Experimental Physics and
Industrial Control System

Well, the vxWorks and RTEMS implementations of epicsEvent use simple binary semaphores.  The POSIX implementation also looks like it will also provide the semantics of a simple binary semaphore.   The WIN32 version I have no idea about.
Assuming that the WIN32 does provide the desired semantics maybe we should update the documentation to state that this is how epicsEvents are to work.

On Oct 28, 2010, at 2:30 PM, Ben Franksen wrote:

The documentation of libCom/osi/epicsEvent in the Developer's Guide
carefully avoids saying anything about what happens if an event gets
signalled and more than one thread waits for the event to happen.

The name "event" and most of what's written in the docs suggest that
*any* thread waiting for an event will be able to continue as soon as
the event gets signalled.

If this is true, how do I get the effect of a (binary) semaphore, i.e.
only one thread waiting on the semaphore will continue, the others have
to wait until the semaphore is given again?

Or, if it is false, i.e. epicsEvent really acts like a binary semaphore,
I suggest that this be more clearly stated in the docs. It should also
be stated how the library or system choses the thread to run; in
VxWorks, this can be influenced when creating the semaphore (FIFO or
priority based), but if other systems do not allow such a distinction
then it should be explicitly stated in the documentation that no
assumptions should be made about which thread is chosen. Note that this
severely complicates things if you want e.g. FIFO semantics, because
you'd have to implement all the queueing yourself.

Thanks
Ben

References:

epicsEvent Ben Franksen

Re: epicsEvent Eric Norum

Navigate by Date:

Prev: Re: epicsEvent Eric Norum

Next: Re: epicsEvent Andrew Johnson

Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  <2010>  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020  2021  2022  2023  2024 

Navigate by Thread:

Prev: Re: epicsEvent Eric Norum

Next: Re: epicsEvent Andrew Johnson

Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  <2010>  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020  2021  2022  2023  2024