update examples/launch.py

Signed-off-by: Sun Ruoxi <sunruoxi@4paradigm.com>

examples/launch.py

@@ -1,14 +1,15 @@
 import os,sys,json,resource,subprocess,signal,time
+from contextlib import nullcontext
 from pathlib import Path
 base=Path(__file__).parent
 resource.setrlimit(resource.RLIMIT_MEMLOCK,(resource.RLIM_INFINITY,resource.RLIM_INFINITY))
 cfg=json.loads((base/"command-serial.json").read_text())
 env=os.environ.copy();env.update(cfg["env"])
-log=base/(sys.argv[1] if len(sys.argv)>1 else "serve-fixed.log")
-with log.open("w") as f:
+log=base/sys.argv[1] if len(sys.argv)>1 else None
+with log.open("w") if log else nullcontext(None) as f:
  p=subprocess.Popen(cfg["args"],env=env,stdout=f,stderr=subprocess.STDOUT,start_new_session=True,cwd="/workspace/pytorch")
 (base/"serve.pid").write_text(str(p.pid))
-print("SERVER_PID",p.pid,"LOG",log,flush=True)
+print("SERVER_PID",p.pid,"LOG",log if log else "stdout",flush=True)
 rc=p.wait()
 print("SERVER_EXIT",rc,flush=True)
 if rc: