Make Readhead more usable in multithread.
There doesn't seem to be a way to get any code at all
to run in a generic way on the thread that will execute
a test in android JUnit. JUnit can do it, but the android
harness imposes a thread hop.
This is inconvenent with ReadHead, because ReadHead can't
be used in multithread for semantic reasons : it would
make no sense at all. ReadHead enforces this today in a
relatively strong fashion.
But technically, the only guarantee that is needed is that
poll() is executed only on one thread in slabs of time
defined between a read barrier and a write barrier, where
the write barrier of the previous slab happen-before the
read barrier of the next slab. This in generally speaking
a bit difficult to achieve, but the tests run satisfy this
condition by starting the thread after executing the
@Before methods and joining it before executing the @After
methods. So in fact, it's safe to use ReadHead during
the befores and afters, if a bit uncomfortable, as long
as only one thread uses it during the before, one thread
during the test, and one thread during the afters.
This patch relaxes the enforcement on ReadHead to accept
the usage above. If any slab of time contains usage of
poll() on multiple threads, this will instead crash with
ConcurrentModificationException in almost all cases. It's
no longer possible to detect every possible misuse of
poll() under these conditions, but with this code it's
going to be very unlikely at each test run that the code
is incorrect and still doesn't crash, so incorrect use
should still cause at least very severe flakiness.
The main drawback, aside from the very slight performance
penalty, is that some use can be accidentally correct and
this code will now accept it. So it's possible that code
that is only accidentally correct is accepted, and a
seemingly unrelated change later breaks that correctness,
causing seemingly unrelated tests to fail.
Still, this is going to be an improvement in usability
of ReadHead. We'll no longer need to have lazy creation
of it, and it will be possible to check remaining events
after a tests runs.
Test: FrameworksNetTests NetworkStackTests
Change-Id: If87eef1686b235e53cb444a32f9985b4c2a0a901
1 file changed
tree: 108619355ca6a5e42d9dcf9a306b333867a7660a
- staticlibs/