gRPC internal thread in C++

[Alex Zuo]

I am trying to understand how many internal threads gRPC creates in async mode. I find some timer threads, and some threads in Executor. Are there any threads? Are there any short-lived thread?

Also are there any threads to receive bytes from socket and deserialize them?

[Jonathan Basseri]

Just to add some detail to this question, Alex and I work on a platform which exerts a lot of control over threads and allocations to guarantee high throughput and low latency. We would like to begin exposing gRPC services from the platform without compromising performance.

Our hope was to write an async server which would enqueue work in our own thread manager and go right back to listening for incoming requests. We have seen the APIs for controlling concurrency in both `ResourceQuota` and `CompletionQueue` (e.g. here) but it seems like there are still internal gRPC threads.

So it comes down to these questions: Can I control the total number of threads, both short-lived and long-lived, that gRPR creates? If not, can I provide a strong guarantee about the max # of threads?

(Getting arenas to work with our custom allocator is probably a topic for a future thread.)

Thanks for your help,
Jonathan

[Craig Tiller]

I don't think we make any guarantees about thread count right now, over and above bounded and relatively small.

We are moving to a new design around a thing called EventEngine, which will allow pluggable IO, thread pools, and timers. I expect once that work is done we'll be in a position to start to write down some level of guarantees (I hope, but can't yet commit to 0 threads outside of EventEngine being a reasonable bar to hit).

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[Alex Zuo]

Thank you Craig. What is the timeline for those work?

I understand the current implementation does not give us control of the thread counts. By reading the code, the Executor can create as many as 2 times the cpu core threads. I have more questions here:

1. What kind of internal threads is gRPC creating, how many for each kind, and what are they for? I know there are timer threads, Executor threads, but I don't know what they are for. What other threads?
2. Where are the threads to receive/send packet to socket? I cannot find any in the gRPC code base, not sure there are threads for that.
3. Are there any places where gRPC creates short-lived threads?

These questions are based on gRPC C++ implementation.

Thanks,

Alex

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