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From "Dave Watson (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (THRIFT-1442) ] TNonblockingServer: Refactor to allow multiple IO
Date Thu, 01 Dec 2011 23:34:40 GMT
] TNonblockingServer: Refactor to allow multiple IO

----------------------------------------------------

                 Key: THRIFT-1442
                 URL: https://issues.apache.org/jira/browse/THRIFT-1442
             Project: Thrift
          Issue Type: Improvement
          Components: C++ - Library
            Reporter: Dave Watson
            Priority: Minor
         Attachments: 0001-TNonblockingServer-Refactor-to-allow-multiple-IO-thr.patch

>From 04fc8cbc24c64e1b68a23a1df2c46056785c269d Mon Sep 17 00:00:00 2001
From: Mark Rabkin <mrabkin@fb.com>
Date: Tue, 18 May 2010 22:16:09 +0000
Subject: [PATCH 01/56] TNonblockingServer: Refactor to allow multiple IO
 threads, not just one

davejwatson: This diff ads multiple IO threads to TNonblocking Server. 
We use it extensively, it's pretty well tested other than merge errors.  
This diff reverts THRIFT-1184, allowing re-use of an existing
event base.  With multiple IO threads, re-using a single event base doesn't
make sense, so this seemed ok

Summary:

The diff creates multiple IO threads at startup -- the number of threads in
this diff is fixed at server start and cannot change for simplicity.  The
first thread (id = 0) also doubles as the listen/accept thread, so there is
still only a single thread doing accepts.  The other IO threads listen only
on their notification pipe and the actual connection sockets.

Also, for simplicity, each accepted connection is simply assigned in a
round-robin fashion to the next IO thread and lives on that IO thread
permanently.

Note that there are only trivial changes to TConnection to get it to work, so
most of the tricky state transitions and buffer management are unchanged.
There is still a single worker pool for processing tasks, so that code is
unchanged as well.

The trickiest part of the diff requiring the most careful review is the new
synchronization code in the TNonblockingServer to manage the connection stack
and counters of active/inactive connections.  We now lock a mutex when
incrementing/decrementing server counters, which is less than ideal for
extremely high-QPS servers -- should I switch to atomic ops?

One important change here is that while connections are created and initialized
by the listen thread (IO thread #0), they may now be assigned to an event_base
owned by a different IO thread.  To work safely, TConnection::init() no longer
calls setFlags() - instead, it immediately calls TConnection::notifyIOThread().
This results in a notification-fd event in the correct event base, which then
calls TConnection::transition() which sets up correct read flags.  This means
that a TConnection now calls notifyIOThread() once upon creation and assignment
to its event_base, and thereafter after each processing call completes.

TNonblocking server: Allow high-priority scheduler for IO threads
Summary:

Adds a boolean option to TNonblockingServer to use sched_setscheduler() to set
a high scheduling priority for the IO thread(s) -- this is a POSIX api and
should be safe on most operating systems.

Please let me know if this is a known terrible idea, but we're experimenting
to see if this helps the situation where we have 40 worker threads and 1 IO
thread and the IO thread doesn't get scheduled nearly often enough.

Reviewers: dreiss,edhall,putivsky

Test Plan:  Need to work with Ed to run his capacity-loadtesting scripts to verify performance.



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