Sending a notification to the main nginx thread

[Eran Kornblau]

> 
> -----Original Message-----
> From: nginx-devel <nginx-devel-bounces at nginx.org> On Behalf Of Maxim Dounin
> Sent: Wednesday, 6 October 2021 16:12
> To: nginx-devel at nginx.org
> Subject: Re: Sending a notification to the main nginx thread
> 
> Hello!
> 
> First of all, you may want to take a look at this warning in the development guide:
> 
> https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fnginx.org%2Fen%2Fdocs%2Fdev%2Fdevelopment_guide.html%23threads_pitfalls&data=04%7C01%7C%7Cd0de648d5c294e07aac008d988cae55b%7C0c503748de3f4e2597e26819d53a42b6%7C1%7C1%7C637691227285308685%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=%2BiDgCqNY6Wtl0elz%2FYAG7UvdOmoW%2BsZg9v0i5Oicc%2FY%3D&reserved=0
> 
> Quoting it here:
> 
> It is recommended to avoid using threads in nginx because it will definitely break things: most nginx functions are not thread-safe. It is expected that a thread will be executing only system calls and thread-safe library functions.
> If you need to run some code that is not related to client request processing, the proper way is to schedule a timer in the init_process module handler and perform required actions in timer handler. Internally nginx makes use of threads to boost IO-related operations, but this is a special case with a lot of limitations.
> 
Thanks Maxim, I completely get that, that is the reason I was looking for way to send a notification to the main thread, and didn't just try to call nginx functions from some other thread.
In my case, I need to integrate with some 3rd party library that has its own event loop, it would require significant changes to the library to make it run inside nginx's event loop...
So, my plan is to run it on a side thread, and send notifications between the threads, which would trigger some handler on the main thread whenever new data arrives.
I can use ngx_notify for this, but if someone will use the module and also nginx's thread pool or some 3rd party module that uses ngx_notify, it will break.
I think I can live with that, but would be nice to have a solution that is complete.

Eran

> 
> --
> Maxim Dounin
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