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lib: introduce constant MAX_TICKS #11199

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lib: introduce constant MAX_TICKS #11199

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b77745c
lib: introduce constant MAX_TICKS
danbev Feb 3, 2017
2d266c0
rename MAX_TICKS -> kMaxCallbacksPerTick
danbev Feb 7, 2017
8788a97
make kMaxCallbacksPerTick a top level const
danbev Feb 7, 2017
eda4d32
rename to kMaxCallbacksUntilQueueIsShortened
danbev Feb 12, 2017
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5 changes: 3 additions & 2 deletions lib/internal/process/next_tick.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ exports.setup = setupNextTick;
function setupNextTick() {
const promises = require('internal/process/promises');
const emitPendingUnhandledRejections = promises.setup(scheduleMicrotasks);
const MAX_TICKS = 1e4;
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perhaps this should just be a top level const?

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If I’m reading the code correctly this should be the maximum number of callbacks that are run in a single event loop iteration – is that correct? Maybe there is a better name than MAX_TICKS, or maybe there should be a comment explaining what this does…

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@bnoordhuis or @trevnorris for more specifics on the exact semantics. Whichever it is, a comment is good

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@Fishrock123 Fishrock123 Feb 6, 2017 •
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@addaleax's interpretation is correct. However, I'm not sure if breaking out in this way runs more nextTicks until the next turn of the event loop or if it runs another loop if more nextTicks remain/are scheduled.

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A name like kMaxCallbacksPerTick is arguably more self-documenting - even if 'tick' is a misnomer by now, because...

if breaking out in this way runs more nextTicks until the next turn of the event loop or if it runs another loop if more nextTicks remain/are scheduled

...the remaining ones run when the next call into the VM is made. Anywhere you see a call to MakeCallback() in the C++ code, that's where nexttick callbacks run.

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@Fishrock123 that interpretation is incorrect. it guards against the nextTickQueue array becoming too large and running the process out of memory. There's a simple test for this which shows the event loop not being allowed to proceed. This is by design, as the alternative was a bit of a pain to work around.

setImmediate(() => process._rawDebug('hi'));
(function runner() { process.nextTick(runner) })();

var nextTickQueue = [];
var microtasksScheduled = false;

Expand Down Expand Up @@ -96,7 +97,7 @@ function setupNextTick() {
// callback invocation with small numbers of arguments to avoid the
// performance hit associated with using `fn.apply()`
_combinedTickCallback(args, callback);
if (1e4 < tickInfo[kIndex])
if (MAX_TICKS < tickInfo[kIndex])
tickDone();
}
tickDone();
Expand All @@ -120,7 +121,7 @@ function setupNextTick() {
// callback invocation with small numbers of arguments to avoid the
// performance hit associated with using `fn.apply()`
_combinedTickCallback(args, callback);
if (1e4 < tickInfo[kIndex])
if (MAX_TICKS < tickInfo[kIndex])
tickDone();
if (domain)
domain.exit();
Expand Down