A university assigns student IDs of the form 1, 2, 3, . such that if n students are currently enrolled, then the next •.. student to enroll will receive and ID of n + 1. Consider the following algorithm that accomplishes this. // Global variable storing number of students currently enrolled current_student_count = 0 // Function that reads the above global variable, calculates new ID, and increments the global count assign_new_id(: count = current_student_count new_id = count + 1 current_student_count = count +1 return new_id (a) If two different threads run the above code in parallel to enroll two different students, it is possible for the two students to receive the same ID, and for the current_student_count to have a wrong value. Explain how this is possible. (b) Modify the code above so that the problem in (a) does not happen. 5:22 PM

Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Question
A university assigns student IDs of the
form 1, 2, 3, ... such that if n students
are currently enrolled, then the next
student to enroll will receive and ID of n
+ 1. Consider the following algorithm
that accomplishes this.
// Global variable storing number of
students currently enrolled
current_student_count = 0
// Function that reads the above global
variable, calculates new ID, and
increments the global count
assign_new_id():
count = current_student_count
new_id = count + 1
current_student_count = count + 1
return new_id
(a) If two different threads run the above
code in parallel to enroll two different
students, it is possible for the two
students to receive the same ID, and for
the current_student_count to have a
wrong value. Explain how this is
possible.
(b) Modify the code above so that the
problem in (a) does not happen. 5:22 PM
Transcribed Image Text:A university assigns student IDs of the form 1, 2, 3, ... such that if n students are currently enrolled, then the next student to enroll will receive and ID of n + 1. Consider the following algorithm that accomplishes this. // Global variable storing number of students currently enrolled current_student_count = 0 // Function that reads the above global variable, calculates new ID, and increments the global count assign_new_id(): count = current_student_count new_id = count + 1 current_student_count = count + 1 return new_id (a) If two different threads run the above code in parallel to enroll two different students, it is possible for the two students to receive the same ID, and for the current_student_count to have a wrong value. Explain how this is possible. (b) Modify the code above so that the problem in (a) does not happen. 5:22 PM
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