This is handling the P5 from bug 1634846 separately as it fits in its own component really.

In bug 1634846; it exposed more frequently an issue happening with the the socket transport service (STS) is starting its event loop.

It does:

nsCOMPtr<nsIThread> thread;
nsresult rv =
    NS_NewNamedThread("Socket Thread", getter_AddRefs(thread), this);
if (NS_FAILED(rv)) return rv;

{
  MutexAutoLock lock(mLock);
  // Install our mThread, protecting against concurrent readers
  thread.swap(mThread);
  mDirectTaskDispatcher = do_QueryInterface(mThread);
}

So it dispatches itself as first task and then set the value of mThread.
However it could happen that nsSocketTransportService::Run() gets called before mThread is set right after the call to NS_NewNamedThread.

This could cause nsSocketTransportService::IsOnCurrentThread() to incorrectly return false when called from nsSocketTransportService::Run()

Additionally, there's lot of unnecessary locking happening to access members like mThread, mShuttingDown and mInitialized

mThread is modified on the main thread and accessed from any thread. Holding a mutex is necessary but not always done.

Locking is only necessary because we clear the value of mThread on shutdown, but this isn't a requirement.

In all, we can make most of the tests atomic and remove most of the mutex locking in place.

The STS dispatched the first event before setting mThread member. It was possible that the STS::Run() task got started before mThread was set and causing one of the nsISerialEventTarget methods to read mThread/mInitialised/mShuttingDown value as null or zero and they would have returned an error.

We rewrite and simplify the access to mThread such that it's a lockless operation.

ApplyPortRemapPreference assert that it's running on the taskqueue; however if called before initialization, it would have been run on whatever thread called ApplyPortRemap.

Backed out for causing Bug 1649333

Backout link: https://hg.mozilla.org/integration/autoland/rev/0e0f336c4e3b06a6df9d11d00a1ae695d41e64b7
Log link: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=307988570&repo=autoland&lineNumber=8543

https://hg.mozilla.org/mozilla-central/rev/f16199c7d45e

https://hg.mozilla.org/mozilla-central/rev/ce326495d23b