On Mon, Mar 21, 2016 at 01:20:35PM -0700, Andy Zhou wrote: > On Fri, Mar 18, 2016 at 6:24 PM, Ben Pfaff <b...@ovn.org> wrote: > > > On Thu, Mar 03, 2016 at 12:13:25AM -0800, Andy Zhou wrote: > > > Add a command queue for the main thread to pass commands to the > > > sessions thread. > > > > > > Defined an implemented a set of IPC messages for creating, > > > closing and managing jsonrpc sessions from the main process to jsonrpc > > > sessions threads. > > > > > > Add a doorbell mechanism for a jsonrpc session to inform other sessions > > > of possible OVSDB changes. > > > > > > Although all supporting functions for running a multithreading OVSDB > > > server have been implemented, multithread is still not turned on, > > > because 'n_max_threads' is still hard coded to zero. Future patches > > > will remove this restriction. > > > > > > Signed-off-by: Andy Zhou <az...@ovn.org> > > > > This is one way to synchronize threads. Maybe it is one that we should > > use. It is nice from the point of view that the sending thread can just > > post a message and does not have to wait for it to be received, but it > > has the disadvantage that it is necessary to define a data structure and > > write marshaling and de-marshaling code for each possible form of > > sychronization. > > > > > > Another form of synchronization with basically opposite properties is to > > give each thread a mutex. Whenever the thread wakes up, take the mutex; > > just before it goes to sleep, release the mutex. To synchronize with > > the thread, take its mutex. To synchronize with every other thread, > > take all of their mutexes. > > > > I'd like to hear your thoughts. > > > > Using messaging passing has a few advantages: > > 1. It can be faster as you have pointed out, a message can be sent without > waiting. > > 2, It is simpler to reason about locking in some cases. For example, when > two threads > want to synchronize with every other thread at the same time, the mutex > scheme > proposed above will require additional mechanism to avoid dead lock, while > it is more > straight forward with message passing. > > I don't feel the marshaling and de-marshing code is much of a burden in > this case. Since > all threads are running within the same address space, we can just pass > pointer of structs > back and forth, so it is not too back. > > What do you think?
Mostly I wanted to make sure that you had considered the alternatives. It sounds like you have. Let's go forward with it this way for now. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
