问题描述
我对单线程编程和多线程编程之间的区别有误解，所以我想对以下问题做出一个答案，以使一切变得清晰.
I have a misunderstanding of the difference between single-threading and multi-threading programming, so I want an answer to the following question to make everything clear.
假设有9个独立的任务，而我想用一个单线程程序和一个多线程程序来完成它们.基本上是这样的:
Suppose that there are 9 independent tasks and I want to accomplish them with a single-threaded program and a multi-threaded program. Basically it will be something like this:
单线程:
- Execute task 1
- Execute task 2
- Execute task 3
- Execute task 4
- Execute task 5
- Execute task 6
- Execute task 7
- Execute task 8
- Execute task 9
多线程:
线程1:
- Execute task 1
- Execute task 2
- Execute task 3
线程2:
- Execute task 4
- Execute task 5
- Execute task 6
线程3:
- Execute task 7
- Execute task 8
- Execute task 9
据我了解，一次将仅执行一个一个线程(获取CPU)，并且在完成量子操作后，线程调度程序会将CPU时间分配给另一个线程.
As I understand, only ONE thread will be executed at a time (get the CPU), and once the quantum is finished, the thread scheduler will give the CPU time to another thread.
那么，哪个程序会更早完成?它是多线程程序(逻辑上)吗?还是单线程程序(因为多线程有很多上下文切换需要一些时间)?为什么呢?请给我一个很好的解释:)
So, which program will be finished earlier? Is it the multi-threaded program (logically)? or is it the single-thread program (since the multi-threading has a lot of context-switching which takes some time)? and why? I need a good explanation please :)
推荐答案
这要视情况而定.
您有多少cpus?您的任务涉及多少I/O?
How many cpus do you have? How much I/O is involved in your tasks?
如果只有1个cpu，并且任务没有阻塞的I/O，则单线程将完成等于或快于多线程的速度，因为切换线程会产生开销.
If you have only 1 cpu, and the tasks have no blocking I/O, then the single threaded will finish equal to or faster than multi-threaded, as there is overhead to switching threads.
如果您有1个cpu，但是任务涉及大量的阻塞I/O，则假定使用I/O时可以完成工作，那么使用线程可能会加快速度.
If you have 1 cpu, but the tasks involve a lot of blocking I/O, you might see a speedup by using threading, assuming work can be done when I/O is in progress.
如果有多个CPU，则应该看到多线程实现比单线程实现了加速，因为可以并行执行多个线程.当然，除非任务由I/O主导，否则限制因素是设备速度，而不是CPU功耗.
If you have multiple cpus, then you should see a speedup with the multi-threaded implementation over the single threaded, since more than 1 thread can execute in parallel. Unless of course the tasks are I/O dominated, in which case the limiting factor is your device speed, not cpu power.
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