lib: fix expensive isNaN call in readable streams

[bnoordhuis]

Replace a call to isNaN(n) with n !== n. Removes most of the
overhead from the following hotspot:

13.59% iojs perf-603.map [.] LazyCompile:*isNaN
native v8natives.js:67

R=@chrisdickinson, /cc @trevnorris

CI: https://jenkins-iojs.nodesource.com/view/iojs/job/iojs+any-pr+multi/784/

[trevnorris]

LGTM

[brendanashworth]

ref: #936

[Fishrock123]

LGTM

[mscdex]

LGTM but perhaps there should be a comment in case someone stumbles upon this and does not understand it?

[thefourtheye]

What if state is undefined?

[trevnorris]

@bnoordhuis What would you like to do here?

[chrisdickinson]

A note: we're really checking for n === undefined here (from read() calls with no argument.) Perhaps it'd be better to make -1 the special arg and always provide it?

[Fishrock123]

@chrisdickinson if you're sure that's what it is then it sounds good to me.

(Also I'll try to get ab installed on my perf machine today so I can test it.) ((why did we think removing that from our deps was a good idea?? it's a pain to get!))

apt-get install apache2-utils

[Fishrock123]

Perhaps the original isn't an issue anymore with a newer v8?

perf report:

 0.11% 0.11% iojs perf-22222.map [.] LazyCompile:*isNaN native v8natives.js:67 

From perf record -c 50000 -e cpu-clock -g -i io.js/iojs --perf_basic_prof io.js/benchmark/http_simple_auto.js -k -t 10 -c 100 -n1000000 on master.

[bnoordhuis]

@Fishrock123 You're not passing a request path. Try bytes/8 or buffer/8.

[dcousens]

This should really just be if (n === undefined || n === null) {.

We are not checking types anywhere else, as can be seen by the possible type explosion: state.buffer.length (cannot read property 'length' of undefined).

[cjihrig]

@bnoordhuis what is the status of this one liner?

[bnoordhuis]

Closing, I'll revisit when it comes up again.