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Python-线程同步

1、线程同步

　　线程同步，线程间协同，通过某种技术，让一个线程访问某些数据时，其他线程不能访问这些数据，直到该线程完成对数的操作做。

　　不同操作系统实现技术有所不同，有临界区（Critical Section），互斥量（Mutex）, 信号量（Semaphore），时间Event等

2、Event

　　Even事件，是线程间通信机制中最简单的实现，使用一个内部的标记flag，通过flag的True或False的变化来进行操作。

名称	含义
set()	标记设置为True
clear()	标记设置为False
is_set()	标记是否为True
wait(timeout=None)	设置等待标记为True的时长，None为无限等待，等到返回True，未等到超时了，返回False

　　测试：需求：老板雇了一个员工，让他生成杯子，老板一直等待这个工人，知道生产了10个杯子。

　　　　　1、普通线程实现：　　　

 1 import threading
 2 import time
 3 
 4 flag = False
 5 
 6 def worker(count=10):
 7     print('im working')
 8     global flag
 9     cpus = []
10     while True:
11         time.sleep(0.1)
12         cpus.append(1)
13         if len(cpus) > 10:
14             flag = True
15             break
16     print(cpus)
17 
18 def boss():
19     global flag
20     while True:
21         time.sleep(2)
22         if flag:
23             print('good job')
24             break
25 
26 w = threading.Thread(target=worker)
27 b = threading.Thread(target= boss)
28 w.start()
29 b.start()

View Code

　　　　　结果：　　　　

1 im working
2 [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
3 good job
4 
5 Process finished with exit code 0

View Code

　　　　2、利用Event 类实现：　　

 1 from threading import Event, Thread
 2 import logging
 3 import time
 4 
 5 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 6 logging.basicConfig(format=FORMAT, level=logging.INFO)
 7 
 8 def boss(event:Event):
 9     logging.info('boss')
10     event.wait()
11     logging.info('good job')
12 
13 def worker(event:Event, count=10):
14     logging.info('working')
15     cups = []
16     while True:
17         logging.info('make 1')
18         time.sleep(0.5)
19         cups.append(1)
20         if len(cups) >= count:
21             event.set()
22             break
23     logging.info('finished {}'.format(cups))
24 
25 event = Event()
26 w = Thread(target=worker, args=(event,))
27 b = Thread(target=boss, args=(event,))
28 w.start()
29 b.start()

View Code

　　　　结果：

 1 2018-10-12 10:58:11,515 Thread-1 8448 working
 2 2018-10-12 10:58:11,515 Thread-1 8448 make 1
 3 2018-10-12 10:58:11,515 Thread-2 1064 boss
 4 2018-10-12 10:58:12,030 Thread-1 8448 make 1
 5 2018-10-12 10:58:12,545 Thread-1 8448 make 1
 6 2018-10-12 10:58:13,060 Thread-1 8448 make 1
 7 2018-10-12 10:58:13,574 Thread-1 8448 make 1
 8 2018-10-12 10:58:14,089 Thread-1 8448 make 1
 9 2018-10-12 10:58:14,604 Thread-1 8448 make 1
10 2018-10-12 10:58:15,119 Thread-1 8448 make 1
11 2018-10-12 10:58:15,634 Thread-1 8448 make 1
12 2018-10-12 10:58:16,148 Thread-1 8448 make 1
13 2018-10-12 10:58:16,663 Thread-1 8448 finished [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
14 2018-10-12 10:58:16,663 Thread-2 1064 good job
15 
16 Process finished with exit code 0

View Code

　　总结：使用同一个Event实例的标记flag，谁wait 就是等到flag变为 True，或等到超时返回False，不限等待个数。

　　wait使用：　

 1 from threading import Event, Thread
 2 import logging
 3 import time
 4 
 5 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 6 logging.basicConfig(format=FORMAT, level=logging.INFO)
 7 
 8 def boss(event:Event):
 9     logging.info('boss')
10     while event.wait(6):
11         logging.info('good job')
12         break
13 
14 
15 def worker(event:Event, count=10):
16     logging.info('working')
17     cups = []
18     while True:
19         logging.info('make 1')
20         time.sleep(0.5)
21         cups.append(1)
22         if len(cups) >= count:
23             event.set()
24             break
25     logging.info('finished {}'.format(cups))
26 
27 event = Event()
28 w = Thread(target=worker, args=(event,))
29 b = Thread(target=boss, args=(event,))
30 w.start()
31 b.start()

View Code

　　Event练习：实现Timer，延时执行的线程，延时计add(x, y)

 1 from threading import Thread, Event
 2 
 3 class Timer:
 4     def __init__(self, interval, fn, args=(), kwargs={}):
 5         self.interval = interval
 6         self.fn = fn
 7         self.args = args
 8         self.kwargs = kwargs
 9         self.event = Event()
10 
11     def start(self):
12         Thread(target=self.run).start()
13 
14     def cancel(self):
15         self.event.set()
16 
17     def run(self):
18         self.event.wait(self.interval)
19         if not self.event.is_set():
20             print(self.args, self.kwargs)
21             self.fn(*self.args, **self.kwargs)
22         self.event.set()
23 def add(x, y):
24     print(x + y)
25 
26 t = Timer(4, add,(4, 5) )
27 print(t.args, t.kwargs)
28 t.start()
29 # t.cancel()
30 
31 print('--------------------------------')
32 print('main thread exit')
33 add(5, 6)

test

　　结果：

1 (4, 5) {}
2 --------------------------------
3 main thread exit
4 11
5 (4, 5) {}
6 9

View Code

　　测试：cancel

 1 from threading import Thread, Event
 2 
 3 class Timer:
 4     def __init__(self, interval, fn, args=(), kwargs={}):
 5         self.interval = interval
 6         self.fn = fn
 7         self.args = args
 8         self.kwargs = kwargs
 9         self.event = Event()
10 
11     def start(self):
12         Thread(target=self.run).start()
13 
14     def cancel(self):
15         self.event.set()
16 
17     def run(self):
18         self.event.wait(self.interval)
19         if not self.event.is_set():
20             self.fn(*self.args, **self.kwargs)
21         self.event.set() # 习惯上 做完了，不允许在做一次了
22         # print(self.event.is_set())
23 def add(x, y):
24     print(x + y)
25 
26 t = Timer(2, add,(4, 5) )
27 t.start()
28 t.cancel()
29 
30 print('--------------------------------')
31 print('main thread exit')
32 add(5, 6)

View Code

　　结果：　

1 --------------------------------
2 main thread exit
3 11
4 
5 Process finished with exit code 0

View Code

3、Lock

　　锁，凡是存在共享资源争抢的地方都可以使用锁，从而保证只有一个使用这可以完全使用这个资源。

　　Lock，锁，一旦线程获得锁，其他试图获取锁的线程将被阻塞。

名称	含义
acquire（blocking=True, timeout=-1）	默认阻塞，阻塞可以设置超时时间，非阻塞时，timeout禁止设置，成功获取锁，返回True，否则返回Fasle
release()	释放锁，可以从任何线程调用释放，已上的锁，会被重置为unlock未上锁的锁上调用，抛RuntimeError异常

　　测试：需求：订单生产1000个杯子，组织10个工人生产。

　　1、非锁模式：

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 cups = []
10 
11 def worker(count=10):
12     logging.info("I'm workin")
13     while len(cups) < count:
14         time.sleep(0.0001)
15         cups.append(1)
16     logging.info("i finished, cups={}".format(len(cups)))
17 
18 for _ in range(10):
19     Thread(target=worker,args=(1000,)).start()

代码

　　结果：从结果看出不是自己想要的结果，因为if判断的时候，也会被其他的线程打断

 1 2018-10-14 17:16:52,317 Thread-1 5444 I'm workin
 2 2018-10-14 17:16:52,348 Thread-2 6896 I'm workin
 3 2018-10-14 17:16:52,348 Thread-3 2900 I'm workin
 4 2018-10-14 17:16:52,348 Thread-4 4104 I'm workin
 5 2018-10-14 17:16:52,348 Thread-5 7448 I'm workin
 6 2018-10-14 17:16:52,348 Thread-6 4276 I'm workin
 7 2018-10-14 17:16:52,348 Thread-7 3752 I'm workin
 8 2018-10-14 17:16:52,348 Thread-8 6156 I'm workin
 9 2018-10-14 17:16:52,348 Thread-9 3568 I'm workin
10 2018-10-14 17:16:52,348 Thread-10 7428 I'm workin
11 2018-10-14 17:16:53,941 Thread-1 5444 i finished, cups=1000
12 2018-10-14 17:16:53,941 Thread-10 7428 i finished, cups=1001
13 2018-10-14 17:16:53,941 Thread-6 4276 i finished, cups=1002
14 2018-10-14 17:16:53,941 Thread-5 7448 i finished, cups=1003
15 2018-10-14 17:16:53,941 Thread-9 3568 i finished, cups=1004
16 2018-10-14 17:16:53,941 Thread-2 6896 i finished, cups=1005
17 2018-10-14 17:16:53,956 Thread-8 6156 i finished, cups=1006
18 2018-10-14 17:16:53,956 Thread-7 3752 i finished, cups=1007
19 2018-10-14 17:16:53,956 Thread-4 4104 i finished, cups=1008
20 2018-10-14 17:16:53,956 Thread-3 2900 i finished, cups=1009
21 
22 Process finished with exit code 0

结果

　　2、加锁测试　

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 cups = []
10 lock = Lock()
11 
12 def worker(count=10):
13     logging.info("I'm workin")
14     flag = False
15 
16     while True:
17         lock.acquire()
18 
19         if len(cups) >= count:
20             flag = True
21         # lock.release() # 注意释放 锁  的位置,这里不合适
22 
23         time.sleep(0.0001)
24         if not flag:
25             cups.append(1)
26         lock.release() # 注意释放 锁  的位置
27         if flag:
28             break
29 
30     logging.info("i finished, cups={}".format(len(cups)))
31 
32 for _ in range(10):
33     Thread(target=worker,args=(1000,)).start()

代码

　　　　结果：可以看到针对同一个资源，使用Lock

 1 D:python3.7python.exe E:/code_pycharm/复习/t1.py
 2 2018-10-14 17:43:42,748 Thread-1 1628 I'm workin
 3 2018-10-14 17:43:42,748 Thread-2 7260 I'm workin
 4 2018-10-14 17:43:42,748 Thread-3 1308 I'm workin
 5 2018-10-14 17:43:42,748 Thread-4 7280 I'm workin
 6 2018-10-14 17:43:42,748 Thread-5 7676 I'm workin
 7 2018-10-14 17:43:42,748 Thread-6 7288 I'm workin
 8 2018-10-14 17:43:42,749 Thread-7 276 I'm workin
 9 2018-10-14 17:43:42,749 Thread-8 1052 I'm workin
10 2018-10-14 17:43:42,749 Thread-9 3144 I'm workin
11 2018-10-14 17:43:42,749 Thread-10 5732 I'm workin
12 2018-10-14 17:43:43,786 Thread-6 7288 i finished, cups=1000
13 2018-10-14 17:43:43,787 Thread-10 5732 i finished, cups=1000
14 2018-10-14 17:43:43,788 Thread-5 7676 i finished, cups=1000
15 2018-10-14 17:43:43,789 Thread-3 1308 i finished, cups=1000
16 2018-10-14 17:43:43,790 Thread-1 1628 i finished, cups=1000
17 2018-10-14 17:43:43,791 Thread-8 1052 i finished, cups=1000
18 2018-10-14 17:43:43,792 Thread-9 3144 i finished, cups=1000
19 2018-10-14 17:43:43,793 Thread-4 7280 i finished, cups=1000
20 2018-10-14 17:43:43,794 Thread-2 7260 i finished, cups=1000
21 2018-10-14 17:43:43,795 Thread-7 276 i finished, cups=1000
22 
23 Process finished with exit code 0

结果

　　　　总结：每个线程获取锁之后，一定要释放锁（但是要注意释放的位置）。对于同一个资源，某线程获锁后，其他线程要不永久等待，要不设置过期时间，过期后，返回False，再跳过有锁的代码块，往下进行。永久等待，就是等获取锁的线程释放后，自己获取锁。锁的释放主要注意一点是线程安全，不会产生不确定结果。

　　测试：无锁，计算类，加减

　　1、无锁测试

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Counter:
10     def __init__(self):
11         self._val = 0
12 
13     @property
14     def value(self):
15         return self._val
16 
17     def inc(self):
18         self._val += 1
19 
20     def dec(self):
21         self._val -= 1
22 
23 def run(c:Counter, count=100):
24     for _ in range(count):
25         for i in range(-50, 50):
26             if i < 0:
27                 c.dec()
28             else:
29                 c.inc()
30 
31 c = Counter()
32 c1 = 100000 # 线程数
33 c2 = 10
34 for i in range(c1):
35     Thread(target=run, args=(c, c2)).start()
36 
37 print(c.value)

无锁测试

　　结果：随着计算量增多，导致出现不确定结果，所以线程不安全（c2 大于100后，就会出现结果不是 0 的结果）　　

0

Process finished with exit code 0

　　　2、加锁，减锁　

　　　　一般来说，加锁就需要减锁，但是加锁后解锁前，还要有一些代码执行，就有可能抛异常，一旦异常出现，锁是无法释放，但是当前线程可能因为这个异常被终止，这就产生了死锁。

　　加锁，解锁常用语句：

　　　　1、使用try。。。finally语句保证锁的释放

　　　　2、with上下文管理，锁对象支持上下文管理

　　测试：锁，计算类，加减

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Counter:
10     def __init__(self):
11         self._val = 0
12         self.lock = Lock()
13 
14     @property
15     def value(self):
16         with self.lock:
17             return self._val
18 
19     def inc(self):
20         with self.lock:
21             self._val += 1
22 
23     def dec(self):
24         try:
25             self.lock.acquire()
26             self._val -= 1
27         finally:
28             self.lock.release()
29 
30 
31 def run(c:Counter, count=100):
32     for _ in range(count):
33         for i in range(-50, 50):
34             if i < 0:
35                 c.dec()
36             else:
37                 c.inc()
38 
39 c = Counter()
40 c1 = 10 # 线程数
41 c2 = 1000
42 for i in range(c1):
43     Thread(target=run, args=(c, c2)).start()
44 
45 print(c.value)
46 # -35
47 
48 
49 因为多线程，执行的时候，主线程中的print早就打印完了，而子线程还没结束，所以得到的值不是0， 是某一时刻值

最后print(c.value)问题

　　正对上面的问题作出修正，获取的值是0，也就是等子线程都结束了，在print

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Counter:
10     def __init__(self):
11         self._val = 0
12         self.lock = Lock()
13 
14     @property
15     def value(self):
16         with self.lock:
17             return self._val
18 
19     def inc(self):
20         with self.lock:
21             self._val += 1
22 
23     def dec(self):
24         try:
25             self.lock.acquire()
26             self._val -= 1
27         finally:
28             self.lock.release()
29 
30 
31 def run(c:Counter, count=100):
32     for _ in range(count):
33         for i in range(-50, 50):
34             if i < 0:
35                 c.dec()
36             else:
37                 c.inc()
38 
39 c = Counter()
40 c1 = 10 # 线程数
41 c2 = 1000
42 
43 # 方式 1：判断当前活着的线程是否为1
44 for i in range(c1):
45     Thread(target=run, args=(c, c2)).start()
46 
47 while True:
48     time.sleep(1)
49     if threading.active_count() == 1: # 只剩下主线程
50         print(threading.enumerate(), '-----')
51         print(c.value)
52         break
53     else:
54         print(threading.enumerate())
55 
56 # 方式 2：使用join，只要有一个线程join  主线程就等待
57 thread = []
58 for i in range(c1):
59     t = Thread(target=run, args=(c, c2))
60     thread.append(t)
61     t.start()
62 
63 for t in thread:
64     t.join()
65 
66 print(c.value)

两种方式实现结果为0

　　锁的应用场景：

　　　　锁适用于访问和修改同一个共享资源的时候，即读写同一资源的时候。

　　　　如果全部都是读取同一个资源时不需要锁的。因为这时可以认为共享资源是不可变得，每一次读取都是一样的值，所以不用加锁。

　　使用锁注意事项：

1. 少用锁，必要时用锁。使用了锁，多线程访问被锁的资源的时候，就成了串行，要么排队，要么争抢。
2. 加锁时间越短越好，不需要立即释放。
3. 一定避免死锁。

　　但是，不使用锁，提高了效率，但是结果如果不是正确的，效率也没用，所以正确性排第一

　　测试：实现非阻塞的锁，也就是说，非等待，没有获取锁，就去干别的事：　

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 def worker(tasks):
10     for task in tasks:
11         time.sleep(0.001)
12         if task.lock.acquire(False):# 非等待模式，没有获取就else 
13             logging.info("{}{} begin to start".format(threading.current_thread(), task.name))
14             # s适当的时机释放锁，为了演示 不释放了
15 
16         else:
17             logging.info("{}{} is working".format(threading.current_thread(), task.name))
18 
19 class Task:
20     def __init__(self, name):
21         self.name = name
22         self.lock = Lock()
23 
24 # 构造10 个任务
25 tasks = [Task('task--{}'.format(x)) for x in range(10)]
26 
27 # 启动5 个线程
28 for i in range(5):
29     threading.Thread(target=worker, name='work -- {}'.format(i), args=(tasks,)).start()

View Code

　　结果：

  1 D:python3.7python.exe E:/code_pycharm/复习/t1.py
  2 1
  3 2018-10-14 20:23:57,046 work -- 0 9316 <Thread(work -- 0, started 9316)>task--0 begin to start
  4 2
  5 2018-10-14 20:23:57,046 work -- 1 10260 <Thread(work -- 1, started 10260)>task--0 is working
  6 2018-10-14 20:23:57,047 work -- 0 9316 <Thread(work -- 0, started 9316)>task--1 begin to start3
  7 4
  8 5
  9 6
 10 7
 11 
 12 2018-10-14 20:23:57,047 work -- 3 5076 <Thread(work -- 3, started 5076)>task--0 is working
 13 2018-10-14 20:23:57,047 work -- 4 8464 <Thread(work -- 4, started 8464)>task--0 is working
 14 2018-10-14 20:23:57,047 work -- 2 6196 <Thread(work -- 2, started 6196)>task--0 is working
 15 2018-10-14 20:23:57,047 work -- 1 10260 <Thread(work -- 1, started 10260)>task--1 is working
 16 2018-10-14 20:23:57,048 work -- 3 5076 <Thread(work -- 3, started 5076)>task--1 is working
 17 2018-10-14 20:23:57,048 work -- 0 9316 <Thread(work -- 0, started 9316)>task--2 begin to start
 18 2018-10-14 20:23:57,048 work -- 2 6196 <Thread(work -- 2, started 6196)>task--1 is working
 19 2018-10-14 20:23:57,048 work -- 1 10260 <Thread(work -- 1, started 10260)>task--2 is working
 20 2018-10-14 20:23:57,048 work -- 4 8464 <Thread(work -- 4, started 8464)>task--1 is working
 21 8
 22 9
 23 10
 24 11
 25 12
 26 13
 27 1415
 28 
 29 16
 30 17
 31 2018-10-14 20:23:57,049 work -- 4 8464 <Thread(work -- 4, started 8464)>task--2 is working
 32 2018-10-14 20:23:57,049 work -- 3 5076 <Thread(work -- 3, started 5076)>task--2 is working
 33 2018-10-14 20:23:57,049 work -- 0 9316 <Thread(work -- 0, started 9316)>task--3 begin to start
 34 2018-10-14 20:23:57,049 work -- 2 6196 <Thread(work -- 2, started 6196)>task--2 is working
 35 2018-10-14 20:23:57,049 work -- 1 10260 <Thread(work -- 1, started 10260)>task--3 is working
 36 18
 37 1920
 38 
 39 2122
 40 
 41 2018-10-14 20:23:57,050 work -- 3 5076 <Thread(work -- 3, started 5076)>task--3 is working
 42 2018-10-14 20:23:57,050 work -- 1 10260 <Thread(work -- 1, started 10260)>task--4 begin to start
 43 2018-10-14 20:23:57,050 work -- 4 8464 <Thread(work -- 4, started 8464)>task--3 is working
 44 2018-10-14 20:23:57,050 work -- 0 9316 <Thread(work -- 0, started 9316)>task--4 is working
 45 2018-10-14 20:23:57,050 work -- 2 6196 <Thread(work -- 2, started 6196)>task--3 is working
 46 2018-10-14 20:23:57,051 work -- 1 10260 <Thread(work -- 1, started 10260)>task--5 begin to start
 47 2018-10-14 20:23:57,051 work -- 4 8464 <Thread(work -- 4, started 8464)>task--4 is working
 48 23
 49 2018-10-14 20:23:57,051 work -- 0 9316 <Thread(work -- 0, started 9316)>task--5 is working
 50 24
 51 2018-10-14 20:23:57,051 work -- 3 5076 <Thread(work -- 3, started 5076)>task--4 is working
 52 25
 53 26
 54 2018-10-14 20:23:57,051 work -- 2 6196 <Thread(work -- 2, started 6196)>task--4 is working
 55 27
 56 2018-10-14 20:23:57,052 work -- 1 10260 <Thread(work -- 1, started 10260)>task--6 begin to start
 57 2018-10-14 20:23:57,052 work -- 3 5076 <Thread(work -- 3, started 5076)>task--5 is working
 58 28
 59 29
 60 30
 61 31
 62 2018-10-14 20:23:57,052 work -- 4 8464 <Thread(work -- 4, started 8464)>task--5 is working
 63 32
 64 2018-10-14 20:23:57,052 work -- 0 9316 <Thread(work -- 0, started 9316)>task--6 is working
 65 2018-10-14 20:23:57,052 work -- 2 6196 <Thread(work -- 2, started 6196)>task--5 is working
 66 2018-10-14 20:23:57,053 work -- 0 9316 <Thread(work -- 0, started 9316)>task--7 begin to start
 67 33
 68 2018-10-14 20:23:57,053 work -- 3 5076 <Thread(work -- 3, started 5076)>task--6 is working
 69 3435
 70 
 71 2018-10-14 20:23:57,053 work -- 4 8464 <Thread(work -- 4, started 8464)>task--6 is working
 72 36
 73 2018-10-14 20:23:57,053 work -- 1 10260 <Thread(work -- 1, started 10260)>task--7 is working
 74 37
 75 2018-10-14 20:23:57,053 work -- 2 6196 <Thread(work -- 2, started 6196)>task--6 is working
 76 2018-10-14 20:23:57,054 work -- 3 5076 <Thread(work -- 3, started 5076)>task--7 is working
 77 38
 78 2018-10-14 20:23:57,054 work -- 0 9316 <Thread(work -- 0, started 9316)>task--8 begin to start
 79 39
 80 40
 81 2018-10-14 20:23:57,054 work -- 4 8464 <Thread(work -- 4, started 8464)>task--7 is working
 82 41
 83 42
 84 2018-10-14 20:23:57,054 work -- 1 10260 <Thread(work -- 1, started 10260)>task--8 is working
 85 2018-10-14 20:23:57,054 work -- 2 6196 <Thread(work -- 2, started 6196)>task--7 is working
 86 43
 87 44
 88 45
 89 46
 90 47
 91 2018-10-14 20:23:57,055 work -- 3 5076 <Thread(work -- 3, started 5076)>task--8 is working
 92 2018-10-14 20:23:57,055 work -- 0 9316 <Thread(work -- 0, started 9316)>task--9 begin to start
 93 2018-10-14 20:23:57,055 work -- 1 10260 <Thread(work -- 1, started 10260)>task--9 is working
 94 2018-10-14 20:23:57,055 work -- 2 6196 <Thread(work -- 2, started 6196)>task--8 is working
 95 2018-10-14 20:23:57,055 work -- 4 8464 <Thread(work -- 4, started 8464)>task--8 is working
 96 48
 97 49
 98 50
 99 2018-10-14 20:23:57,056 work -- 2 6196 <Thread(work -- 2, started 6196)>task--9 is working
100 2018-10-14 20:23:57,056 work -- 3 5076 <Thread(work -- 3, started 5076)>task--9 is working
101 2018-10-14 20:23:57,056 work -- 4 8464 <Thread(work -- 4, started 8464)>task--9 is working
102 
103 Process finished with exit code 0

加了一个count的结果

4、可重入锁RLock，也叫递归锁

　　可重入锁，是线程相关的锁。

　　线程A 获得可重入锁，并可以多次成功获取，不会阻塞，最后要在线程A 中做和acquire次数相同的release

　　测试单线程：

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 lock = threading.RLock()
10 
11 print(lock.acquire())
12 print('----------------')
13 print(lock.acquire(False))
14 print(lock.acquire())
15 print(lock.acquire(timeout=4))
16 print('lock in main thread{}'.format(lock))
17 # ------------------------------------------------------
18 lock.release()
19 lock.release()
20 lock.release()
21 lock.release()
22 print("main thread {}".format(threading.current_thread().ident))
23 print('lock in main thread{}'.format(lock))
24 # ------------------------------------------------------
25 # lock.release() # 多release()一次，抛异常
26 #
27 # print('lock in main thread{}'.format(lock))
28 
29 # ------------------------------------------------------
30 print(lock.acquire(False))
31 print('lock in main thread{}'.format(lock))
32 # threading.Thread(3, lambda x:x.release(), args=(lock,)).start() # 上一句的锁是主线程的，但是像现在夸线程了，所以抛异常
33 lock.release()

View Code

　　结果：

 1 True
 2 ----------------
 3 True
 4 True
 5 True
 6 lock in main thread<locked _thread.RLock object owner=9060 count=4 at 0x0000000002930E68>
 7 main thread 9060
 8 lock in main thread<unlocked _thread.RLock object owner=0 count=0 at 0x0000000002930E68>
 9 True
10 lock in main thread<locked _thread.RLock object owner=9060 count=1 at 0x0000000002930E68>
11 
12 Process finished with exit code 0

View Code

　　测试多线程：

 1 import threading
 2 from threading import Thread , Lock
 3 import logging
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 lock = threading.RLock()
10 
11 print(lock.acquire())
12 print('----------------')
13 print(lock.acquire(False))
14 print(lock.acquire())
15 print(lock.acquire(timeout=4))
16 print('lock in main thread{}'.format(lock))
17 # ------------------------------------------------------
18 lock.release()
19 lock.release()
20 lock.release()
21 # lock.release()
22 print('==',  'lock in main thread{}'.format(lock))
23 
24 def sub(l):
25     logging.info('sub thread')
26     l.acquire()
27     logging.info('end sub')
28     print('2', lock)
29 
30 t = threading.Thread(target=sub, args=(lock,))
31 t.start()
32 
33 print('1', lock)
34 
35 print('===== end ====')

View Code

　　结果：

 1 True
 2 ----------------
 3 True
 4 True
 5 True
 6 lock in main thread<locked _thread.RLock object owner=9720 count=4 at 0x00000000021F0E68>
 7 == lock in main thread<locked _thread.RLock object owner=9720 count=1 at 0x00000000021F0E68>
 8 1 <locked _thread.RLock object owner=9720 count=1 at 0x00000000021F0E68>
 9 ===== end ====
10 2018-10-14 21:51:46,765 Thread-1 10840 sub thread
11 
12 
13 可以看出：主线程的lock的count > 0, 子线程是无法获取锁，只能等待
14

View Code

　　可重入锁，与线程相关，可在一个线程中获取锁，并可继续在同一线程中不阻塞获取锁。当锁未释放完，其他线程获取锁会被阻塞，直到当前持有锁的线程释放完锁。

5、Condition

　构造方法Condition( lock = None)，可以传入一个Lock或一个RLock对象，默认是RLock()

名称	含义
acquire(*args)	获取锁
wait(self,timeout=None)	等待或超时
notify(n=1)	唤醒至多指定数目个数的等待线程，没有等待的线程就没有任何操作
notify_all()	唤醒所有等待的线程

　　Condition 用于生产者，消费者模型，为了解决生产者消费者速度匹配问题。

　　测试：消费者消费速度大于生产者生产速度　　　

 1 import threading
 2 from threading import Thread , Lock, Event
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Disptcher:
10     def __init__(self):
11         self.data = None
12         self.event = Event()
13 
14     def produce(self, total):
15         for _ in range(total):
16             data = random.randint(0, 100)
17             logging.info(data)
18             self.data = data
19             self.event.wait(1)
20         self.event.set()
21 
22     def consume(self):
23         while not self.event.is_set():
24             data = self.data
25             logging.info('recieved {}'.format(data))
26             self.data = None
27             self.event.wait(0.5)
28 
29 d = Disptcher()
30 p = Thread(target=d.produce, args=(10,), name='producer')
31 c = Thread(target=d.consume, name='consumer')
32 
33 c.start()
34 p.start()

不考虑线程安全

　　结果：

 1 2018-10-15 10:45:08,751 consumer 7676 recieved None
 2 2018-10-15 10:45:08,798 producer 8032 43
 3 2018-10-15 10:45:09,303 consumer 7676 recieved 43
 4 2018-10-15 10:45:09,824 consumer 7676 recieved None
 5 2018-10-15 10:45:09,824 producer 8032 68
 6 2018-10-15 10:45:10,339 consumer 7676 recieved 68
 7 2018-10-15 10:45:10,838 producer 8032 57
 8 2018-10-15 10:45:10,854 consumer 7676 recieved 57
 9 2018-10-15 10:45:11,371 consumer 7676 recieved None
10 2018-10-15 10:45:11,854 producer 8032 71
11 2018-10-15 10:45:11,886 consumer 7676 recieved 71
12 2018-10-15 10:45:12,400 consumer 7676 recieved None
13 2018-10-15 10:45:12,868 producer 8032 10
14 2018-10-15 10:45:12,915 consumer 7676 recieved 10
15 2018-10-15 10:45:13,430 consumer 7676 recieved None
16 2018-10-15 10:45:13,882 producer 8032 51
17 2018-10-15 10:45:13,945 consumer 7676 recieved 51
18 2018-10-15 10:45:14,460 consumer 7676 recieved None
19 2018-10-15 10:45:14,896 producer 8032 51
20 2018-10-15 10:45:14,974 consumer 7676 recieved 51
21 2018-10-15 10:45:15,489 consumer 7676 recieved None
22 2018-10-15 10:45:15,910 producer 8032 26
23 2018-10-15 10:45:16,004 consumer 7676 recieved 26
24 2018-10-15 10:45:16,519 consumer 7676 recieved None
25 2018-10-15 10:45:16,924 producer 8032 87
26 2018-10-15 10:45:17,034 consumer 7676 recieved 87
27 2018-10-15 10:45:17,548 consumer 7676 recieved None
28 2018-10-15 10:45:17,938 producer 8032 99
29 2018-10-15 10:45:18,063 consumer 7676 recieved 99
30 2018-10-15 10:45:18,578 consumer 7676 recieved None
31 
32 Process finished with exit code 0

View Code

　　　　　　从上例可以看出，消费者浪费大量时间来主动查看有没有数据。

　　测试：使用Condition ，匹配生产者和消费者速度：

 1 import threading
 2 from threading import Thread , Lock, Event, Condition
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Disptcher:
10     def __init__(self):
11         self.data = None
12         self.event = Event()
13         self.cond = Condition() # 默认是RLock,t 同一线程可以获取多个锁
14 
15     def produce(self, total):
16         for _ in range(total):
17             data = random.randint(0, 100)
18             with self.cond: #  获取锁
19                 logging.info(data)
20                 self.data = data
21                 self.cond.notify_all() # 通知所有等待的线程
22             self.event.wait(1) # 模拟产生数据速度
23 
24 
25     def consume(self):
26         while True:
27             print('==============')
28             with self.cond:
29                 self.cond.wait() # 阻塞等待通知
30                 logging.info('recieved {}'.format(self.data))
31                 self.data = None
32             self.event.wait(0.5) # 模拟消费速度
33             print('--------------')
34 
35 d = Disptcher()
36 p = Thread(target=d.produce, args=(10,), name='producer')
37 c = Thread(target=d.consume, name='consumer')
38 
39 c.start()
40 p.start()

不考虑线程安全

　　结果：可以看到每产生一个数据，就通知一次消费者，最终没有数据产生，消费者一直等待。

 1 D:python3.7python.exe E:/code_pycharm/复习/t1.py
 2 2018-10-15 11:17:25,393 producer 7912 39
 3 ==============
 4 2018-10-15 11:17:25,393 consumer 4356 recieved 39
 5 --------------
 6 ==============
 7 2018-10-15 11:17:26,408 producer 7912 78
 8 2018-10-15 11:17:26,408 consumer 4356 recieved 78
 9 --------------
10 ==============
11 2018-10-15 11:17:27,422 producer 7912 89
12 2018-10-15 11:17:27,422 consumer 4356 recieved 89
13 --------------
14 ==============
15 2018-10-15 11:17:28,436 producer 7912 7
16 2018-10-15 11:17:28,436 consumer 4356 recieved 7
17 --------------
18 ==============
19 2018-10-15 11:17:29,450 producer 7912 7
20 2018-10-15 11:17:29,450 consumer 4356 recieved 7
21 --------------
22 ==============
23 2018-10-15 11:17:30,464 producer 7912 100
24 2018-10-15 11:17:30,464 consumer 4356 recieved 100
25 --------------
26 ==============
27 2018-10-15 11:17:31,478 producer 7912 17
28 2018-10-15 11:17:31,478 consumer 4356 recieved 17
29 --------------
30 ==============
31 2018-10-15 11:17:32,492 producer 7912 12
32 2018-10-15 11:17:32,492 consumer 4356 recieved 12
33 --------------
34 ==============
35 2018-10-15 11:17:33,506 producer 7912 100
36 2018-10-15 11:17:33,506 consumer 4356 recieved 100
37 --------------
38 ==============
39 2018-10-15 11:17:34,520 producer 7912 97
40 2018-10-15 11:17:34,520 consumer 4356 recieved 97
41 --------------
42 ==============

View Code

　　测试：一个生产者，多个消费者，每次只通知两个线程

 1 import threading
 2 from threading import Thread , Lock, Event, Condition
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Disptcher:
10     def __init__(self):
11         self.data = None
12         self.event = Event()
13         self.cond = Condition() # 默认是RLock,t 同一线程可以获取多个锁
14 
15     def produce(self, total):
16         for _ in range(total):
17             data = random.randint(0, 100)
18             with self.cond: #  获取锁
19                 logging.info(data)
20                 self.data = data
21                 self.cond.notify(2) # 通知所有等待的线程
22             self.event.wait(1) # 模拟产生数据速度
23 
24 
25     def consume(self):
26         while True:
27             # print('==============')
28             with self.cond:
29                 self.cond.wait() # 阻塞等待通知
30                 logging.info('recieved {}'.format(self.data))
31                 self.data = None
32             self.event.wait(0.5) # 模拟消费速度
33             # print('--------------')
34 
35 d = Disptcher()
36 
37 p = Thread(target=d.produce, args=(10,), name='producer')
38 
39 for i in range(5):
40     c = Thread(target=d.consume, name='consumer --{}'.format(i))
41     c.start()
42 
43 p.start()

View Code

　　结果：可以看到每次通知的线程都是随机的。

 1 D:python3.7python.exe E:/code_pycharm/复习/t1.py
 2 2018-10-15 11:24:08,780 producer 7220 64
 3 2018-10-15 11:24:08,780 consumer --0 7488 recieved 64
 4 2018-10-15 11:24:08,780 consumer --1 7556 recieved None
 5 2018-10-15 11:24:09,780 producer 7220 65
 6 2018-10-15 11:24:09,780 consumer --2 4824 recieved 65
 7 2018-10-15 11:24:09,781 consumer --3 7036 recieved None
 8 2018-10-15 11:24:10,794 producer 7220 31
 9 2018-10-15 11:24:10,794 consumer --4 6256 recieved 31
10 2018-10-15 11:24:10,795 consumer --0 7488 recieved None
11 2018-10-15 11:24:11,809 producer 7220 60
12 2018-10-15 11:24:11,809 consumer --1 7556 recieved 60
13 2018-10-15 11:24:11,809 consumer --2 4824 recieved None
14 2018-10-15 11:24:12,826 producer 7220 44
15 2018-10-15 11:24:12,827 consumer --3 7036 recieved 44
16 2018-10-15 11:24:12,828 consumer --0 7488 recieved None
17 2018-10-15 11:24:13,836 producer 7220 18
18 2018-10-15 11:24:13,836 consumer --2 4824 recieved 18
19 2018-10-15 11:24:13,837 consumer --4 6256 recieved None
20 2018-10-15 11:24:14,850 producer 7220 3
21 2018-10-15 11:24:14,850 consumer --3 7036 recieved 3
22 2018-10-15 11:24:14,851 consumer --1 7556 recieved None
23 2018-10-15 11:24:15,864 producer 7220 33
24 2018-10-15 11:24:15,864 consumer --0 7488 recieved 33
25 2018-10-15 11:24:15,864 consumer --4 6256 recieved None
26 2018-10-15 11:24:16,878 producer 7220 44
27 2018-10-15 11:24:16,878 consumer --2 4824 recieved 44
28 2018-10-15 11:24:16,879 consumer --3 7036 recieved None
29 2018-10-15 11:24:17,892 producer 7220 39
30 2018-10-15 11:24:17,892 consumer --0 7488 recieved 39
31 2018-10-15 11:24:17,892 consumer --1 7556 recieved None

View Code

　　注意：上面的例子只为理解，存在很多瑕疵。

　　　　如果一个生产者，多个消费者，若只通知部分线程，就是多播，若都通知，就是广播。

　　　　一般消费者在前，避免数据丢失，如果不在意，也就无所谓。

　　　　正常情况下，消费者速度很慢，对数据做一定处理，所以匹配很难，所以增加消费者来解决。

　　总结：

　　　　Conditon 用于生产者消费者模型中，解决生产者消费者速度匹配问题

　　　　采用了通知机制

　　　　使用方式：

　　　　　　使用Conditon，必须先acquire，用完了，release，因为内部使用了锁。默认是RLock，最好使用with上下文。

　　　　　　消费者wait，等待通知。

　　　　　　生产者生产好消息，对消费者法通知，可以使用notify或notify_all方法

6、Barrier　　　　　

　　叫栅栏，屏障，可以想成路障，道闸。3.2引入的新功能。

名称	含义
Barrier(parties, action=None,timeout=None	g构建Barrier对象，指定参与方数目，timeout是wait方法未指定超时的默认值。
n_waiting	当前在屏障中等待的线程数
parties	各方数，就是需要多少个等待
wait(timeout=None)	等待通过屏障，返回0到线程数-1 的整数，每个线程返回不同，如果wait方法设置了超时，并超时发送，屏障将处于broken状态。

　　测试：线程数小于等于 parties

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Barrier
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 barrier = Barrier(3)
10 
11 def worker(bar:Barrier):
12     print(' working', barrier.n_waiting)   # bar.n_waiting
13     t = bar.wait()
14     print(t)
15     print('finished---', bar.n_waiting)
16 
17 ts = []
18 for  i in range(2):
19     t = Thread(target=worker, args=(barrier,))
20     t.start()
21     ts.append(t)
22 
23 
24 while True:
25     time.sleep(1)
26     print(barrier.n_waiting)

View Code

　　结果：

1  working 0
2  working 1
3 2
4 2
5 2
6 2

View Code

　　从上述可以看出，当线程数少于 parties的时候，n_waitin 是当前线程数，在等待。

　　而刚启动第一个线程的时候，此时n_waiting = 0,还没有一个线程在等待，因为等执行完wait后，在知道有一个在等待。

　　所以，当线程数为2 的时候，n_waiting = 1,但是在主线程中，n_waiting = 2,因为当两个线程都处于wait时，主线程发现有两个哎等待，如果没有sleep（1），主线程中可能也会出现0 或 1.

　　测试：如果出现abort，即损坏，需要异常处理来解决，正常的线程还是会继续执行

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Barrier
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 barrier = Barrier(3)
10 
11 def worker(bar:Barrier):
12     print(' working', barrier.n_waiting)   # bar.n_waiting
13     try:
14         bar.wait()
15     except threading.BrokenBarrierError:
16         print('broken')
17     print('finished---', bar.n_waiting)
18 
19 ts = []
20 for  i in range(3):
21     if i == 2:
22         barrier.abort()
23     # if i == 4:
24     #     barrier.reset()
25     t = Thread(target=worker, args=(barrier,))
26     t.start()
27     ts.append(t)
28 
29 
30 while True:
31     time.sleep(2)
32     print(barrier.n_waiting, barrier.broken)

View Code

　　结果：从结果可看到 0,1线程也都完成了

 1  working 0
 2  working broken0 working 0
 3 broken
 4 broken
 5 finished--- 0
 6 
 7 
 8 finished---finished--- 0
 9  0
10 0 True
11 0 True
12 0 True
13 
14 Process finished with exit code 1

View Code

　　测试：通过异常处理来解决abrot ---> broken

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Barrier
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 barrier = Barrier(3)
10 
11 def worker(bar:Barrier):
12     print(' working', barrier.n_waiting)   # bar.n_waiting
13     try:
14         bar.wait()
15     except threading.BrokenBarrierError:
16         print('broken')
17     print('finished---', bar.n_waiting)
18 
19 ts = []
20 for  i in range(7):
21     if i == 2:
22         barrier.abort()
23     if i == 4:
24         barrier.reset()
25     t = Thread(target=worker, args=(barrier,))
26     t.start()
27     ts.append(t)
28 
29 
30 while True:
31     time.sleep(0.5)
32     print(barrier.n_waiting, barrier.broken)

View Code

　　结果：测试发现，只要线程是3 的倍数，即便abort了，也就是损坏了，还是可以往下执行

 1 D:python3.7python.exe E:/code_pycharm/复习/t2.py
 2  working 0
 3  working 1
 4 broken working
 5 finished---  0
 6 brokenbroken
 7 finished--- 0
 8 0
 9  working 0
10 
11  working 1
12 finished--- 2
13  working 2
14 finished--- 0
15 finished--- 0
16  working 0
17 finished--- 0
18 1 False
19 1 False
20 1 False
21 1 False
22 1 False
23 1 False
24 1 False
25 
26 Process finished with exit code 1

View Code

　　测试：如果wait超时，就会将barrier broken，而且一直处于broken，除非reset，也就是说，如果broken后，即便线程数不是partes的整数倍，都会往下走，不会处于等待，也就是说，来一个线程，不等，直接往下走。如下测试2

　　没有broken之前正常等待，出现broken之后，就不用再等，直接执行后面的代码，直到修复

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Barrier
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 barrier = Barrier(3)
10 
11 def worker(bar:Barrier):
12     print(' working', barrier.n_waiting)   # bar.n_waiting
13     try:
14         bar.wait(1)
15     except threading.BrokenBarrierError:
16         print('broken')
17     print('finished---', bar.n_waiting)
18 
19 ts = []
20 for  i in range(6):
21     t = Thread(target=worker, args=(barrier,))
22     t.start()
23     time.sleep(1)
24     ts.append(t)
25 
26 
27 while True:
28     time.sleep(0.5)
29     print(barrier.n_waiting, barrier.broken)

View Code

　　结果：

 1 D:python3.7python.exe E:/code_pycharm/复习/t2.py
 2  working 0
 3  working 1
 4 broken
 5 broken
 6 finished--- 0finished--- 0
 7 
 8  working 0
 9 broken
10 finished--- 0
11  working 0
12 broken
13 finished--- 0
14  working 0
15 broken
16 finished--- 0
17  working 0
18 broken
19 finished--- 0
20 0 True
21 0 True
22 0 True
23 0 True
24 0 True

View Code

　　手动reset（）

　　测试2：

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Barrier
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 barrier = Barrier(3)
10 
11 def worker(bar:Barrier):
12     print(' working', barrier.n_waiting)   # bar.n_waiting
13     try:
14         bar.wait(1)
15     except threading.BrokenBarrierError:
16         print('broken')
17     print('finished---', bar.n_waiting)
18 
19 ts = []
20 for  i in range(6):
21     t = Thread(target=worker, args=(barrier,))
22     t.start()
23     time.sleep(1)
24     ts.append(t)
25 
26 time.sleep(3)
27 print('--------------------------------------------------')
28 
29 for  _ in range(3):
30     tt = threading.Thread(target=worker,args=(barrier,))
31     tt.start()
32 
33 
34 while True:
35     time.sleep(0.5)
36     print(barrier.n_waiting, barrier.broken)

View Code

　　结果：

 1 D:python3.7python.exe E:/code_pycharm/复习/t2.py
 2  working 0
 3  working 1
 4 broken
 5 finished--- 0
 6 broken
 7 finished--- 0
 8  working 0
 9 broken
10 finished--- 0
11  working 0
12 broken
13 finished--- 0
14  working 0
15 broken
16 finished--- 0
17  working 0
18 broken
19 finished--- 0
20 --------------------------------------------------
21  working 0
22 broken
23 finished--- 0
24  working 0
25 broken
26 finished--- 0
27  working 0
28 broken
29 finished--- 0
30 0 True
31 0 True
32 0 True
33 0 True
34 0 True
35 0 True
36 0 True
37 
38 Process finished with exit code 1

View Code

　　Barrier应用：

　　　　并发初始化：

　　　　所有线程都必须初始化完成后，才能继续工作，例如运行前加载数据，检查，如果这些工作没有完成就开始运行，将不能正常进行。

　　　　10个线程做10种工作准备，每个线程负责一种工作，只有这10个线程完成后，才能继续工作，先完成的要等待后完成的线程。

　　例如：启动一个程序，需要先加载磁盘文件，缓存预热，初始化里链接池等工作，这些工作可以齐头并进，不过只有都满足了，成序才能继续向后执行。假设数据库链接失败，则初始化工作失败，就要abort，barrier置为broken，所有线程收到异常退出。

　　工作量：

　　　　有10个计算任务，完成6 个，就算完成工作。

7、semaphore 信号量

　　和 Lock很像，信号量对象内部维护一个倒计数器，每一次acquire都会减1，当acquire方法发现技术为0 就阻塞请求的线程，直到其他线程对信号量release后，计数大于 0，恢复阻塞的线程。

名称	含义
Semaphore(value=1)	构造方法，value小于0，抛ValueError异常
acquire(blocking=True, timeout=None)	获取信号量，计数器减一，获取成功返回True
release()	释放信号量，计数器加1

　　计数器永远不会低于0，因为acquire的时候，发现是0，都会被阻塞

　　测试1：

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Semaphore
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 s = Semaphore(3)
10 
11 print(s._value)
12 
13 print(s.acquire())
14 print(s.acquire())
15 print(s._value)
16 
17 Thread(target=lambda s:s.acquire(), args=(s,)).start()
18 time.sleep(2)
19 print(s._value)
20 
21 s.release()
22 s.release()
23 s.release()
24 s.release()
25 s.release()
26 
27 print('=========== end ==============')
28 
29 print(s._value)

release超过value定义数

　　结果：可以看到release 超过了value后，在看_value的值，就变了, 所以一般用带边界的信号量、

 1 D:python3.7python.exe E:/code_pycharm/复习/t1.py
 2 3
 3 True
 4 True
 5 1
 6 0
 7 =========== end ==============
 8 5
 9 
10 Process finished with exit code 0

View Code

　　在BoundedSemaphore 下，如果没有acquire信号量的时候，就release，就会报错

　　BoundedSemaphore类：

　　　　有界的信号量，不允许使用release查出初始化的范围，否则ValueError

　　应用举例：

　　　　连接池：因为资源有限，且开启一个连接成本高，所以使用连接池。

　　　　一个简单的链接池：

　　　　　　链接池应该有容量（总数），有一个工厂方法可以获取链接，能够把不用的链接返回，供其他调用者使用。

　　测试: 此代码是用来演示，并不能用于生产

 1 import threading
 2 from threading import Thread , Lock, Event, Condition, Semaphore,BoundedSemaphore
 3 import logging, random
 4 import time
 5 
 6 FORMAT = '%(asctime)s %(threadName)s %(thread)d %(message)s'
 7 logging.basicConfig(format=FORMAT,level=logging.INFO)
 8 
 9 class Conn:
10     def __init__(self, name):
11         self.name = name
12 
13 class Pool:
14     def __init__(self, count:int):
15         self.count = count
16         self.pool = [self.__connect('conn - {}'.format(x)) for x in range(self.count)]
17         self.semaphore = Semaphore(count)
18 
19 
20     def _connect(self, conn_name):
21         return Conn(conn_name)
22 
23     def get_conn(self):
24         print('------------------')
25         self.semaphore.acquire()
26         print('===================')
27         conn = self.pool.pop()
28         return conn
29 
30     def return_conn(self,conn:Conn):
31         self.pool.append(conn)
32         self.semaphore.release()
33 
34 pool = Pool(3)
35 
36 def worer(pool:Pool):
37     conn = pool.get_conn()
38     logging.info(conn)
39 
40     threading.Event().wait(random.randint(1, 4))
41     pool.return_conn(conn)
42 
43 for i in range(6):
44     threading.Thread(target=worer, name='w --{}'.format(i), args=(pool,)).start()

View Code

　　信号量和锁：

　　　　锁，只允许同一个时间一个线程独占资源，它是特殊的信号量，即信号量计数器初始值为 1

　　　　信号量，可以多个线程访问共享资源，但是这个共享资源是有限的。

　　　　锁，可以看做特殊的信号量。

8、数据结构和 GIL：

　　Queue是线程安全的，到目前为止。

　　因为 if语句执行和put 、get执行，中间，其他线程也插进来

　　GIL 全局解释器锁：

　　第一段话的意思就是说：如果多线程的时候，每个线程分配到不同的cpu核心上，但是，还是同一时间只有一个线程执行字节码。

　　IO密集型：比如print，会调用os模块下的stdout，这个时间，就会有其他线程深入执行。

　　事实上，通过测试一个cpu密集型的代码，CPython多线程是没有任何优势的。和一个线程执行时间相当。因为GIL存在，

　　事实上，python支持使用单线程，因为里边有一个协程。效率也不亚于多进程

　　所以多线程，相当于串行执行，因为GIL ，每次只能执行一个线程代码，只不过时间片不一样。

　　墙上时间（手表看的时间）

    
  
    5个100那块 再看一次，什么时候不会出现500
    


多线程-锁：
    共享锁，排他锁，锁力度
    线程相关：lock  Rlock

    一般来说消费者先启动。避免数据丢失

    condition：
        生产速度  匹配消费速度
        一份数据多人使用
        广播策略
        多播策略

    复习：正则出现的 切片

    Barrier：

        Bounded 边界


    一个资源 lock
    多个有限资源 信号量
    with不能夸函数


    Queue代码中
        互斥量！！！

    内置数据结构本身不是线程安全的。在GIL下，安全，仅在CPython

为什么要坚持，想一想当初！

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原文地址：https://www.cnblogs.com/JerryZao/p/9776961.html