tree f32c06d513e90ba1fcb8fe56f9cd055cccc7d01b
parent d1bf37780d0bcaca3e6046171f958ebfea34bde1
author Elliott Hughes <enh@google.com> 1403221141 -0700
committer Elliott Hughes <enh@google.com> 1403280417 -0700

Cache getpid.

In practice, with this implementation we never need to make a system call.
We get the main thread's tid (which is the same as our pid) back from
the set_tid_address system call we have to make during initialization.
A new pthread will have the same pid as its parent, and a fork child's
main (and only) thread will have a pid equal to its tid, which we get for
free from the kernel before clone returns.

The only time we'd actually have to make a getpid system call now is if
we take a signal during fork and the signal handler calls getpid. (That,
or we call getpid in the dynamic linker while it's still dealing with its
own relocations and hasn't even set up the main thread yet.)

Bug: 15387103
Change-Id: I6d4718ed0a5c912fc75b5f738c49a023dbed5189