Thread Pool

Abstract

A group of fixed-number worker Thread that are reused to execute tasks submitted to Task Queue by a client. The number of Thread is usually the number of cores the system has. Less will lead to wasted CPU power, more will introduce Context Switch which has overhead, unless the task isn’t cpu-bounded
Commonly used in scenarios where tasks are small, numerous, and independent(stateless). Examples include web servers handling HTTP requests and applications that perform many asynchronous I/O operations

By limiting the number of Thread that can be active at any one time
A thread pool can help to ensure that the system does not become overwhelmed with too many concurrent threads, which can reduce performance due to Context Switch or lead to resource thrashing

Creating a new thread is an expensive operation, so reusing threads can improve performance

Make sure the Task Queue is manipulated by one Thread at a time
Otherwise, we may we may have more than 1 thread processing the same task where Race Condition (竞态条件) happens
Thus, we need to have Mutex (互斥体) on the Task Queue

Make sure Thread that is idle not keep checking for tasks which will result in wasted computation

Tasks that need to be executed are placed in a queue
When a Thread becomes available, it pulls a task from the queue and executes it
After completing the task, the thread returns to the pool to await the next assignment