onsider a system in which processes post resource requests that are treated as follows. If the resource is free $($not currently held by any other process$),$ it is granted to the process. If the resource is currently held by some other process, the requesting process is thus notified. A process that could not obtain a requested resource can continue to post requests for more resources. However it cannot complete its work without obtaining all the resources it has requested. Whenever a process terminates it releases all the resources it had obtained.

In the following sequence of requests, let REQ$($A$,$ B$)$ denote process A requesting resource B: