Python child process in while True loop blocks parent

[Jen Kris]

I can't find any support for your comment that "Fork creates a new
process and therefore also a new thread."  From the Linux man pages https://www.man7.org/linux/man-pages/man2/fork.2.html, "The child process is created with a single thread—the one that called fork()." 

I have a one-core one-thread instance at Digital Ocean available running Ubuntu 18.04.  I can fork and create a new process on it, but it doesn't create a new thread because it doesn't have one available. 

You may also want to see "Forking vs Threading" (https://www.geekride.com/fork-forking-vs-threading-thread-linux-kernel), "Fork vs Thread" (https://medium.com/obscure-system/fork-vs-thread-38e09ec099e2), and "Linux process and thread" (https://zliu.org/post/linux-process-and-thread) ("This means that to create a normal process fork() is used that further calls clone() with appropriate arguments while to create a thread or LWP, a function from pthread library calls clone() with relvant flags. So, the main difference is generated by using different flags that can be passed to clone() funciton(to be exact, it is a system call"). 

You may be confused by the fact that threads are called light-weight processes. 

Or maybe I'm confused :)

If you have other information, please let me know.  Thanks. 

Jen


Dec 5, 2021, 18:08 by hjp-python at hjp.at:

> On 2021-12-06 00:51:13 +0100, Jen Kris via Python-list wrote:
>
>> The C program creates two threads (using pthreads), one for itself and
>> one for the child process.  On creation, the second pthread is pointed
>> to a C program that calls fork-execv to run the Python program.  That
>> way Python runs on a separate thread. 
>>
>
> I think you have the relationship between processes and threads
> backwards. A process consists of one or more threads. Fork creates a new
> process and therefore also a new thread.
>
>  hp
>
> -- 
>  _  | Peter J. Holzer    | Story must make more sense than reality.
> |_|_) |                    |
> | |   | hjp at hjp.at         |    -- Charles Stross, "Creative writing
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>