GIL Global Interprete Lock

Table of Contents

GIL Overview

  • GIL enables cooperative mmultitasking
  • A running thread holds the GIL
  • GIL released on I/O (read, write, readv, writev)
  • `sys.setcheckinterval(n)
    • check for async events every n instructions
    • how long threads switches

GIL Releases and Acquisitions

The currently running thread:


  • Reset the tick counter
  • Run signal handlers if in the main thread
  • Releases the GIL
  • Reacquires the GIL

Multicore Event Handling

CPU-bound threads make GIL acquisition difficult for threads that want to handle events

Behavior of I/O Handling

  • I/O ops often do not block
  • Due to buffering, the OS is able to fulfill I/O requests immediately and keep a thread running
  • Results in GIL thrashing under heavy load