Single threaded client application

[nickjmeyer]

According to the documentation about the changes between V1 and V2, it sounds like all subscriptions have their own thread.

Is it possible to keep the entire event loop on a single thread?

[bretambrose]

v1 and v2 are a bit overloaded terms, unfortunately. Within the v2 device SDKs, GG IPC has two different clients:

v1 IPC clients - callbacks all occur on the event loop thread that the network connection is bound to. It was a common occurrence for developers to accidentally deadlock their components by waiting on a completion event within a callback. This led the Greengrass team to develop "v2"/higher-level IPC clients that execute callbacks on a thread pool, avoiding the deadlock scenario.

From a language-SDK perspective:

• C++ - only has the v1 client. Overall, can be difficult to use and we'd like to improve the experience but haven't had time yet. To answer your question directly, C++ IPC callbacks only occur on a single thread -- the thread the connection is bound to.
• Java - both v1 and v2 IPC clients
• Python - both v1 and v2 IPC clients
• JS - v2-esque client (doesn't run on a thread pool, just integrates naturally into node's event loop)

[nickjmeyer]

Gotcha. Thanks! The explanation is much appreciated.