Question

Since each area on a computer's display can be used by only one process at a time (otherwise the image on the screen would be unreadable), these areas are nonshareable resources that are allocated by the window manager. Which of the three conditions necessary for deadlock does the window manager remove in order to avoid deadlock?

Short answer

The window manager removes the 'hold and wait' condition to avoid deadlock.

Step-by-step solution

Identify the Three Necessary Conditions for Deadlock

To solve this problem, we need to recognize the three necessary conditions for a deadlock to occur in a system: mutual exclusion, hold and wait, and no preemption. Mutual exclusion means that resources cannot be shared among multiple processes simultaneously. Hold and wait allows processes holding resources to also request additional ones. No preemption means that resources cannot be forcibly taken from processes; they must be released voluntarily by the holding process.

Determine Which Condition the Window Manager Controls

The window manager allocates display areas, which are nonshareable resources. By its role, it primarily controls the allocation and request process of these areas. It cannot change 'mutual exclusion', as only one process can use a display area at a time. Also, it cannot force processes to release resources, so it does not control 'no preemption'.

Analyze How the Window Manager Removes Deadlock Conditions

The window manager can prevent 'hold and wait' by making sure that a process can only obtain a display area if it does not currently hold any other resources, or by requiring that a process requests and is granted all needed resources before it begins execution.

Key concepts

Mutual Exclusion

Mutual exclusion is a fundamental concept that can lead to the occurrence of a deadlock. This term describes a situation where particular resources cannot be shared among different processes simultaneously. In essence, only one process can be in possession of a nonshareable resource at any one time.

Imagine this like wanting to watch a movie, but you have only one seat available in the cinema. Only one person can sit in that seat at a time, similar to how only one process can utilize a specific resource, like a display area, at once. This necessity for resources to be used exclusively is unavoidable in the context of a window manager managing display areas.

Unfortunately, mutual exclusion is a condition that cannot be eliminated by the window manager. This is because the essential capability of these display areas is that they must be used individually to ensure the image remains clear and readable.

• Mutual exclusion places one process in control of resources. Its essential nature helps manage resources effectively but can lead to potential deadlocks if not managed cautiously.
• Typically, it's required for ensuring resources are handled correctly and data integrity is maintained when processes access shared resources.

Hold and Wait

Hold and wait is another condition that can contribute to deadlock. This condition occurs when processes that already have certain resources hold them while they wait to acquire more resources that are currently being used by others.

Consider it like a person who occupies a computer station in a library while they wait for another computer station to become available. They effectively lock up two resources, leading to inefficiencies and potential conflicts.

The window manager can mitigate this condition by ensuring that processes do not hold onto one resource while waiting for another. For example, a strategy could be implemented where a process is only granted a display area if it doesn't hold any other resources, or it must request all needed resources upfront before starting.

• By avoiding hold-and-wait conditions, systems can significantly reduce the chance of falling into a state of deadlock.
• This prevention ensures smoother and more effective processing by minimizing resource contention and potential deadlock scenarios.

No Preemption

No preemption is a condition in which resources cannot be forcibly taken from a process. Instead, they must be released willingly by the process that currently holds them.

This concept is like lending a book from a library, where you must return it willingly when you're done, rather than having it taken forcibly.

In the scenario of managing display areas, the window manager cannot forcibly take these areas from a process. This implies that if a process has been allocated a screen display, it holds onto it until it chooses to release it, further cementing the no preemption condition as a critical aspect that can lead to deadlock.However, no preemption is not controlled by the window manager because it cannot force a process to relinquish its resource.

• Without the ability to preempt resources, systems need to carefully orchestrate resource allocation to avoid deadlock.
• The lack of preemption requires proactive resource management to maintain process flow and efficiency.