Reduce scope of locking

README.md

@@ -210,17 +210,6 @@ load of metadata will not cause a pause or memory exhaustion):
 The `phonenumberslite` version of the package does not include the geocoding, carrier and timezone metadata,
 which can be useful if you have problems installing the main `phonenumbers` package due to space/memory limitations.
 
-Thread Safety
--------------
-
-The on-demand metadata loading described in the previous section means that synchronization is needed to allow
-for the library being used in a multi-threaded environment. This synchronization (and its overheads) can be avoided by
-either:
-
-* calling `PhoneMetadata.load_all()` to load all metadata in advance
-* setting `phonenumbers.phonemetadata.THREAD_SAFE_METADATA` to `False` (in a single-threaded
-  environment).
-
 Project Layout
 --------------
 

python/HISTORY.md

@@ -12,16 +12,6 @@ This file does not generally include descriptions of patch releases (vX.Y.Z
 changes.  (Metadata updates are best checked
 [upstream](https://github.com/google/libphonenumber/blob/master/release_notes.txt).)
 
-What's new in 8.12.??
----------------------
-
-On-demand metadata loading is now protected by a mutex to allow use in a multi-threaded
-environment.  This synchronization (and its overheads) can be avoided by either:
-
-- calling `PhoneMetadata.load_all()` to load all metadata in advance
-- setting `phonenumbers.phonemetadata.THREAD_SAFE_METADATA` to `False` (in a single-threaded
-  environment).
-
 What's new in 8.12.0
 ---------------------
 

python/phonenumbers/phonemetadata.py

@@ -22,18 +22,6 @@
 
 REGION_CODE_FOR_NON_GEO_ENTITY = u("001")
 
-# This global flag indicates whether on-demand loading of metadata should be
-# done in a thread-safe (mutex-protected) manner.
-#
-# - Setting to True (the default) is safer but slower.
-# - Setting to False avoids the mutex overhead, but means that metadata
-#   loading is not thread-safe.  This should only be used if the application
-#   is single threaded.
-#
-# Calling PhoneMetadata.load_all() also avoids the mutex overhead, at the
-# cost of increasing startup time and occupancy.
-THREAD_SAFE_METADATA = True
-
 
 class NumberFormat(UnicodeMixin, ImmutableMixin):
     """Representation of way that a phone number can be formatted for output"""
@@ -262,6 +250,9 @@ class PhoneMetadata(UnicodeMixin, ImmutableMixin):
     to warn about breaking changes.
 
     """
+    # Lock that protects the *_available fields while they are being modified.
+    # The modificiation involves loading data from a file, so we cannot just
+    # rely on the GIL.
     _metadata_lock = threading.Lock()
     # If a region code is a key in this dict, metadata for that region is available.
     # The corresponding value of the map is either:
@@ -283,40 +274,34 @@ class PhoneMetadata(UnicodeMixin, ImmutableMixin):
 
     @classmethod
     def metadata_for_region(kls, region_code, default=None):
-        if THREAD_SAFE_METADATA:
-            kls._metadata_lock.acquire()
         loader = kls._region_available.get(region_code, None)
         if loader is not None:
             # Region metadata is available but has not yet been loaded.  Do so now.
+            kls._metadata_lock.acquire()
             loader(region_code)
             kls._region_available[region_code] = None
-        if THREAD_SAFE_METADATA:
             kls._metadata_lock.release()
         return kls._region_metadata.get(region_code, default)
 
     @classmethod
     def short_metadata_for_region(kls, region_code, default=None):
-        if THREAD_SAFE_METADATA:
-            kls._metadata_lock.acquire()
         loader = kls._short_region_available.get(region_code, None)
         if loader is not None:
             # Region short number metadata is available but has not yet been loaded.  Do so now.
+            kls._metadata_lock.acquire()
             loader(region_code)
             kls._short_region_available[region_code] = None
-        if THREAD_SAFE_METADATA:
             kls._metadata_lock.release()
         return kls._short_region_metadata.get(region_code, default)
 
     @classmethod
     def metadata_for_nongeo_region(kls, country_code, default=None):
-        if THREAD_SAFE_METADATA:
-            kls._metadata_lock.acquire()
         loader = kls._country_code_available.get(country_code, None)
         if loader is not None:
             # Region metadata is available but has not yet been loaded.  Do so now.
+            kls._metadata_lock.acquire()
             loader(country_code)
             kls._country_code_available[country_code] = None
-        if THREAD_SAFE_METADATA:
             kls._metadata_lock.release()
         return kls._country_code_metadata.get(country_code, default)
 
@@ -351,10 +336,6 @@ def load_all(kls):
             if loader is not None:
                 loader(country_code)
                 kls._country_code_available[region_code] = None
-        # There will be no more writes to the metadata, so no longer any need to
-        # do synchronization.
-        global THREAD_SAFE_METADATA
-        THREAD_SAFE_METADATA = False
 
     @mutating_method
     def __init__(self,