Multithreading allows multiple threads to execute in parallel within a single process, enabling more efficient utilization of system resources and faster execution for certain workloads. There are three primary models for enabling multithreading in applications: green threads, native threads, and thread pools.
Green Threads
Green threads, also known as virtual threads, are threads that are managed by a runtime library or virtual machine, rather than natively by the operating system. With green threads, a single native thread is used to multiplex multiple green threads.
greenThread1();
greenThread2();
greenThread3();The benefit of green threads is that they allow the runtime to optimize and schedule threads itself, without relying on the operating system. However, only one green thread actually executes at a time, limiting parallelism.
Native Threads
Native threads are threads created and managed directly by the operating system. The OS is responsible for scheduling and switching between native threads.
thread t1(function1);
thread t2(function2);
t1.join();
t2.join();Native threads fully leverage parallelism as the OS schedules threads across available CPU cores. However, creating too many threads can overload the system.
Thread Pools
A thread pool maintains a pool of threads for executing tasks. Instead of creating a new thread for each task, tasks are submitted to the pool.
ExecutorService pool = Executors.newFixedThreadPool(4);
pool.submit(task1);
pool.submit(task2);Thread pools allow limiting the number of threads, reducing resource usage. However, having too few threads can limit parallelism.
The choice between these models depends on the workload and desired system behavior. Green threads provide portability, while native threads maximize performance. Thread pools balance resource usage. Understanding these tradeoffs helps build efficient, scalable multithreaded applications.