Doc and cleanup.

pex/cache/access.py

@@ -21,22 +21,28 @@
 
 _LOCK = None  # type: Optional[Tuple[bool, int, str]]
 
+_PEX_CACHE_ACCESS_LOCK_ENV_VAR = "_PEX_CACHE_ACCESS_LOCK"
+
 
 def save_lock_state():
     # type: () -> None
+    """Records any current lock state in a manner that can survive un-importing of this module."""
+
+    # N.B.: This supports the sole case of a Pex PEX, whose runtime obtains a lock that it must hand
+    # off to the Pex CLI it spawns.
 
     global _LOCK
     if _LOCK is not None:
         exclusive, lock_fd, lock_file = _LOCK
-        os.environ["_PEX_CACHE_ACCESS_LOCK"] = "|".join(
+        os.environ[_PEX_CACHE_ACCESS_LOCK_ENV_VAR] = "|".join(
             (str(int(exclusive)), str(lock_fd), lock_file)
         )
 
 
 def _maybe_restore_lock_state():
     # type: () -> None
 
-    saved_lock_state = os.environ.pop("_PEX_CACHE_ACCESS_LOCK", None)
+    saved_lock_state = os.environ.pop(_PEX_CACHE_ACCESS_LOCK_ENV_VAR, None)
     if saved_lock_state:
         encoded_exclusive, encoded_lock_fd, lock_file = saved_lock_state.split("|", 2)
         global _LOCK