python多處理沒有使用多核心

Question

閱讀文檔：https://docs.python.org/2/library/multiprocessing.html 我決定編寫一個cpu密集型代碼，並將多處理與串行計算進行比較。 首先，如果這個庫使用多處理，那麼爲什麼我只看到1個python.exe進程？ 其次，爲什麼串行計算需要12秒，而多處理需要22秒？

串行代碼：

from datetime import datetime 

def calc_fib(ind): 
    fb = 1 
    if ind >= 3: 
     prev = 1 
     i = 2 
     while i < ind: 
      prev_tmp = fb 
      fb += prev 
      prev = prev_tmp 
      i += 1 
    return fb 


def long_calc_fib(ind): 
    val = 0 
    for j in range(500): 
     val = calc_fib(ind) 
    return val 

if __name__ == "__main__": 
    t1 = datetime.now() 
    for i in range(10): 
     tmp = long_calc_fib(10000) 
    t2 = datetime.now() 
    print str(t2 - t1) 

多池代碼：

from datetime import datetime 
from multiprocessing.pool import ThreadPool 

def calc_fib(ind): 
    fb = 1 
    if ind >= 3: 
     prev = 1 
     i = 2 
     while i < ind: 
      prev_tmp = fb 
      fb += prev 
      prev = prev_tmp 
      i += 1 
    return fb 


def long_calc_fib(ind): 
    val = 0 
    for j in range(500): 
     val = calc_fib(ind) 
    return val 


if __name__ == "__main__": 
    t1 = datetime.now() 

    pool = ThreadPool(processes=10) 
    async_results = [] 
    for i in range(10): 
     async_results.append(pool.apply_async(long_calc_fib, (10000,))) 
    for res in async_results: 
     tmp = res.get() 

    t2 = datetime.now() 
    print str(t2 - t1) 

Answer 1

我的錯。 我必須使用Pool而不是ThreadPool。 通過將ThreadPool轉換爲池，我將時間縮短爲3秒。