The python thread GIL

前言：

• C python global interpreter lock has GIL

• The impact of the use of multi-threading performance

test 4 核的 window电脑

    
    import time
    
    def time_need(func):
        def inner(*args, **kwargs):
            start = time.time()
            ret =  func(*args, **kwargs)
            stop = time.time()
            print(stop - start)
            return ret
        return inner
    
    @time_need
    def countdown(n):
        while n > 0:
            n -= 1
    
    if __name__ == '__main__':
        COUNT = 100000000
        countdown(COUNT)
    
    
    时间  4.45 平均

    
    import time
    from threading import Thread
    
    def time_need(func):
        def inner(*args, **kwargs):
            start = time.time()
            ret =  func(*args, **kwargs)
            stop = time.time()
            print(stop - start)
            return ret
        return inner
    
    @time_need
    def countdown(n):
        while n > 0:
            n -= 1
    
    if __name__ == '__main__':
        COUNT = 100000000
        大专栏  python中的线程与GILs="n">t1 = Thread(target=countdown, args=(COUNT//2,))
        t2 = Thread(target=countdown, args=(COUNT//2,))
        t1.start();t2.start()
        t1.join();t2.join()
    
    
    time  15.05

python thread

• System-level threads

    • Python threads are real system threads 
        • POSIX threads (pthreads)
        • Windows threads
  

• The main thread control

  • Fully managed by the host operating system
  

• It represents the Python interpreter threaded execution process (is written in C)

  • Represent threaded execution of the Python interpreter process (written in C)
  

You can not be executed in parallel

GIL interpreter so that only one thread running

• When a thread is running, it holds the GIL
• GIL released on I/O (read,write,send,recv,etc.)

CPU bound compute-intensive tasks

CPU密集型的线程(Not execute IO operations) are treated specially

Periodically checks per check every 100 ticks

通过设置 sys.setcheckinterval() 可以修改周期
  
ticks 不是时间概念，它对应着python解释器的指令 

Currently running thread will execute a periodic motion:

• Resets the tick counter  重置tick counter
• Runs signal handlers if the main thread  主线程会运行 signal handler
• Releases the GIL       释放GIL锁
• Reacquires the GIL     获取GIL锁

GIL and principles thread switch

(1) python lock

python interpreter provides only one type of lock (in C language), constructed to achieve 线程同步的原型

不是简单的互斥锁

It is a binary structure 二进制信号量 pthreads互斥锁and条件变量

Lock structure:

locked = 0                  # Lock status
mutex = pthreads_mutex()   # Lock for the status
cond = pthreads_cond()     # Used for waiting/wakeup

Operating mode:

(2) the thread switch