transp-dist-deadlock

transp-dist-deadlock - Distributed Deadlock Detection...

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Distributed Deadlock Detection Deadlock prevention is achieved by denying the existence of one or more of the necessary conditions for deadlock. Commonly adopted strategies include: (1) having a process acquire all needed resources simultaneously before it begins execution, or (2) using a liner ordering scheme for resource acquisition to prevent circular waits. Unless information about resource availability and process requests are maintained centrally on one site, such an approach is impractical for a distributed system. In deadlock avoidance, a resource is granted to a process if the resulting state is safe. For a distributed system, the safe state checking must examine the global state that involves all processes and resources in all sites. This approach is impractical for distributed systems because: (1) The need to maintain information on the global state for every site leads to huge storage requirements and extensive communication costs, (2) the safe state checking will be computationally expensive due to the potentially large number of processes and resources involved, and (3) the safe state checking for the global state must be mutually exclusive. If we allow multiple sites to perform safe state checking concurrently, each site for a different request, they may find the state safe but the net global state may not be. In light of the difficulty in deadlock detection for the general resource system, the study of deadlock problems in distributed systems usually adopts a simpler system model assuming: Reusable resources only Only exclusive accesses to resources Each resource has only one instance With the simpler system model as defined above, deadlock detection can be achieved by finding a cycle in the Wait For Graph (WFG) of the resource system. One major difficulty in deadlock detection in distributed systems is the potential for detecting phantom deadlocks.
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Control Organization for Distributed Deadlock Detection The following three control organizations are common for deadlock detection in distributed systems: Centralized Control In centralized deadlock detection algorithms, a designated site (often called a control site ) has the responsibility of constructing the global WFG and searching it for cycles. The control site may maintain the global WFG constantly or it may build it whenever a deadlock detection is to be carried out by soliciting the local WFG from every site. Advantages of centralized algorithms include: detection as well as resolution are conceptually simple and easy to implement since the control site has complete information of the WFG and the deadlock cycle. Disadvantages include: single point of failure, congestion likely at the control site and at communication links near that site, design not scalable to growth of system. Distributed Control
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transp-dist-deadlock - Distributed Deadlock Detection...

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