Ref upstream as MG-791.

We can define pthread_setname_np easily enough. It'll use the same guts that thrd_create_with_name does.

thrd_create_with_name is gated on _ALL_SOURCE, which I think we've put other things behind. My recollection is that I leaned a bit towards defining our own _MX_SOURCE or _FUCHSIA_SOURCE but was convinced by mcgrathr that we should just use _ALL_SOURCE. I think it makes very little difference to the Magenta or Fuchsia build itself what we pick, but we will guard nonstandard extensions behind _something_. So if you experience more or less pain based on the details of how we guard nonportable extensions, we can adjust.

Names on kernel objects (for some types that support it, which does include processes) are manipulated by mx_object_{get,set}_property: https://fuchsia.googlesource.com/magenta/+/HEAD/docs/syscalls/object_get_property.md#MX_PROP_NAME and in fact the c11 thread stuffs plumbs through to that.

This object property is what is used in our logging, the output of ps, etc. etc.

After a bit of typing and thought:

pthread_setname_np is easy, and I should do it since we have the C11 version. Presumably the Linux/OpenBSD-ish variant, which takes a pthread_t argument, rather than the OS X-ish one that only operates on the calling thread, as it's a bit more general.

I'd still suggest you cut out the middleman and operate on the mx_handle_t.

Thanks! I'll use mx_object_set_property().

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7682c6e584d676e2f002ab15aa8480df383ac0d5

commit 7682c6e584d676e2f002ab15aa8480df383ac0d5
Author: scottmg <scottmg@chromium.org>
Date: Wed May 24 15:37:25 2017

fuchsia: Implement platform thread functions

BUG=706592, 725726 

Review-Url: https://codereview.chromium.org/2888043009
Cr-Commit-Position: refs/heads/master@{#474298}

[modify] https://crrev.com/7682c6e584d676e2f002ab15aa8480df383ac0d5/base/BUILD.gn
[add] https://crrev.com/7682c6e584d676e2f002ab15aa8480df383ac0d5/base/threading/platform_thread_fuchsia.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6124dadce4bd8c918cef7f7f7e5642faea83dac4

commit 6124dadce4bd8c918cef7f7f7e5642faea83dac4
Author: Wez <wez@chromium.org>
Date: Thu Oct 19 22:23:20 2017

Set the platform thread kernel object name in PlatformThread::SetName().

In addition to registering the name with the global ThreadIdManager, the
platform thread object's name is set with zx_object_set_property(), so
that it will be reflected in logging from e.g. the platform's crash
handler.

Bug:  725726 
Change-Id: Id47efa77857b35c2317b5eed05aa2e630a044113
Reviewed-on: https://chromium-review.googlesource.com/727699
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510238}
[modify] https://crrev.com/6124dadce4bd8c918cef7f7f7e5642faea83dac4/base/threading/platform_thread_fuchsia.cc
[modify] https://crrev.com/6124dadce4bd8c918cef7f7f7e5642faea83dac4/base/threading/platform_thread_unittest.cc