Experimental Physics and
Industrial Control System

All,

 

I have discovered that a PCAS hang can occur when clients are fetching very large arrays as strings. Just to convert the number of elements that fit in a very large EPICS_CA_MAX_ARRAY_SIZE buffer with epicsSnPrintf can take a very long time. It appears that this required about 33 seconds during testing with EPICS_CA_MAX_ARRAY_SIZE of 10,000,000. Based on that I calculate 33 / ( 10,000,000 / MAX_STRING_SIZE ) is 0.000132 seconds per conversion. Is epicsSnPrintf() really that slow?

 

The solution appears to be to use the cvtFast library where it is in range in GDD’s aitConvert.cc. The cvtFast functions are a bit scary in today’s world - because a buffer size isn’t passed in – BTW. The current workaround is to just not use them for buffer sizes below some threshold.