gh-116738: Make _json module safe in the free-threading build

Include/internal/pycore_critical_section.h

@@ -128,6 +128,12 @@ extern "C" {
  } \
  }
 
+# define Py_RETURN_CRITICAL_SECTION_SEQUENCE_FAST(value) \
+ if (_should_lock_cs) { \
+ _PyCriticalSection_End(&_cs); \
+ } \
+ return value;
+
 // Asserts that the mutex is locked. The mutex must be held by the
 // top-most critical section otherwise there's the possibility
 // that the mutex would be swalled out in some code paths.
@@ -159,6 +165,7 @@ extern "C" {
 # define Py_END_CRITICAL_SECTION2()
 # define Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original)
 # define Py_END_CRITICAL_SECTION_SEQUENCE_FAST()
+# define Py_RETURN_CRITICAL_SECTION_SEQUENCE_FAST(value)
 # define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
 # define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
 #endif /* !Py_GIL_DISABLED */

Modules/_json.c

@@ -10,6 +10,7 @@
 
 #include "Python.h"
 #include "pycore_ceval.h" // _Py_EnterRecursiveCall()
+#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION()
 #include "pycore_runtime.h" // _PyRuntime
 
 #include "pycore_global_strings.h" // _Py_ID()
@@ -1615,12 +1616,14 @@
 
  } else {
  Py_ssize_t pos = 0;
+ Py_BEGIN_CRITICAL_SECTION(dct);
  while (PyDict_Next(dct, &pos, &key, &value)) {
  if (encoder_encode_key_value(s, writer, &first, key, value,
  new_newline_indent,
  current_item_separator) < 0)
  goto bail;
  }
+ Py_END_CRITICAL_SECTION();
  }
 
  if (ident != NULL) {
@@ -1663,9 +1666,13 @@
  s_fast = PySequence_Fast(seq, "_iterencode_list needs a sequence");
  if (s_fast == NULL)
  return -1;
+
+ Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(seq);
+
  if (PySequence_Fast_GET_SIZE(s_fast) == 0) {
  Py_DECREF(s_fast);
- return _PyUnicodeWriter_WriteASCIIString(writer, "[]", 2);
+ int r = _PyUnicodeWriter_WriteASCIIString(writer, "[]", 2);
+ Py_RETURN_CRITICAL_SECTION_SEQUENCE_FAST(r);
  }
 
  if (s->markers != Py_None) {
@@ -1718,7 +1725,6 @@
  goto bail;
  Py_CLEAR(ident);
  }
-
  if (s->indent != Py_None) {
  Py_CLEAR(new_newline_indent);
  Py_CLEAR(separator_indent);
@@ -1730,14 +1736,16 @@
  if (_PyUnicodeWriter_WriteChar(writer, ']'))
  goto bail;
  Py_DECREF(s_fast);
- return 0;
+ Py_RETURN_CRITICAL_SECTION_SEQUENCE_FAST(0);
 
 bail:
+ Py_END_CRITICAL_SECTION_SEQUENCE_FAST();
  Py_XDECREF(ident);
  Py_DECREF(s_fast);
  Py_XDECREF(separator_indent);
  Py_XDECREF(new_newline_indent);
  return -1;
+
 }
 
 static void