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faster destroyfid calls

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rsc 2006-03-21 18:57:37 +00:00
parent de1168dd9c
commit aff51ee51f
1 changed files with 42 additions and 2 deletions
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44
src/lib9p/srv.c
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@ -805,8 +805,49 @@ if(chatty9p)
abort();
}
assert(n > 2);
/*
* There is a race here - we must remove the entry before
* the write, so that if the client is very fast and reuses the
* tag, the read loop won't think it is still in use.
*
* By removing the entry before the write, we open up a
* race with incoming Tflush messages. Specifically, an
* incoming Tflush might not see r even though it has not
* yet been responded to. It would then send an Rflush
* immediately, potentially before we do the write. This can't
* happen because we already old srv->wlock, so nothing
* is going out on the wire before this write.
*/
if(r->pool) /* not a fake */
closereq(removereq(r->pool, r->ifcall.tag));
qlock(&r->lk);
r->responded = 1;
if(r->pool)
if(r->ref.ref == 1+r->nflush)
if(r->fid){
/*
* There are no references other than in our r->flush array,
* so no one else should be accessing r concurrently.
* Close the fid now, before responding to the message.
*
* If the client is behaving (there are no outstanding T-messages
* that reference r->fid) and the message is a Tclunk or Tremove,
* then this closefid will call destroyfid.
*
* This means destroyfid can't piddle around
* indefinitely (we're holding srv->wlock!), but it provides
* for tighter semantics as to when destroyfid is called.
*
* LANL has observed cases where waiting until after the write
* can delay a closefid on a Twrite for many 9P transactions,
* so that a handful of transactions can happen including a Tclunk
* and a Topen, and the original fid will still not be destroyed.
*/
closefid(r->fid);
r->fid = nil;
}
qunlock(&r->lk);
m = write(srv->outfd, srv->wbuf, n);
if(m != n)
sysfatal("lib9p srv: write %d returned %d on fd %d: %r", n, m, srv->outfd);
@ -814,8 +855,7 @@ if(chatty9p)
free:
qlock(&r->lk); /* no one will add flushes now */
r->responded = 1;
for(i=0; i<r->nflush; i++)
respond(r->flush[i], nil);
free(r->flush);