How the devil can gettid() return 1?

[Tom Horsley]

Every once in a while google-chrome goes into a 100% cpu loop.
I got curious and examined the thread that was running at 100%
and strace says this over and over again till I interrupt it:

gettid()                                = 1
gettid()                                = 1
gettid()                                = 1
gettid()                                = 1
^Cstrace: Process 18863 detached
 <detached ...>

Clearly Process 18863 isn't the init process, how can it
have a tid of 1?

This is on a fedora 24 box with a 4.6 kernel:

Linux tomh 4.6.4-301.fc24.x86_64 #1 SMP Tue Jul 12 11:50:00 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Just curious...