Re: rwlocks, correctness over speed.

On Sat, 24 Nov 2007, Attilio Rao wrote:

I must have missed recursion arriving then -- I'll modify uipc_usrreq.c to set the recursion flag on the rwlock in UNIX domain sockets rather than doing the nasty hack that was previously required. At the time, the hack was added because it seemed recursion was not going to be added to rwlocks, but sonewconn() behavior for listen sockets really ended up requiring it.

attilio 2007-06-26 21:31:56 UTC

FreeBSD src repository

Modified files:
sys/kern kern_rwlock.c
sys/sys _rwlock.h rwlock.h
Log:
Introduce a new rwlocks initialization function: rw_init_flags.
This is very similar to sx_init_flags: it initializes the rwlock using
special flags passed as third argument (RW_DUPOK, RW_NOPROFILE,
RW_NOWITNESS, RW_QUIET, RW_RECURSE).
Among these, the most important new feature is probabilly that rwlocks
can be acquired recursively now (for both shared and exclusive paths).

Yes, that was four months after I added rw_wowned(9) to work around the lack of recursion support. :-) However, it looks like the man page was never updated? It contains the following rather explicit language:

Another important property is that shared holders of rwlock can recurse,
but exclusive locks are not allowed to recurse.

Robert N M Watson
Computer Laboratory
University of Cambridge
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Relevant Pages

  • Re: rwlocks, correctness over speed.
    ... doing the nasty hack that was previously required. ... was added because it seemed recursion was not going to be added to rwlocks, ... but sonewconnbehavior for listen sockets really ended up requiring it. ... This is very similar to sx_init_flags: it initializes the rwlock using ...
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  • Re: rwlocks, correctness over speed.
    ... doing the nasty hack that was previously required. ... was added because it seemed recursion was not going to be added to rwlocks, ... but sonewconnbehavior for listen sockets really ended up requiring it. ... This is very similar to sx_init_flags: it initializes the rwlock using ...
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