TINE-Core meeting 26.4.2016

C-Lib changes:
- problem with select() -> poll()
- select() standard since the 1980s
  pass nfds, descriptor set (a la bit-pattern macro), read sets, write sets, err sets
  select returns nready on the passed sets (-1 on error)
  max nfds is 1024

- poll()
  pass nfds, array of descriptors, set the 'events' flag to POLLIN/ POLLOUT etc.
  return nready : but this contains errors !
  
  poll returns only a certain category of errors.
  
- problem with a client hanging up a TCP connection.


- single threaded apps use common client/server descriptors 
  'addClientSocketsToSet', addServerSocketsToSet
  but due to array of poll rather than bit pattern of select, the call now takes an offset
  
  so the n += add() is wrong here !
  
  ended up claiming there were another 4 descriptors which had only '0' (stdin)
  
  due to ??? these had an error .revents which dropped thru the poll() and ended up 'spinning'
  
  
- format elevation for MCA single elements

- property "P" is an MCA and wants to return an array of FLOATS but can return a single element
- if caller 'monitors' a single element then server coerces the contract to get the entire array and informs client which element is wished for

- question: what if one of the e.g. ion pumps has a problem (hardware_error)?
    either the entire array is 'bad' (hardware error) or 'okay' (what data is used in the array access?)
    
    Overload property "P" to deliver a FLOAT array or a FLTINT array (value-status doublet).  
    monitor a single element as FLOAT is 'elevated' to an MCA of FLTINTs.  The desired element and its status are plucked out of the incoming array.
    
    
- last time:

 MACOS (Free BSD?) doesn't like in-situ memcpy (overlapped memory areas)

e.g. prepare PropertyQuerySTructure array (first 64 bytes are the property name)
but caller just wants a list of names (array of 64-char fixed length strings)
for (i=0; i<length; i++) memcpy(names[i],structs[i].name,64);

if names and structs point to the same area MACOS doesn't like it!