From 340eebff1b550fc2a52a3b140074334c445d3022 Mon Sep 17 00:00:00 2001
From: yuchen <yuchen@tsinghua.edu.cn>
Date: Wed, 6 May 2015 12:41:12 +0800
Subject: [PATCH] add python threading examples and intros for lec 18 spoc
 discuss

---
 related_info/lab7/semaphore_condition/README.md  | 337 +++++++++++++++++++++++
 related_info/lab7/semaphore_condition/thr-ex0.py |  24 ++
 related_info/lab7/semaphore_condition/thr-ex1.py |  43 +++
 related_info/lab7/semaphore_condition/thr-ex2.py |  16 ++
 related_info/lab7/semaphore_condition/thr-ex3.py |  33 +++
 related_info/lab7/semaphore_condition/thr-ex4.py |  13 +
 related_info/lab7/semaphore_condition/thr-ex5.py |  53 ++++
 related_info/lab7/semaphore_condition/thr-ex6.py |  22 ++
 related_info/lab7/semaphore_condition/thr-ex7.py |  46 ++++
 related_info/lab7/semaphore_condition/thr-ex8.py |  42 +++
 10 files changed, 629 insertions(+)
 create mode 100644 related_info/lab7/semaphore_condition/README.md
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex0.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex1.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex2.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex3.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex4.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex5.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex6.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex7.py
 create mode 100644 related_info/lab7/semaphore_condition/thr-ex8.py

diff --git a/related_info/lab7/semaphore_condition/README.md b/related_info/lab7/semaphore_condition/README.md
new file mode 100644
index 0000000..801acb1
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/README.md
@@ -0,0 +1,337 @@
+
+From:
+
+- http://www.laurentluce.com/posts/python-threads-synchronization-locks-rlocks-semaphores-conditions-events-and-queues/
+- http://yoyzhou.github.io/blog/2013/02/28/python-threads-synchronization-locks/
+- http://blog.chinaunix.net/uid-429659-id-3186991.html
+- http://blog.csdn.net/yidangui/article/details/8707187
+- http://blog.csdn.net/yidangui/article/details/8707205
+- http://blog.csdn.net/yidangui/article/details/8707209
+- http://blog.csdn.net/yidangui/article/details/8707197
+
+## threads: Python threads synchronization: Locks, RLocks, Semaphores, Conditions, Events and Queues.
+
+### threading简介
+python是支持多线程的，并且是native的线程。主要是通过thread和threading这两个模块来实现的。
+
+#### 实现模块
+ - thread：多线程的底层支持模块，一般不建议使用；
+ - threading：对thread进行了封装，将一些线程的操作对象化。
+
+#### threading模块 
+
+ - Timer与Thread类似，但要等待一段时间后才开始运行；
+ - Lock 锁原语，这个我们可以对全局变量互斥时使用；
+ - RLock 可重入锁，使单线程可以再次获得已经获得的锁；
+ - Condition 条件变量，能让一个线程停下来，等待其他线程满足某个“条件”；
+ - Event 通用的条件变量。多个线程可以等待某个事件发生，在事件发生后，所有的线程都被激活；
+ - Semaphore为等待锁的线程提供一个类似“等候室”的结构；
+ - BoundedSemaphore 与semaphore类似，但不允许超过初始值；
+ - Queue：实现了多生产者（Producer）、多消费者（Consumer）的队列，支持锁原语，能够在多个线程之间提供很好的同步支持。
+
+
+thread是比较底层的模块，threading是对thread做了一些包装的，可以更加方便的被使用。创建thread的方式有：
+ - 第一种方式:创建一个threading.Thread()的实例对象，给它一个函数。在它的初始化函数（__init__）中将可调用对象作为参数传入
+ - 第二种方式:创建一个threading.Thread的实例，传给它一个可调用类对象，类中使用__call__()函数调用函数
+ - 第三种方式:是通过继承Thread类，重写它的run方法；
+
+第一种和第三种常用。
+
+
+
+第一种方式举例：
+
+```
+#coding=utf-8
+import threading  
+  
+def thread_fun(num):  
+    for n in range(0, int(num)):  
+        print " I come from %s, num: %s" %( threading.currentThread().getName(), n)  
+  
+def main(thread_num):  
+    thread_list = list();  
+    # 先创建线程对象  
+    for i in range(0, thread_num):  
+        thread_name = "thread_%s" %i  
+        thread_list.append(threading.Thread(target = thread_fun, name = thread_name, args = (20,)))  
+      
+    # 启动所有线程     
+    for thread in thread_list:  
+        thread.start()  
+      
+    # 主线程中等待所有子线程退出  
+    for thread in thread_list:  
+        thread.join()  
+  
+if __name__ == "__main__":  
+    main(3)  
+```
+
+第三种方式举例1：
+```
+#!/usr/bin/env python
+import threading
+import time
+count=1
+
+class KissThread(threading.Thread):
+        def run(self):
+                global count
+                print "Thread # %s:Pretending to do stuff" % count
+                count+=1
+                time.sleep(2)
+                print "done with stuff"
+
+
+for t in range(5):
+        KissThread().start()
+```
+第三种方式举例2：
+```
+import threading  
+  
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        print "I am %s" % (self.name)  
+      
+if __name__ == "__main__":  
+    for i in range(0, 5):  
+        my_thread = MyThread()  
+        my_thread.start()          
+```
+
+
+
+
+### Thread类常用方法
+#### getName(self) 
+返回线程的名字
+#### setName方法
+可以指定每一个thread的name
+```
+def __init__(self):  
+    threading.Thread.__init__(self)  
+    self.setName("new" + self.name)  
+```
+#### isAlive(self) 
+布尔标志，表示这个线程是否还在运行中
+####  isDaemon(self) 
+返回线程的daemon标志
+####   run(self) 
+定义线程的功能函数
+####  start方法
+启动线程
+####  join方法
+ join方法原型如下，这个方法是用来程序挂起，直到线程结束，如果给出timeout，则最多阻塞timeout秒
+``` 
+def join(self, timeout=None):  
+```
+#### setDaemon方法
+当我们在程序运行中，执行一个主线程，如果主线程又创建一个子线程，主线程和子线程就分兵两路，当主线程完成想退出时，会检验子线程是否完成。如果子线程未完成，则主线程会等待子线程完成后再退出。但是有时候我们需要的是，只要主线程完成了，不管子线程是否完成，都要和主线程一起退出，这时就可以用setDaemon方法，并设置其参数为True。
+
+
+### Queue提供的类
+ - Queue队列
+ - LifoQueue后入先出（LIFO）队列
+ - PriorityQueue 优先队列
+
+### 互斥锁
+Python编程中，引入了对象互斥锁的概念，来保证共享数据操作的完整性。每个对象都对应于一个可称为" 互斥锁" 的标记，这个标记用来保证在任一时刻，只能有一个线程访问该对象。在Python中我们使用threading模块提供的Lock类。添加一个互斥锁变量mutex = threading.Lock()，然后在争夺资源的时候之前我们会先抢占这把锁mutex.acquire()，对资源使用完成之后我们在释放这把锁mutex.release()。
+
+当一个线程调用Lock对象的acquire()方法获得锁时，这把锁就进入“locked”状态。因为每次只有一个线程可以获得锁，所以如果此时另一个线程试图获得这个锁，该线程就会变为同步阻塞状态。直到拥有锁的线程调用锁的release()方法释放锁之后，该锁进入“unlocked”状态。线程调度程序从处于同步阻塞状态的线程中选择一个来获得锁，并使得该线程进入运行（running）状态。
+
+```
+import threading  
+import time  
+   
+counter = 0  
+mutex = threading.Lock()  
+   
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        global counter, mutex  
+        time.sleep(1);  
+        if mutex.acquire():  
+            counter += 1  
+            print "I am %s, set counter:%s" % (self.name, counter)  
+            mutex.release()  
+      
+if __name__ == "__main__":  
+    for i in range(0, 100):  
+        my_thread = MyThread()  
+        my_thread.start()   
+```        
+
+### Condition条件变量
+ Python提供的Condition对象提供了对复杂线程同步问题的支持。Condition被称为条件变量，除了提供与Lock类似的acquire和release方法外，还提供了wait和notify方法。使用Condition的主要方式为：线程首先acquire一个条件变量，然后判断一些条件。如果条件不满足则wait；如果条件满足，进行一些处理改变条件后，通过notify方法通知其他线程，其他处于wait状态的线程接到通知后会重新判断条件。不断的重复这一过程，从而解决复杂的同步问题。
+ 
+另外：Condition对象的构造函数可以接受一个Lock/RLock对象作为参数，如果没有指定，则Condition对象会在内部自行创建一个RLock；除了notify方法外，Condition对象还提供了notifyAll方法，可以通知waiting池中的所有线程尝试acquire内部锁。由于上述机制，处于waiting状态的线程只能通过notify方法唤醒，所以notifyAll的作用在于防止有线程永远处于沉默状态。
+
+#### “生产者-消费者”模型
+代码中主要实现了生产者和消费者线程，双方将会围绕products来产生同步问题，首先是2个生成者生产products ，而接下来的4个消费者将会消耗products.
+
+
+实现举例：
+```
+#coding=utf-8
+#!/usr/bin/env python
+  
+import threading  
+import time  
+   
+condition = threading.Condition()  
+products = 0  
+   
+class Producer(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+          
+    def run(self):  
+        global condition, products  
+        while True:  
+            if condition.acquire():  
+                if products < 10:  
+                    products += 1;  
+                    print "Producer(%s):deliver one, now products:%s" %(self.name, products)  
+                    condition.notify()  
+                else:  
+                    print "Producer(%s):already 10, stop deliver, now products:%s" %(self.name, products)  
+                    condition.wait();  
+                condition.release()  
+                time.sleep(1)  
+          
+class Consumer(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+          
+    def run(self):  
+        global condition, products  
+        while True:  
+            if condition.acquire():  
+                if products > 1:  
+                    products -= 1  
+                    print "Consumer(%s):consume one, now products:%s" %(self.name, products)  
+                    condition.notify()  
+                else:  
+                    print "Consumer(%s):only 1, stop consume, products:%s" %(self.name, products)  
+                    condition.wait();  
+                condition.release()  
+                time.sleep(2)  
+                  
+if __name__ == "__main__":  
+    for p in range(0, 2):  
+        p = Producer()  
+        p.start()  
+          
+    for c in range(0, 4):  
+        c = Consumer()  
+        c.start() 
+```
+### 信号量semaphore
+semaphore是一个变量，控制着对公共资源或者临界区的访问。信号量维护着一个计数器，指定可同时访问资源或者进入临界区的线程数。每次有一个线程获得信号量时，计数器-1。若计数器为0，其他线程就停止访问信号量，直到另一个线程释放信号量。
+
+```
+#coding=utf-8
+import threading  
+import random  
+import time  
+  
+class SemaphoreThread(threading.Thread):  
+    """class using semaphore"""  
+     
+    availableTables=['A','B','C','D','E']
+     
+    def __init__(self,threadName,semaphore):  
+       """initialize thread"""  
+         
+       threading.Thread.__init__(self,name=threadName)  
+       self.sleepTime=random.randrange(1,6)  
+       #set the semaphore as a data attribute of the class  
+       self.threadSemaphore=semaphore
+    def run(self):  
+       """Print message and release semaphore"""  
+         
+       #acquire the semaphore  
+       self.threadSemaphore.acquire()  
+       #remove a table from the list  
+       table=SemaphoreThread.availableTables.pop()  
+       print "%s entered;seated at table %s." %(self.getName(),table),  
+       print SemaphoreThread.availableTables  
+       time.sleep(self.sleepTime)  
+       #free a table  
+       print " %s exiting;freeing table %s." %(self.getName(),table),  
+       SemaphoreThread.availableTables.append(table)  
+       print SemaphoreThread.availableTables  
+       #release the semaphore after execution finishes  
+       self.threadSemaphore.release()  
+         
+threads=[] #list of threads  
+#semaphore allows five threads to enter critical section  
+threadSemaphore=threading.Semaphore(len(SemaphoreThread.availableTables))  
+#创建一个threading.Semaphore对象，他最多允许5个线程访问临界区。  
+#Semaphore类的一个对象用计数器跟踪获取和释放信号量的线程数量。  
+#create ten threads  
+for i in range(1,11):  
+   threads.append(SemaphoreThread("thread"+str(i),threadSemaphore))  
+#创建一个列表，该列表由SemaphoreThread对象构成，start方法开始列表中的每个线程  
+#start each thread  
+for thread in threads: 
+   thread.start()   
+```
+SemaphoreThread类的每个对象代表饭馆里的一个客人。类属性availableTables跟踪饭馆中可用的桌子。
+信号量有个内建的计数器，用于跟踪他的acquire和release方法调用的次数。内部计数器的初始值可作为参数传给Semaphore构造函数。默认值为1.计数器大于0，Semaphore的acquire方法就为线程获得信号量，并计数器自减。
+
+
+### 死锁现象
+所谓死锁： 是指两个或两个以上的进程在执行过程中，因争夺资源而造成的一种互相等待的现象，若无外力作用，它们都将无法推进下去。此时称系统处于死锁状态或系统产生了死锁，这些永远在互相等待的进程称为死锁进程。 由于资源占用是互斥的，当某个进程提出申请资源后，使得有关进程在无外力协助下，永远分配不到必需的资源而无法继续运行，这就产生了一种特殊现象死锁。
+```
+import threading  
+   
+counterA = 0  
+counterB = 0  
+   
+mutexA = threading.Lock()  
+mutexB = threading.Lock()  
+   
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        self.fun1()  
+        self.fun2()  
+          
+    def fun1(self):  
+        global mutexA, mutexB  
+        if mutexA.acquire():  
+            print "I am %s , get res: %s" %(self.name, "ResA")  
+              
+            if mutexB.acquire():  
+                print "I am %s , get res: %s" %(self.name, "ResB")  
+                mutexB.release()  
+             
+        mutexA.release()   
+          
+    def fun2(self):  
+        global mutexA, mutexB  
+        if mutexB.acquire():  
+            print "I am %s , get res: %s" %(self.name, "ResB")  
+              
+            if mutexA.acquire():  
+                print "I am %s , get res: %s" %(self.name, "ResA")  
+                mutexA.release()  
+             
+        mutexB.release()   
+      
+if __name__ == "__main__":  
+    for i in range(0, 100):  
+        my_thread = MyThread()  
+        my_thread.start()  
+```
diff --git a/related_info/lab7/semaphore_condition/thr-ex0.py b/related_info/lab7/semaphore_condition/thr-ex0.py
new file mode 100644
index 0000000..0211527
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex0.py
@@ -0,0 +1,24 @@
+#coding=utf-8
+import threading  
+  
+def thread_fun(num):  
+    for n in range(0, int(num)):  
+        print " I come from %s, num: %s" %( threading.currentThread().getName(), n)  
+  
+def main(thread_num):  
+    thread_list = list();  
+    # 先创建线程对象  
+    for i in range(0, thread_num):  
+        thread_name = "thread_%s" %i  
+        thread_list.append(threading.Thread(target = thread_fun, name = thread_name, args = (20,)))  
+      
+    # 启动所有线程     
+    for thread in thread_list:  
+        thread.start()  
+      
+    # 主线程中等待所有子线程退出  
+    for thread in thread_list:  
+        thread.join()  
+  
+if __name__ == "__main__":  
+    main(3)  
diff --git a/related_info/lab7/semaphore_condition/thr-ex1.py b/related_info/lab7/semaphore_condition/thr-ex1.py
new file mode 100644
index 0000000..f7d9f2b
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex1.py
@@ -0,0 +1,43 @@
+#!/bin/env python
+ # -*- coding: utf-8 -*-
+ #filename: peartest.py
+
+import threading, signal
+
+is_exit = False
+
+def doStress(i, cc):
+    global is_exit
+    idx = i
+    while not is_exit:
+        if (idx < 10000000):
+            print "thread[%d]: idx=%d"%(i, idx)
+            idx = idx + cc
+        else:
+            break
+    if is_exit:
+        print "receive a signal to exit, thread[%d] stop."%i
+    else:
+        print "thread[%d] complete."%i
+
+def handler(signum, frame):
+    global is_exit
+    is_exit = True
+    print "receive a signal %d, is_exit = %d"%(signum, is_exit)
+
+if __name__ == "__main__":
+    signal.signal(signal.SIGINT, handler)
+    signal.signal(signal.SIGTERM, handler)
+    cc = 5
+    threads = []
+    for i in range(cc):
+        t = threading.Thread(target=doStress, args=(i,cc))
+        t.setDaemon(True)
+        threads.append(t)
+        t.start()
+    while 1:
+        alive = False
+        for i in range(cc):
+            alive = alive or threads[i].isAlive()
+        if not alive:
+            break
diff --git a/related_info/lab7/semaphore_condition/thr-ex2.py b/related_info/lab7/semaphore_condition/thr-ex2.py
new file mode 100644
index 0000000..edf41de
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex2.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+import threading
+import time
+count=1
+
+class KissThread(threading.Thread):
+        def run(self):
+                global count
+                print "Thread # %s:Pretending to do stuff" % count
+                count+=1
+                time.sleep(2)
+                print "done with stuff"
+
+
+for t in range(5):
+        KissThread().start()
diff --git a/related_info/lab7/semaphore_condition/thr-ex3.py b/related_info/lab7/semaphore_condition/thr-ex3.py
new file mode 100644
index 0000000..caf55bb
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex3.py
@@ -0,0 +1,33 @@
+#coding=utf-8
+#!/usr/bin/env python
+import subprocess
+from threading import Thread
+from Queue import Queue
+
+num_thread=3  #定义线程的数量
+queue=Queue() #创建队列实例
+ips=['192.168.1.100','192.168.1.110','192.168.1.120','192.168.1.130','192.168.1.200']
+
+def pinger(i,q):
+        while True:
+                ip=q.get() #获取Queue队列传过来的ip，队列使用队列实例queue.put(ip)传入ip，通过q.get() 获得
+                print "Thread %s:Pinging %s" %(i,ip)
+                ret=subprocess.call("ping -c 1 %s" % ip,shell=True,stdout=open('/dev/null','w'),stderr=subprocess.STDOUT)
+                #调用子进程执行命令，获取退出状态。不能使用subprocess.Popen也可以 
+                if ret==0:
+                        print "%s:is alive" % ip
+                else:
+                        print "%s:did not respond" % ip
+                q.task_done() #告诉queue.join()已完成队列中提取元组的工作
+
+for i in range(num_thread):#各线程开始工作
+        worker=Thread(target=pinger,args=(i,queue)) #创建一个threading.Thread()的实例，给它一个函数以及函数的参数
+        worker.setDaemon(True)    #在start方法被调用之前如果没有进行设置，程序会不定期挂起。
+        worker.start()     #开始线程的工作，没有设置程序会挂起，不会开始线程的工作，因为pinger程序是while True循环
+
+for ip in ips:
+        queue.put(ip)    #将IP放入队列中。函数中使用q.get(ip)获取
+
+print "Main Thread Waiting"
+queue.join()    #防止主线程在其他线程获得机会完成队列中任务之前从程序中退出。
+print "Done"
diff --git a/related_info/lab7/semaphore_condition/thr-ex4.py b/related_info/lab7/semaphore_condition/thr-ex4.py
new file mode 100644
index 0000000..29c26a9
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex4.py
@@ -0,0 +1,13 @@
+import threading  
+  
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        print "I am %s" % (self.name)  
+      
+if __name__ == "__main__":  
+    for i in range(0, 5):  
+        my_thread = MyThread()  
+        my_thread.start()  
diff --git a/related_info/lab7/semaphore_condition/thr-ex5.py b/related_info/lab7/semaphore_condition/thr-ex5.py
new file mode 100644
index 0000000..c39b4b6
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex5.py
@@ -0,0 +1,53 @@
+#coding=utf-8
+#!/usr/bin/env python
+  
+import threading  
+import time  
+   
+condition = threading.Condition()  
+products = 0  
+   
+class Producer(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+          
+    def run(self):  
+        global condition, products  
+        while True:  
+            if condition.acquire():  
+                if products < 10:  
+                    products += 1;  
+                    print "Producer(%s):deliver one, now products:%s" %(self.name, products)  
+                    condition.notify()  
+                else:  
+                    print "Producer(%s):already 10, stop deliver, now products:%s" %(self.name, products)  
+                    condition.wait();  
+                condition.release()  
+                time.sleep(2)  
+          
+class Consumer(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+          
+    def run(self):  
+        global condition, products  
+        while True:  
+            if condition.acquire():  
+                if products > 1:  
+                    products -= 1  
+                    print "Consumer(%s):consume one, now products:%s" %(self.name, products)  
+                    condition.notify()  
+                else:  
+                    print "Consumer(%s):only 1, stop consume, products:%s" %(self.name, products)  
+                    condition.wait();  
+                condition.release()  
+                time.sleep(2)  
+                  
+if __name__ == "__main__":  
+    for p in range(0, 2):  
+        p = Producer()  
+        p.start()  
+          
+    for c in range(0, 10):  
+        c = Consumer()  
+        c.start() 
diff --git a/related_info/lab7/semaphore_condition/thr-ex6.py b/related_info/lab7/semaphore_condition/thr-ex6.py
new file mode 100644
index 0000000..1a12867
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex6.py
@@ -0,0 +1,22 @@
+import threading  
+import time  
+   
+counter = 0  
+mutex = threading.Lock()  
+   
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        global counter, mutex  
+        time.sleep(1);  
+        if mutex.acquire():  
+            counter += 1  
+            print "I am %s, set counter:%s" % (self.name, counter)  
+            mutex.release()  
+      
+if __name__ == "__main__":  
+    for i in range(0, 100):  
+        my_thread = MyThread()  
+        my_thread.start()
diff --git a/related_info/lab7/semaphore_condition/thr-ex7.py b/related_info/lab7/semaphore_condition/thr-ex7.py
new file mode 100644
index 0000000..cdb1927
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex7.py
@@ -0,0 +1,46 @@
+#coding=utf-8
+import threading  
+import random  
+import time  
+  
+class SemaphoreThread(threading.Thread):  
+    """classusing semaphore"""  
+     
+    availableTables=['A','B','C','D','E']
+     
+    def __init__(self,threadName,semaphore):  
+       """initialize thread"""  
+         
+       threading.Thread.__init__(self,name=threadName)  
+       self.sleepTime=random.randrange(1,6)  
+       #set the semaphore as a data attribute of the class  
+       self.threadSemaphore=semaphore  
+    def run(self):  
+       """Print message and release semaphore"""  
+         
+       #acquire the semaphore  
+       self.threadSemaphore.acquire()  
+       #remove a table from the list  
+       table=SemaphoreThread.availableTables.pop()  
+       print "%s entered;seated at table %s." %(self.getName(),table),  
+       print SemaphoreThread.availableTables  
+       time.sleep(self.sleepTime)  
+       #free a table  
+       print " %s exiting;freeing table %s." %(self.getName(),table),  
+       SemaphoreThread.availableTables.append(table)  
+       print SemaphoreThread.availableTables  
+       #release the semaphore after execution finishes  
+       self.threadSemaphore.release()  
+         
+threads=[] #list of threads  
+#semaphore allows five threads to enter critical section  
+threadSemaphore=threading.Semaphore(len(SemaphoreThread.availableTables))  
+#创建一个threading.Semaphore对象，他最多允许5个线程访问临界区。  
+#Semaphore类的一个对象用计数器跟踪获取和释放信号机的线程数量。  
+#create ten threads  
+for i in range(1,11):  
+   threads.append(SemaphoreThread("thread"+str(i),threadSemaphore))  
+#创建一个列表，该列表由SemaphoreThread对象构成，start方法开始列表中的每个线程  
+#start each thread  
+for thread in threads: 
+   thread.start()  
diff --git a/related_info/lab7/semaphore_condition/thr-ex8.py b/related_info/lab7/semaphore_condition/thr-ex8.py
new file mode 100644
index 0000000..1204bcd
--- /dev/null
+++ b/related_info/lab7/semaphore_condition/thr-ex8.py
@@ -0,0 +1,42 @@
+import threading  
+   
+counterA = 0  
+counterB = 0  
+   
+mutexA = threading.Lock()  
+mutexB = threading.Lock()  
+   
+class MyThread(threading.Thread):  
+    def __init__(self):  
+        threading.Thread.__init__(self)  
+      
+    def run(self):  
+        self.fun1()  
+        self.fun2()  
+          
+    def fun1(self):  
+        global mutexA, mutexB  
+        if mutexA.acquire():  
+            print "I am %s , get res: %s" %(self.name, "ResA")  
+              
+            if mutexB.acquire():  
+                print "I am %s , get res: %s" %(self.name, "ResB")  
+                mutexB.release()  
+             
+        mutexA.release()   
+          
+    def fun2(self):  
+        global mutexA, mutexB  
+        if mutexB.acquire():  
+            print "I am %s , get res: %s" %(self.name, "ResB")  
+              
+            if mutexA.acquire():  
+                print "I am %s , get res: %s" %(self.name, "ResA")  
+                mutexA.release()  
+             
+        mutexB.release()   
+      
+if __name__ == "__main__":  
+    for i in range(0, 100):  
+        my_thread = MyThread()  
+        my_thread.start()