A deadlock in the Operating System

A deadlock in the Operating System is a known phenomenon in the tech-savvy world. In the blog, the extensive idea about what deadlock is in the Operating System will be discussed. But before that, we shall have a quick and brief understanding of what an operating system is. You can only have a clear idea about deadlock if you can have the detailed knowledge about the operating system where it works. This blog will help in understanding the concept to those who are already enriched about the basic tech knowledge. Besides this, it will also help those who are willing to gain some insight into this topic from the beginning.

An operating system, in general, refers to the consolidated set of software which is present in a computer. When the system of hardware and software work together they result in providing the required service to the end consumer. The concept of an operating system is made clear. Now, some examples shall be put forward to relate it in the real world and clarify any other query. The common examples of Operating Systems are Microsoft Windows, Apple iOS, Google’s Android OS, Apple macOS, and Linux OS. So, let’s begin with the definition of deadlock and the types of deadlock and so forth. Now our experts from will you more about deadlock.

Deadlock: A Frequent Problem for Operators

Deadlock is nowadays a very frequent problem in multiprocessing. It occurs when numerous processes share a specific resource famous as software or soft lock. The interaction among various processes as well as resources can cause problems known as deadlock. It is a non-deterministic bug that can occur in a parallel system. These kinds of bugs are difficult to check and debug. A deadlock in an operating system is a condition when every process waits for a resource acquired by other processes.

It is a series of blocked processes holding a resource and waiting for accessing extra resources assigned with another one. In the situation of deadlock, none of the programs can continue until another program releases resources. Therefore, it becomes difficult for the users to continue with their programs. Besides this, it is also annoying when the system hangs frequently.

This usually occurs in multitasking as well as client-server circumstances. Earlier, systems used to run only a single program at a time assigning all the resources to that program. Afterwards, multiples programs were run simultaneously on the operating system. In this case, programs needed to identify the resources in advance they require to complete their tasks.

This method is used for avoiding conflicts with another task executing simultaneously. Ultimately, some OS provided an active distribution of resources. Programs ask for further distribution of the resources after starting their execution and this led to the occurrence of deadlock.

Deadlock can also be defined as a situation two computer program uses the same resource of data and they share access. During the deadlock situation, these computer programs will hinder each others’ way. Most importantly, access to the shared resource would be denied to both of these programs during deadlocks.

Furthermore, as an ultimate result, the functions of both of these computer programs stop or collapse. As already said, the problems of the deadlock were relatively lower in the OS of computers earlier. This is because the previous operating systems allowed the functioning of only one computer at a time. This minimized any chance of conflict regarding the access of resources between two or multiple computer programs.

Hence deadlocks in the Operating System were less. However, in the recently programmed OS, with better interface and processors, multiple programs run at the same time. When that happens, the probability and instances of the programs overstepping the other while accessing the resources also increase. The existence of deadlocks affects the performance of the programs. In addition to this, it also negatively influences the output and slows down the process.

To curtail this situation, provisions were made. The operators of the programs were required to give prior notifications and specifications about the resources that they operate on. This would minimize the conflicts of the co-existing programs. However, in recent times, operating systems have come up with the allocation of resources that are dynamic. In this system, programs that started running with a specific resource can request other resources while the program is running. This again takes the problem of deadlock to square one.


The system has a definite number of resources to be distributed among the processes. It is evident that the computer processes need various types of resources to complete the execution of activities. However, these resources are approved in systematic order. These include- requesting, waiting and realizing:

Requesting: Resources are asked for by the processes.

Waiting: The operating system grants accessible resources. In the case of unavailability of resources as well as demanding resources, the process is required to wait.

Realizing: The process utilizes the accessible resources and releases it on completion of the tasks.

If there is no resource available, none of the programs can execute since the release of resources they need. The request resources are associated with other programs that are also waiting for resources held by some other programs. Now, we shall move forward to the causes of deadlock. Now our experts from will tell you about the causes of deadlocks in the operating system.

Causes of deadlocks in the operating system

A deadlock in operating system arises when the following four conditions hold at the same time in the system:

Mutual Exclusion

At least one or more than one of the allocated resources are not shareable. Each resource is assigned with only one process at a time. If any other process demands the same resources. The demanding process is required to wait until the executing process releases it. The process of mutual exclusion or rather the condition of mutual exclusion is said to exist in case of a deadlock. This happens when there is a single resource that can possibly be allocated to one program and not more than that.

Hold and Wait

The requesting process already holds a resource and waits for other resources that are currently being used by the other process. Hold and wait is another condition that can lead to a deadlock situation in an Operating System. According to this condition, it is provided that a single program can use multiple resources for its functioning. Even after that, it requests resources from other programs. A hypothetical example can be considered. Process P is using Resource 5 and resource 6. Process Q is using resource 2. Even then Process P requests from Resource 2 from Process Q.


Resources that are assigned to the other tasks cannot be prompted. Once if a resource is held by a process, it can be not taken away from the active process. The requesting process has to wait until the process of holding this resource releases it willingly. This condition provides that a resource can in no way be preempted from a process. A process and resource will only be detached if the program by a voluntary measure let go the resources. Hence a process cannot pre-empt a resource from another process before it is done with the execution. On trying to do so, deadlock arises.

Circular wait

A circular wait causing a deadlock is a kind of a circular loop. This is generally caused due to an interconnected circular chain of processes and resources. Besides this, a series of processes that are waiting for each other in a chain system must exist. Here, each process in the chain waits for that resource detained by another process in the circular chain. This occurs when the first process is waiting to hold the resource that is held by the second process. On the other hand, the second process also waits to hold the resource that is held by the third process. This continues depending on the number of process and its resources. The endpoint of this circular loop lies where the last process waits to hold the resource held by the first process. Sounds a bit confusing, but in a practical scenario, deadlocks can hamper or cause a delay in the activities.

When we are aware of the causes of deadlock, now we can discuss the methods to handle such situations.

Methods for Handling Deadlocks

Since the description and the conditions leading to a situation of deadlock has been described. Now, we will shed light on what are the different ways of handling deadlock in an OS. One can handle deadlock issues as well as situations. There are mainly three ways to deal up with the deadlock in the operating system and they are:

Deadlock prevention or avoidance

Deadlock detection and recovery

Ignore the problem altogether

Deadlock Prevention of Avoidance

The deadlock prevention method is the easiest method for handling deadlock. In this method, deadlock can be prevented by avoiding any one of the mentioned four conditions necessary for the deadlock. Most importantly, as these four conditions are mandatory, the system can prevent deadlock in eliminating one of them.

Effective measures must be taken so that no transaction between the processes and resources takes place leading to a deadlock. Besides this, the system evaluates every transaction beforehand. If any possibility of a deadlock is seen, the transaction is seized from the action. For the prevention of deadlocks, time schemes like wait-die schemes and wound-wait schemes are used. The underlying idea behind the occurrence of deadlock is that all the instances of the Coffman Condition function at once. Deadlock can be prevented by the simple concept of failing even either of these conditions. No matter how easy or simple this may sound, the implementation of this method physically is still debatable. But then again, operators use such an interface to deal with the situations of deadlock.

In deadlock avoidance, it is checked by the OS whether the system is in a safe stage or unsafe stage. Most importantly, the avoiding process works until the system comes to safe states. Besides this, the operating system determines the distribution of resources ensuring that the resources and not creating deadlocks. This approach includes the elimination of the condition of mutual exclusion, no prompt, hold and wait and circular wait. We can prompt a resource from one process and provides it to another requesting process. This will not allow the system to go into a deadlock state.

Detection and Recovery from Deadlocks

If deadlock prevention or avoidance approach fails, detection and recovery from deadlocks is another way to deal with deadlocks. Moreover, deadlock detection is a process used to determine whether the deadlock exists or not. This approach identifies the resources as well as the process causing the deadlocks. The basic thing is to test the distribution of resources. Once the deadlock is detected, you are required to break it. It can be done using various methods such as eliminating one or more processes waiting in a circular chain. In addition to this, taking away the resources from other processes which are also deadlocks is used for recovery.

In this mechanism, OS neither neglect the occurrence of deadlocks nor utilize any method to avoid or prevent the deadlocks. For overcoming the situations of deadlocks, the OS every so often checks the systems on a regular basis. If there is any deadlock available, recovery techniques are used by the operating system for recovering the system. The recovery method includes the ending of the process in deadlocks. After ending all the process it again looks for the deadlocks. You need to repeat this process until the system becomes deadlocks free.

A deadlock can be easily detected by employing a resource scheduler. The work of a resource scheduler is to track all the resources and processes available in the system. It can track the different resources that are held by different processes. Once the tracking is done and the deadlock is detected what can be done is that all the processes employed should be terminated even though that means the loss of complete progress. After that, a few resources can be extracted and allocated to other processes before the deadlock situation is completely resolved.

Ignorance of Deadlocks Altogether

Ignorance of deadlock is an effective way of handling deadlocks by avoiding the situation to arise. Wait for graph technique can be used where the existence of an edge in the graph shows the presence of deadlock. The method of avoidance of deadlock is mainly analyzing the activities in the operating system. At every step process is followed to evaluate whether the process is safe or not. Once an unsafe activity is detected, the OS takes a step back to prevent the deadlock

This is one of the most widely used mechanisms to deal with deadlocks.