代做comp3511、代写Python/Java编程

日期：2023-11-12 10:06

When accessing the logical address at <segment # = 2, offset = 400>, the results after

address translation is:

A) No such segment

B) Return address 4400

C) Invalid permission

D) Address out of range

9) In a system with 32-bit address, given the logical address 0x0000F1AE (in

hexadecimal) with a page size of 256 bytes, what is the page offset?

A) 0xAE

B) 0xF1

C) 0xA

D) 0xF100

10) A computer based on dynamic storage memory allocation has a main memory with

the capacity of 55MB (initially empty). A sequence of operations including main

memory allocation and release is as follows: 1. allocate 15MB; 2. allocate 30MB; 3.

release 15MB; 4. allocate 8MB; 5. allocate 6MB. Using the best-fit algorithm, what is the

size of the largest leftover hole in the main memory after the above five operations?

A) 7MB

B) 9MB

C) 10MB

D) 15MB

2. [20 points] Synchronization

You are asked to implement the second reader-writer solution, in which once a writer

is ready, it needs to perform update as soon as possible. There are two classes of

processes accessing shared data, readers and writers. Readers never modify data, thus

multiple readers can access the shared data simultaneously. Writers modify shared

data, so at most one writer can access data (no other writers or readers). This solution

gives priority to writers in the following manner: when a reader tries to access shared

data, if there is a writer accessing the data or if there are any writer(s) waiting to access

shared data, the reader must wait. In another word, readers must wait for all writer(s),

if any, to update shared data, or a reader can access shared data, only when there is no

writer either accessing or waiting.

The following variables will be used:

semaphore mutex =1; /* lock for accessing shared variables */

semaphore readerlock=0; /* readers waiting queue */

semaphore writerlock=0; /* writers waiting queue */

int R_count = 0; /* number of readers accessing data */

int W_count = 0; /* number of writer accessing data */

int WR_count = 0; /* number of readers waiting */

int WW_count = 0; /* number of writers waiting*/

TA Yixin YANG ( yyangfe@cse.ust.hk ) is responsible for questions before the deadline

TA Peng YE ( pyeac@cse.ust.hk ) is responsible for grading and appeal handling after the deadline

Please fill in the blanks to design Writer  s and Reader  s code.

Writer() {

// Writer tries to enter

wait(mutex);

while (BLANK1) { // Is it safe to write?

WW_count++;

BLANK2

WW_count--;

}

W_count++; // Writer inside

signal(mutex);

// Perform actual read/write access

// Writer finishes update

BLANK3

W_count--; // No longer active

if (BLANK4){ // Give priority to writers

signal(writerlock); // Wake up one writer

} else if (WR_count > 0) { // Otherwise, wake reader

BLANK5

}

signal(mutex);

}

Reader() {

// Reader tries to enter

wait(mutex);

while (BLANK6) { // writer inside or waiting?

BLANK7

wait(readerlock); // reader waits on readerlock

BLANK8

}

Rcount++; // Reader inside!

signal(mutex);

// Perform actual read-only access

// Reader finishes accessing

wait(mutex);

R_count--; // No longer active

if (BLANK9) // No other active readers

BLANK10

signal(mutex);

}

3. [30 points] Deadlocks

Consider the following snapshot of a system:

TA Yixin YANG ( yyangfe@cse.ust.hk ) is responsible for questions before the deadline

TA Peng YE ( pyeac@cse.ust.hk ) is responsible for grading and appeal handling after the deadline

Allocation Max Available

A B C D A B C D A B C D

P0 2 0 0 1 4 2 3 4 3 3 2 1

P1 3 1 2 1 5 2 3 2

P2 2 1 0 3 2 3 1 6

P3 1 3 1 2 1 4 2 4

P4 1 4 3 2 3 6 6 5

Please answer the following questions using the banker  s algorithm:

1) (5 points) What is the content of the matrix Need denoting the number of resources

needed by each process?

2) (10 points) Is the system in a safe state? Why?

3) (5 points) If a request from process P1 arrives for (1, 1, 0, 0), can the request be

4) (10 points) If a request from process P4 arrives for (0, 0, 2, 0), can the request be

granted immediately? Why?

TA Yixin YANG ( yyangfe@cse.ust.hk ) is responsible for questions before the deadline

TA Peng YE ( pyeac@cse.ust.hk ) is responsible for grading and appeal handling after the deadline

4. [30 points] Memory Management

1) (15 points) Consider the segment table shown in Table A. Translate each of the

virtual addresses in Table B into physical addresses. Indicate errors (out of range, no

such segment) if an address cannot be translated.

Table A

Segment number Starting address Segment length

0 260 90

1 1466 160

2 2656 130

3 146 50

4 2064 370

Table B

Segment number Offset

0 420

1 144

2 198

3 296

4 50

5 32

2) (15 points) Consider a virtual memory system providing 128 pages for each user

program; the size of each page is 8KB. The size of main memory is 256KB. Consider

one user program occupied 4 pages, and the page table of this program is shown as

below:

Logical page number Physical block number

TA Yixin YANG ( yyangfe@cse.ust.hk ) is responsible for questions before the deadline

TA Peng YE ( pyeac@cse.ust.hk ) is responsible for grading and appeal handling after the deadline

Assume there are three requests on logical address 040AFH, 140AFH, 240AFH. First

please describe the format of the logical address and the physical address. Then please

illustrate how the virtual memory system will deal with these requests.