A thread is a single execution sequence that represents a separately schedulable task. Doing so, threads provide the illusion of an infinite number of processors.
- Single execution sequence: Each thread executes a sequence of instructions, just as in the familiar sequential programming model.
- Separately schedulable task: The operating system can run, suspend (block), or resume a thread at any time.
Threads can run either in a process or in the kernel; there is also shared state that is not saved or restored when switching the processor between threads.
Advantages
Using threads to express and manage concurrency has several advantages.
- Expressing logically concurrent tasks: Threads eneable the expression of an applicationās natural concurrency by writing each concurrent task as a separate thread.
- Shifting work to run in the background: To improve user responsiveness and performance, a common design pattern is to create threads to perform work that in the background, without the user waiting for the result.
- Exploiting multiple processors: Programs can use threads on a multiprocessor to do work in parallel; they can do the same work in less time or more work in the same elapsed time.
- Managing I/O devices: By running tasks as separate threads, when one task is waiting for I/O, the processor can make progress on a different task.