Concurrency Interview Questions
What Is Concurrency?
Concurrency means parallel processing. The English word “process” means to go through a procedure or an operation, and parallel means that things happen at the same time, like threads of yarn running together in rope. Concurrency is about many things happening at the same time on one computer system; some mathematical expressions while others are calculating your body mass index while some other ones are classifying your body fluid for disease detection; while someone else is thinking about making a new invention. There may be two or more people at work on the task at the same time depending on their skill and availability for this work. let’s read further and get to know about Concurrency Interview Questions .
Some Example Concurrency Interview Questions Along With Answers:
Below are few Concurrency Interview Questions
1. What is multi-threading?
Multi-threading is the concurrent execution of program code as time slices allotted by a scheduler (time-slicing). The operating system kernel sets up a context for each thread, which includes its call stack, registers, and data space. A program can have several themes running at the same time. Running programs on a single processor requires that they share use of that processor, either with a time-sharing scheduler or with a multitasking operating system capable of switching from one task to another so rapidly as to appear to be executing them concurrently.
2. What are the challenges of multitasking programming?
Multitasking refers to several tasks being executed at the same time. This can be done by an operating system that allows processes to overlap in execution, as in virtual memory (RAM) overcommitment, oversubscribed processors, or distributed processing.
Multi-threading is a broader concept; it refers to the concurrent execution of program code as time slices allotted by a scheduler independent of any particular process (thread). Multiple interleaved threads can execute simultaneously: interleaving references and communication between threads serves the purpose of sharing common resources and avoids re-entrant code.
3. What is the difference between concurrency and parallelism?
One of the major challenges of concurrent programming is how to synchronize two or more actions that have to happen at the same time. The difference between concurrency and parallelism is that concurrency allows process execution to be divisible by time, while parallelism implies simultaneously running multiple processes. Parallel computing isomorphically means doing similar things at approximately the same time, but it might also mean not doing the things similarly.
4. What are some real-world applications of concurrency?
Applications include security rating systems, system load balancing, image processing, and compiler optimization.
5. What are some possible problems of concurrency?
The concurrency issue can have several sub-problems, which are communication problems between threads, synchronization problems, and mutual exclusion problems. The communication problem can be solved by communication libraries. The synchronization problem is known as race condition or deadlock. Mutual exclusion problems are usually caused by deadlocks or infinite loops.
6. How do you overload a single CPU to handle different types of tasks?
Multi-threaded applications, especially servers, require the ability to concurrently handle multiple concurrent requests. There are two ways to achieve this:
The main challenge in designing a concurrent application is to coordinate the threads to share common resources without interfering with each other. The challenge is harder for multiprocessor architectures, as they require additional attention to avoid what is described as a data-races problem where one thread modifies a memory location while another one reads from it causing inconsistency in the computation. The solution used by modern programming languages is the separation of mutable and immutable data. This separation has proved effective enough to create a viable alternative approach in computer architecture called Software Transactional Memory.
Operating systems provide multiple threads of execution within one process address space, which is particularly useful in multi-threaded servers. These threads can be distinguished by the different priorities assigned by the scheduler, the wait time they have to experience before getting access to the processor, or for others to finish their work. This approach is useful in multitasking kernel designs.
7. What are ‘lightweight threads’ and what are their uses?
Light Weight Threads are processes that are not given real-time priority but are given some amount of CPU time among all the other processes that may also be running on that machine at that particular point in time. They operate more like a normal process with an open file descriptor table so they can do things like fork themselves. They are useful in a few cases, namely for a pre-load library, where the amount of time it takes to load the library is factored into the overall execution speed of the process. A common use case is a logging thread that does not run as a separate process but as a thread in the main program.
8. What is asynchrony?
In computer science, asynchrony refers to the concept of independence between parts of a single program or across multiple communicating programs or threads. It means that an operation or event that normally would be synchronous need not be complete before another start, and multiple operations may run in parallel without waiting for each other.
9. What are some challenges of async/await?
The challenge of asynchronous programming is to give the illusion of synchronous execution. Concurrency can be achieved by simply deferring the execution of one or more computations until the outcome of another computation is known. This approach however results in significant overhead, as several instances of the same computation must be kept track of and manipulated by separate threads. Another approach is to use cooperative data structures where two or more computations are placed into queues that run in parallel, with each waiting on the outcome of the other before its result is computed.
10. How are GUI threads different from worker threads?
GUI thread is a thread that is used to handle the graphic user interface while worker threads handle the processing of background tasks. The main difference between the two is that while the GUI thread facilitates direct interaction between the application and the user, worker threads are used for background processing.
11. How are GUI threads different from multi-threading?
The main difference between GUI threads from multi-threading is that GUI thread allows an application to interact with the user directly while multi-threading allows all tasks running in a computer to be executed at the same time and not necessarily in an order which makes sense.
12. What is a UI thread and how is it different from other threads?
The UI thread is used to maintain the interface with the user and has a dedicated message loop for listening for events such as window messages or mouse clicks. As such, there can only be one instance of this type of thread, as opposed to worker threads, where many instances may exist at once.
13. What is the difference between UI thread and timer thread?
The main difference between UI threads and timer threads is that, while UI threads are used for handling the event-driven interface, timer threads are used as a way to perform a certain task at given intervals, such as checking for updates or downloading data from a server. Timer threads have the advantage of being non-blocking so their execution does not halt other actions from being executed by the computer. Since they use system timers, they do not require much code and can be quite easy to implement. start: do: end:
14. What is the difference between UI thread and worker thread?
The main difference between UI threads and worker threads is that, while the former facilitates direct interaction with the user, the latter is used for background processing. Worker threads can run many times at once, with each worker having its independent memory stack. The maximum number of worker threads that can be created at once depends on system resources. Worker threads also have their dedicated event loop so they can interact with windows through windows messages.
15. What are some factors that influence thread creation?
Creating threads requires that run time support be enabled on the system for thread creation and management. Ideally, the threads will run on different cores. However, there is no guarantee that this will happen because processors only support a certain number of cores and it is up to the operating system to decide which threads get assigned to which core. This means that thread creation cannot be 100% strictly controlled. There are also situations when two or more applications attempt to use the same core at once, so there may be a wait time before a thread can be assigned a core. Another factor that influences thread creation is the locality of reference in code objects being used by the application. Code objects can be stored in memory while being executed, stored on a disk for future use, or stored in ROM for permanent storage. This results in considerable overhead when creating application threads.
To choose the right programming language for your next project, you should always evaluate your requirements, especially if it’s related to any specific platform. Your choice of language boils down to the OS it supports and the libraries you want to use.
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