`os` needs fix to detect CPUs or fall back to 1

[trusktr]

NPM fails when os.cpus() returns undefined. Maybe os.cpus() should output something better with sane fallback default values?

Just an idea. Not sure if it's preferable to expect other programs to check for undefined.

[devsnek]

imo the sanest output for not being able to detect cpus is undefined. a computer with 30cpus could still fail to operate with os.cpus()

EDIT:
after thinking about this for a few min in my mind it might even be better to throw if os.cpus actually is unable to get cpu info. an empty array is another option but thats pretty misleading (not indicative of an error)

[bnoordhuis]

Yeah, I could see us raising an exception but not fabricating data. The error message will mostly be a generic 'operation failed' error, though.

The linked issue is about Android. The reason it fails there is because /proc/stat isn't readable any more in recent releases. If anyone knows of a fix, please submit it to libuv; src/unix/linux-core.c is the relevant file.

[benjamingr]

I think this needs to be fixed on NPM and not Node, if we can't detect the # of CPUs I'd rather not fabricate it. We should probably add docs.

@bnoordhuis is there an open issue? Can't we just read /sys/devices/system/cpu/ on Android? Alternatively, the NDK has a android_getCpuCount() method.

[bnoordhuis]

No issue. Android is self-serve.

[benjamingr]

There are two possible fixes (reading it from sys/devices/system/cpu) or using an NDK API and calling android_getCpuCount() directly - however I don't think I'm at capacity to build & test an Android specific fix.

[gireeshpunathil]

how about a new api os.cpucount() ?

#include <stdio.h>
#include <unistd.h>

int main() {
  fprintf(stderr, "# of CPUs: %ld\n", sysconf( _SC_NPROCESSORS_ONLN));
}

seem to be fairly portable across UNIX, and does not have the overhead of file system access.

[bnoordhuis]

How do you think sysconf( _SC_NPROCESSORS_ONLN) is implemented? :-)

[gireeshpunathil]

aix:
17825890: 39059491: sysconfig(8, 0x2FF22A90, 192) = 0

linux:

open("/sys/devices/system/cpu/online", O_RDONLY|O_CLOEXEC) = 3
read(3, "0-7\n", 8192)                  = 4
close(3)                                = 0

ok - so you meant to say at least in Linux, it is all one and the same! thanks.

[davisjam]

If Node throws for os.cpus(), would a variety of other APIs also need to throw?

I think documenting the "Couldn't detect -> undefined" behavior seems OK.

[gireeshpunathil]

I guess the issue is with the overloaded usage of the API - the original and intended usage for obtaining CPU model, speed etc. and the derived usage of obtaining the CPU count via. the length of the resultant array. While the first one if complex and may not have support from all the platforms, second one is well covered, straight-forward and error free.

From an end user's point, os.cpus().length being interpreted as the cpu count makes sense, but its value being undefined does not, as there is at least one CPU on which this API was invoked!

So I suggest we have another API for cpucount alone that is reliable and deterministic.

[gibfahn]

Looking at the linked issue (rvagg/node-worker-farm@0b2349c) the fact that you have to get the length of the object is a bit of a pain.

I'd imagine a natural API to look like:

const cpus = os.cpus() || 1

Instead of which you have to do:

const cpus = (require('os').cpus() || { length: 1 }).length

which isn't exactly obvious. Given that getting the number of cpus is probably the largest use-case for this API, I think I'd be +1 on a separate api for it.