6CHAPTERProcessSynchronizationPractice Exercises61In Section 64 We Mentioned
6
CHAPTER
Process
Synchronization
Practice Exercises
6.1
In Section 6.4, we mentioned that disabling interrupts frequently can affect the system’s clock. Explain why this can occur and how such effects can be minimized.
Answer:
The system clock is updated at every clock interrupt. If interrupts were disabled —particularly for a long period of time —it is possible the system clock could easily lose the correct time. The system clock is also used for scheduling purposes. For example, the time quantum for a process is expressed as a number of clock ticks. At every clock interrupt, the scheduler determines if the time quantum for the currently running process has expired. If clock interrupts were disabled, the scheduler could not accurately assign time quantums. This effect can be minimized by disabling clock interrupts for only very short periods.
6.2
The Cigarette-Smokers Problem. Consider a system with three smoker processes and one agent process. Each smoker continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker needs three ingredients: tobacco, paper, and matches. One of the smoker processes has paper, another has tobacco, and the third has matches. The agent has an infinite supply of all three materials. The agent places two of the ingredients on the table. The smoker who has the remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The agent then puts out another two of the three ingredients, and the cycle repeats. Write a program to synchronize the agent and the smokers using Java synchronization.
Answer:
Please refer to the supporting Web site for source code solution. 6.3
Explain why Solaris, Windows XP, and Linux implement multiple locking mechanisms. Describe the circumstances under which they use spinlocks, mutexes, semaphores, adaptive mutexes, and condition variables.
In each case, explain why the mechanism is needed.
Answer: These operating systems provide different
CHAPTER
Process
Synchronization
Practice Exercises
6.1
In Section 6.4, we mentioned that disabling interrupts frequently can affect the system’s clock. Explain why this can occur and how such effects can be minimized.
Answer:
The system clock is updated at every clock interrupt. If interrupts were disabled —particularly for a long period of time —it is possible the system clock could easily lose the correct time. The system clock is also used for scheduling purposes. For example, the time quantum for a process is expressed as a number of clock ticks. At every clock interrupt, the scheduler determines if the time quantum for the currently running process has expired. If clock interrupts were disabled, the scheduler could not accurately assign time quantums. This effect can be minimized by disabling clock interrupts for only very short periods.
6.2
The Cigarette-Smokers Problem. Consider a system with three smoker processes and one agent process. Each smoker continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker needs three ingredients: tobacco, paper, and matches. One of the smoker processes has paper, another has tobacco, and the third has matches. The agent has an infinite supply of all three materials. The agent places two of the ingredients on the table. The smoker who has the remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The agent then puts out another two of the three ingredients, and the cycle repeats. Write a program to synchronize the agent and the smokers using Java synchronization.
Answer:
Please refer to the supporting Web site for source code solution. 6.3
Explain why Solaris, Windows XP, and Linux implement multiple locking mechanisms. Describe the circumstances under which they use spinlocks, mutexes, semaphores, adaptive mutexes, and condition variables.
In each case, explain why the mechanism is needed.
Answer: These operating systems provide different