add python threading examples and intros for lec 18 spoc discuss

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()