Hi! On 07:32 Sat 04 Apr , Devesh Sharma wrote: > Hi michi and peter, Nice discussion. > > On Fri, Apr 3, 2009 at 10:09 PM, Michael Blizek > <michi1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hi! ... > > Devesh wanted to do trylock of a semaphore inside a workqueue and return > > ERESTARTSYS if locking fails. There are some things which are wrong with > > this approach. ... > > 2) I have never used trylock and I still do not know what he wants to do with > > it. > I am just trying to understand trylock APIs and analysing the > differences b/w the _interruptible and trylock.. Basically try to lock the mutex/semaphore and fail without waiting if it is currently locked. I have never used it so far, but it may be useful, if you can process something else in the mean time. e.g. You have a queue of requests and if you fail to lock 1 request, you can put it at the end of the queue and process the next request. > > 3) ERESTARTSYS is for use with the _interruptable functions of mutex_lock > > and others. It makes only sense inside system calls, because its purpose is > > to exit the system call prematurely in order to let a signal be delivered to > > the user space process. The system call will then fail with errno set to > > EINTR. > > 3.1) Returning ERESTARTSYS in a workqueue will not not work. The workqueue > > function has to return void, so the return code will get lost. > > 3.2) Returning ERESTARTSYS is only valid for the _interruptable functions if > > a signal is pending. Returning it after trylock if something is currently > > locked will not work (why would you want to do this anyway?). > Ohh......its this way!! I was in an impression that...if ERESTARTSYS > is returned, _anyhow_ (I mean independent of _interruptible or > trylock), the execution context (system call) > will restart. That is why I was thinking, that one can return > ERESTARTSYS even with trylock..:( > Are you saying that using ERESTARTSYS is worthless with trylock? Can > you clarify "Is only valid for the _interruptable" if its returned > even with trylock then will functioning of ERESTARTSYS will be droped? > or its inherent prperty of implementation to by-pass the functioning? See the last posting of Peter Teoh. -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
