标签：tps new done join queue 一个 任务 target cti
在Python中，使用多线程multi-threading可以『同时』执行多个任务，比如你需要一个线程来复制读取信息，另一个线程来解析。为什么这里的同时要加引号呢，这是由于Python中GIL，也就是全局锁，看似同时执行多个任务，实际上是分布执行的，只不过各自完成不同的任务会提高工作效率。如果你不了解GIL，请看下图
实例1
import threading
def job():
info = "this is an added thread, which is %s" % threading.current_thread
print(info)
def main():
print(threading.active_count())
print(threading.enumerate())
#print(threading.current_thread())
# 创建一个Thread对象，让他来复制job任务
new_thread = threading.Thread(target=job)
# 执行线程任务
new_thread.start()
print(threading.active_count())
if __name__ == '__main__':
main()运行结果：
1
[<_MainThread(MainThread, started 140637982934784)>]
this is an added thread, which is <function current_thread at 0x7fe8cd92d378>
2解释一下：
实例2
import threading
import time
def job():
print('T1 start\n')
# 让任务延迟一下
for i in range(10):
time.sleep(0.1)
print('T1 finish\n')
def job2():
print('T2 start\n')
# 任务不延迟
print('T2 finish\n')
def main():
thread1 = threading.Thread(target=job,name='T1')
thread2 = threading.Thread(target=job2,name='T2')
thread1.start()
thread2.start()
#thread1.join()
print('all done')
if __name__ == '__main__':
main()运行结果：
T1 start
T2 start
T2 finish
all done
T1 finish会发现all done并不是在最后执行的，怎么办呢？试试把join方法解除封（注）印（释），请看结果：
T1 start
T2 start
T2 finish
T1 finish
all done解释一下：
实例3
import threading
from queue import Queue
import time
def job(l,q):
for i in range(len(l)):
l[i] = l[i]**2
q.put(l)
def multithreading(data):
q = Queue()
threads = []
THREAD_NUM = 4
for i in range(THREAD_NUM):
t = threading.Thread(target=job,args=(data[i],q))
t.start()
threads.append(t)
for t in threads:
t.join()
results = []
for _ in range(THREAD_NUM):
results.append(q.get())
print(results)
def unithreading(data):
for i in range(len(data)):
l = data[i]
for j in range(len(l)):
data[i][j] = data[i][j]**2
print(data)
if __name__ == '__main__':
data1 = [[1],[2,3],[4,5,6],[7,8,9,10]]
data2 = [[1],[2,3],[4,5,6],[7,8,9,10]]
time1 = time.clock()
unithreading(data1)
time2 = time.clock()
multithreading(data2)
time3 = time.clock()
runtime_uni = time2 - time1
runtime_multi = time3 - time2
print("Runtime for unithreading is %s seconds." % runtime_uni)
print("Runtime for multithreading is %s seconds." % runtime_multi)运行结果：
[[1], [4, 9], [16, 25, 36], [49, 64, 81, 100]]
[[1], [4, 9], [16, 25, 36], [49, 64, 81, 100]]
Runtime for unithreading is 4.300000000000137e-05 seconds.
Runtime for multithreading is 0.001118000000000001 seconds.解释一下：
实例4
import threading
def job1():
global A
#global A,lock
#lock.acquire()
for i in range(10):
A += 1
print('job1',A)
#lock.release()
def job2():
global A
#global A,lock
#lock.acquire()
for i in range(10):
A += 10
print('job2',A)
#lock.release()
if __name__ == '__main__':
lock = threading.Lock()
A = 0
t1 = threading.Thread(target=job1)
t2 = threading.Thread(target=job2)
t1.start()
t2.start()
t1.join()
t2.join()运行结果：
job1job2 111
job1job2 1222
job1job2 2333
job1job2 3444
job1job2 4555
job1job2 5666
job1job2 6777
job1job2 7888
job1job2 8999
job1job2 100110你会发现这打印得错乱了，这也是多个线程交替工作得原因，如果先想要规定一个线程工作的时候防止别的线程干扰，需要怎么做呢？试试使用lock（注释部分）吧，再运行一下：
job1 1
job1 2
job1 3
job1 4
job1 5
job1 6
job1 7
job1 8
job1 9
job1 10
job2 20
job2 30
job2 40
job2 50
job2 60
job2 70
job2 80
job2 90
job2 100
job2 110解释一下：
多线程的简单应用就到这里，我们最开始说过由于GIL，Python得多线程并不是真正的去同时执行多个任务，那么有没有办法弥补呢？有，那就是多进程！你一定听说过多核吧，下次再讲：）
标签：tps new done join queue 一个 任务 target cti
原文地址：https://www.cnblogs.com/mrdoghead/p/12121416.html
