Safety Algorithm – It is a safety algorithm used to check whether or not a system is in a safe state or follows the safe sequence in a banker’s algorithm: 1. There are two vectors Wok and Finish of length m and n in a safety algorithm.
- Initialize: Work = Available Finish = false; for I = 0, 1, 2, 3, 4 n – 1.
- 2. Check the availability status for each type of resources, such as:
- Need <= Work Finish == false
- If the i does not exist, go to step 4.
- 3. Work = Work +Allocation(i) // to get new resource allocation
- Finish = true
- Go to step 2 to check the status of resource availability for the next process.
4. If Finish == true; it means that the system is safe for all processes.
- 1 What is Banker’s algorithm in OS?
- 2 What are the 3 ways to prevent deadlock?
- 3 Which technique is used to prevent the deadlock in OS?
- 4 Is bankers algorithm used for deadlock?
- 5 What are the 4 conditions for deadlock?
- 6 What are the two options for breaking a deadlock?
- 7 Which is Banker’s algorithm for deadlock prevention?
What are the safety algorithms for deadlock detection?
The Banker’s Algorithm is a deadlock avoidance and resource allocation algorithm. It determines if allocating a resource will cause a deadlock or whether allocating a resource to a process is safe, and if not, the resource is not assigned to that process.
What is Banker’s algorithm in OS?
Frequently Asked Questions(FAQs) – Below are some FAQs on Bankers Algorithm in OS 1. How does the Bankers Algorithm in OS work? The Bankers Algorithm in OS works by maintaining a matrix of maximum and allocated resources for each process, and then checking if the system is in a safe state before allowing a process to request additional resources.
The algorithm checks if the request can be granted without compromising the safety of the system, by ensuring that the request does not cause a process to exceed its maximum resource needs and that there are enough resources available to grant the request.2. What are the key components of the Bankers Algorithm? The key components of the Bankers Algorithm in OS include the allocation matrix, the maximum matrix, the need matrix, the available vector, and the work vector.
The allocation matrix represents the resources that are currently allocated to each process, the maximum matrix represents the maximum resources required by each process, the need matrix represents the resources still needed by each process, the available vector represents the resources that are currently available, and the work vector is used to keep track of the available resources during the algorithm’s execution.3.
What is a safe state in the context of the Bankers Algorithm? A safe state in the context of the Bankers Algorithm in OS is a state in which there exists a sequence of processes such that each process can be completed without encountering deadlocks. In other words, it is a state in which all processes can be executed to completion without any deadlocks or resource starvation.4.
What is an unsafe state in the context of the Bankers Algorithm? An unsafe state in the context of the Bankers Algorithm in OS is a state in which the execution of processes may result in deadlocks or resource starvation. In an unsafe state, processes may be blocked waiting for resources that will never become available, resulting in a deadlock.
Which algorithm is used to find safe state of the processes?
Banker’s algorithm Algorithm used for program correctness Banker’s algorithm is a and avoidance developed by that tests for safety by simulating the allocation of predetermined maximum possible amounts of all, and then makes an “s-state” check to test for possible deadlock conditions for all other pending activities, before deciding whether allocation should be allowed to continue.
- The algorithm was developed in the design process for the and originally described (in ) in EWD108.
- When a new process enters a system, it must declare the maximum number of instances of each resource type that it may ever claim; clearly, that number may not exceed the total number of resources in the system.
Also, when a process gets all its requested resources it must return them in a finite amount of time.
What are the 3 ways to prevent deadlock?
- Deadlock can be prevented by eliminating any of the four necessary conditions, which are mutual exclusion, hold and wait, no preemption, and circular wait.
- Mutual exclusion, hold and wait and no preemption cannot be violated practically.
- Circular wait can be feasibly eliminated by assigning a priority to each resource. The request is granted if the process requests a resource of higher priority than the resources it currently holds.
Which technique is used to prevent the deadlock in OS?
Conclusion – In conclusion, preventing deadlocks is crucial for ensuring the smooth operation and optimal performance of computer systems. The techniques used for preventing deadlocks, such as resource allocation graph, preemptive scheduling, and detection and recovery, help in identifying and avoiding potential deadlocks.
By adopting appropriate deadlock prevention techniques, computer systems can improve their efficiency, reduce delays, and avoid the risk of system failure caused by deadlocks. The prevention of deadlocks is an ongoing challenge for computer scientists, and as technology evolves, new techniques and approaches may need to be developed to keep pace with changing demands and requirements of modern computing systems.
: Deadlock prevention
Is bankers algorithm used for deadlock?
What is Banker’s algorithm? In the last blog, we have discussed four i.e. deadlock prevention, deadlock avoidance, deadlock detection and recovery, and deadlock ignorance. In this blog, we will learn about one of the deadlock avoidance strategies i.e. banker’s algorithm,
- So, let’s get started.
- Banker’s Algorithm is a deadlock avoidance algorithm,
- It is also used for deadlock detection.
- This algorithm tells that if any system can go into a deadlock or not by analyzing the currently allocated resources and the resources required by it in the future.
- There are various data structures which are used to implement this algorithm.
So, let’s learn about these first.
- Available: It is a 1-D array that tells the number of each resource type (instance of resource type) currently available. Example: Available= A, means that there are A instances of R1 resources are currently available.
- Max: It is a 2-D array that tells the maximum number of each resource type required by a process for successful execution. Example: Max = A, specifies that the process P1 needs a maximum of A instances of resource R1 for complete execution.
- Allocation: It is a 2-D array that tells the number of types of each resource type that has been allocated to the process. Example: Allocation = A, means that A instances of resource type R1 have been allocated to the process P1.
- Need: It is a 2-D array that tells the number of remaining instances of each resource type required for execution. Example: Need= A tells that A instances of R1 resource type are required for the execution of process P1.
Need= Max – Allocation, where i corresponds any process P(i) and j corresponds to any resouce type R(j) The Bankers Algorithm consists of the following two algorithms
- Request-Resource Algorithm
- Safety Algorithm
Whenever a process makes a request of the resources then this algorithm checks that if the resource can be allocated or not. It includes three steps:
- The algorithm checks that if the request made is valid or not. A request is valid if the number of requested resources of each resource type is less than the Need( which was declared previously by the process ). If it is a valid request then step 2 is executed else aborted.
- Here, the algorithm checks that if the number of requested instances of each resource is less than the available resources. If not then the process has to wait until sufficient resources are available else go to step 3.
- Now, the algorithm assumes that the resources have been allocated and modifies the data structure accordingly.
Available = Available – Request(i) Allocation(i) = Allocation(i) + Request(i) Need(i) = Need(i) – Request(i) After the allocation of resources, the new state formed may or may not be a safe state. So, the safety algorithm is applied to check whether the resulting state is a safe state or not.
- If it is a safe state, then the requested resources are allocated to the process in actual.
- If the resulting state is an unsafe state then it rollbacks to the previous state and the process is asked to wait longer.
The safety algorithm is applied to check whether a state is in a safe state or not. This algorithm involves the following four steps:
Suppose currently all the processes are to be executed. Define two data structures as work and finish as vectors of length m(where m is the length of Available vector)and n(is the number of processes to be executed).
Work = Available Finish =false for i = 0, 1,, n — 1.2. This algorithm will look for a process that has Need value less than or equal to the Work, So, in this step, we will find an index i such that Finish ==false && Need<= Work If no such ‘i' is present then go to step 4 else to step 3.3. The process ' i' selected in the above step runs and finishes its execution. Also, the resources allocated to it gets free. The resources which get free are added to the Work and Finish(i) of the process is set as true. The following operations are performed: Work = Work + Allocation Finish = true After performing the 3rd step go to step 2.4. If all the processes are executed in some sequence then it is said to be a safe state. Or, we can say that if Finish==true for all i,
- then the system is said to be in a safe state,
- Let’s take an example to understand this more clearly.
Suppose we have 3 processes(A, B, C) and 3 resource types(R1, R2, R3) each having 5 instances. Suppose at any time t if the snapshot of the system taken is as follows then find the system is in a safe state or not. So, the total allocated resources(total_alloc)are,
- Also Finish=false, for i=0,1,2, are set as false as none of these processes have been executed.
- Now, we check that Need≤Work, By seeing the above Need matrix we can tell that only B process can be executed. So, process B( i=1 )is allocated the resources and it completes its execution. After completing the execution, it frees up the resources.
- Again, Work=Work+Available i.e. Work=+= and Finish= true.
- Now, as we have more instances of resources available we will check that if any other process resource needs can be satisfied. With the currently available resources, we can see that only process A can be executed. So, process A( i=0 ) is allocated the resources and it completes its execution. After completing the execution, it frees up the resources.
- Again, Work=Work+Available i.e. Work=+= and Finish= true.
- Now, as we have more instances of resources available we will check that if the remaining last process resource requirement can be satisfied. With the currently available resources, we can see that process C can be executed. So, process C( i=2 ) is allocated the resources and it completes its execution. After completing the execution, it frees up the resources.
- Fianlly, Work=Work+Available i.e. Work=+= and Finish= true.
- Finally, all the resources are free and there exists a safe sequence B, A, C in which all the processes can be executed. So. the system is in a safe state and deadlock will not occur.
This is how Banker’s Algorithm is used to check if the system is in a safe state or not. Hope you learned something new today. Do share this blog with your friends to spread the knowledge. Visit our for more content. You can read more blogs from, Keep Learning 🙂 Team AfterAcademy! : What is Banker’s algorithm?
What is bankers algorithm for deadlock detection in OS?
- Banker’s Algorithm in Operating System
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- Mutual Exclusion
- Hold & wait
- Circular wait
The banker’s algorithm is a resource allocation and deadlock avoidance algorithm that tests for safety by simulating the allocation for the predetermined maximum possible amounts of all resources, then makes an “s-state” check to test for possible activities, before deciding whether allocation should be allowed to continue.
What are the 4 conditions for deadlock?
A deadlock in OS is a situation in which more than one process is blocked because it is holding a resource and also requires some resource that is acquired by some other process. The four necessary conditions for a deadlock situation are mutual exclusion, no preemption, hold and wait and circular set. There are four methods of handling deadlocks – deadlock avoidance, deadlock prevention, deadline detection and recovery and deadlock ignorance. We can prevent a deadlock by preventing any one of the four necessary conditions for a deadlock. There are different ways of detecting and recovering a deadlock in a system. A starvation is a situation in which lower priority processes are postponed indefinitely while higher priority processes are executed. The advantages of deadlock handling methods are that no preemption is needed and it is good for activities that require a single burst of activity. The disadvantages of deadlock handling methods are it delays process initiation and preemptions are frequently encountered in it.
What are 4 conditions required for deadlock to occur?
What is the Condition for Deadlock? – In the system, the deadlock occurs when the system has these four conditions simultaneously that are as follows:
For a deadlock to occur, all four conditions must be met. The impasse is broken if any one of them is averted or resolved.
How can we handle deadlock?
Deadlock is a situation where a process or a set of processes is blocked, waiting for some other resource that is held by some other waiting process. It is an undesirable state of the system. The following are the four conditions that must hold simultaneously for a deadlock to occur.
- Mutual Exclusion – A resource can be used by only one process at a time. If another process requests for that resource then the requesting process must be delayed until the resource has been released.
- Hold and wait – Some processes must be holding some resources in the non-shareable mode and at the same time must be waiting to acquire some more resources, which are currently held by other processes in the non-shareable mode.
- No pre-emption – Resources granted to a process can be released back to the system only as a result of voluntary action of that process after the process has completed its task.
- Circular wait – Deadlocked processes are involved in a circular chain such that each process holds one or more resources being requested by the next process in the chain.
Methods of handling deadlocks: There are four approaches to dealing with deadlocks.1. Deadlock Prevention 2. Deadlock avoidance (Banker’s Algorithm) 3. Deadlock detection & recovery 4. Deadlock Ignorance (Ostrich Method) These are explained below.1. Deadlock Prevention : The strategy of deadlock prevention is to design the system in such a way that the possibility of deadlock is excluded.
- The indirect methods prevent the occurrence of one of three necessary conditions of deadlock i.e., mutual exclusion, no pre-emption, and hold and wait.
- The direct method prevents the occurrence of circular wait.
- Prevention techniques – Mutual exclusion – are supported by the OS.
- Hold and Wait – the condition can be prevented by requiring that a process requests all its required resources at one time and blocking the process until all of its requests can be granted at the same time simultaneously.
But this prevention does not yield good results because:
- long waiting time required
- inefficient use of allocated resource
- A process may not know all the required resources in advance
No pre-emption – techniques for ‘no pre-emption are’
- If a process that is holding some resource, requests another resource that can not be immediately allocated to it, all resources currently being held are released and if necessary, request again together with the additional resource.
- If a process requests a resource that is currently held by another process, the OS may pre-empt the second process and require it to release its resources. This works only if both processes do not have the same priority.
Circular wait One way to ensure that this condition never holds is to impose a total ordering of all resource types and to require that each process requests resources in increasing order of enumeration, i.e., if a process has been allocated resources of type R, then it may subsequently request only those resources of types following R in ordering.2.
Deadlock Avoidance : The deadlock avoidance Algorithm works by proactively looking for potential deadlock situations before they occur. It does this by tracking the resource usage of each process and identifying conflicts that could potentially lead to a deadlock. If a potential deadlock is identified, the algorithm will take steps to resolve the conflict, such as rolling back one of the processes or pre-emptively allocating resources to other processes.
The Deadlock Avoidance Algorithm is designed to minimize the chances of a deadlock occurring, although it cannot guarantee that a deadlock will never occur. This approach allows the three necessary conditions of deadlock but makes judicious choices to assure that the deadlock point is never reached.
- Process initiation denial
- Resource allocation denial
Advantages of deadlock avoidance techniques:
- Not necessary to pre-empt and rollback processes
- Less restrictive than deadlock prevention
- Future resource requirements must be known in advance
- Processes can be blocked for long periods
- Exists a fixed number of resources for allocation
Banker’s Algorithm : The Banker’s Algorithm is based on the concept of resource allocation graphs. A resource allocation graph is a directed graph where each node represents a process, and each edge represents a resource. The state of the system is represented by the current allocation of resources between processes.
- For example, if the system has three processes, each of which is using two resources, the resource allocation graph would look like this: Processes A, B, and C would be the nodes, and the resources they are using would be the edges connecting them.
- The Banker’s Algorithm works by analyzing the state of the system and determining if it is in a safe state or at risk of entering a deadlock.
To determine if a system is in a safe state, the Banker’s Algorithm uses two matrices: the available matrix and the need matrix. The available matrix contains the amount of each resource currently available. The need matrix contains the amount of each resource required by each process.
- The Banker’s Algorithm then checks to see if a process can be completed without overloading the system.
- It does this by subtracting the amount of each resource used by the process from the available matrix and adding it to the need matrix.
- If the result is in a safe state, the process is allowed to proceed, otherwise, it is blocked until more resources become available.
The Banker’s Algorithm is an effective way to prevent deadlocks in multiprogramming systems. It is used in many operating systems, including Windows and Linux. In addition, it is used in many other types of systems, such as manufacturing systems and banking systems.
- The Banker’s Algorithm is a powerful tool for resource allocation problems, but it is not foolproof.
- It can be fooled by processes that consume more resources than they need, or by processes that produce more resources than they need.
- Also, it can be fooled by processes that consume resources in an unpredictable manner.
To prevent these types of problems, it is important to carefully monitor the system to ensure that it is in a safe state.3. Deadlock Detection : Deadlock detection is used by employing an algorithm that tracks the circular waiting and kills one or more processes so that the deadlock is removed.
- This technique does not limit resource access or restrict process action.
- Requested resources are granted to processes whenever possible.
- It never delays the process initiation and facilitates online handling.
- The disadvantage is the inherent pre-emption losses.
4. Deadlock Ignorance : In the Deadlock ignorance method the OS acts like the deadlock never occurs and completely ignores it even if the deadlock occurs. This method only applies if the deadlock occurs very rarely. The algorithm is very simple. It says ” if the deadlock occurs, simply reboot the system and act like the deadlock never occurred.” That’s why the algorithm is called the Ostrich Algorithm,
- Ostrich Algorithm is relatively easy to implement and is effective in most cases.
- It helps in avoiding the deadlock situation by ignoring the presence of deadlocks.
- Ostrich Algorithm does not provide any information about the deadlock situation.
- It can lead to reduced performance of the system as the system may be blocked for a long time.
- It can lead to a resource leak, as resources are not released when the system is blocked due to deadlock.
Last Updated : 14 Dec, 2022 Like Article Save Article
What is an example of a deadlock?
Another real-world example of deadlock is the use of a single track by multiple trains. Say multiple tracks converge onto one; there is a train on each individual track, leading to the one track. All trains are stopped, waiting for another to go, though none of them move.
What is the drawback of Banker’s algorithm?
Disadvantages of the Banker’s Algorithm It requires the number of processes to be fixed; no additional processes can start while it is executing. It requires that the number of resources remain fixed; no resource may go down for any reason without the possibility of deadlock occurring.
What are the two options for breaking a deadlock?
When a detection algorithm determines that a deadlock exists, several alternatives are available. One possibility is to inform the operator that a deadlock has occurred and to let the operator deal with the deadlock manually. Another possibility is to let the system recover from the deadlock automatically.
There are two options for breaking a deadlock. One is simply to abort one or more processes to break the circular wait. The other is to preempt some resources from one or more of the deadlocked processes. To eliminate deadlocks by aborting a process, we use one of two methods. In both methods, the system reclaims all resources allocated to the terminated processes.
» Abort all deadlocked processes. This method clearly will break the deadlock cycle, but at great expense; the deadlocked processes may have computed for a long time, and the results of these partial computations must be discarded and probably will have to be recomputed later.
• Abort one process at a time until the deadlock cycle is eliminated. This method incurs considerable overhead, since, after each process is aborted, a deadlock-detection algorithm must be invoked to determine whether any processes are still deadlocked. Aborting a process may not be easy. If the process was in the midst of updating a file, terminating it will leave that file in an incorrect state.
Similarly, if the process was in the midst of printing data on a printer, the system must reset the printer to a correct state before printing the next job. If the partial termination method is used, then we must determine which deadlocked process (or processes) should be terminated.
- This determination is a policy decision, similar to CPU-scheduling decisions.
- The question is basically an economic one; we should abort those processes whose termination will incur the minimum cost.
- Unfortunately, the term minimum cost is not a precise one.
- Many factors may affect which process is chosen, including: 1.
What the priority of the process is 2. How long the process has computed and how much longer the process will compute before completing its designated task 3. How many and what type of resources the process has used (for example, whether the resources are simple to preempt) 4.
- How many more resources the process needs in order to complete 5.
- How many processes will need to be terminated 6.
- Whether the process is interactive or batch To eliminate deadlocks using resource preemption, we successively preempt some resources from processes and give these resources to other processes until the deadlock cycle is broken.
If preemption is required to deal with deadlocks, then three issues need to be addressed: 1. Selecting a victim. Which resources and which processes are to be preempted? As in process termination, we must determine the order of preemption to minimize cost.
Cost factors may include such parameters as the number of resources a deadlocked process is holding and the amount of time the process has thus far consumed during its execution.2. Rollback. If we preempt a resource from a process, what should be done with that process? Clearly, it cannot continue with its normal execution; it is missing some needed resource.
We must roll back the process to some safe state and restart it from that state. Since, in general, it is difficult to determine what a safe state is, the simplest solution is a total rollback: Abort the process and then restart it. Although it is more effective to roll back the process only as far as necessary to break the deadlock, this method requires the system to keep more information about the state of all running processes.3.
Starvation. How do we ensure that starvation will not occur? That is, how can we guarantee that resources will not always be preempted from the same process? In a system where victim selection is based primarily on cost factors, it may happen that the same process is always picked as a victim. As a result, this process never completes its designated task, a starvation situation that must be dealt with in any practical system.
Clearly, we must ensure that a process can be picked as a victim only a (small) finite number of times. The most common solution is to include the number of rollbacks in the cost factor. + Deadlock Avoidance Ans: Deadlock Avoidance Deadlock-prevention algorithms, as discussed in Section 7.4, prevent deadlocks by restraining how requests can be made.
The restraints ensure that at least one of the necessary conditions for deadlock cannot occur and, hence, that deadlocks cannot hold. Possible side effects of preventing deadlocks by this method, however, are low device utilization and reduced system throughput. An alternative method for avoiding deadlocks is to require additional information about how resources are to be requested.
For example, in a system with one tape drive and one printer, the system might need to know that process P will request first the tape drive and then the printer before releasing both resources, whereas process Q will request first the printer and then the tape drive.
- With this knowledge of the complete sequence of requests and releases for each process, the system can decide for each request whether or not the process should wait in order to avoid a possible future deadlock.
- View more.
- Deadlock prevention Ans: Deadlock Prevention As we noted in Section 7.2.1, for a deadlock to occur, each of the four necessary conditions must hold.
By ensuring that at least one of these conditions cannot hold, we can prevent the occurrence of a deadlock. We elaborate on this approach by examining each of the four necessary conditions separately. view more. + Virtual machines Ans: Virtual Machines The layered approach described in Section 2.7.2 is taken to its logical conclusion in the concept of a virtual machine.
The fundamental idea behind a virtual machine is to abstract the hardware of a single computer (the CPU, memory, disk drives, network interface cards, and so forth) into several different execution environments, thereby creating the illusion that each separate execution environment is running its own private computer.
By using CPU scheduling (Chapter 5) and virtual-memory techniques (Chapter 9), an operating system can create the illusion that a process has its own processor with its own (virtual) memory. Normally, a process has additional features, such as system calls and a file system, that are not provided by the bare hardware.
- View more.
- Deadlock Recovery Ans: Recovery From Deadlock When a detection algorithm determines that a deadlock exists, several alternatives are available.
- One possibility is to inform the operator that a deadlock has occurred and to let the operator deal with the deadlock manually.
- Another possibility is to let the system recover from the deadlock automatically.
There are two options for breaking a deadlock. One is simply to abort one or more processes to break the circular wait. The other is to preempt some resources from one or more of the deadlocked processes. view more. + Stable Storage Implementation Ans: Stable-Storage Implementation We introduced the write-ahead log, which requires the availability of stable storage.
By definition, information residing in stable storage is never lost. To implement such storage, we need to replicate the needed information on multiple storage devices (usually disks) with independent failure modes. We need to coordinate the writing of updates in a way that guarantees that a failure during an update will not leave all the copies in a damaged state and that, when we are recovering from a failure, we can force all copies to a consistent and correct value, even if another failure occurs during the recovery.
In this section, we discuss how to meet these needs. view more. + File System Mounting Ans: File-System Mounting Just as a file must be opened before it is used, a file system must be mounted before it can be available to processes on the system. More specifically, the directory structure can be built out of multiple volumes, which must be mounted to make them available within the file-system name space.
- The mount procedure is straightforward.
- The operating system is given the name of the device and the mount point—the location within the file structure where the file system is to be attached.
- Typically, a mount point is an empty directory.
- View more.
- File Access methods Ans: Access Methods Files store information.
When it is used, this information must be accessed and read into computer memory. The information in the file can be accessed in several ways. Some systems provide only one access method for files. Other systems, such as those of IBM, support many access methods, and choosing the right one for a particular application is a major design problem.
- View more.
- Directory Implementation Ans: Directory implementation The selection of directory-allocation and directory-management algorithms significantly affects the efficiency, performance, and reliability of the file system.
- In this section, we discuss the trade-offs involved in choosing one of these algorithms.
view more. + Swap Space Management Ans: Swap-Space Use Swap space is used in various ways by different operating systems, depending on the memory-management algorithms in use. For instance, systems that implement swapping may use swap space to hold an entire process image, including the code and data segments.
- Paging systems may simply store pages that have been pushed out of main memory.
- The amount of swap space needed on a system can therefore vary depending on the amount of physical memory, the amount of virtual memory it is backing, and the way in which the virtual memory is used.
- It can range from a few megabytes of disk space to gigabytes.
view more. + Copy on write Ans: Copy-on-Write we illustrated how a process can start quickly by merely demandpaging in the page containing the first instruction. However, process creation using the fork () system call may initially bypass the need for demand paging by using a technique similar to page sharing (covered in Section 8.4.4).
This technique provides for rapid process creation and minimizes the number of new pages that must be allocated to the newly created process. view more. + File Replication Ans: File Replication Replication of files on different machines in a distributed file system is a useful redundancy for improving availability.
Multimachine replication can benefit performance too: Selecting a nearby replica to serve an access request results in shorter service time. view more. + Special purpose systems Ans: Special-Purpose Systems The discussion thus far has focused on general-purpose computer systems that we are all familiar with.
There are, however, different classes of computer systems whose functions are more limited and whose objective is to deal with limited computation domains. view more. + Computing Environments- Traditional Computing, Client-Server Computing, Peer-to-Peer Computing, Web-Based Computing Ans: Computing Environments : Traditional Computing, Client-Server Computing, Peer-to-Peer Computing, Web-Based Computing view more.
+ Scheduling Criteria Ans: Scheduling Criteria Different CPU scheduling algorithms have different properties, and the choice of a particular algorithm may favor one class of processes over another. In choosing which algorithm to use in a particular situation, we must consider the properties of the various algorithms.
- Many criteria have been suggested for comparing CPU scheduling algorithms.
- Which characteristics are used for comparison can make a substantial difference in which algorithm is judged to be best.
- The criteria include the following: • CPU utilization.
- We want to keep the CPU as busy as possible.
- Conceptually, CPU utilization can range from 0 to 100 percent.
In a real system, it should range from 40 percent (for a lightly loaded system) to 90 percent (for a heavily used system). view more. + Thread scheduling Ans: Thread Scheduling we introduced threads to the process model, distinguishing between user-level and kernel-level threads.
On operating systems that support them, it is kernel-level threads—not processes—that are being scheduled by the operating system. User-level threads are managed by a thread library, and the kernel is unaware of them. To run on a CPU, user-level threads must ultimately be mapped to an associated kernel-level thread, although this mapping may be indirect and may use a lightweight process (LWP).
In this section, we explore scheduling issues involving user-level and kernel-level threads and offer specific examples of scheduling for Pthreads. view more. + Thread Libraries Ans: Thread Libraries A thread library provides the programmer an API for creating and managing threads.
- There are two primary ways of implementing a thread library.
- The first approach is to provide a library entirely in user space with no kernel support.
- All code and data structures for the library exist in user space.
- This means that invoking a function in the library results in a local function call in user space and not a system call.
view more. + Petersons’s Solution Ans: we illustrate a classic software-based solution to the critical-section problem known as Peterson’s solution. Because of the way modern computer architectures perform basic machine-language instructions, such as load and store, there are no guarantees that Peterson’s solution will work correctly on such architectures.
However, we present the solution because it provides a good algorithmic description of solving the critical-section problem and illustrates some of the complexities involved in designing software that addresses the requirements of mutual exclusion, progress, and bounded waiting requirements. Peterson’s solution is restricted to two processes that alternate execution between their critical sections and remainder sections.
The processes are numbered Po and Pi. view more. + Synchronization Hardware Ans: Synchronization Hardware We have just described one software-based solution to the critical-section problem. In general, we can state that any solution to the critical-section problem requires a simple tool—a lock.
How does Windows handle deadlocks?
Scientist-SC/SDE(Software Development Engineer) || Ex-Walmart ll M.Tech IIITB – Published May 23, 2023 Welcome to the latest edition of CodeCraft Chronicles, your go-to resource for all things tech-related. In this edition, we’ll be diving into deadlock handling strategies for different operating systems, specifically focusing on Windows and Linux.
Deadlocks can be a frustrating issue, so let’s explore some effective strategies to tackle them head-on. Understanding Deadlocks A deadlock occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. This can result in a complete system halt and adversely affect the overall performance of your operating system.
Deadlock Handling in Windows Windows offers various mechanisms to detect and resolve deadlocks efficiently. Here are some essential strategies used in Windows:
Resource Allocation Graph: Windows employs a graph-based algorithm to detect potential deadlocks. It utilizes a resource allocation graph to identify cycles that indicate a potential deadlock. Once a deadlock is detected, Windows takes appropriate actions to break the deadlock and allow processes to proceed.Deadlock Detection and Recovery: Windows uses a timeout mechanism to detect deadlocks. If a resource is not released within a certain time, Windows assumes a deadlock and takes necessary recovery actions. It can terminate one or more processes involved in the deadlock or force the release of resources to break the deadlock.Deadlock Prevention: Windows emphasizes a prevention-oriented approach by ensuring that the necessary conditions for deadlocks are not allowed to occur. It achieves this by employing techniques such as resource ordering, which ensures that resources are requested and released in a specific order, thereby preventing circular waits.
Deadlock Handling in Linux Linux also provides several strategies for deadlock handling. Let’s explore a couple of key techniques used in Linux:
Ostrich Algorithm: Linux employs the “ostrich algorithm” or “ignorance algorithm,” which essentially ignores the possibility of deadlocks. The underlying assumption is that deadlocks are rare occurrences and it’s better to focus on other system improvements. While this approach may not address deadlocks directly, it emphasizes building robust systems and avoiding resource contention issues.Deadlock Detection with OOM Killer: Linux’s Out-of-Memory (OOM) Killer plays a crucial role in handling deadlocks caused by resource exhaustion. When the system runs out of memory and processes are unable to allocate resources, the OOM Killer identifies and terminates processes that are causing the deadlock, freeing up resources for other processes to continue.
Best Practices for Deadlock Handling Regardless of the operating system you’re using, there are some general best practices to keep in mind when it comes to deadlock handling:
Avoid Resource Contention: Design your applications and systems in a way that minimizes resource contention. This includes proper resource allocation, releasing resources in a timely manner, and avoiding unnecessary resource dependencies.Implement Timeout Mechanisms: Set appropriate timeouts when acquiring resources to avoid indefinite waits. If a resource is not acquired within the specified time, the process can take alternative actions instead of waiting indefinitely.Monitor and Analyze: Employ monitoring tools and techniques to identify potential deadlocks. Regularly analyze system logs and performance metrics to proactively detect and resolve deadlock issues before they impact critical operations.
Remember, prevention is key when it comes to deadlocks. By implementing proactive measures and leveraging the available strategies, you can minimize the occurrence and impact of deadlocks in your operating system. That’s all for this edition of CodeCraft Chronicles! We hope you found this overview of deadlock handling strategies for Windows and Linux informative.
Which is Banker’s algorithm for deadlock prevention?
Introduction – Banker’s Algorithm is a Deadlock avoidance algorithm and is also used as a Deadlock detection Algorithm, Deadlock condition arises when there is a Mutual Exclusion, Circular wait, No Preemtion, and Circular wait situation. The banker’s Algorithm tests for a safe state check the condition for possible activities and decides whether to continue the allocation of resources or not.
What is safe in deadlock?
Resources still needed –
|Process||Type 1||Type 2||Type 3||Type 4|
E = (7 6 8 4) P = (6 2 8 3) A = (1 4 0 1) Above tables and vector E, P and A describes the resource allocation state of a system. There are 4 processes and 4 types of the resources in a system. Table 1 shows the instances of each resource assigned to each process.
- A state of the system is called safe if the system can allocate all the resources requested by all the processes without entering into deadlock.
- If the system cannot fulfill the request of all processes then the state of the system is called unsafe.
- The key of Deadlock avoidance approach is when the request is made for resources then the request must only be approved in the case if the resulting state is also a safe state.
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: Deadlock avoidance