threads

• Threads


  A basic unit of CPU utilization comprising of a Thread ID, Program counter (PC), Register set and Stack
• Threads


  • Threads share with other threads belonging to the same process its code section, data section, and other operating-system resources, such as open files and signals
• Single-threaded process


  A traditional process has a single thread of control
• Multi-threaded process


  If a process has multiple threads of control, it can perform more than one task at a time
• Applications using threads


  • Application that creates photo thumbnails from a collection of images
  • Web browser
  • Word processor
• User Level Threads (ULTs)

  Threads that are created and managed by a user-level library or runtime environment, rather than by the operating system

  
• Kernel threads


  Threads that are supported and managed directly by the operating system

  
• User Level Threads


  • POSIX threads (pthreads)
  • Java threads
  • Python threads
  • Ruby threads
• Kernel Threads


  • Linux kernel threads (kthread, keventd, ksoftirqd, kworker)
  • Windows kernel threads (System threads, Driver threads, System service threads)
  • macOS kernel threads (kernel_task, sysctl_thread, mach_thread)

  
• Many-to-one model


  Maps many user-level threads to one kernel thread

  
• One-to-one model


  Maps each user thread to a kernel thread

  
• Many-to-many model


  Multiplexes many user-level threads to a smaller or equal number of kernel threads

  
• Processes have their own resources while threads share the resources with the parent process
• Processes have separate memory spaces, while threads share the memory of the process
• Processes use IPC mechanism, while threads use shared memory and synchronization primitives
• Processes are independent, while threads are executed in the context of the parent process
• Processes are heavyweight, while threads are lightweight