put callback fails if async writing completes immediately

[GoogleCodeExporter]

Reported by Kay Kasemir:

I think I found the problem in driver.py:

   def writeNotify(self, context, value):
            success = self.writeValue(value)
            # do asynchronous only if PV supports
            if success and self.info.asyn:
                # async write will finish later
                self.startAsyncWrite(context)


In response to a "caput -c …", it will
1) Call writeValue(), i.e. eventually my write implementation
2) startAsyncWrite()

If my write operation takes a long time before invoking callbackPV(), all is 
fine.
But our write operations don't always take a long time. They may in fact be 
very fast, but we need the put-callback for instrument control to assert that 
the operation really finished.
So if my write finished quickly, it will in step one already call callbackPV() 
before the startAsyncWrite() in step 2 created it.

Needs to be somewhat like this:

   def writeNotify(self, context, value):
            if self.info.asyn:
                   self.startAsyncWrite(context)
                      success = self.writeValue(value)
                      …

Original issue reported on code.google.com by xiaoqian...@gmail.com on 16 Sep 2014 at 12:21

[GoogleCodeExporter]

This has been fixed in commit 
https://code.google.com/p/pcaspy/source/detail?r=1b6280cbbd79dcdaf4142af037aa260
d3017cef6

Original comment by xiaoqian...@gmail.com on 19 Sep 2014 at 12:59

• Changed state: Fixed