When D runs, it first call the countDownLatch. A, B, and C each will use the countDownLatch. And when all of them three finish running, the counter will be reduced to 0; then, the await method of D will be triggered to end A, B, and C, and D will start to go on executing. Therefore, CountDownLatch is suitable for the situation where one thread needs to wait for multiple threads. Three runners prepare themselves apart, and then they start to run at the same time after each of them is ready.
This time, each of the three threads A, B, and C need to prepare separately, and then they start to run simultaneously after all of them three are ready. How should we achieve that? The CountDownLatch above can be used to count down, but when the count is completed, only one of the threads' await method will get a response, so multiple threads cannot be triggered at the same time.
In order to achieve the effect of threads' waiting for each other, we can use the CyclicBarrier data structure, and its basic usage is:. The implementation code is as follows. Imagine that there are three runners who need to start to run simultaneously, so they need to wait for others until all of them are ready.
In actual development, often we need to create child threads to do some time-consuming tasks, and then pass the execution results back to the main thread.
So how to implement this in Java? So generally, when creating the thread, we'll pass the Runnable object to Thread for execution. Runnable interface or extending java.
Thread class and then extending run method. Thread has its own variables and methods, it lives and dies on the heap. But a thread of execution is an individual process that has its own call stack. Thread are lightweight process in java. A: Yes, Threads have their own stack. This is very interesting question, where interviewer tends to check your basic knowledge about how threads internally maintains their own stacks. Shown in figure below. Q: What is multithreading?
A: Multithreading is a process of executing multiple threads simultaneously. Multithreading is used to obtain the multitasking. It consumes less memory and gives the fast and efficient performance.
Its main advantages are: Threads share the same address space. The thread is lightweight. The cost of communication between the processes is low. Q: What do you understand by inter-thread communication? A: The process of communication between synchronized threads is termed as inter-thread communication. Inter-thread communication is used to avoid thread polling in Java. The thread is paused running in its critical section, and another thread is allowed to enter or lock in the same critical section to be executed.
It can be obtained by wait , notify , and notifyAll methods. Q: How can you say Thread behaviour is unpredictable? A: Thread behaviour is unpredictable because execution of Threads depends on Thread scheduler, thread scheduler may have different implementation on different platforms like windows, unix etc. Same threading program may produce different output in subsequent executions even on same platform.
To achieve we are going to create 2 threads on same Runnable Object, create for loop in run method and start both threads. There is no surety that which threads will complete first, both threads will enter anonymously in for loop. Q: How can you ensure all threads that started from main must end in order in which they started and also main should end in last? A: We can use join methodto ensure all threads that started from main must end in order in which they started and also main should end in last.
In other words waits for this thread to die. Calling join method internally calls join 0. Q: What is difference between starting thread with run and start method? A: When you call start method, main thread internally calls run method to start newly created Thread, so run method is ultimately called by newly created thread. When you call run method main thread rather than starting run method with newly thread it start run method by itself.
Q: What is significance of using Volatile keyword? A: Java allows threads to access shared variables. As a rule, to ensure that shared variables are consistently updated, a thread should ensure that it has exclusive use of such variables by obtaining a lock that enforces mutual exclusion for those shared variables.
If a field is declared volatile, in that case the Java memory model ensures that all threads see a consistent value for the variable. Note: volatile is only a keyword, can be used only with variables.
Q: What is race condition in multithreading and how can we solve it? A: When more than one thread try to access same resource without synchronization causes race condition.
So we can solve race condition by using either synchronized block or synchronized method. When no two threads can access same resource at a time phenomenon is also called as mutual exclusion.
Q: When should we interrupt a thread? A: We should interrupt a thread when we want to break out the sleep or wait state of a thread. We can interrupt a thread by calling the interrupt throwing the InterruptedException.
Q: What is the purpose of the Synchronized block? A: The Synchronized block can be used to perform synchronization on any specific resource of the method. Only one thread at a time can execute on a particular resource, and all other threads which attempt to enter the synchronized block are blocked. Synchronized block is used to lock an object for any shared resource.
The scope of the synchronized block is limited to the block on which, it is applied. Its scope is smaller than a method. Q: What is the difference between notify and notifyAll? A: The notify is used to unblock one waiting thread whereas notifyAll method is used to unblock all the threads in waiting state. Q: How to detect a deadlock condition? How can it be avoided? A: We can detect the deadlock condition by running the code on cmd and collecting the Thread Dump, and if any deadlock is present in the code, then a message will appear on cmd.
Ways to avoid the deadlock condition in Java: Avoid Nested lock: Nested lock is the common reason for deadlock as deadlock occurs when we provide locks to various threads so we should give one lock to only one thread at some particular time. However, my question is more like, how could I get two on-screen elements to communicate to one another, rather than having them communicate with the UI.
How many threads are you using and what is each thread responsible for? Before either thread performs an action it could check the member variable of the other thread and respond accordingly. Back to your question - here are a couple of thoughts: If this is a GUI application and you want to have a background thread do some work, check out SwingWorker. Anyhow, good luck. Guido Simone Guido Simone 7, 2 2 gold badges 17 17 silver badges 19 19 bronze badges.
Using multiple threads is not always better Would this be accomplished through concurrency techniques or instead something like an ActionListener? Peter Lawrey Peter Lawrey k 73 73 gold badges silver badges bronze badges.
I understand that they can both be doing things if they aren't waiting. The question is how to have them communicate while both are running. Essentially, how to have them "send messages to one another" as you say, without one waiting on the other to do so.
Then you need a producer-consumer queue, I guess. Many threads loop around P-C queue reads - very common design. The inter-thread messages queue up until the consumer gets around to actioning them. I would use an ExecutorService to have threads working together. You give the thread pool work and correct the results when you need them — Peter Lawrey. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. It's right time to invest in Cryptocurrencies Dogecoin!
Basic units of execution in concurrent programming. Is concurrency possible on simple single processor systems without multiple processors? Define Processes. Define Threads. What is the default thread of every Java application? When does Thread Interference occur? Thread Objects. How do you create a Thread? Which approach is recommended? Does Thread class implements Runnable? What is the signature of Thread run method?
Define synchronization. Can a thread be interrupted when it is in sleep? Does sleep method throws any Exception? Can the start method be called twice on the same Thread? OR Can the start method invoked again on the same thread object after start been called first time? Why do we call Thread. Consumer Producer problem. Difference between Thread. How do you interrupt an thread that does not call any method that throws InterruptedException?
Interrupts An example for join long milliseconds. Explain the interrupt mechanism. Can run method throw exception? Difference between sleep and wait method in Java. What is thread starvation? What is livelock in multithreading? Explain race condition in multithreading. What causes starvation in threads? Difference between deadlock and livelock in Java multithreading. What is Slipped Condition in multithreading?
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