什么是进程？
- 进程是执行中的程序
- 拥有独立地址空间、内存、数据栈等
- 操作系统管理
- 派生（fork或spawn）新进程
- 进程间通信（IPC）方式共享信息
什么是线程？
- 同进程下执行，并共享相同的上下文
- 线程间的信息共享和通信更加容易
- 多线程并发执行
- 需要同步原语
Python线程
- 解释器主循环
- 主循环中只有一个控制线程在运行
- 使用全局解释器锁（GIL）
GIL保证一个线程
- 设置GIL
- 切换进一个线程去运行
- 执行下面操作之一
1.指定数量的字节码指令
2.线程主动让出控制权 - 把线程设置回睡眠状态（切换出线程）
- 解锁GIL
- 重复上述步骤
两种线程管理
- _thread：提供了基本的线程和锁
- threading：提供了更高级别、功能更全面的线程管理
1.支持同步机制
2.支持守护线程
代码实践
1.举例 打印日志 (不使用线程)
import logging
from time import sleep, ctime
logging.basicConfig(level=logging.INFO)
def loop0():
logging.info("start loop0 at " + ctime())
sleep(4)
logging.info("end looo0 at " + ctime())
def loop1():
logging.info("start loop1 at " + ctime())
sleep(2)
logging.info("end looo1 at " + ctime())
def main():
logging.info("start all at " + ctime())
_thread.start_new_thread(loop0, ())
_thread.start_new_thread(loop1, ())
sleep(6) # 保护主线程运行 让子线程执行完
logging.info("end all at " + ctime())
if __name__ == '__main__':
main()
2.举例 打印日志 （使用_thread 加锁执行）
import logging
import _thread
from time import sleep, ctime
logging.basicConfig(level=logging.INFO)
loops = [2, 4]
def loop(nloop, nsec, lock):
logging.info("start loop" + str(nloop) + " at " + ctime())
sleep(nsec)
logging.info("end loop" + str(nloop) + " at " + ctime())
lock.release()
def main():
logging.info("start all at " + ctime())
locks = []
nloops = range(len(loops))
for i in nloops:
lock = _thread.allocate_lock()
lock.acquire()
locks.append(lock)
for i in nloops:
_thread.start_new_thread(loop, (i, loops[i], locks[i]))
for i in nloops:
while locks[i].locked(): pass
logging.info("end all at " + ctime())
if __name__ == '__main__':
main()
3.举例 打印日志 （使用threading 自带锁（join）执行）
import logging
import threading
from time import sleep, ctime
logging.basicConfig(level=logging.INFO)
loops = [2, 4]
def loop(nloop, nsec):
logging.info("start loop" + str(nloop) + " at " + ctime())
sleep(nsec)
logging.info("end loop" + str(nloop) + " at " + ctime())
def main():
logging.info("start all at " + ctime())
threads = []
nloops = range(len(loops))
for i in nloops:
t = threading.Thread(target=loop, args=(i, loops[i]))
threads.append(t)
for i in nloops:
threads[i].start()
for i in nloops:
threads[i].join() //自行判断进程是否结束 否则阻塞
logging.info("end all at " + ctime())
if __name__ == '__main__':
main()
4.举例 打印日志 （使用类继承 Thread threading执行）
import logging
import threading
from time import sleep, ctime
logging.basicConfig(level=logging.INFO)
loops = [2, 4]
class MyThread(threading.Thread):
def __init__(self, func, args, name=''):
threading.Thread.__init__(self)
self.func = func
self.args = args
self.name = name
def run(self):
self.func(*self.args)
def loop(nloop, nsec):
logging.info("start loop" + str(nloop) + " at " + ctime())
sleep(nsec)
logging.info("end loop" + str(nloop) + " at " + ctime())
def main():
logging.info("start all at " + ctime())
threads = []
nloops = range(len(loops))
for i in nloops:
t = MyThread(loop, (i, loops[i]), loop.__name__)
threads.append(t)
for i in nloops:
threads[i].start()
for i in nloops:
threads[i].join() #自行判断进程是否结束 否则阻塞
logging.info("end all at " + ctime())
if __name__ == '__main__':
main()
课后延伸
了解 同步原语 ，例如 锁 、信号量
