![]() Otherwise, some of these tasks may be put into a queue to wait for their turn. This means that if the number of simultaneously running tasks is always less than or equal to two, they get executed right away. Here, we instantiate a ThreadPoolExecutor with a fixed thread count of 2. (ThreadPoolExecutor) Executors.newFixedThreadPool(2) ĪssertEquals(1, executor.getQueue().size()) This means that the number of threads in this thread pool is always the same: ThreadPoolExecutor executor = newFixedThreadPool method creates a ThreadPoolExecutor with equal corePoolSize and maximumPoolSize parameter values and a zero keepAliveTime. These parameters cover a wide range of use cases, but the most typical configurations are predefined in the Executors static methods. In order to apply the same removal policy to core threads, we can use the allowCoreThreadTimeOut(true) method. By default, the ThreadPoolExecutor only considers non-core threads for removal. The keepAliveTime parameter is the interval of time for which the excessive threads (instantiated in excess of the corePoolSize) are allowed to exist in the idle state. When a new task comes in, if all core threads are busy and the internal queue is full, the pool is allowed to grow up to maximumPoolSize. ![]() The corePoolSize parameter is the number of core threads that will be instantiated and kept in the pool. It also consists of some excessive threads that may be spawned and then terminated when they are no longer needed. The pool consists of a fixed number of core threads that are kept inside all the time. The main configuration parameters that we’ll discuss here are corePoolSize, maximumPoolSize and keepAliveTime. The ThreadPoolExecutor is an extensible thread pool implementation with lots of parameters and hooks for fine-tuning. Both of these are functional interfaces, and we can pass them as lambdas (starting with Java 8). Here, we overload the submit method to take either Runnable or Callable. Of course, in a real-life scenario, we usually don’t want to call future.get() right away but defer calling it until we actually need the value of the computation. Now we’ll create an ExecutorService, submit a task and then use the returned Future‘s get method to wait until the submitted task finishes and the value is returned: ExecutorService executorService = Executors.newFixedThreadPool(10) įuture future = executorService.submit(() -> "Hello World") Using this interface, we can submit the tasks for execution and also control their execution using the returned Future instance. The ExecutorService interface contains a large number of methods to control the progress of the tasks and manage the termination of the service. We’ll submit the task as a lambda (a Java 8 feature), which is inferred to be Runnable: Executor executor = Executors.newSingleThreadExecutor() Įxecutor.execute(() -> ("Hello World")) 3.1.2. Here, we run a single task that simply prints “Hello World “ on the screen.
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