[Ushiba, YamaT]

Today we faced user code error of OMC_LSC guardian to try locking OMC by guardian.
To be honest, I haven’t identified an exact cause. I have simply fixed a part that seemed suspicious.
If a same problem will be still reproduced, additional investigation and a code modification will be necessary.

Error logs and the relevant code are shown in Fig.1 and Fig.2, respectively. This error was slightly strange. This user code error was occurred in counter==3 of FIND_RESONANCE state. In this state, guardian receives an result of the mode analysis. Mode information is received at L305. Guardian logs shows "USERMSG 0: Locked to a HOM with mode number = 0". This message is provided at L319. After then, user code error occurs due to "a = self.p.communicate()". But L305 after executing L319, ezca.swith at L323 should be executed and some kind of ezca log should be remained in guardian logs before L305 is executed again. So if this python codes are sequentially executed, this bug is never occurred.

I guessed the reason why the code isn't executed sequentially is that p.communicate triggers garbage collection. GC is done in lazy when Python judges relevant objects become unnecessary. For this reason, this lazy GC is conflict after p.stdout.close in L329. I'm not sure my guess is really correct or not. But it's an only plausible scenario for now. So I commented out the relevant code. If a problem will be still reproduced, I'll do additional investigation.