多线程模块比python中的多处理慢

Multithreading module slower than multiprocessing in python

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我发现线程模块对同一任务的处理时间比多处理要长。

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import time
import threading
import multiprocessing

def func():
result = 0
for i in xrange(10**8):
result += i

num_jobs = 10

# 1. measure, how long it takes 10 consistent func() executions
t = time.time()
for _ in xrange(num_jobs):
func()
print ("10 consistent func executions takes:
{:.2f} seconds
".format(time.time() - t))

# 2. threading module, 10 jobs
jobs = []
for _ in xrange(num_jobs):
jobs.append(threading.Thread(target = func, args=()))
t = time.time()
for job in jobs:
job.start()
for job in jobs:
job.join()
print ("10 func executions in parallel (threading module) takes:
{:.2f} seconds
".format(time.time() - t))

# 3. multiprocessing module, 10 jobs
jobs = []
for _ in xrange(num_jobs):
jobs.append(multiprocessing.Process(target = func, args=()))
t = time.time()
for job in jobs:
job.start()
for job in jobs:
job.join()
print ("10 func executions in parallel (multiprocessing module) takes:
{:.2f} seconds
".format(time.time() - t))

结果：

10 consistent func executions takes:
25.66 seconds

10 func executions in parallel (threading module) takes:
46.00 seconds

10 func executions in parallel (multiprocessing module) takes:
7.92 seconds

1)为什么使用多处理模块的实现比使用线程模块更好？

2)为什么一致的func执行比使用线程模块花费更少的时间？