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Deadlock in Operating Systems
- 2. Presented By Sadnam Saniat ID: 192-15-2794 Section: PC-C Department of CSE Daffodil International University
- 3. Contents โข Introduction of Deadlock โข Characteristics of Deadlocks โข Strategies For handling Deadlock โข Deadlock Prevention โข Deadlock Avoidance โข Recovery from Deadlock
- 4. Deadlock SITUATION PROCESS WAITS RESOURCE ASSIGNED ANOTHER PROCESS
- 5. Process 2 Process 1 Resource 1 Resource 2 DEADLOCK! Requested For Assigned To Requested For Assigned To
- 6. Mutual Exclusion 1 Hold & Wait 2 No Preemption 3 Circular Wait 4 Characteristics of Deadlocks
- 7. Strategies For Handling Deadlock Ensure 1. Deadlock prevention 2. Deadlock avoidance Allow Allow the system to enter a deadlock state and then recover Ignore Ignore the problem and pretend that deadlocks never occur in the system
- 8. Deadlock Prevention Mutual Exclusion Not required for sharable resources (e.g., read-only files); must hold for non-sharable resources Hold and Wait Must guarantee that whenever a process requests a resource, it does not hold any other resources No Preemption If a process that is holding some resources requests another resource that cannot be immediately allocated to it, then all resources currently being held are released Circular Wait Impose a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration
- 9. Deadlock Avoidance Resource Allocation Graph โ Claim Edge Single Instance Bankerโs Algorithm Multiple Instances
- 10. โข Abort all deadlocked processes โข Abort one process at a time until the deadlock cycle is eliminated Process Termination โข Selecting a victim โ minimize cost โข Rollback โ return to some safe state, restart process for that state โข Starvation โ same process may always be picked as victim, include number of rollback in cost facto Resource Preemption Deadlock Recovery
- 11. Thank You
Editor's Notes
- A Deadlock is a situation where each of the computer process waits for a resource which is being assigned to some another process. In this situation, none of the process gets executed since the resource it needs, is held by some other process which is also waiting for some other resource to be released.
- 1. Mutual Exclusion : Mutual exclusion means that a resource can be used by only one process at a time.ย For example,ย if a process P1 locks the resource R in exclusive mode, no other process can acquire this resource R. If another process requests, this resource, the requesting process must be delayed until the resource has been Ans. released. 2. Hold and Wait : The processes involved in deadlock acquires at least one resource and wait for at least another resource that has been acquired by another process. 3. No preemption : Resources held by a process cannot be preempted. A resource can be released only voluntarily by the process holding it, after that process has completed its task. 4. Circular Wait : A circular chain or a circular relationship exists among the processes involved in a deadlock. In such a chain each process waits for a resource that is held by the next process in the chain.ย For example, there are three processes, P1, P2 and P3. The process P1 is waiting for a resource which is held by the process P2, P2 is waiting for a resource held by P3 and P3 is waiting for a resource that is held by the process P1.
- Ensure that the system will never enter a deadlock state: ๏ฌ Deadlock prevention ๏ฌ Deadlock avoidence ๏ฎ Allow the system to enter a deadlock state and then recover ๏ฎ Ignore the problem and pretend that deadlocks never occur in the system; used by most operating systems, including UNIX