IIUC, After fork and execute the program, shepherd will wait for the pid
file to appear. This is a block operation.

Shepherd on Fiber make this operation non-blocking (because the pid file
is created by Linux kernel, Shepherd just need to wait for it), every
service activation runs on its own fiber. after fork+exec, shepherd
suspend current fiber, andspawn another fiber to start another service
immediately.

But finally all fibers are co-operatively scheduled on 1 thread.

"pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de> writes:

> On Sat, Mar 26, 2022 at 07:09:12PM +0800, Zhu Zihao wrote:
>> > So shepherd service authors still cannot write blocking code but need
>> > to yield?
>> 
>> IMO, service should not block service, if they have something important
>> to do before running a program, why not fork first and do it in the
>> child-process (maybe wrap the actual startup program in Guile script)?
>
> In other words, all stays the same as without fibers?
>
> Regards,
> Florian


-- 
Retrieve my PGP public key:

  gpg --recv-keys D47A9C8B2AE3905B563D9135BE42B352A9F6821F

Zihao