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timers: Avoid linear scan in _unrefActive.
Before this change, _unrefActive would keep the unrefList sorted when adding a new timer. Because _unrefActive is called extremely frequently, this linear scan (O(n) at worse) would make _unrefActive show high in the list of contributors when profiling CPU usage. This commit changes _unrefActive so that it doesn't try to keep the unrefList sorted. The insertion thus happens in constant time. However, when a timer expires, unrefTimeout has to go through the whole unrefList because it's not ordered anymore. It is usually not large enough to have a significant impact on performance because: - Most of the time, the timers will be removed before unrefTimeout is called because their users (sockets mainly) cancel them when an I/O operation takes place. - If they're not, it means that some I/O took a long time to happen, and the initiator of subsequents I/O operations that would add more timers has to wait for them to complete. With this change, _unrefActive does not show as a significant contributor in CPU profiling reports anymore. Fixes: nodejs/node-v0.x-archive#8160 Signed-off-by: Timothy J Fontaine <tjfontaine@gmail.com> Conflicts: lib/timers.js Fixes: nodejs/node-convergence-archive#23 Ref: #268 PR-URL: #2540 Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>
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Original file line number | Diff line number | Diff line change |
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'use strict'; | ||
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/* | ||
* This test is aimed at making sure that unref timers queued with | ||
* timers._unrefActive work correctly. | ||
* | ||
* Basically, it queues one timer in the unref queue, and then queues | ||
* it again each time its timeout callback is fired until the callback | ||
* has been called ten times. | ||
* | ||
* At that point, it unenrolls the unref timer so that its timeout callback | ||
* is not fired ever again. | ||
* | ||
* Finally, a ref timeout is used with a delay large enough to make sure that | ||
* all 10 timeouts had the time to expire. | ||
*/ | ||
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const common = require('../common'); | ||
const timers = require('timers'); | ||
const assert = require('assert'); | ||
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var someObject = {}; | ||
var nbTimeouts = 0; | ||
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/* | ||
* libuv 0.10.x uses GetTickCount on Windows to implement timers, which uses | ||
* system's timers whose resolution is between 10 and 16ms. See | ||
* http://msdn.microsoft.com/en-us/library/windows/desktop/ms724408.aspx | ||
* for more information. That's the lowest resolution for timers across all | ||
* supported platforms. We're using it as the lowest common denominator, | ||
* and thus expect 5 timers to be able to fire in under 100 ms. | ||
*/ | ||
const N = 5; | ||
const TEST_DURATION = 100; | ||
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timers.unenroll(someObject); | ||
timers.enroll(someObject, 1); | ||
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someObject._onTimeout = function _onTimeout() { | ||
++nbTimeouts; | ||
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if (nbTimeouts === N) timers.unenroll(someObject); | ||
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timers._unrefActive(someObject); | ||
}; | ||
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timers._unrefActive(someObject); | ||
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setTimeout(function() { | ||
assert.equal(nbTimeouts, N); | ||
}, TEST_DURATION); |