Total English Advanced. Teacher's Resource Book (+ CD-ROM)

This request from task 2 is safe and is allowed. If task 4 were to make the same request for R1 and if such a request were granted, this process would prevent task 2 from completing, which would result in a deadlock such that no task could resume execution. The request from task 4 is an unsafe request, and the deadlock avoidance algorithm would reject the request and put task 4 on hold while allowing other tasks to continue. In order for deadlock avoidance to work, each task must estimate in advance its maximum resource requirement per resource type. This estimation is often difficult to predict in a dynamic system. For more static embedded systems or for systems with predictable operating environments, however, deadlock avoidance can be achieved. The estimations from all tasks are used to construct the demand table, D. This resource estimation only identifies the potential maximum resource requirement through certain execution paths. In the majority of cases, there would be overestimation. Overestimation by each task can lead to inefficient resource utilization in a heavily loaded system ...»