python如何控制进程或者线程的个数
背景
日常开发中，难免遇到并发场景，而并发场景难免需要做流量控制，即需要对并发的进程或者线程的总量进行控制。今天简单总结两种常用的控制线程个数的方法。
方法一：进程池/线程池
如下例demo所示，创建了一个大小是4的进程池，然后创建5个进程，并启动
frommultiprocessingimportPool
importos,time,random
deflong_time_task(name):
print('Runtask%s(%s)...'%(name,os.getpid()))
start=time.time()
time.sleep(random.random()*3)
end=time.time()
print('Task%sruns%0.2fseconds.'%(name,(end-start)))
if__name__=='__main__':
print('Parentprocess%s.'%os.getpid())
p=Pool(4)
foriinrange(5):
p.apply_async(long_time_task,args=(i,))
print('Waitingforallsubprocessesdone...')
p.close()
p.join()
print('Allsubprocessesdone.')
运行结果如下，可以看到第5个进程会等池子里的进程完成一个后才会被启动
Runtask0(32952)... Runtask1(32951)... Runtask2(32953)... Runtask3(32954)... Task2runs0.68seconds. Runtask4(32953)... Task1runs1.41seconds. Task0runs1.44seconds. Task4runs2.15seconds. Task3runs2.98seconds. Allsubprocessesdone.
方法二：queue
queue模块即队列，特别适合处理信息在多个线程间安全交换的多线程程序中。下面的demo展示了如何通过queue来限制线程的并发个数
importthreading
importqueue
importtime
importrandom
importos
maxThreads=4
classStore(threading.Thread):
def__init__(self,q):
threading.Thread.__init__(self)
self.queue=q
#self.store=store
defrun(self):
try:
print('Runtask(%s)...'%(os.getpid()))
start=time.time()
time.sleep(random.random()*3)
end=time.time()
t=threading.currentThread()
#线程ID
print('Threadid:%d'%t.ident)
print('Threadname:%s'%t.getName())
print('Taskruns%0.2fseconds.'%(end-start))
exceptExceptionase:
print(e)
finally:
self.queue.get()
self.queue.task_done()
defmain():
q=queue.Queue(maxThreads)
forsinrange(6):
q.put(s)
t=Store(q)
t.start()
q.join()
print('over')
if__name__=='__main__':
main()
运行结果如下：
Runtask(33259)... Runtask(33259)... Runtask(33259)... Runtask(33259)... Threadid:123145444999168 Threadname:Thread-13 Taskruns0.04seconds. Runtask(33259)... Threadid:123145394630656 Threadname:Thread-10 Taskruns1.02seconds. Runtask(33259)... Threadid:123145428209664 Threadname:Thread-12 Taskruns1.20seconds. Threadid:123145394630656 Threadname:Thread-17 Taskruns0.68seconds. Threadid:123145444999168 Threadname:Thread-14 Taskruns1.79seconds. Threadid:123145411420160 Threadname:Thread-11 Taskruns2.96seconds. over
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