IPC communication between Python and Cadence 

Hi All,

 I am trying to open a IPC channel between python and cadence. I managed to get one way communication from either to the other, but unable to get two way communication.

 Please help to point me in the right direction!

 Thanks in advance,

Vijay

I've done it this way:

Skill:
pyIpc = ipcBeginProcess("my.py " "" 'myIpcDataHandler 'myIpcErrHandler 'myIpcFinishHandler "/tmp/py.log")
procedure(myIpcDataHandler(ipcId data)
  let((result)
    ;printf("in myIpcDataHandler with %L\n" data)
    foreach(d parseString(data "\n")
        unless(errset(result=evalstring(d))
             printf("ERROR: %L\n" errset.errset)
             ipcWriteProcess(ipcId sprintf(nil "ERROR %L\n" errset.errset))
        ) ; unless
    )
  )
)

procedure(myIpcErrHandler(ipcId data)
    println(list("ERROR: myIpcErrHandler called with:" ipcId data))
)

procedure(myIpcFinishHandler(ipcId data)
  let((exitStatus)
    printf("Finished at %s: %L %L  " getCurrentTime() ipcId data)
    exitStatus = ipcGetExitStatus(ipcId)
    printf("Return value = %L\n" exitStatus)
    if(exitStatus==0 then
        printf("The IPC call has finished!!\n")
    else
        printf("**ERROR: operation failed\n")
    )
  )
)

procedure(mySkillCommand(data)
    println(data)
    ipcWriteProcess(pyIpc "Skill says hello")
)

Python file my.py:
import sys
data = 'Hello from the Python world'
sys.stdout.write('mySkillCommand("%s")\n' % data)
sys.stdout.flush()
returnData = sys.stdin.readline()
#Write to a file since stdout goes to Cadence
outFile = open('/tmp/myPy.out','w')   
outFile.writelines( returnData )
outFile.close()

When done, /tmp/py.log shows commands sent from Python to skill through stdout and /tmp/myPy.out shows the Skill response.

Derek

Hi Derek,

Thank you for your quick help. Everything goes fine but I am not able to read the returnData. The log file has only the "mySkillCommand..."

I seem to have some issue with read timing.

I tried doing it another way like the following:

Python:

import sys
import os
sys.stdout.flush()

os.write(3,"(println \"Hello World!!\")")
os.write(3,"(println \"Second time, Hello World!!\")")
os.write(3,"(3+3)")

a="(nil)"

while "(nil)" in a:

    a="Start:",os.read(4,4096)

SKILL:

cid = ipcSkillProcess("python ~/scripts/skill/ipc_py/test2.py")

 I still have some timing issue, which improved with that while loop. Cadence seemed to return "(nil)" each time the read timing missed. Is there anyway to permanently resolve this issue?

Thanks,

Vijay

I had trouble with ipcSkillProcess and the 3&4 streams. That is why I chose to use ipcBeginProcess and used stdin and stdout instead. Also, in the Python, I limited my code to one readLine and had my skill code only send a string that contained one \n as the terminating character. This helped me with my communication problems. What I found was that if I sent multiple carriage returns, I needed a readline for each one. If I only performed one readline, then the next one was queued up for next time. If I used a while or a readLines, the Python would hang waiting on the stdin to finish. Maybe you can send it an EOF type character to get the Python to continue. I just coded around it so that Cadence always sent only one line back to Python for every command Python sent to Cadence. This was sufficient for me.

Derek

Hi Derek,

Thanks for the explanation! Caught the reason why your way failed for me. I had terminated the return with a "\n". So the readline was failing. I added the newline character and now it seems to be working fine.

Thanks a lot for your help!

Thanks once again,

Vijay