Re: [Gluster-devel] Is it safe to use synctask_{wake, yield} outside of __wake and __yield macros?

[krish]

The strategy is to defer yield'ing of the task till a mgmt operation is sent to all the peers.

If I understand it right, the following theorem is true,
- A function which begins execution in a synctask (ie. thread from syncenv's thread pool), would always
  resume execution (ie, wake) in the same thread (viz. part of syncenv's thread pool).

If the above theorem is correct, then all syncops performed by mgmt operation handlers are
guaranteed to be called from a syncenv. The synctask is spawned at rpcsvc layer for all glusterd mgmt
operations programs.

Following is an example code snippet.

<code>
gd_lock_op_phase (struct list_head *peers, char **op_errstr, int npeers) {

....

 list_for_each_entry (peerinfo, peers, op_peers_list) {
                gd_syncop_mgmt_lock (peerinfo->rpc, aggr, index,
                                     MY_UUID, peer_uuid);
                index++;
        }
synctask_yield (aggr->task);
//note: block in the above line until all the cbks return - call_cnt mechanism

....

}

#define GD_SYNCOP(rpc, stb, cbk, req, prog, procnum, xdrproc) do {      \
                int                 ret     = 0;                        \
                struct  synctask    *task   = NULL;                     \
                                                                        \
                task = synctask_get ();                                 \
                stb->task = task;                                       \
                ret = gd_syncop_submit_request (rpc, req, stb,          \
                                                prog, procnum, cbk,     \
                                                (xdrproc_t)xdrproc);    \
            // note: yield here has been removed
        } while (0)

</code>

Let me know if we can come up with a generic framework for what I am
trying to do here.

thanks,
krish

On 02/14/2013 05:23 AM, Anand Avati wrote:

So you are not using the SYNCOP() macro, right? Can you show a code snippet of how you are trying to fan-out and yield? We could probably come up with a generic framework for such fan-out->yield->wake pattern.

You should be able to call syncop_yield() instead of __yield() if you are _sure_ that the caller is going to be from within a syncenv.

Avati

On Wed, Feb 13, 2013 at 11:29 AM, Krishnan Parthasarathi <address@hidden> wrote:

In glusterd, I am trying to perform a series of syncops in a batch. ie, yield the thread
once all the non-blocking operations are queued. The wakeup back to the yielded thread
happens as part of the call_cnt mechanism in the callback(s).

Given this, I wanted to know if I would be flouting any of assumptions, if I used
synctask_yield and synctask_wake as opposed to their macro counterparts. More specifically,
is there a chance that synctask_get() would return NULL on a thread which is part of a syncenv's
thread pool?

thanks,
krish


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