| Commit message (Collapse) | Author | Age |
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This changes the signature of the aio cancellation routines
to take the argument for cancellation directly, so we do not
need to lookup the argument using the nni_aio_get_prov_data.
We should probably consider eliminating nni_aio_get_prov_data,
and co, and changing the prov_extra to reflect prov_data. Later.
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fixes #326 consider nni_taskq_exec_synch()
fixes #410 kqueue implementation could be smarter
fixes #411 epoll_implementation could be smarter
fixes #426 synchronous completion can lead to panic
fixes #421 pipe close race condition/duplicate destroy
This is a major refactoring of two significant parts of the code base,
which are closely interrelated.
First the aio and taskq framework have undergone a number of simplifications,
and improvements. We have ditched a few parts of the internal API (for
example tasks no longer support cancellation) that weren't terribly useful
but added a lot of complexity, and we've made aio_schedule something that
now checks for cancellation or other "premature" completions. The
aio framework now uses the tasks more tightly, so that aio wait can
devolve into just nni_task_wait(). We did have to add a "task_prep()"
step to prevent race conditions.
Second, the entire POSIX poller framework has been simplified, and made
more robust, and more scalable. There were some fairly inherent race
conditions around the shutdown/close code, where we *thought* we were
synchronizing against the other thread, but weren't doing so adequately.
With a cleaner design, we've been able to tighten up the implementation
to remove these race conditions, while substantially reducing the chance
for lock contention, thereby improving scalability. The illumos poller
also got a performance boost by polling for multiple events.
In highly "busy" systems, we expect to see vast reductions in lock
contention, and therefore greater scalability, in addition to overall
improved reliability.
One area where we currently can do better is that there is still only
a single poller thread run. Scaling this out is a task that has to be done
differently for each poller, and carefuly to ensure that close conditions
are safe on all pollers, and that no chance for deadlock/livelock waiting
for pfd finalizers can occur.
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This closes a fundamental flaw in the way aio structures were
handled. In paticular, aio expiration could race ahead, and
fire before the aio was properly registered by the provider.
This ultimately led to the possibility of duplicate completions
on the same aio.
The solution involved breaking up nni_aio_start into two functions.
nni_aio_begin (which can be run outside of external locks) simply
validates that nni_aio_fini() has not been called, and clears certain
fields in the aio to make it ready for use by the provider.
nni_aio_schedule does the work to register the aio with the expiration
thread, and should only be called when the aio is actually scheduled
for asynchronous completion. nni_aio_schedule_verify does the same thing,
but returns NNG_ETIMEDOUT if the aio has a zero length timeout.
This change has a small negative performance impact. We have plans to
rectify that by converting nni_aio_begin to use a locklesss flag for
the aio->a_fini bit.
While we were here, we fixed some error paths in the POSIX subsystem,
which would have returned incorrect error codes, and we made some
optmizations in the message queues to reduce conditionals while holding
locks in the hot code path.
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This introduces enough of the HTTP API to support fully server
applications, including creation of websocket style protocols,
pluggable handlers, and so forth.
We have also introduced scatter/gather I/O (rudimentary) for
aios, and made other enhancements to the AIO framework. The
internals of the AIOs themselves are now fully private, and we
have eliminated the aio->a_addr member, with plans to remove the
pipe and possibly message members as well.
A few other minor issues were found and fixed as well.
The HTTP API includes request, response, and connection objects,
which can be used with both servers and clients. It also defines
the HTTP server and handler objects, which support server applications.
Support for client applications will require a client object to be
exposed, and that should be happening shortly.
None of this is "documented" yet, bug again, we will follow up shortly.
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We introduced richer, deeper tests for UDP functionality.
These tests uncovered a number of issues which this commit fixes.
The Windows IOCP code needs to support multiple aios on a single
nni_win_event. A redesign of the IOCP handling addresses that.
The POSIX UDP code also needed fixes; foremost among them is the
fact that the UDP file descriptor is not placed into non-blocking
mode, leading to potential hangs.
A number of race conditions and bugs along the implementation of
the above items were uncovered and fixed. To the best of our knowledge
the current code is bug-free.
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We only compile files that are appropriate for the platform. (We
still have guards in place, to allow for a future single .C file
to be built from all the sources.) We also remove the subsystem defines;
if a new platform needs to deviate from POSIX in ways beyond what we
intended here, then that platform should just copy those parts into
a new platform directory, rather than cross including portions from
POSIX.
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If the underlying platform fails (FreeBSD is the only one I'm aware
of that does this!), we use a global lock or condition variable instead.
This means that our lock initializers never ever fail.
Probably we could eliminate most of this for Linux and Darwin, since
on those platforms, mutex and condvar initialization reasonably never
fails. Initial benchmarks show little difference either way -- so we
can revisit (optimize) later.
This removes a lot of otherwise untested code in error cases and so forth,
improving coverage and resilience in the face of allocation failures.
Platforms other than POSIX should follow a similar pattern if they need
this. (VxWorks, I'm thinking of you.) Most sane platforms won't have
an issue here, since normally these initializations do not need to allocate
memory. (Reportedly, even FreeBSD has plans to "fix" this in libthr2.)
While here, some bugs were fixed in initialization & teardown.
The fallback code is properly tested with dedicated test cases.
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This passes valgrind 100% clean for both helgrind and deep leak
checks. This represents a complete rethink of how the AIOs work,
and much simpler synchronization; the provider API is a bit simpler
to boot, as a number of failure modes have been simply eliminated.
While here a few other minor bugs were squashed.
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We have seen leaks of pipes causing test failures (e.g. the Windows
IPC test) due to EADDRINUSE. This was caused by a case where we
failed to pass the pipe up because the AIO had already been canceled,
and we didn't realize that we had oprhaned the pipe. The fix is to
add a return value to nni_aio_finish, and verify that we did finish
properly, or if we did not then we must free the pipe ourself. (The
zero return from nni_aio_finish indicates that it accepts ownership
of resources passed via the aio.)
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This logic leaves a race condition in the dial side, which will
be fixed with a subsequent change to convert that to fully asynchronous
as well.
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This is only lightly tested, and I expect that there remain
some race conditions. Endpoint logic in particular needs
work.
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We are still seeing likely errors with pipes outliving their associated
endpoints, so work is still needed here.
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The IOCP code has been refactored to improve reuse, and hopefully
will be easier to use with TCP now. Windows IPC using Named Pipes
is mostly working -- mostly because there is a gnarly close-race.
It seems that we need to take some more care to ensure that the
pipe is not released while requests may be outstanding -- so some
deeper synchronization between the IOCP callback logic and the
win_event code is needed. In short, we need to add a condvar to
the event, and notice when we have submitted work for async completion,
and make sure we flag the event "idle" after either completion or
cancellation of the event.
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