本篇文章给大家带来的内容是关于python多线程的详细介绍（代码示例），有一定的参考价值，有需要的朋友可以参考一下，希望对你有所帮助。
global interpreter lock（cpython）
同一时刻只有一个线程运行在一个cpu上执行字节码（无法将多个线程映射到多个cpu上）
import dis def add(a): a = a + 1 return a print(dis.dis(add))
每次的结果都不一样 线程之间的安全问题
GIL会根据执行的直接码行数或者时间片释放GIL
遇到IO操作时主动释放
total = 0 def add(): #1. dosomething1 #2. io操作 # 1. dosomething3 global total for i in range(1000000): total += 1 def desc(): global total for i in range(1000000): total -= 1 import threading thread1 = threading.Thread(target=add) thread2 = threading.Thread(target=desc) thread1.start() thread2.start() thread1.join() thread2.join() print(total)
操作系统能够调度的的最小单位是进程，因为进程对系统的资源消耗非常大，所以后期就演变成了线程，线程实际上是依赖于我们的进程（任务管理器中我们实际上能看到的其实是进程 ），操作系统能调度的最小单元是线程。
对于io操作为主的编程来说，多进程和多先产出的性能差别不大，甚至多线程比多进程的性能还高，因为多线程编程更加轻量级。
import time
from threading import Thread
def get_detail_html(url):
print("get detail html started")
time.sleep(2)
print("get detail html end")
def get_detail_url(url):
print("get detail url started")
time.sleep(4)
print("get detail url end")
if __name__ == '__main__':
thread1 = Thread(target=get_detail_html, args=("",))
thread2 = Thread(target=get_detail_url, args=("",))
# 设置为守护线程 当主线程运行完时 子线程被kill掉
thread1.setDaemon(True)
thread2.setDaemon(True)
start_time = time.time()
thread1.start()
thread2.start()
# 设置为阻塞 等待线程运行完再关闭主线程
thread1.join()
thread2.join()
# 默认情况下 主线程退出与时 子线程不会被kill掉
print("last time: {}".format(time.time() - start_time))import time
import threading
def get_detail_html(url):
print("get detail html started")
time.sleep(2)
print("get detail html end")
def get_detail_url(url):
print("get detail url started")
time.sleep(4)
print("get detail url end")
#2. 通过集成Thread来实现多线程
class GetDetailHtml(threading.Thread):
def __init__(self, name):
super().__init__(name=name)
def run(self):
print("get detail html started")
time.sleep(2)
print("get detail html end")
class GetDetailUrl(threading.Thread):
def __init__(self, name):
super().__init__(name=name)
def run(self):
print("get detail url started")
time.sleep(4)
print("get detail url end")
if __name__ == "__main__":
thread1 = GetDetailHtml("get_detail_html")
thread2 = GetDetailUrl("get_detail_url")
start_time = time.time()
thread1.start()
thread2.start()
thread1.join()
thread2.join()
#当主线程退出的时候， 子线程kill掉
print ("last time: {}".format(time.time()-start_time))使用queue
# filename: thread_queue_test.py
# 通过queue的方式进行线程间同步
from queue import Queue
import time
import threading
def get_detail_html(queue):
# 死循环 爬取文章详情页
while True:
url = queue.get()
# for url in detail_url_list:
print("get detail html started")
time.sleep(2)
print("get detail html end")
def get_detail_url(queue):
# 死循环 爬取文章列表页
while True:
print("get detail url started")
time.sleep(4)
for i in range(20):
# put 等到有空闲位置 再放入
# put_nowait 非阻塞方式
queue.put("http://projectsedu.com/{id}".format(id=i))
print("get detail url end")
# 1. 线程通信方式- 共享变量
if __name__ == "__main__":
detail_url_queue = Queue(maxsize=1000)
thread_detail_url = threading.Thread(target=get_detail_url, args=(detail_url_queue,))
for i in range(10):
html_thread = threading.Thread(target=get_detail_html, args=(detail_url_queue,))
html_thread.start()
start_time = time.time()
# 调用task_down从主线程退出
detail_url_queue.task_done()
# 从queue的角度阻塞
detail_url_queue.join()
print("last time: {}".format(time.time() - start_time))在多线程编程中必须要面对的问题
# 没有锁 def add1(a): a += 1 def desc1(a): a -= 1 """add 1. load a a = 0 2. load 1 1 3. + 1 4. 赋值给a a=1 """ """add 1. load a a = 0 2. load 1 1 3. - 1 4. 赋值给a a=-1 """ import dis print(dis.dis(add1)) print(dis.dis(desc1))
用锁会影响性能，锁会引起死锁（两次获取锁，获取锁之后不释放，互相等待（a需要b的资源 b需要a的资源））
import threading from threading import Lock total = 0 # 定义一把锁 lock = Lock() def add(): global total global lock for i in range(1000000): # 获取锁 lock.acquire() total += 1 # 释放锁 lock.release() def desc(): global total for i in range(1000000): lock.acquire() total -= 1 lock.release() thread1 = threading.Thread(target=add) thread2 = threading.Thread(target=desc) thread1.start() thread2.start() thread1.join() thread2.join() print(total)
""" A(a、b) acquire (a) acquire (b) B(a、b) acquire (b) acquire (a) # 解决办法 B(a、b) acquire (a) acquire (b) """
import threading from threading import RLock total = 0 # 可重入锁 可以在同一个线程中可载入多次 lock = RLock() def add(lock): global total for i in range(1000000): # 获取锁 lock.acquire() lock.acquire() total += 1 do_something(lock) # 释放锁 lock.release() lock.release() def desc(): global total for i in range(1000000): lock.acquire() total -= 1 lock.release() def do_something(lock): lock.acquire() # do something lock.release() thread1 = threading.Thread(target=add) thread2 = threading.Thread(target=desc) thread1.start() thread2.start() thread1.join() thread2.join() print(total)
用于复杂的线程间同步
# 没有条件锁 不能实现对话
import threading
class XiaoAi(threading.Thread):
def __init__(self, lock):
super().__init__(name="小爱")
self.lock = lock
def run(self):
self.lock.acquire()
print("{} : 在 ".format(self.name))
self.lock.release()
self.lock.acquire()
print("{} : 好啊 ".format(self.name))
self.lock.release()
class TianMao(threading.Thread):
def __init__(self, lock):
super().__init__(name="天猫精灵")
self.lock = lock
def run(self):
self.lock.acquire()
print("{} : 小爱同学 ".format(self.name))
self.lock.release()
self.lock.acquire()
print("{} : 我们来对古诗吧 ".format(self.name))
self.lock.release()
if __name__ == "__main__":
cond = threading.Condition()
xiaoai = XiaoAi(cond)
tianmao = TianMao(cond)
xiaoai.start()
tianmao.start()# 条件锁
import threading
class XiaoAi(threading.Thread):
def __init__(self, cond):
super().__init__(name="小爱")
self.cond = cond
def run(self):
with self.cond:
self.cond.wait()
print("{} : 在 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 好啊 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 君住长江尾 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 共饮长江水 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 此恨何时已 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 定不负相思意 ".format(self.name))
self.cond.notify()
class TianMao(threading.Thread):
def __init__(self, cond):
super().__init__(name="天猫精灵")
self.cond = cond
def run(self):
with self.cond:
print("{} : 小爱同学 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 我们来对古诗吧 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 我住长江头 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 日日思君不见君 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 此水几时休 ".format(self.name))
self.cond.notify()
self.cond.wait()
print("{} : 只愿君心似我心 ".format(self.name))
self.cond.notify()
self.cond.wait()
if __name__ == "__main__":
from concurrent import futures
cond = threading.Condition()
xiaoai = XiaoAi(cond)
tianmao = TianMao(cond)
# 启动顺序很重要
# 在调用with cond之后才能调用wait或者notify方法
# condition有两层锁， 一把底层锁会在线程调用了wait方法的时候释放，
# 上面的锁会在每次调用wait的时候分配一把并放入到cond的等待队列中，
# 等到notify方法的唤醒
xiaoai.start()
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