相关疑难解决方法(0)

怎么if __name__ == "__main__":办？

# Threading example
import time, thread

def myfunction(string, sleeptime, lock, *args):
    while True:
        lock.acquire()
        time.sleep(sleeptime)
        lock.release()
        time.sleep(sleeptime)

if __name__ == "__main__":
    lock = thread.allocate_lock()
    thread.start_new_thread(myfunction, ("Thread #: 1", 2, lock))
    thread.start_new_thread(myfunction, ("Thread #: 2", 2, lock))

我刚刚开始使用Joblib模块,我正在尝试理解Parallel函数的工作原理.下面是并行化导致运行时间更长的示例,但我不明白为什么.我在1 cpu上的运行时间为51秒,而在2 cpu上为217秒.

我的假设是并行运行循环会将列表a和b复制到每个处理器.然后将item_n分配给一个cpu,将item_n + 1分配给另一个cpu,执行该函数,然后将结果写回列表(按顺序).然后抓住接下来的两个项目,依此类推.我显然错过了一些东西.

这是一个糟糕的例子还是使用joblib？我只是简单地构造了错误的代码吗？

这是一个例子:

import numpy as np
from matplotlib.path import Path
from joblib import Parallel, delayed

## Create pairs of points for line segments
a = zip(np.random.rand(5000,2),np.random.rand(5000,2))

b = zip(np.random.rand(300,2),np.random.rand(300,2))

## Check if one line segment contains another. 
def check_paths(path, paths):
    for other_path in paths:
        res='no cross'
        chck = Path(other_path)
        if chck.contains_path(path)==1:
            res= 'cross'
            break
    return res

res = Parallel(n_jobs=2) (delayed(check_paths) (Path(points), a) for points in b)