Deadlock in Operating System | GeeksforGeeks
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0:06 Hello and welcome to Geeks for Geeks. In this video, we are going to understand a very important concept of deadlock in operating systems in a simple manner
0:15 with the help of some real-life examples. So, let us understand deadlock by a real-life example. You can't get a job without experience and experience
0:23 can only come when you do some job. So, here we end up in a deadlock. Let's see a formal definition of deadlock. So, deadlock is a situation
0:32 where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process.
0:41 Let us understand it with the help of an example. So, in this example, process one is waiting for resource Y but it is assigned to process two.
0:52 Process two is not getting completed because it requires resource X which is assigned to process one ending up in a deadlock situation. Let's understand
1:02 deadlock with one more real-life example of a wrongly managed school. The school never performs good in board exams. Almost all the students get failed. When
1:12 the principal is asked why, his straightforward answer is that teachers doesn't teach well. When the teachers were asked about why the
1:20 students were getting failed, they said that they were not given their wages. Then again, when the principal was asked why they are not giving the wages, he
1:28 replies that parents don't want to pay the fees and he does not have the funds to give them. Pay to the teachers.
1:35 The parents give the reason that school does not provide enough facilities but obviously principal cannot provide facilities unless the fees is paid
1:44 which is depicted in this diagram and parents are not ready to pay the fees until facilities are enhanced in the school.
1:51 So, here we end up in a deadlock situation and there's not much we can do for the school. In the previous example, we saw a
1:58 deadlock between only two processes, namely school and parents. But a real operating system deadlock can be complex, and it usually involves
2:07 multiple processes and resources. So, now we are going to study four necessary conditions for a deadlock to
2:15 happen. So, they are mutual exclusion, hold and wait, no preemption, and circular wait. Let's see them all one by
2:25 one. So, let's understand mutual exclusion. If some resources are non-shareable, which means that only a single process
2:32 can use it. For example, here process one can use resource one, and no other process can use resource one. If this is not the case, then process cannot be
2:41 stopped from using the resource when they require it. For example, full-screen processes in our computer cannot be used by two apps
2:48 simultaneously. So, let's understand hold and wait now. If a process holds some resource and waits for some other resource, then the
2:57 hold and wait is occurred. If this is not the case, then the cycle of deadlock, which we saw in the first diagram, will not get completed, and no
3:05 deadlock will occur. The above school example is a classic example of hold and wait. As the school holds the facilities,
3:14 and parents hold the resources. School needs the resources, and parent need the facilities. Hence, creating a hold and wait
3:23 situation. Now, let's understand the third condition of no preemption. A resource cannot be taken from a
3:30 process unless the process releases the resource. If preemption was allowed, deadlock would never occur because then there
3:40 would have been no process able to hold a resource for long amount of time. For example, if your speaker is running an audio and after some time you click
3:49 on some another audio, it starts playing it. But in case if no preemption was allowed, we would have to wait for the first audio to end. It was on an
3:57 infinite loop. We will end up in a deadlock. So, let's understand the last condition, circular wait.
4:03 A set of processes are waiting for each other in a circular form, then circular wait happens. For example, if you extend the first
4:10 example to multiple processes and resources waiting for each other's held resources in a circular fashion, we will end up in
4:17 a circular wait condition. So, hope you understood the concept of deadlock in operating system. Please don't forget to subscribe to the GeeksforGeeks YouTube
4:24 channel and click on the bell icon.