线程：操作系统进行运算调度的最小单位，是一串单一顺序指令的集合。在python中的线程是C语言原生线程（操作系统），由操作系统管理。
由于GIL的存在，使任何时刻同一进程里只能有一个线程正在运行。
python里是不能多线程并发的，无论cpu是多少核的！
python 线程知识点：
（1）线程的创建 ：
方法一
import threading，time
def run(n):
print(n, 'start',threading.get_ident)
time.sleep(1)
print(n, 'done')
t = threading.Thread(target=run, args=(i,2))
t.start()
print(threading.current_thread())
方法二
import threading,time
class Mythread(threading.Thread):
def __init__(self,n):
super(Mythread, self).__init__()
self.n = n
def run(self):
print("xxxx %s"%self.n)
t1= Mythread('t1')
t2= Mythread('t2')
t1.start()
t2.start()
（2）线程锁：
import threading,time
num = 0
lock = threading.Lock()
def run(n):
global num
start =time.time()
lock.acquire() #进程锁(互斥锁)
for i in range(1000000):
num +=1
time.sleep(1)
lock.release()
print(n,time.time()-start)
t_obj =[]
for i in range(2):
t = threading.Thread(target=run,args=(i,))
t.start()
t_obj.append(t)
for t in t_obj:
t.join()
print("num",num)
递归锁
import threading, time
def run1():
print("grab the first part data")
lock.acquire()
global num
num += 1
lock.release()
return num
def run2():
print("grab the second part data")
lock.acquire()
global num2
num2 += 1
lock.release()
return num2
def run3():
lock.acquire()
res = run1()
print('--------between run1 and run2-----')
res2 = run2()
lock.release()
print(res, res2)
num, num2 = 0, 0
lock = threading.RLock()#递归锁
for i in range(1):
t = threading.Thread(target=run3)
t.start()
while threading.active_count() != 1:
print(threading.active_count())
else:
print('----all threads done---')
print(num, num2)
（3）守护进程：
for i in range(50):
t = threading.Thread(target=run,args=(i,))
t.setDaemon(True)#设置守护进程，主线程不需要等子线程执行完毕，程序完毕
t.start()
（4）信号量：
import threading, time
def run(n,a):
semaphore.acquire()
print("run the thread: %s\n" % n)
time.sleep(a)
semaphore.release()
if __name__ == '__main__':
semaphore = threading.BoundedSemaphore(5) # 最多允许5个线程同时运行
for i in range(22):
t = threading.Thread(target=run, args=(i,i))
t.start()
while threading.active_count() != 1:
pass # print threading.active_count()
else:
print('----all threads done---')
#print(num)
（5）队列：
queue.Queue(n)先进先出 queque.LifiQueue(n)后进先出 queue.PriorityQueue(n)可设置优先级的队列 n允许放多少个数据 queue.put(maxsize,block,timeout)放数据 block 是否堵塞 timeout 堵塞时间 queue.get(block,timeout)取数据 queue.size
import queue
q = queue.Queue(3)
q.put(1)
q.put(2)
q.put(3)
print(q.qsize())
print(q.get())
print(q.get())
print(q.get())
try:
print(q.get(block=False))
except queue.Empty as e:
print("queue is empty")
（6）事件
事件，线程之间用来同步的工具even.set()设定标志位even.clear()清除标志位even.is_set()判断是否设置even = threading.Even()
import threading,time
state_list = ['red','yellow','green']
state =''
lock = threading.Lock()
even = threading.Event()
even1 = threading.Event()
def run():
count =0
while True:
if count <10:
even.clear()
print('led state is: \033[41;1m red \033[0m \n')
elif count >=10 and count <15:
print('led state is: \033[43;1m yellow \033[0m \n')
elif count >=15 and count <25:
even.set()
print('led state is: \033[42;1m green \033[0m \n')
else:
count = 0
count +=1
time.sleep(1)
def run1():
global state
while True:
if even.is_set():
print("i am go\n")
time.sleep(1)
else:
print("i am stop\n")
even.wait()
t = threading.Thread(target=run)
t.start()
t1 = threading.Thread(target=run1)
t1.start()