commit 4167d1bb4b7965b13b3453ec7c45fc5117428d9c
author Ryan Savitski <rsavitski@google.com> Thu Apr 18 13:25:26 2019 +0100
committer Ryan Savitski <rsavitski@google.com> Thu Apr 18 13:25:26 2019 +0100
tree 7b807d0c20d97484e0a2d550659c8273b3b3e811
parent f950764a4c1cdb1452615dcdd45d74d122895218

heapprofd_client: SIGABRT on timed out spinlock instead of indefinite spin

As discussed, we want to interfere with the host process where possible, but
this is a "should never happen" situation where it's better to get a clear
indication of an issue.

I'm not changing the interface of ScopedSpinlock in this cl, but acknowledging
that it:
  * doesn't have a way to configure the timeout (atm ~10ms in the
absence of spurious wakeups from usleep).
  * makes it easy to forget the failed-to-acquire case.

The host process can still try to handle SIGABRT (for example toybox/top does
this to restore terminal state), and if that results in a "normal" exit, we
won't get a tombstone. But that isn't a scenario worth handling specially.

Code structure notes:
* headers reordered by clang-format, imo let's just submit this version and
  stop manually fixing up the formatter.
* abort() over PERFETTO_FATAL as it tries harder to actually exit the process
  (while our macro simply sends a one-off SIGTRAP).
* could restructure the code to return the lock from a function that handles
  the timeout inline, but the explicit mention of the possibility of aborting
  at the call site seemed reasonable.

Change-Id: I86d18c3e625601a48236a2a43916afe0933605a6