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******************************************************************************
* *
* Open Issues, Queustions, and Comments about the I/O Core *
* *
******************************************************************************
+--------------+
| proxy/List.h |
+--------------+
DLL<class T>::in((C *c,Link<C> &l)
what is the meaning of in() ?
- is c a member of this list ?
- is c a member of some list ?
+-----------------------+
| proxy/NetProcessor.cc |
+-----------------------+
server open
The user interface for accepting on a port with the server()
call is a bit weird. We currently get notified that a new
connection occurred as a side-effect of the vc clone() call.
That's really a hack.
Can we pass in a continuation for notification, list we do with
all these other calls?
void detach_read();
void detach_write();
Hide VConnection::detach_read(VIO * vio = NULL) and
VConnection::detach_write(VIO * vio = NULL)
+---------------------+
| proxy/VConnection.h |
+---------------------+
old code
How many of the methods in VConnection.h are really supported
anymore? Can we delete the vestiges of old designs so we don't
confuse people?
inline void VConnection::clear_vio_queue()
When blowing away unexecuted VIOs, if there is a passing
continuation, we call it with a return_state of -1. What
does -1 signify, and what other values are legal? Can we be
sure the user won't use -1?
We need to document these APIs.
Mutex * mutex
What is the meaning of mutex field in class VConnection. When is it
used ? It looks that IOVConnection constructor creates it, but never
uses it. It also looks that locking is done through the mutex passed in
VIO. Should we remove the mutex field from class VConnection ?
activate_io()
Is it part of the public interface ?
+---------------+
| proxy/Event.h |
+---------------+
void EventContinuation::disable()
We disable timeout events by setting their timeout to a large
value. We disable quiescence events by patching them out of the
queue. Wouldn't it be better to have disabling work the same way
for both?
For example, could disabling timeout events just move the events
from the active queue to the disabled queue?
Finally, the disabled timeout value is set to 200 years past some
unknown time in the past. Do we have any guarantees about that
unknown base reference point? I'd hate the base point to be set to
200 years in the past at some new OS revision, and our timeouts
start acting screwy. Should we change the ink_hrtime routines to
explicitly subtract off some startup base time, such as the time
when the system starts up? This way ink_hrtime would represent
nanoseconds since proxy startup.
timeout_absolute
What is this field? The time of the final timeout, after which no
timeouts should occur?
+----------------+
| proxy/Event.cc |
+----------------+
types of timeouts
I need to precisely understand the different types of timeouts,
such as absolute, periodic, immediate. Can I timeout be both
absolute & periodic? The intended semantics aren't immediately
obvious from the code alone.
void EventThread::execute()
What is the purpose of the execute_hook_main() and execute_hook_init_select()
virtual hooks?
We have code to check for reference counts going to zero in the
EventThread main loop. Is it possible to have a global memory
manager do this checking, or have the decrementer do this? Are
we doing this to make the locking easier? It seems minorly
annoying for every Thread to have to worry about its own
garbage collection.
void EventContinuation::check_timeout()
What does the (timeout_at >= EVENT_DISABLE_TIMEOUT) do? It
presumably handles disabled timeouts, but I'm not sure how.
There appears to be an abstraction violation here, where
IOVConnection and EventContinuation functionality is mixed. We
are casting the EventContinuation into an IOVConnection, and running
IOVConnection methods on the continuation. There appear to be two
bits: read_event and write_event that enable this.
If EventContinuation and IOVConnection are really supposed to be
separate, then we should probably fix up this routine.
Also, periodic events have their timeout_at value incremented by the
timeout period, independent of the current wallclock time. It seems
possible for small timeout periods, and some processing delay, that
the timeout timestamps could end up shifting permanently behind the
real wallclock time. In other words, the scheduler can't keep up
with the timing requests. Is this something we should check for?
void EventContinuation::destroy_event()
The semantics of destruction appear to be undocumented. What happens?
What should the user expect? What is the free list used for?
void EventThread::execute_hook_init()
Is execute_hook_init() only called at thread startup time? It appears
that execute_hook_init() is called once each time the execute() main loop
is called --- is the main loop only invoked once?
If this is only called once, why do we have to sort the timeout
events? It seems like no events should be set up yet, right?
I'm confused about the control flow to this routine.
static void sort_timeout_events(EventThread * thr)
We patch out the list from the EventThread's timeout queue and
explicitly set head to NULL. We should have a method for doing
this, so we can change the structure of the DLL.
EventContinuation::add_timeout()
After scanning for the right timeout slot, why do we need this line?
cur = prev ? prev->timeout.next : thr()->timeout_events.head;
quiescence
Is quiescence implemented at all? What is it intended to do? Do
we care about it? Should we keep the support?
void EventThread::execute_hook_scan_events(int n)
What is a "zombie" event?
void EventContinuation::reset_periodic_timeout(ink_hrtime t)
Why do we remove the timeout twice?
+-------------+
| proxy/IO.cc |
+-------------+
IO semantics
What is the basic model implemented by IO processors? Is it the
"open vconnection and enqueue operations on the vconnection" model?
IO.cc doesn't seem to implement open(), but it does implement
read/write an real connections, so I'm confused.
Are the read_event and write_event flags still used, or are they
superceded by active_read_vio and active_write_vio?
void IOProcessor::accept_read
What is accept_read? Why is the accept stuff in IO?
void IOThread::drain_queues()
Why two input queues? What purpose does each serve?
void spawn_io_event(IOThread * thr, IOVConnection * e)
How can destroyed events end up here?
The relationship of IOVConnections and vio_queues still
isn't quite clear to me.
What does activate_io() do?
Why the close case, what do the read_vio and write_vio flags
signify, and how do they relate to the vio queue?
void IOThread::execute_hook_scan_events(int n)
Should accept handling really be handled here?
There are a lot of jumps to Lrestart, running the entire scan
from the beginning. Will this ever infinite loop? Could we
do it more efficiently & cleanly?
This comment is in the code:
??? shouldn't we update the timeout queue first ???
I don't understand how flush() works.
+---------------------------+
| proxy/DiskProcessor.h |
+---------------------------+
new do_io() interface
Are open_fd(), close(), read(), write(), fseek() and lstat() part of
the interface ? Sould they be removed from the DiskIOVConnection
interface ?
void * buf;
What is the meaning of this field ? Where is it used ?
Is it part of the public interface ?
+---------------------------+
| lib/ts/ink_hrtime.h |
+---------------------------+
conversion routines
I added a bunch of hrtime-->units and units-->hrtime converters
that we should use.
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