Python的thread解析

一，在import thread之后，我们help(thread)一下，可以看到如下信息：

NAME thread
FILE (built-in)
DESCRIPTION
This module provides primitive operations to write multi-threaded programs.
The 'threading' module provides a more convenient interface.
CLASSES
__builtin__.object
lock
exceptions.Exception(exceptions.BaseException)
error
FUNCTIONS
...

我们看到其并没有thread或相似的类，只包含了两个类lock&error以及一些方法。

现主要关注接口函数，暂时忽略其它：

①lock相关的函数说明：

分配一个锁：allocate_lock() -> lock object (allocate() is an obsolete synonym)

操作锁的方法：

acquire() -- lock the lock, possibly blocking until it can be obtained

release() -- unlock the lock

locked() -- test whether the lock is currently locked

/* Deadlocks may ensue. */由程序员来保证不死锁。

②线程相关的函数说明：

创建一个新线程：start_new_thread(function,args[,kwargs]) (start_new() is an obsolete synonym) 

退出线程：exit()和exit_thread() (PyThread_exit_thread() is an obsolete synonym)

二，lock相关的函数使用示例（略去error）:

import thread

def print_status(a_lock):
    if a_lock.locked():
        print "locked"
    else:
        print "not locked"

a_lock = thread.allocate_lock()
print_status(a_lock)
a_lock.acquire()
print_status(a_lock)
a_lock.release()
print_status(a_lock)

三，thread相关的函数使用示例：

import thread

def run(n):
    # a back door, can not be run 4 times
    if n == 4:
        thread.exit()
    for i in range(n):
        print i

thread.start_new_thread(run,(5,))

四，解决一个同步问题

试解决以下同步问题：使用两个线程交替输出“Hello”与“World”各5次，以“Hello”开始以“World”结束。

①HelloWorld问题的同步模型建立：

semaphore h = 1, w = 0
# because the semaphore w is 0,so we should acquire the lock w to let it be zero(locked) when we use python to .
thread1()
{
    while(true)
    {
        p(h)
        do something;
        v(w)
    }
}
thread2()
{
    while(true)
    {
        p(w)
        do something;
        v(h)
    }
}

②使用Python实现上述同步模型，两个解决方案如下。

方案A用main线程和另一个线程来交替打印。

方案B使用除main线程外的另两个线程交替打印“Hello”与“World"。

import thread

def world():
    for i in range(5):
        w_lock.acquire()    # i want to print world
        print "world"
        h_lock.release()    # you can print hello now
    w_lock.release()

# main thread
print "use two threads to print hello&world"

h_lock = thread.allocate_lock()
w_lock = thread.allocate_lock()

w_lock.acquire(); # "print world" can not be started first
thread.start_new_thread(world,())
for i in range(5):
    h_lock.acquire()
    print "hello"
    w_lock.release()

# raw_input("finished")

import thread

def hello():
    for i in range(5):
        h_ok.acquire()
        print "hello"
        w_ok.release()
def world():
    for i in range(5):
        w_ok.acquire()
        print "world"
        h_ok.release()

# main thread
print "use two threads to print hello&world"
h_ok = thread.allocate_lock()
w_ok = thread.allocate_lock()
w_ok.acquire()
thread.start_new_thread(hello,())
thread.start_new_thread(world,())

raw_input("finished") # !!it is necessary,in case main thread exit too early