![]() Each thread has the consciousness of constantly having the CPU to itself, but the CPUs time is actually sliced between all the threads. With threads, the CPU will pop around and give each thread some of its time. The threading model is a programming convenience to simplify juggling several operations at the same time within a single program. ![]() Some types of problems, such as simulationa video game, for exampleare very difficult to solve without support for concurrency. ![]() However, multithreading provides a very important organizational benefit, so that the design of your program can be greatly simplified. Therefore, it must also be possible to write the same program without using any threads. One thing to keep in mind is that a program with many threads must be able to run on a single-CPU machine. This is often the case with powerful multiprocessor web servers, which can distribute large numbers of user requests across CPUs in a program that allocates one thread per request. If you have a multiprocessor machine, multiple threads may be distributed across multiple processors, which can dramatically improve throughput. Without threading, the only reasonable solution is to poll the I/O port, which is awkward and can be difficult. For example, you might be able to do important work while youre stuck waiting for input to arrive on an I/O port. FeedbackĬoncurrency can also be used to optimize throughput. In fact, this sounds like an impossible thing to accomplish, as if the CPU must be in two places at once, but this is precisely the illusion that concurrency provides. FeedbackĪ conventional method cannot continue performing its operations and at the same time return control to the rest of the program. If you have a quit button, you dont want to be forced to poll it in every piece of code you write in your program, and yet you want the quit button to be responsive, as if you were checking it regularly. The basic problem is that the program needs to continue performing its operations, and at the same time it needs to return control to the user interface so that the program can respond to the user. Consider a program that performs some CPU-intensive operation and thus ends up ignoring user input and being unresponsive. One of the most compelling reasons for concurrency is to produce a responsive user interface. Be aware that you can easily become overconfident, so if you are writing anything complex, you will need to study dedicated books on the topic. The goal of this chapter is to give you a solid foundation in the basics of concurrency so that you can understand the concepts and write reasonable multithreaded programs. If you apply some effort, you can fathom the basic mechanism, but it generally takes deep study and understanding in order to develop a true grasp of the subject. ![]() Understanding concurrent programming is on the same order of difficulty as understanding polymorphism. Looks similar to thread support in other languages, so when you understandĪnd although support for threads can make Java a more complicated language, this isnt entirely the fault of Javathreads are tricky.Seems mysterious and requires a shift in the way you think about.With the appearance of thread support in most microcomputer operating systems, extensions for threads have also been appearing in programming languages or libraries. FeedbackĬoncurrent programming is like stepping into an entirely new world and learning a new programming language, or at least a new set of language concepts. So, you create a thread associated with that event or resource and let it run independently of the main program. There are many possible uses for multithreading, but in general, youll have some part of your program tied to a particular event or resource, and you dont want that to hold up the rest of your program. A single process can thus have multiple concurrently executing threads. A thread is a single sequential flow of control within a process. A multitasking operating system is capable of running more than one process (program) at a time, while making it look like each one is chugging along on its own, by periodically switching the CPU from one task to another. FeedbackĪ process is a self-contained running program with its own address space. Some underlying mechanism is actually dividing up the CPU time for you, but in general, you dont have to think about it, which makes programming with multiple threads a much easier task. Often, you also need to turn a program into separate, independently running subtasks.Įach of these independent subtasks is called a thread, and you program as if each thread runs by itself and has the CPU to itself. Objects provide a way to divide a program into independent sections.
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