1. Why does deadlock occur?
Because concurrent processes have a part of the resources, and want to preempt the resources of other processes. (If there is only one process, there is absolutely no deadlock)
//Resources include: CPU, I/O channels, various storage, devices and data, files, databases, semaphores (and require resources not to die suddenly)
2. Deadlock Model
P stands for process R stands for resources, and the number of dots in R stands for the number of resources
No deadlock will occur, because P3 will release R3 after using it
A deadlock will occur.
No deadlocks (although there are loops)
4. Characteristics of deadlock (just a necessary condition for deadlock)
(1) Mutual exclusion : resources can only be owned by one process at the same time, if they can be owned at the same time, there will be no deadlock
(2) Hold and wait : The process holds at least one resource and is waiting to acquire additional resources held by other processes
(3) No preemption : a resource can only be automatically released by the process after completing the task
(4) Circular waiting: that is, several processes wait for each other
5. Deadlock handling