指定Python线程数目

　　可以通过threading.semaphore()来指定并行运行的Python线程的数目。

#!/usr/bin/python2.7
#File: threadsNum.py
#Author: lxw
#Time: 2014-09-07
#Usage: Demonstration for control the number of threads.

import threading
from myThread import MyThread
from time import sleep

def fib(x):
    sleep(0.005)
    if x < 2:
        return 1
    return fib(x-2) + fib(x-1)

argList = [13, 11, 15, 12, 14]

def main():
    #Limit the number of threads to 3.
    threadingNum = threading.Semaphore(3)
    threads = []
    for arg in argList:
        t = MyThread(fib, (arg,), threadingNum, fib.__name__+str(arg))
        threads.append(t)

    #There are 5 threads in all, but at most 3 of them run at the same time.
    for thread in threads:
        thread.start()

    for thread in threads:
        #if t is threading.currentThread():
        #    continue
        thread.join()
        print(thread.getResult())

if __name__ == '__main__':
    main()
else:
    print('Being imported as a module.')

其中用到的myThread.py如下：

#!/usr/bin/python2.7
#File: myThread.py
#Author: lxw
#Time: 2014-09-06

import threading
from time import ctime

class MyThread(threading.Thread):
    def __init__(self, func, args, num, name=""):
        #if the subclass overrides the constructor, it must make sure to invoke the base class constructor (Thread.__init__()) before doing anything else to the thread.
        threading.Thread.__init__(self)
        self.func = func
        self.args = args
        self.threadingNum = num
        self.name = name

    def getResult(self):
        return self.res

    def run(self):
        #NOTE: "with".
        with self.threadingNum:
            print("start {0} at: {1}".format(self.name, ctime()))
            self.res = apply(self.func, self.args)
            print("end {0} at: {1}".format(self.name, ctime()))

Output:

lxw@lxw-PC:TASK2$ python threadsNum.py
start fib13 at: Sun Sep   ::
start fib11 at: Sun Sep   ::
start fib15 at: Sun Sep   ::
end fib11 at: Sun Sep   ::
start fib12 at: Sun Sep   ::
end fib12 at: Sun Sep   ::
start fib14 at: Sun Sep   ::
end fib13 at: Sun Sep   :: 

end fib14 at: Sun Sep   ::
end fib15 at: Sun Sep   :: 

通过下面的输出结果我们能够更好地了解(最多允许5个线程同时运行):

lxw GetIPMultiThread$ python getIP.py
start  at: Wed Mar  ::
start  at: Wed Mar  ::
start  at: Wed Mar  ::
start  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
start  at: Wed Mar  ::
end  at: Wed Mar  ::
end  at: Wed Mar  ::
end  at: Wed Mar  ::
end  at: Wed Mar  :: 

Reference:

Python继承类的方式实现多线程及控制线程数: http://lihuipeng.blog.51cto.com/3064864/1322247