1、线程同步

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! /usr/bin/evn python3# ---- coding: utf-8 ----

from threading import Lock,RLockimport threading

说明：# 1、用锁会影响性能（必然存在的）# 2、锁会引起死锁# 死锁两种常见的情况：# 1、lock.acquire() lock.acquire()两次使用锁而无释放# 2、资源竞争'''A（a,b） acquire(a) acquire(b) B(a,b) acquire(a) acquire(b)'''# 3、两次调用lock.acquire()# 解决办法：Python中引入了可重入的锁from threading import RLock# 说明：在同一个线程里面，可以连续调用多次acquire(),一定要注意acquire()调用要和release()调用次数一致''' def add(): global total global lock for i in range(1000000): lock.acquire() dosomething(lock) total += 1 lock.release() def dosomething(): lock.acquire() lock.release()

'''#锁解决数据不一致问题
total = 0lock = Lock()
def add(): global total global lock for i in range(1000000): lock.acquire() total += 1 lock.release()
def desc(): global total global lock for j in range(1000000): lock.acquire() total -= 1 lock.release()
threading1 = threading.Thread(target = add)threading2 = threading.Thread(target= desc)
threading1.start()threading2.start()
threading1.join()threading2.join()print(total)

解决可以多次使用acquire()问题

total = 0lock = RLock()
def add(): global total global lock for i in range(1000000): lock.acquire() lock.acquire() total += 1 lock.release() lock.release()
def desc(): global total global lock for j in range(1000000): lock.acquire() total -= 1 lock.release()
threading1 = threading.Thread(target = add)threading2 = threading.Thread(target= desc)
threading1.start()threading2.start()
threading1.join()threading2.join()print(total)

2、条件变量

! /usr/bin/evn python3# ---- coding: utf-8 ----

线程中的条件变量（）# 通知天猫与小爱之间的来回切换

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":# lock = threading.Lock()# xiaoai = XiaoAi(lock)# tianmao = TianMao(lock)## tianmao.start()# xiaoai.start()

wait() 等待某个条件变量的通知#notify() 通知调用了wait()方法的启动from threading import Condition

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() self.cond.wait()
class TianMao(threading.Thread): def init(self,cond): super().init(name="天猫精灵") self.cond = cond
def run(self): with self.cond:#也可以这样调用：self.cond.acquire()方法，但一定要self.cond.release()方法 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": cond = threading.Condition() xiaoai = XiaoAi(cond) tianmao = TianMao(cond)
#启动顺序很重要 #我们先要一定调用Condition with()方法，with就相当于调用 #在调用with之后 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condition等待队列中，等待notify（）方法的唤醒。 xiaoai.start() tianmao.start()