make a logging warning once (#1108)

- fixes #1107
Co-authored-by: Min Xu <min.xu.public@gmail.com>

fairscale/internal/version.py

@@ -11,13 +11,15 @@ import torch
 
 __all__: List[str] = ["torch_version"]
 
+_logged = False
 
 def torch_version(version: str = torch.__version__) -> Tuple[int, ...]:
     numbering = re.search(r"^(\d+).(\d+).(\d+)([^\+]*)(\+\S*)?$", version)
     if not numbering:
         return tuple()
     # Catch torch version if run against internal pre-releases, like `1.8.0a0fb`,
-    if numbering.group(4):
+    global _logged
+    if numbering.group(4) and not _logged:
         # Two options here:
         # - either skip this version (minor number check is not relevant)
         # - or check that our codebase is not broken by this ongoing development.
@@ -25,5 +27,6 @@ def torch_version(version: str = torch.__version__) -> Tuple[int, ...]:
         # Assuming that we're interested in the second use-case more than the first,
         # return the pre-release or dev numbering
         logging.warning(f"Pytorch pre-release version {version} - assuming intent to test it")
+        _logged = True
 
     return tuple(int(numbering.group(n)) for n in range(1, 4))