Bissoy.com
Doctors Medicines MCQs Q&A

Consider the methods used by processes P1 and P2 for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S1 and S2 are randomly assigned. Method used by PI Method used by P2 While (S1 == S2); Critical Section S1 = S2; While (S1 != S2); Critical Section S2 = not (S1);   Which one of the following statements describes the properties achieved?

Consider the methods used by processes P1 and P2 for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S1 and S2 are randomly assigned. Method used by PI Method used by P2 While (S1 == S2); Critical Section S1 = S2; While (S1 != S2); Critical Section S2 = not (S1);   Which one of the following statements describes the properties achieved? Correct Answer Mutual exclusion but not progress

Key Points

The given mechanism is based on strict alternation, which guarantees always mutual exclusion and never progress.

In this mutual exclusion is satisfied because at any point of time either S1=S2 or S1 != S2, but not both. But here progress is not satisfied because suppose S1=1 and S2=0 and P1 is not interested to enter into the critical section but P2 wants to enter into the critical section, and P2 will not be able to enter, because until P1 will not enter the critical section, S1 will not become equal to S2. So if one process is not interested in entering the critical section, it will not allow the other process to enter the critical section which is interested. So progress is not satisfied.

Hence the correct answer is Mutual exclusion but not progress.

Related Questions

Two processes X and Y need to access a critical section. Consider the following synchronization construct used by both the processes Process ? /* other code for process ? */ while(true) { varP = true; while(varQ == true) { /* Critical Section */ varP = false; } } /* other code for process ?? */   Process ? /* other code for process ? */ while(true) { varQ = true; while(varP == true) { /* Critical Section */ varQ = false; } } /* other code for process ? */   Here, varP and varQ are shared variables and both are initialized to false. Which one of the following statements is true?
Consider the string abbccddeee. Each letter in the string must be assigned a binary code satisfying the following properties: 1. For any two letters, the code assigned to one letter must not be a prefix of the code assigned to the other letter. 2. For any two letters of the same frequency, the letter which occurs earlier in the dictionary order is assigned a code whose length is at most the length of the code assigned to the other letter. Among the set of all binary code assignments which satisfy the above two properties, what is the minimum length of the encoded string? 
Suppose we want to design a synchronous circuit that processes a string of 0’s and 1’s. Given a string, it produces another string by replacing the first 1 in any subsequence of consecutive 1’s by a 0. Consider the following example. Input sequence: 00100011000011100 Output sequence: 00000001000001100 A Mealy Machine is a state machine where both the next state and the output are functions of the present state and the current input. The above mentioned circuit can be designed as a two-state Mealy machine. The states in the Mealy machine can be represented using Boolean values 0 and 1. We denote the current state, the next state, the next incoming bit, and the output bit of the Mealy machine by the variables s, t, b and y respectively. Assume the initial state of the Mealy machine is 0. What are the Boolean expressions corresponding to t and y in terms of s and b ?
In the two sets given below, Set – I specifies the methods of research while Set – Il describes the critical feature associated with a method of research. Match the two and select from the code to indicate your answer.   Set – I  (Research method)    Set – II (Critical features associated) (a)    Experimental method  (i)  Generalizing to the population from a large sample (b)  Ex post facto method   (ii)   Establishing the patterns of events which have happened, through primary and secondary sources (c)  Historical method   (iii)   Studying shared behaviour patterns (d)  Ethnographic method   (iv)   Establishing cause and effect through control       (v)    Probing into the causal factors from the observed effects 
Consider the following solution to the producer-consumer synchronization problem. The shared buffer size is ?. Three semaphores empty, full and mutex are defined with respective initial values of 0, ? and 1. Semaphore empty denotes the number of available slots in the buffer, for the consumer to read from. Semaphore denotes the number of available slots in the buffer, for the producer to write to. The placeholder variables, denoted by P, Q, R, and S, in the code below can be assigned either empty or full. The valid semaphore operations are: wait ( ) and signal ( ). Producer: Consumer: do {         wait (P) ;         wait (mutex) ;         //Add item to buffer         signal (mutex) ;         signal (Q) ; } while (1) ; do {          wait (R) ;          wait (mutex) ;          //Consume item from buffer          signal (mutex) ;          signal (S) ; } while (1) ;   Which one of the following assignments to P, Q, R and S will yield the correct solution?
Which of the following statements regarding static methods are correct?
1. Static methods are difficult to maintain, because you can not change their implementation.
2. Static methods can be called using an object reference to an object of the class in which this method is defined.
3. Static methods are always public, because they are defined at class-level.
4. Static methods do not have direct access to non-static methods which are defined inside the same class.
Read the following sentences and choose the correct option. (i) Variables can only take discrete values while Attributes can take continuous values. (ii) Variables can only take continuous values while Attributes take discrete value. (iii) Attributes and variables are dependent on each other. (iv) Width of an impeller blade is a variable but no. of defective blades in a lot is an attribute.
Last year, there were three sections in a competitive exam. Out of them 33 students cleared the cut-off in Section A, 34 students cleared the cut-off in Section B and 32 students cleared the cut-off in Section C. 10 students cleared the cut-off in section A and section B, 9 cleared the cut-off in section B and section C and 8 cleared the cut-off in section A and section C. The number of students who cleared only one section was equal and was 21 for each section. How many students cleared all the three sections?
The question given below consists of a statement, followed by three arguments I, II and III. You have to decide which of the arguments is/are ‘strong’ arguments is/are ‘weak’ arguments and accordingly choose your answer from the alternatives given below each question. Statement: Chat bots and other interfaces are saving employees and HR heads time for more productive activities by providing information and replies to diverse queries or concerns. A few years ago, business communication was driven by multiple faxes in a day and emails were the only quick mode of exchanging information. This information went through the organisation's who's who, while the others were mostly engaged in the daily rut of redundant activities, preventing them from directing their capabilities towards more productive areas. Which of the following arguments brig out the idea that introduction of chat bots and other interfaces is not helping in boosting up the processes? Arguments: I. Using these conversational interfaces, HR departments are successfully aligning themselves with the swiftly-changing organisational processes. These platforms represent people friendly technologies that keep employee experience at the centre, continuously evolving with them.  II. HR technologies are increasingly using advanced machine learning for measuring and analysing workforce engagement. Sentiment analysis is a unique way of gauging an employee's disposition towards the organisation, providing valuable insights essential for improving productivity and predicting attrition rates.  III. The seamless experience chat bots provide makes employees focus on activities that require critical abilities and strategic thinking. Besides enabling HR processes such as generating leave applications and reimbursement forms, the use of chatbots provides quick and smooth access to data from anywhere, anytime.  
interface Base{ boolean m1 (); byte m2(short s);}

which two code fragments will compile?
1. interface Base2 implements Base {}2. abstract class Class2 extends Base { public boolean m1(){ return true; }}3. abstract class Class2 implements Base {}4. abstract class Class2 implements Base { public boolean m1(){ return (7 > 4); }}5. abstract class Class2 implements Base { protected boolean m1(){ return (5 > 7) }}