[Zope] Which method to generate IDs for objects?

[Dieter Maurer]

Thomas Guettler writes:
 > On Wed, Jan 16, 2002 at 12:21:45PM -0000, Tim Hicks wrote:
 > > I don't know if this is very efficient/elegant/etc*, but I use it to get a
 > > unique id within a folder...
 > > 
 > > -------------
 > > intid = 1
 > > while 1:
 > >    if hasattr(photo_folder, str(intid)):
 > >      intid = intid + 1
 > >    else:
 > 
 > 
 > How thread-safe is this? I Java I would write a syncronise block
 > around i=i+1, because of the following example:
It is not thread safe and therefore the later "_setObject"
may raise a BadRequest exception due to duplicate ids.

It is therefore better, to use the "_setObject" directly:

   while 1:
     try: self._setObject(str(intid),o); break;
     except BadRequest: intid= intid+1

   This, still, is not thread safe. But conflicting threads
   write the same object. The standard ZODB conflict resolution
   will normally abort one of the conflicting transactions
   and restart the corresponding request.

   I store the "intid" counter in an object attribute, in order
   not to make so many unsuccessful trials. True, usually,
   ZODB objects should not be used for counting. But I write
   the object anyway (for the new object), thus there is no
   additional penalty to write the counter.


Dieter