[joblib] Log once the context warning argument. (#13865)

Co-authored-by: Ameer Haj Ali <ameerhajali@ameers-mbp.lan>
Co-authored-by: Alex Wu <alex@anyscale.io>
Co-authored-by: Alex Wu <itswu.alex@gmail.com>
Co-authored-by: Eric Liang <ekhliang@gmail.com>
Co-authored-by: Ameer Haj Ali <ameerhajali@Ameers-MacBook-Pro.local>

python/ray/util/multiprocessing/pool.py

@@ -9,6 +9,7 @@ import queue
 import copy
 
 import ray
+from ray.util import log_once
 
 logger = logging.getLogger(__name__)
 
@@ -336,7 +337,7 @@ class Pool:
         self._maxtasksperchild = maxtasksperchild or -1
         self._actor_deletion_ids = []
 
-        if context:
+        if context and log_once("context_argument_warning"):
             logger.warning("The 'context' argument is not supported using "
                            "ray. Please refer to the documentation for how "
                            "to control ray initialization.")