Java supports single-thread as well as multi-thread operations. A single-thread program has a single entry point (the main() method) and a single exit point. A multi-thread program has an initial entry point (the main() method), followed by many entry and exit points, which are run concurrently with the main(). The term "concurrency" refers to doing multiple tasks at the same time.
Java has built-in support for concurrent programming by running multiple threads concurrently within a single program. A thread, also called a lightweight process, is a single sequential flow of programming operations, with a definite beginning and an end. During the lifetime of the thread, there is only a single point of execution. A thread by itself is not a program because it cannot run on its own. Instead, it runs within a program. The following figure shows a program with 3 threads running under a single CPU:
Modern operating systems (such as Windows and UNIX) are multitasking system. A multitasking system can perform many tasks concurrently by sharing the computing resources, such as CPU(s), main memory, and I/O channels. In a single-CPU machine, only one task can be executed at one time – through time-slicing of the CPU. In a multi-CPU machine, a few tasks can be executed simultaneously, either distributed among or time-slicing the CPUs.
Multitasking is necessary in today's operating systems for better performance by making full use and optimize the usage of the computing resources. There are generally two kinds of multitasking operating systems:
Java has built-in support for concurrent programming by running multiple threads concurrently within a single program. A thread, also called a lightweight process, is a single sequential flow of programming operations, with a definite beginning and an end. During the lifetime of the thread, there is only a single point of execution. A thread by itself is not a program because it cannot run on its own. Instead, it runs within a program. The following figure shows a program with 3 threads running under a single CPU:
1.1 Multitasking (or Multi-processing)
Modern operating systems (such as Windows and UNIX) are multitasking system. A multitasking system can perform many tasks concurrently by sharing the computing resources, such as CPU(s), main memory, and I/O channels. In a single-CPU machine, only one task can be executed at one time – through time-slicing of the CPU. In a multi-CPU machine, a few tasks can be executed simultaneously, either distributed among or time-slicing the CPUs.
Multitasking is necessary in today's operating systems for better performance by making full use and optimize the usage of the computing resources. There are generally two kinds of multitasking operating systems:
- Co-operative multitasking systems: Each task must voluntarily yield control to other tasks. This has the drawback that a run-away or uncooperative task may hang the entire system.
- Pre-emptive multitasking systems: Tasks are given time-slices of the CPU(s) and will be forced to yield control to other tasks once their allocation is used up.
