Thread Dump is a very useful tool for diagnosing problems with Java applications. Every Java virtual machine has the ability to generate a thread-dump of the state of all threads at a given point in time. Although the thread dump printed by each Java virtual machine varies slightly, most of them provide a snapshot of the currently active thread and a stack trace of all Java threads in the JVM. The stack information usually contains the full class name and the methods executed and, if possible, the source code line number.
Java’s multithreading mechanism essentially accomplishes two things, asynchronous computation and concurrency. Concurrency is solved by a series of APIs that address thread safety; asynchronous computation, on the other hand, is commonly used with Runnable and Callable in conjunction with threads.
FutureTask is a cancelable asynchronous callable API based on the Runnable implementation.
Basic usage Future represents the result of an asynchronous computation, and is executed via the ExecutorService’s Future<? > submit(Runnable task) method of the ExecutorService, which is used as the return value.
Introduction By default, ForkJoinPool creates a thread for each processor, and parallelStream will use this shared thread pool to submit tasks if not specified.
So how do we handle a specific situation where we want to use a custom ForkJoinPool?
Common operations If we want to do an addition from 1 to 1000, we can use parallel stream like this.
List<Integer> integerList= IntStream.range(1,1000).boxed().collect(Collectors.toList()); ForkJoinPool customThreadPool = new ForkJoinPool(4); Integer total= integerList.
Virtual threading is something I’m really excited about. It’s a long-awaited feature in the language and we’ve made very few attempts to implement it in the past, but it’s finally here and it’s been merged into Java 19. This means that it will be included as a preview feature and we will be able to use it as soon as JDK 19 is released.
Most of the content on the virtual (green) threads is written by non-Java developers, why is that?
Project Loom ( JEP 425 ) is probably one of the most anticipated additions to Java ever. Its implementation of virtual threading (or “green threading”) ensures that developers can create highly concurrent applications, such as those with hundreds of thousands of open HTTP connections, adhering to the well-known thread-per-request programming model without resorting to less familiar and often more complex reactive methods.
Only recently, after several years of effort, has Loom been merged into the main line of the OpenJDK and made available as a preview feature in the latest Java 19 early access release.
Introduction In modern computer systems, there can be multiple CPUs, and each CPU can have multiple cores. In order to take full advantage of the capabilities of modern CPUs, JAVA introduced multithreading, where different threads can run on different CPUs or different CPU cores at the same time. However, for JAVA programmers it is possible to control how many threads are created, but which CPU the threads are running on is generally difficult to know.
Preface In Java, threads are the counterpart of system threads and are used to handle a range of system resources. The number of threads that can be opened is limited in both windows and linux, so if you create unlimited threads in your java program, you will encounter a situation where no threads can be created.
CPU cores are limited and if there are multiple threads running at the same time, the CPU will rotate according to the priority of the threads and allocate a specific amount of CPU time to each thread.
Preface Fork join framework is the introduction of java 7 framework, the introduction of this framework is mainly to improve the ability of parallel computing.
Fork join has two main steps, the first is fork, a large task into many small tasks, the second is join, the results of the first task join up to generate the final result. If there is no return value in the first step, join will wait until all the small tasks are finished.
Preface There are two types of threads in java, user threads and daemon threads.
User threads are high priority threads and the JVM will wait for all the User Threads to finish running before it finishes running.
daemon threads are low-priority threads that serve User Threads. Because daemon threads are low priority and serve only user threads, the JVM will automatically exit when all user threads are finished, regardless of whether there are still daemon threads running.
Preface In the previous articleAbstractQueuedSynchronizer implementation principle - 1, we explained the acquisition and release of exclusive synchronization state in AbstractQueuedSynchronizer, and here we start to explain the acquisition and release of shared synchronization state in AbstractQueuedSynchronizer.
Shared Synchronous State Acquisition and Release Shared lock as the name implies is that multiple threads can share a lock, use acquireShared in the synchronizer to get the shared lock (synchronous state), the source code of the method is as follows.
