![]() No preemption: a resource can be released only voluntarily by the process holding it, afterĬircular wait: there exists a set, the set consisting of all resource types in the systemĪssignment edge directed edge Rj Pi Resource-Allocation Graph (Cont.) Process Resource type with 4 instances Pi requests instance of Rj Pi is holding an instance of RjĬTU_LNK REF. Hold and wait: a process holding at least one resource is waiting to acquire additional Mutual exclusion: only one process at a time can use a resource # Coffman (1971) - Deadlock can arise if four conditions hold simultaneously. SILBERSCHATZ, GALVIN, GAGNE©2018 5 Request Use Release 4 conditions for Deadlock Each process utilizes a resource as follows: System ModelĬTU_LNK REF. ![]() , Rm CPU cycles, memory space, I/O devices Each resource type Ri has Wi instances. SILBERSCHATZ, GALVIN, GAGNE© Deadlock problem A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set Example System has 2 disk drives P 1 and P 2 each hold one disk drive and each needs another one Deadlock definitions Two or more processes each blocked and waiting for resources they will never get without drastic actions Something preempts a resource A process is killed A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause, thus, no process can Run Release resources Be awakened System consists of resources Resource types R 1, R 2. 2 0 09.ĬTU_LNK 2 The Deadlock Problem System Model 4 conditions for Deadlock (deadlock characterization) Methods for Handling Deadlock Deadlock Prevention Deadlock Avoidance Deadlock Detection Recovery from Deadlock SI LBER SCH ATZ, GA LV IN, GAG NE © 20 18 ![]() OP E RATIN G SY STEM CO NC EP TS 10 T H ED.
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