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_SC_NPROCESSORS_ONLN may not be reliable on Android #34

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Ms2ger opened this issue Jan 23, 2017 · 3 comments · Fixed by #45 or #51
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_SC_NPROCESSORS_ONLN may not be reliable on Android #34

Ms2ger opened this issue Jan 23, 2017 · 3 comments · Fixed by #45 or #51

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@Ms2ger
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Ms2ger commented Jan 23, 2017

Quoting from mozilla.dev.platform:

sysconf(_SC_NPROCESSORS_ONLN) is used a number of places in the tree to get
a core count for parallel algorithms. The web says that that phrase does
not really return the number of available cores on ARM Linuxish systems in
general, including Android - because the return value does not account for
cores that are sleeping for power saving reasons. (I've confirmed this
locally on an ARM board.) So you may get lucky when you ask. Or not.

sysconf(_SC_NPROCESSORS_CONF) works better here.

JS engine issue with some background and links to other discussions:
https://bugzilla.mozilla.org/show_bug.cgi?id=1333059.
@seanmonstar
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Sounds like a reasonable change to me, then.

@GabrielMajeri GabrielMajeri mentioned this issue Jun 22, 2017
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@seanmonstar
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#45 had to be reverted, _SC_NPROCESSORS_CONF is not defined in libc on Android.

@seanmonstar seanmonstar reopened this Jun 23, 2017
@GabrielMajeri GabrielMajeri mentioned this issue Jun 24, 2017
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@GabrielMajeri
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Sorry my pull request did not work, I submitted a pull request to libc now to add the _SC_NPROCESSORS_CONF constant.

Once the pull request gets accepted, perhaps this issue could finally be closed.

bors added a commit to rust-lang/libc that referenced this issue Jun 24, 2017
@bors
Auto merge of #627 - GuildMasterInfinite:master, r=alexcrichton
2f28640 
Add missing Android constant

This pull requests add the `_SC_NPROCESSORS_CONF` constant to `libc` for Android targets. The similar `_SC_NPROCESSORS_ONLN` already existed.

The reason for adding only this constant is to help fix an [issue with `num_cpus`](seanmonstar/num_cpus#34).
@GabrielMajeri GabrielMajeri mentioned this issue Jul 19, 2017
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@echesakov echesakov mentioned this issue May 18, 2018
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@gasche gasche mentioned this issue Mar 15, 2023
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@seanmonstar @Ms2ger @GabrielMajeri