Bug for multi-thread

[zjazczjazc]

Hi Author,

Thanks very much for sharing your project of C++ version YCSB.

I try to use it locally with redis. It works with single thread, but for multi-thread, I test as follows:
./ycsbc -db redis -threads 2 -P workloads/workloada.spec -host 127.0.0.1 -port 6379 -slaves 0

After 3 hours, it does not complete. I use gdb to debug the codes and actually the system is stuck in
"pthread_join" function.
Do you have any idea on solving this problem?