Python学习之线程

Posted 2021-03-07 w_boy

#线程锁 又叫 互斥锁(Mutex)
import threading,time
def run(n):
    lock.acquire() #申请锁
    global num
    num+=1
    time.sleep(1)
    lock.release()  #释放锁

lock = threading.Lock()  #生成实例
num = 0
t_obj = [] #存放线程实例
for i in range(1000):
    t = threading.Thread(target=run,args=("t-%s"%i,))
    t.start()
    t_obj.append(t)
    #为了不阻塞后面线程的启动，不在这里join()，先放到列表里
for r in t_obj: #遍历线程实例列表，等待所有线程执行完毕
    t.join()  #join()的作用是为了防止子线程没结束主线程就先结束
    # 表明主线程会等待子线程执行完毕再结束。

print("finished..",threading.current_thread(),threading.active_count())
print("num:",num)

#ubuntu python2.6 可以看到num小于1000，原因如下
#python2.6每100条指令换一次gil锁，换线程执行
#thread线程执行，100条指令到了还没执行完，释放锁，不执行了，换thread2线程执行
#thread2申请锁，假设thread2执行完了，赋值count=1并释放锁
#这时thread1又可以（再次）执行了，申请gil锁，重复之前第一次执行的所有过程
#执行完count++，count=1,因为线程1执行了一半，记住了上下文放在寄存器里
#再次执行的时候从寄存器里拿数据，运算完还是1，把线程2的给覆盖了，结果还是1

# Python在同一时刻只允许一个线程修改数据，线程锁，解决上面问题
# 加了锁程序就变串行了，所以使用时数据量不要特别大，获取锁立刻释放

守护线程
import threading,time
def run(n):

    print("task",n)
    time.sleep(2)
    print("done")

start_time= time.time()
for i in range(50):
    t = threading.Thread(target=run,args=("t-%s"%i,))
    t.setDaemon(True) #把当前线程设置为守护线程，主线程结束整个程序结束
    #socket一个连接启动一个线程，设置为守护线程，当socketserver停掉整个
    #程序结束，不用等线程结束
    t.start()

#查看主线程和当前线程数
print("finished..",threading.current_thread(),threading.active_count())
print("cost:",time.time()-start_time)

简单线程

普通方法
 import threading,time
 def run(n):
     print("task",n)
     time.sleep(2)
t1=threading.Thread(target=run,args=("t1",)) t2=threading.Thread(target=run,args=("t2",))
t1.start()
t2.start()

类方法
class MyThread(threading.Thread):
    def __init__(self,n):
        super(MyThread,self).__init__()
        self.n=n

    def run(self): #必须是run
        print("running task",self.n)

t1=MyThread("t1")
t2=MyThread("t2")
t1.start()
t2.start()

 

线程间通信，使用event

# 通过Event来实现两个或多个线程间的交互，下面是一个红绿灯的例子，
# 即起动一个线程做交通指挥灯，生成几个线程做车辆，车辆行驶按红灯#
# 停，绿灯行的规则。

# event.setO
# event.clear()
# If the flag is set,the wait method doesn‘t do anything.
# 标志位设定了，代表绿灯，直接通行
# If the flag is cleared,wait will block until it becomes set again.
# 标志位被清空，代表红灯，wait等待变绿灯
# Any number of threads may wait for the same event.

import time,threading

event=threading.Event()
def lighter():
    count = 0
    event.set() #先设置绿灯
    while True:
        if count >5 and count <10: #改成红灯
            event.clear() #把标志位清了
            print("33[41;1mred light is on...33[0m")
        elif count>10:
            event.set()  #变绿灯
            print("33[42;1mgreen light is on...33[0m")
            count=0
        else:
            print("33[42;1mgreen light is on...33[0m")
        time.sleep(1)
        count+=1

def car(name):
    while True:
        if event.is_set(): #代表绿灯
            print("[%s] running..."%name)
            time.sleep(1)
        else:
            print("[%s] sees red light,waiting..." % name)
            event.wait()
            print("33[34;1m[%s] green light is on, start going..." % name)

light=threading.Thread(target=lighter,)
light.start()
car1 = threading.Thread(target=car,args=("tesila",))
car1.start()

线程间通信，使用event

# 通过Event来实现两个或多个线程间的交互，下面是一个红绿灯的例子，
# 即起动一个线程做交通指挥灯，生成几个线程做车辆，车辆行驶按红灯#
# 停，绿灯行的规则。

# event.setO
# event.clear()
# If the flag is set,the wait method doesn‘t do anything.
# 标志位设定了，代表绿灯，直接通行
# If the flag is cleared,wait will block until it becomes set again.
# 标志位被清空，代表红灯，wait等待变绿灯
# Any number of threads may wait for the same event.

import time,threading

event=threading.Event()
def lighter():
    count = 0
    event.set() #先设置绿灯
    while True:
        if count >5 and count <10: #改成红灯
            event.clear() #把标志位清了
            print("33[41;1mred light is on...33[0m")
        elif count>10:
            event.set()  #变绿灯
            print("33[42;1mgreen light is on...33[0m")
            count=0
        else:
            print("33[42;1mgreen light is on...33[0m")
        time.sleep(1)
        count+=1

def car(name):
    while True:
        if event.is_set(): #代表绿灯
            print("[%s] running..."%name)
            time.sleep(1)
        else:
            print("[%s] sees red light,waiting..." % name)
            event.wait()
            print("33[34;1m[%s] green light is on, start going..." % name)

light=threading.Thread(target=lighter,)
light.start()
car1 = threading.Thread(target=car,args=("tesila",))
car1.start()