TAILIEUCHUNG - Factory Automation Part 13

Tham khảo tài liệu 'factory automation part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 472 Factory Automation Four conditions are identified in the literature for a deadlock to occur. First tasks claiming exclusive control of the resource they acquire may lead to deadlock the mutual exclusion condition . Second deadlock may occur when resources cannot be forcibly removed from the tasks holding them until the resources are used to completion the no-preemption condition . Third processes holding resources allocated to them while waiting for additional ones may prevent proper termination of all tasks the wait-for condition . Fourth circular claims of tasks such that each task holds one or more resources that are being requested by the next task s in the claim the circular wait condition will cause indefinite blockage of a system. In Automated Manufacturing Systems the first three conditions always hold true. Orchestrators do claim exclusive control of the resources machines robots conveyors they acquire. Once acquired a resource must complete the processing it was originally contracted for a device cannot be forcibly stopped while processing in order to start machining for a different requestor. Last but not least orchestrators hold resources allocated to them until some of the needed future transportation devices become available. Therefore deadlocks can be excluded only if the circular wait condition is falsified. Three main strategies have been identified for resolving deadlock problems prevention detection recovery and avoidance. Deadlock prevention is an offline technique involving static resource allocation policies for eliminating deadlocks. Knowledge of the system state is not required to realize the control. However with this method the utilization of resources is low and production flexibility is limited. The detection and recovery technique aims at resolving blockages after they have occurred. The recovery process is assisted by special buffers reserved for breaking deadlocks. This solution enables higher resource utilization however it .

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