What is the difference between a deadlock and a livelock?

If you are developing or deploying cloud applications, you may encounter concurrency issues that affect the performance and reliability of your system. One of these issues is when two or more processes are waiting for each other to release a resource, resulting in a deadlock. Another issue is when two or more processes are repeatedly changing their state in response to each other, resulting in a livelock. In this article, you will learn what is the difference between a deadlock and a livelock, how to identify them, and how to prevent or resolve them.

1 Deadlock definition

A deadlock is a situation where two or more processes are holding a resource that another process needs, and none of them can proceed until the other releases the resource. For example, suppose process A has a lock on file X and needs a lock on file Y, and process B has a lock on file Y and needs a lock on file X. Neither process can continue until the other releases the file they need, so they are stuck in a deadlock.

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TARUN KUMAR CHOUKSEY

B.E./ B.TECH at GYAN GANGA COLLEGE OF TECHNOLOGY, JABALPUR
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A deadlock is a situation that occurs when processes block each other with resource acquisition and makes no further progress. Livelock is a deadlock-like situation in which processes block each other with a repeated state change yet make no progress.

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2 Livelock definition

A livelock is a situation where two or more processes are constantly changing their state in response to each other, but none of them can make any progress. For example, suppose process A and process B are trying to access a shared resource, and they use a random backoff algorithm to avoid collisions. If they happen to choose the same backoff time repeatedly, they will keep retrying and failing to access the resource, so they are stuck in a livelock.

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3 Deadlock detection

One way to detect a deadlock is to use a resource allocation graph, which shows the processes and the resources they hold or request. A deadlock exists if the graph has a cycle, meaning that there is a circular dependency among the processes and resources. For example, the following graph shows a deadlock between processes A, B, and C, and resources X, Y, and Z.

A -> X
X -> B
B -> Y
Y -> C
C -> Z
Z -> A

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4 Livelock detection

One way to detect a livelock is to monitor the state changes and the progress of the processes over time. A livelock exists if the processes are changing their state frequently, but none of them are moving closer to their goal. For example, the following table shows the state changes and the progress of processes A and B over time, as they try to access a shared resource.

Time | Process A | Process B | Progress
0    | Request   | Request   | None
1    | Fail      | Fail      | None
2    | Backoff   | Backoff   | None
3    | Request   | Request   | None
4    | Fail      | Fail      | None
5    | Backoff   | Backoff   | None
...

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5 Deadlock prevention

One way to prevent a deadlock is to use a resource ordering protocol, which assigns a unique priority to each resource and requires the processes to request the resources in ascending order of priority. This way, no process can hold a lower-priority resource while waiting for a higher-priority resource, and no cycle can form in the resource allocation graph. For example, if we assign X = 1, Y = 2, and Z = 3, then process A must request X before Y, and process B must request Y before Z.

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Teguh Sutanto
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Banker's algorithm is one of the solution. The Banker's Algorithm is a resource allocation and deadlock avoidance algorithm used in operating systems to manage multiple processes requesting resources. Developed by Edsger Dijkstra, it aims to avoid deadlocks by determining whether a resource allocation request will leave the system in a safe state.

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6 Livelock prevention

One way to prevent a livelock is to use a fair arbitration mechanism, which ensures that each process has a chance to access the shared resource in a reasonable time. This way, no process can be starved or blocked by another process for too long, and no process can waste time by retrying too frequently. For example, if we use a round-robin scheduling algorithm, then process A and process B will take turns to access the resource, and each of them will make progress every other time slot.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Teguh Sutanto
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In summary, a deadlock involves processes waiting for each other, resulting in a complete halt, while a livelock involves processes actively trying to resolve a conflict but getting stuck in an unproductive loop, leading to a perpetual state of contention without progress. Both scenarios can disrupt the normal flow of a concurrent system and require careful design and handling to avoid or resolve.

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What is the difference between a deadlock and a livelock?

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1 Deadlock definition

2 Livelock definition

3 Deadlock detection

4 Livelock detection

5 Deadlock prevention

6 Livelock prevention

7 Here’s what else to consider

Computer Science

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What is the difference between a deadlock and a livelock?

1

2

3

4

5

6

7

1 Deadlock definition

2 Livelock definition

3 Deadlock detection

4 Livelock detection

5 Deadlock prevention

6 Livelock prevention

7 Here’s what else to consider

Computer Science

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