python16线程

python对于I/O密集型应用比较好，具体根据是什么类型应用来查看

对于cpu密集型应用可以借助python的一些扩展去实现

thread模块是比较早期的模块，thresding是比较新的模块，对thread模块进行了新的封装，

import threading

def loop():
    """新线程执行的代码"""
    loop_now_thread = threading.current_thread()
    print("loop现在的线程是{}".format(loop_now_thread))
    n = 0
    while n <5:
        print(n)
        n += 1

def use_thread():
    """使用线程来实现"""
    #当前正在执行的线程名称
    now_thread = threading.current_thread()
    print("现在的线程是{}".format(now_thread))
    #设置线程
    t = threading.Thread(target=loop,name="loop_thread")
    t.start()
    #挂起线程
    t.join()

if __name__ == "__main__":
    use_thread()

结果：
现在的线程是<_MainThread(MainThread, started 15572)>
loop现在的线程是<Thread(loop_thread, started 3980)>
0
1
2
3
4

用类来实现：

import threading
import time

class LoopThrea(threading.Thread):
    n = 0
    def run(self, n=None):
        while self.n < 5:
            print(self.n)
            now_thread = threading.current_thread()
            print("现在的线程是{}".format(now_thread))
            time.sleep(1)
            self.n += 1

if __name__ == "__main__":
    t = LoopThrea(name = "quanzhiqiang_loop")
    t.start()
    t.join()

结果；
0
现在的线程是<LoopThrea(quanzhiqiang_loop, started 16708)>
1
现在的线程是<LoopThrea(quanzhiqiang_loop, started 16708)>
2
现在的线程是<LoopThrea(quanzhiqiang_loop, started 16708)>
3
现在的线程是<LoopThrea(quanzhiqiang_loop, started 16708)>
4
现在的线程是<LoopThrea(quanzhiqiang_loop, started 16708)>

import threading
import time

balance = 0
def change_it(n):
    global balance
    balance = balance +n
    time.sleep(2)
    balance = balance -n
    print("##################{0}#".format(balance))
    time.sleep(1)

class ChageBlance(threading.Thread):

    def __init__(self, num, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.num = num

    def run(self):
        for i in range(100000):
            change_it(self.num)

if __name__ == "__main__":
    t1 = ChageBlance(5)
    t2 = ChageBlance(8)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("aaaa{0}".format(balance))

结果：有时候不为零

##################5###################0#

##################8#
##################0#
##################5###################0#

##################5###################0#

import threading
import time

my_lock = threading.Lock()
your_lock = threading.Lock()
balance = 0
def change_it(n):
    global balance
    try:
        # 添加锁
        my_lock.acquire()
        #my_lock.acquire()如果再加如一个锁，就会出现死锁
        balance = balance +n
        time.sleep(2)
        balance = balance -n
        print("##################{0}#".format(balance))
        #释放锁
    finally:
        my_lock.release()
    time.sleep(1)

class ChageBlance(threading.Thread):

    def __init__(self, num, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.num = num

    def run(self):
        for i in range(100000):
            change_it(self.num)

if __name__ == "__main__":
    t1 = ChageBlance(5)
    t2 = ChageBlance(8)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("aaaa{0}".format(balance))

结果；
##################0#
##################0#
##################0#
##################0#
##################0#
##################0#

因为都是零，这是每个线程都加了锁，防止被修改

Rlock,在一个线程里面可以多次进行自锁

import threading
import time

my_lock = threading.Lock()
your_lock = threading.RLock()
balance = 0
def change_it(n):
    global balance
    try:
        # 添加锁
        your_lock.acquire()
        your_lock.acquire()
        balance = balance +n
        time.sleep(2)
        balance = balance -n
        print("##################{0}#".format(balance))
        #释放锁R
    finally:
        your_lock.release()
        your_lock.release()
    time.sleep(1)

class ChageBlance(threading.Thread):

    def __init__(self, num, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.num = num

    def run(self):
        for i in range(100000):
            change_it(self.num)

if __name__ == "__main__":
    t1 = ChageBlance(5)
    t2 = ChageBlance(8)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("aaaa{0}".format(balance))

结果：

##################0#
##################0#
##################0#
##################0#
##################0#

利用线程池，减少创建线程和销毁线程所带来的系统性能消耗

另外i一个也是线程池，只不过更加厉害

import time
import threading
from concurrent.futures.thread import ThreadPoolExecutor
from multiprocessing.dummy import Pool

def run(n):
    time.sleep(2)
    print(threading.current_thread().name,n)

def main():
    t1 = time.time()
    for n in range(5):
        run(n)

    print(time.time() - t1)

def main_use_thread():
    ls = []
    t1 = time.time()
    for count in range(10):
        for i in range(10):
            t = threading.Thread(target=run,args=(i,))
            ls.append(t)
            t.start()

        for l in ls:
            l.join()
    print(time.time() - t1)

def main_use_pool():
    t1 = time.time()
    n_list = range(100)
    pool = Pool(10)
    pool.map(run,n_list)
    pool.close()
    pool.join()
    print(time.time() - t1)

def main_use_thread():
    t1 = time.time()
    n_list = range(100)
    with ThreadPoolExecutor(max_workers=10) as executor:
        executor.map(run,n_list)
    print(time.time() - t1)

if __name__ == "__main__":
    #main()
    #下面的执行都是使用十个线程去处理的，效率比较高
    #main_use_thread()
    #main_use_pool()这个24秒
    main_use_thread()#这个20秒

map函数：

map是python内置函数，会根据提供的函数对指定的序列做映射。

map()函数的格式是：

map(function,iterable,...)
第一个参数接受一个函数名，后面的参数接受一个或多个可迭代的序列，返回的是一个集合。

把函数依次作用在list中的每一个元素上，得到一个新的list并返回。注意，map不改变原list，而是返回一个新list。

通过map还可以实现类型转换
将元组转换为list：

map(int,(1,2,3))

# 结果如下：
[1,2,3]
将字符串转换为list：

map(int,'1234')

# 结果如下：
[1,2,3,4]
提取字典中的key，并将结果放在一个list中：

map(int,{1:2,2:3,3:4})

# 结果如下
[1,2,3]