8000 Replacing four process.nextTick calls with four setImmediate calls. S… by deltaepsilon · Pull Request #806 · foreversd/forever · GitHub
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Replacing four process.nextTick calls with four setImmediate calls. S… #806

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deltaepsilon
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Response to #715

The process.nextTick deprecation warnings are causing problems on one of my servers. This appears to resolve those problems. Two tests were broken pre-commit, and those two tests are still broken, but no more have broken.

Replacing four process.nextTick calls with four setImmediate calls. S…
baeb49b 
…hould get rid of the node warnings that are blowing up my call stack.
@kibertoad
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What are the problems that this addresses?

@SgtPooki
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SgtPooki commented May 4, 2019

This pull request is 2 years old.

@kibertoad https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/ is the official explanation of whats going on, but some important bits are below:

You may have noticed that process.nextTick() was not displayed in the diagram, even though it's a part of the asynchronous API. This is because process.nextTick() is not technically part of the event loop. Instead, the nextTickQueue will be processed after the current operation is completed, regardless of the current phase of the event loop. Here, an operation is defined as a transition from the underlying C/C++ handler, and handling the JavaScript that needs to be executed.

Looking back at our diagram, any time you call process.nextTick() in a given phase, all callbacks passed to process.nextTick() will be resolved before the event loop continues. This can create some bad situations because it allows you to "starve" your I/O by making recursive process.nextTick() calls, which prevents the event loop from reaching the poll phase.

...
Why use process.nextTick()?
There are two main reasons:

Allow users to handle errors, cleanup any then unneeded resources, or perhaps try the request again before the event loop continues.

At times it's necessary to allow a callback to run after the call stack has unwound but before the event loop continues.

And in summary:

We recommend developers use setImmediate() in all cases because it's easier to reason about (and it leads to code that's compatible with a wider variety of environments, like browser JS.)

They give a few examples of why someone may want to explicitly use nextTick.. but ultimately you're breaking out of the event loop in an unexpected way.

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@deltaepsilon @kibertoad @SgtPooki
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