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doc: note synchronous part of child_process.spawn #21234

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doc: note synchronous part of child_process.spawn
davisjam Jun 9, 2018
3119e9b
doc: add reference to V8 issue
davisjam Jun 10, 2018
217acc4
nit: UNIX-like OSes
davisjam Jun 15, 2018
bbfd361
nits: relocate and drop prefix 'Note:'
davisjam Jun 15, 2018
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doc: note synchronous part of child_process.spawn 
If an application has a large RSS (GB), jorangreef
observed that child_process.spawn will block the
event loop for ms-s.

This is surprising behavior and merits documentation.

Refs: #14917
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davisjam committed Jun 9, 2018
commit d9fcde6cdec62b5ec0749509fc7a66d5ab28ac69
5 changes: 5 additions & 0 deletions doc/api/child_process.md
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Expand Up @@ -39,6 +39,11 @@ without blocking the Node.js event loop. The [`child_process.spawnSync()`][]
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.

*Note*: On some operating systems, the [`child_process.spawn()`][] method
performs memory operations synchronously before decoupling the event loop
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@bnoordhuis bnoordhuis Jun 10, 2018

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I'd be more specific and write "On UNIX-like operating systems" and tweak the wording to clarify that it's the underlying fork() system call that is responsible for copying memory, not child_process.spawn() (directly.)

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@davisjam davisjam Jun 15, 2018 •
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I like "UNIX-like" (217acc4), but I don't think we need to go into detail on the root cause. The V8 link explains things.

from the child. Applications with a large memory footprint may find frequent
[`child_process.spawn()`][] calls to be a bottleneck.

For convenience, the `child_process` module provides a handful of synchronous
and asynchronous alternatives to [`child_process.spawn()`][] and
[`child_process.spawnSync()`][]. *Note that each of these alternatives are
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