1. 主线程启动了子线程之后，主线程与子线程之间是相互独立的。默认情况下主线程是不会等待子线程执行完毕的，主线程只会按照自己的步调执行。
所以在主线程中是没法测定子线程的运行时间的。
#主线程启动子线程之后，两者是并行的，相互之间是独立的。
import threading,time
def run(n):
print('task',n)
time.sleep(2)
start_time=time.time()
for i in range(10):
t=threading.Thread(target=run,args=("t-%s"%i,))
t.start()
print("cost time is:",time.time()-start_time)
运行结果：
task t-0
task t-1
task t-2
task t-3
task t-4
task t-5
task t-6
task t-7
task t-8
task t-9
cost: 0.002000093460083008
Process finished with exit code 0
2. 用join()函数等待每个的执行结果，每个都执行完了再打印总用了的时间。
#主线程启动子线程之后，两者是并行的，相互之间是独立的。
import threading,time
def run(n):
print('task',n)
time.sleep(2)
start_time=time.time()
t_objs=[] #存线程实例
for i in range(10):
t=threading.Thread(target=run,args=("t-%s"%i,))
t.start()
t_objs.append(t) #为了不阻塞后面线程的启动，不在这里join,先放到一个列表里面。
for t in t_objs: #循环线程实例列表，等待所有线程执行完毕。
t.join() #join=wait,意思是等t的运行结果
print("All threads have finished,cost time is:",time.time()-start_time)
运行结果：
task t-0 task t-1 task t-2 task t-3 task t-4 task t-5 task t-6 task t-7 task t-8 task t-9 All threads have finished,cost time is: 2.0012001991271973 Process finished with exit code 0
3. 用 threading.current_thread 命令查看当前线程是主线程还是子线程。启用了10个线程，实际上有11个线程在执行（1个主线程+10个子线程）
#主线程启动子线程之后，两者是并行的，相互之间是独立的。
import threading,time
def run(n):
print('task',n)
time.sleep(2)
print('task done',threading.current_thread()) #打印当前线程是主线程还是子线程
start_time=time.time()
t_objs=[]
for i in range(10):
t=threading.Thread(target=run,args=("t-%s"%i,))
t.start()
t_objs.append(t)
for t in t_objs:
t.join() #join=wait,意思是等t的运行结果
print('----All threads has finished',threading.current_thread())
print("Cost time is:",time.time()-start_time)
运行结果：
task t-0 task t-1 task t-2 task t-3 task t-4 task t-5 task t-6 task t-7 task t-8 task t-9 task done <Thread(Thread-4, started 468)> task done <Thread(Thread-1, started 7768)> task done <Thread(Thread-5, started 11480)> task done <Thread(Thread-3, started 11520)> task done <Thread(Thread-6, started 7248)> task done <Thread(Thread-2, started 6752)> task done <Thread(Thread-7, started 2728)> task done <Thread(Thread-10, started 10260)> task done <Thread(Thread-8, started 12244)> task done <Thread(Thread-9, started 2112)> ----All threads has finished <_MainThread(MainThread, started 11372)> Cost time is: 2.002200126647949 Process finished with exit code 0
4. 用threading.active_count() 来查看当前活跃的线程的个数。
#主线程启动子线程之后，两者是并行的，相互之间是独立的。
import threading,time
def run(n):
print('task',n)
time.sleep(2)
print('task done',threading.current_thread()) #打印当前线程是主线程还是子线程
start_time=time.time()
t_objs=[]
for i in range(10):
t=threading.Thread(target=run,args=("t-%s"%i,))
t.start()
t_objs.append(t)
#for t in t_objs:
# t.join() #join=wait,意思是等t的运行结果
print('----All threads has finished',threading.current_thread(),threading.active_count())
print("Cost time is:",time.time()-start_time)
运行结果：
task t-0 task t-1 task t-2 task t-3 task t-4 task t-5 task t-6 task t-7 task t-8 task t-9 ----All threads has finished <_MainThread(MainThread, started 9096)> 11 Cost time is: 0.0010001659393310547 task done <Thread(Thread-1, started 10804)> task done <Thread(Thread-2, started 11564)> task done <Thread(Thread-3, started 11532)> task done <Thread(Thread-4, started 10896)> task done <Thread(Thread-7, started 1596)> task done <Thread(Thread-6, started 11116)> task done <Thread(Thread-8, started 10088)> task done <Thread(Thread-9, started 10156)> task done <Thread(Thread-10, started 10820)> task done <Thread(Thread-5, started 12180)> Process finished with exit code 0