Students who want to enroll in Model Railroading II at the...

Students who want to enroll in Model Railroading II at the local university are required to obtain permission from the instructor and pay a laboratory fee. The two requirements are fulfilled independently in either order and at different locations on campus, Enrollment is limited to 20 students; this limit is maintained by both the instructor, who will grant permission to only 20 students, and the financial office, which will allow only 20 students to pay the laboratory fee. Suppose that this registration system has resulted in 19 students having successfully registered for the course, but with the final space being claimed by two students-one who has only obtained permission from the instructor and another who has only paid the fee. Which requirement for deadlock is removed by each of the following solutions to the problem? a. Both students are allowed in the course. b. The class size is reduced to $19,$ so neither of the two students is allowed to register for the course. c. The competing students are both denied entry to the class and a third student is given the twentieth space. d. It is decided that the only requirement for entry into the course is the payment of the fee. Thus the student who has paid the fee gets into the course, and entry is denied to the other student.

Students who want to enroll in Model Railroading II at the local university are required to obtain permission from the instructor and pay a laboratory fee. The two requirements are fulfilled independently in either order and at different locations on campus, Enrollment is limited to 20 students; this limit is maintained by both the instructor, who will grant permission to only 20 students, and the financial office, which will allow only 20 students to pay the laboratory fee. Suppose that this registration system has resulted in 19 students having successfully registered for the course, but with the final space being claimed by two students-one who has only obtained permission from the instructor and another who has only paid the fee. Which requirement for deadlock is removed by each of the following solutions to the problem?
a. Both students are allowed in the course.
b. The class size is reduced to $19,$ so neither of the two students is allowed to register for the course.
c. The competing students are both denied entry to the class and a third student is given the twentieth space.
d. It is decided that the only requirement for entry into the course is the payment of the fee. Thus the student who has paid the fee gets into the course, and entry is denied to the other student.

Key Concepts

Mutual Exclusion

This concept means that resources are held in a non?sharable mode; only one process can use a given resource at a time. In the context of the registration system, if a course seat (or any resource) is allowed to be shared by more than one student, then the exclusive allocation requirement is relaxed. Hence, a solution that permits both students to register undermines the mutual exclusion condition, one of the necessary conditions for deadlock.

Hold and Wait

The hold and wait condition is present when a process is holding at least one resource while waiting to obtain additional resources that are currently being held by other processes. In a registration system where students complete requirements sequentially, a student may hold one credential (like instructor permission) and wait for another (like fee payment). By reducing the class capacity such that neither of the two partially?registered students is allowed to complete registration, the system prevents the scenario in which a student holds one resource and waits for another, thereby removing the hold and wait condition.

No Preemption

The no preemption condition states that resources cannot be forcibly removed from a process that is holding them; they must be released voluntarily. In the scenario where both competing students are denied entry after holding one of the required credentials, the system effectively takes away the held resource (or invalidates it) and assigns the final slot to another student. By preempting the resources already in the hands of the deadlocking processes, the no preemption condition is removed.

Circular Wait

Circular wait is the condition where a set of processes are waiting for each other in a circular chain, with each process holding at least one resource needed by the next process in the chain. In the registration example, the circular wait condition can occur when one student holds the instructor’s permission and waits for the fee payment while another holds the fee payment and waits for the permission. By eliminating one of the required conditions – for example, by eliminating the need for instructor permission and making the fee the sole requirement – the cycle is broken and circular wait is removed.

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