, each allocation/de-allocation
request for insertions or deletions respectively involves interacting with the operating
system’s memory manager. System calls have a large overhead associated with them.
The processor must stop the execution of the user process, switch to executing system
code, spend time performing the requested system function, and as such, the calls to the
memory manager hinder the performance of the linked list. In this assignment, we will
explore a solution to this problem which will produce a high performance and efficient
implementation of a linked list.
In this assignment, the program you create will serve as the memory manager instead of
relying on the operating system to do the dirty work. Your program should obtain/reserve a fixed amount of memory from the operating system’s memory manager during
initialization (this is done by calling either malloc or new). After initially acquiring memory from the system, your program should use this memory to manage the linked list
throughout its execution. Consequently, extraneous and expensive calls to the system’s
memory manager will no longer be necessary.
Each element of the linked list occupies a specific amount of space, known as the basic
block size and denoted by the variable b. The memory size as a whole is determined by
the parameter m. As such, there can be at most m/b elements in the list. Any insertion
requests that would attempt to insert more than m/b elements into the list should be
immediately rejected.
The list should be managed through a Head Pointer (HP) and a Free Pointer (FP). The
former points to the head of the list, and the latter points to where the next insertion
should happen.
Each linked list item can be separated into two sections: a header and a payload. The
header contains necessary information for maintaining the list (i.e. the next pointer, the
previous pointer (for doubly linked lists), other metadata, etc...). The payload portion
consists of a key-value pair. The key is a 4 byte integer, and the value is of variable
length, but has a maximum size that is determined by the header and key size.
Figure #1 visually demonstrates how a singly linked list should be organized. In the top
1

CSCE-313

Fall 2016

of the figure, a linked list item is shown in detail. Note that the size of pointers depend
on the machine/OS type (i.e. in a 64-bit machine, pointers are 8-bytes as opposed to the
4-byte pointers present in 32-bit machines).
Figure #1: Structural view of a linked list in memory
Header
Next Ptr
(8B)

Payload

Key(4B)

Value
Value (rest)
Len (4B)
b

Linked List
Head

Free Pointer
(FP)
Memory Pool (MP)

H

P

H

P

H

P

M

Assignment:
You are to implement a singly-linked list with the mentioned features in C/C++.
• There should be 3 files in your program: main.c/cpp, linked list.h, and linked list.c/cpp.
A sample main file will be provided for you to finish.
• Your implementation should contain at least the following functions (declared in
the .h file and defined in the .c/.cpp file).
v o i d I n i t ( i n t M, i n t C) ; /∗ I n i t i a l l y o b t a i n s M b y t e s o f memory by
c a l l i n g t h e s t a n d a r d l i b r a r y f u n c t i o n m a l l o c ( ) and i n i t i a l i z e s t h e
l i n k e d l i s t ∗/
v o i d Destr o y ( ) ; /∗ D e s t r o y s t h e l i n k e d l i s t and r e t u r n s memory t o t h e
system by c a l l i n g a n o t h e r l i b r a r y f u n c t i o n , f r e e ( ) . ∗/
i n t I n s e r t ( i n t x , cha r ∗ v a l u e p t r , i n t v a l u e
key−v a l u e p a i r , where t h e key i s an i n t e g e r ,
da ta p o i n t e d t o by t h e p o i n t e r v a l u e \ p t r o f
s h o u l d use t h e l i b r a r y f u n c t i o n , memcpy ( ) t o

l e n ) ; /∗ I n s e r t s a
x , and t h e v a l u e i s some
l e n g t h v a l u e \ l e n . You
copy t h e v a l u e . ∗/

v o i d D e l e t e ( i n t x ) ; /∗ D e l e t e s t h e f i r s t item from t h e b e g i n n i n g with
t h e key x . ∗/
cha r ∗ Lookup ( i n t x ) ; /∗ Finds t h e g i v e n key i n a l i s t and r e t u r n s a
p o i n t e r t o t h e f i r s t o c c u r r e n c e o f t h a t key . ∗/
v o i d P r i n t L i s t ( ) ; /∗ P r i n t s out a l l t h e i t e m s ’ key−v a l u e p a i r s

2

CSCE-313

Fall 2016

s e q u e n t i a l l y s t a r t i n g from t h e head o f t h e l i s t . P r i n t o n l y t h e key
and t h e va lue −l e n g t h . Do not p r i n t t h e a c t u a l v a l u e a s i t c o u l d
c o n t a i n b i n a r y /non−p r i n t a b l e da ta . ∗/

• Your implementation should include a program called testlist which reads the basic
block size and the memory size (in bytes) from the command line, initializes the
memory, makes some insertion/deletion calls, prints the list using the PrintList()
function, and then destroys the allocated memory using Destroy(). Note that all
these calls should go inside testlist’s main function.
• Use the getopt() C library function to parse the command line for arguments. The
usage for your program should be as follows:
./testlist [-b <blocksize>] [-s <memsize>]
-b <blocksize> Defines the basic block size, b, in bytes. Default = 128 bytes
-s <memsize> Defines size of memory allocated in bytes. Default = 512 kB
• Make sure that your program does not crash in any case. Here are a number
of scenarios that your program should account for. In these cases, your program
should simply print an errir, skip the given instrution, and continue to work (i.e. do
not exit for any reason).
– Deleting non-existent keys from the list.
– Trying to insert keys after the given memory is full.
– Trying to insert values that do not fit in the payload section.

Report Documentation
Provide a PDF report describing your findings and answering all the following questions.
Do you notice any wastage of memory when items are deleted? If so, can your program
avoid such wastage? How would you do so? Can you think of a scenario where there
is space in the memory but no insertion is possible? What is the maximum size of the
value when the pointers are 8 bytes?
Submission Instructions
Submit a zipped folder containing your code and the PDF report named MP1.pdf. There
should be 3 c/cpp/h files: linked list.h, linked list.c/cpp, and main.c/cpp. Demonstrate your work during lab meetings. Make sure that your program runs on one of
the CSE department’s linux servers (e.g., linux2.cse.tamu.edu, compute.cse.tamu.edu,
build.tamu.edu). Remember that we are using a new platform Vocareum (available at
vocareum.com) for submitting machine problems. Please register as a student on this
website, play around with it, and become familiar with it so that there will be no issues
before the assignment’s deadline. Please don’t be afraid to talk to your TA or instructor
if you have any issues.
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