[3.12] gh-105699: Use a Thread-Local Variable for PKGCONTEXT (gh-105740) (gh-105765)

This fixes a race during import. The existing _PyRuntimeState.imports.pkgcontext is shared between interpreters, and occasionally this would cause a crash when multiple interpreters were importing extensions modules at the same time. To solve this we add a thread-local variable for the value. We also leave the existing state (and infrequent race) in place for platforms that do not support thread-local variables.
(cherry picked from commit b87d288)
Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

Author: miss-islington

Python/import.c

@@ -703,28 +703,43 @@ _PyImport_ClearModulesByIndex(PyInterpreterState *interp)
  _PyRuntime.imports.pkgcontext, and PyModule_Create*() will
  substitute this (if the name actually matches).
 */
+
+#ifdefHAVE_THREAD_LOCAL
+_Py_thread_localconstchar*pkgcontext=NULL;
+# undef PKGCONTEXT
+# definePKGCONTEXT pkgcontext
+#endif
+
 constchar*
 _PyImport_ResolveNameWithPackageContext(constchar*name)
 {
+#ifndefHAVE_THREAD_LOCAL
 PyThread_acquire_lock(EXTENSIONS.mutex, WAIT_LOCK);
+#endif
 if (PKGCONTEXT!=NULL) {
 constchar*p=strrchr(PKGCONTEXT, '.');
 if (p!=NULL&&strcmp(name, p+1) ==0) {
 name=PKGCONTEXT;
 PKGCONTEXT=NULL;
  }
  }
+#ifndefHAVE_THREAD_LOCAL
 PyThread_release_lock(EXTENSIONS.mutex);
+#endif
 returnname;
 }
 
 constchar*
 _PyImport_SwapPackageContext(constchar*newcontext)
 {
+#ifndefHAVE_THREAD_LOCAL
 PyThread_acquire_lock(EXTENSIONS.mutex, WAIT_LOCK);
+#endif
 constchar*oldcontext=PKGCONTEXT;
 PKGCONTEXT=newcontext;
+#ifndefHAVE_THREAD_LOCAL
 PyThread_release_lock(EXTENSIONS.mutex);
+#endif
 returnoldcontext;
 }
 

Tools/c-analyzer/c_parser/parser/_regexes.py

@@ -58,6 +58,7 @@ def _ind(text, level=1, edges='both'):
  extern |
  register |
  static |
+ _Thread_local |
  typedef |
 
  const |
@@ -137,7 +138,7 @@ def _ind(text, level=1, edges='both'):
 #######################################
 # variable declarations
 
-_STORAGE='auto register static extern'.split()
+_STORAGE='auto register static extern _Thread_local'.split()
 STORAGE_CLASS=rf'(?: \b (?: {" | ".join(_STORAGE)} ) \b )'
 TYPE_QUALIFIER=r'(?: \b (?: const | volatile ) \b )'
 PTR_QUALIFIER=rf'(?: [*] (?: \s* {TYPE_QUALIFIER} )? )'

Tools/c-analyzer/c_parser/preprocessor/gcc.py

@@ -219,6 +219,7 @@ def _strip_directives(line, partial=0):
 line=line[m.end():]
 
 line=re.sub(r'__extension__', '', line)
+line=re.sub(r'__thread\b', '_Thread_local', line)
 
 while (m:=COMPILER_DIRECTIVE_RE.match(line)):
 before, _, _, closed=m.groups()

Tools/c-analyzer/cpython/ignored.tsv

@@ -168,6 +168,12 @@ Modules/_xxinterpchannelsmodule.c	-	_globals	-
 
 Python/pyfpe.c	-	PyFPE_counter	-
 
+##-----------------------
+## thread-local variables
+
+Python/import.c	-	pkgcontext	-
+Python/pystate.c	-	_Py_tss_tstate	-
+
 ##-----------------------
 ## should be const
 # XXX Make them const.