gh-112075: Add critical sections for most dict APIs (#114508)

Starts adding thread safety to dict objects.


Use @critical_section for APIs which are exposed via argument clinic and don't directly correlate with a public C API which needs to acquire the lock
Use a _lock_held suffix for keeping changes to complicated functions simple and just wrapping them with a critical section
Acquire and release the lock in an existing function where it won't be overly disruptive to the existing logic

Include/internal/pycore_critical_section.h

@@ -104,12 +104,37 @@ extern "C" {
 # define Py_END_CRITICAL_SECTION2()                                     \
         _PyCriticalSection2_End(&_cs2);                                 \
     }
+
+// 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.
+#define  _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex) \
+    _PyCriticalSection_AssertHeld(mutex)
+
+// Asserts that the mutex for the given object 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.
+#ifdef Py_DEBUG
+
+#define  _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)                           \
+    if (Py_REFCNT(op) != 1) {                                                    \
+        _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(&_PyObject_CAST(op)->ob_mutex); \
+    }
+
+#else   /* Py_DEBUG */
+
+#define  _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
+
+#endif  /* Py_DEBUG */
+
 #else  /* !Py_GIL_DISABLED */
 // The critical section APIs are no-ops with the GIL.
 # define Py_BEGIN_CRITICAL_SECTION(op)
 # define Py_END_CRITICAL_SECTION()
 # define Py_BEGIN_CRITICAL_SECTION2(a, b)
 # define Py_END_CRITICAL_SECTION2()
+# define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
+# define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
 #endif  /* !Py_GIL_DISABLED */
 
 typedef struct {
@@ -236,6 +261,27 @@ _PyCriticalSection2_End(_PyCriticalSection2 *c)
 PyAPI_FUNC(void)
 _PyCriticalSection_SuspendAll(PyThreadState *tstate);
 
+#ifdef Py_GIL_DISABLED
+
+static inline void
+_PyCriticalSection_AssertHeld(PyMutex *mutex) {
+#ifdef Py_DEBUG
+    PyThreadState *tstate = _PyThreadState_GET();
+    uintptr_t prev = tstate->critical_section;
+    if (prev & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
+        _PyCriticalSection2 *cs = (_PyCriticalSection2 *)(prev & ~_Py_CRITICAL_SECTION_MASK);
+        assert(cs != NULL && (cs->base.mutex == mutex || cs->mutex2 == mutex));
+    }
+    else {
+        _PyCriticalSection *cs = (_PyCriticalSection *)(tstate->critical_section & ~_Py_CRITICAL_SECTION_MASK);
+        assert(cs != NULL && cs->mutex == mutex);
+    }
+
+#endif
+}
+
+#endif
+
 #ifdef __cplusplus
 }
 #endif

Modules/_sre/sre.c

@@ -39,6 +39,7 @@ static const char copyright[] =
     " SRE 2.2.2 Copyright (c) 1997-2002 by Secret Labs AB ";
 
 #include "Python.h"
+#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION
 #include "pycore_dict.h"             // _PyDict_Next()
 #include "pycore_long.h"             // _PyLong_GetZero()
 #include "pycore_moduleobject.h"     // _PyModule_GetState()
@@ -2349,26 +2350,28 @@ _sre_SRE_Match_groupdict_impl(MatchObject *self, PyObject *default_value)
     if (!result || !self->pattern->groupindex)
         return result;
 
+    Py_BEGIN_CRITICAL_SECTION(self->pattern->groupindex);
     while (_PyDict_Next(self->pattern->groupindex, &pos, &key, &value, &hash)) {
         int status;
         Py_INCREF(key);
         value = match_getslice(self, key, default_value);
         if (!value) {
             Py_DECREF(key);
-            goto failed;
+            Py_CLEAR(result);
+            goto exit;
         }
         status = _PyDict_SetItem_KnownHash(result, key, value, hash);
         Py_DECREF(value);
         Py_DECREF(key);
-        if (status < 0)
-            goto failed;
+        if (status < 0) {
+            Py_CLEAR(result);
+            goto exit;
         }
+    }
+exit:
+    Py_END_CRITICAL_SECTION();
 
     return result;
-
-failed:
-    Py_DECREF(result);
-    return NULL;
 }
 
 /*[clinic input]

Objects/clinic/dictobject.c.h

@@ -2,6 +2,7 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_critical_section.h"// Py_BEGIN_CRITICAL_SECTION()
 #include "pycore_modsupport.h"    // _PyArg_CheckPositional()
 
 PyDoc_STRVAR(dict_fromkeys__doc__,
@@ -65,6 +66,21 @@ PyDoc_STRVAR(dict___contains____doc__,
 #define DICT___CONTAINS___METHODDEF    \
     {"__contains__", (PyCFunction)dict___contains__, METH_O|METH_COEXIST, dict___contains____doc__},
 
+static PyObject *
+dict___contains___impl(PyDictObject *self, PyObject *key);
+
+static PyObject *
+dict___contains__(PyDictObject *self, PyObject *key)
+{
+    PyObject *return_value = NULL;
+
+    Py_BEGIN_CRITICAL_SECTION(self);
+    return_value = dict___contains___impl(self, key);
+    Py_END_CRITICAL_SECTION();
+
+    return return_value;
+}
+
 PyDoc_STRVAR(dict_get__doc__,
 "get($self, key, default=None, /)\n"
 "--\n"
@@ -93,7 +109,9 @@ dict_get(PyDictObject *self, PyObject *const *args, Py_ssize_t nargs)
     }
     default_value = args[1];
 skip_optional:
+    Py_BEGIN_CRITICAL_SECTION(self);
     return_value = dict_get_impl(self, key, default_value);
+    Py_END_CRITICAL_SECTION();
 
 exit:
     return return_value;
@@ -130,7 +148,9 @@ dict_setdefault(PyDictObject *self, PyObject *const *args, Py_ssize_t nargs)
     }
     default_value = args[1];
 skip_optional:
+    Py_BEGIN_CRITICAL_SECTION(self);
     return_value = dict_setdefault_impl(self, key, default_value);
+    Py_END_CRITICAL_SECTION();
 
 exit:
     return return_value;
@@ -209,7 +229,13 @@ dict_popitem_impl(PyDictObject *self);
 static PyObject *
 dict_popitem(PyDictObject *self, PyObject *Py_UNUSED(ignored))
 {
-    return dict_popitem_impl(self);
+    PyObject *return_value = NULL;
+
+    Py_BEGIN_CRITICAL_SECTION(self);
+    return_value = dict_popitem_impl(self);
+    Py_END_CRITICAL_SECTION();
+
+    return return_value;
 }
 
 PyDoc_STRVAR(dict___sizeof____doc__,
@@ -301,4 +327,4 @@ dict_values(PyDictObject *self, PyObject *Py_UNUSED(ignored))
 {
     return dict_values_impl(self);
 }
-/*[clinic end generated code: output=f3ac47dfbf341b23 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=c8fda06bac5b05f3 input=a9049054013a1b77]*/

Objects/odictobject.c

@@ -467,6 +467,7 @@ later:
 #include "Python.h"
 #include "pycore_call.h"             // _PyObject_CallNoArgs()
 #include "pycore_ceval.h"            // _PyEval_GetBuiltin()
+#include "pycore_critical_section.h" //_Py_BEGIN_CRITICAL_SECTION
 #include "pycore_dict.h"             // _Py_dict_lookup()
 #include "pycore_object.h"           // _PyObject_GC_UNTRACK()
 #include "pycore_pyerrors.h"         // _PyErr_ChainExceptions1()
@@ -1039,6 +1040,8 @@ _odict_popkey_hash(PyObject *od, PyObject *key, PyObject *failobj,
 {
     PyObject *value = NULL;
 
+    Py_BEGIN_CRITICAL_SECTION(od);
+
     _ODictNode *node = _odict_find_node_hash((PyODictObject *)od, key, hash);
     if (node != NULL) {
         /* Pop the node first to avoid a possible dict resize (due to
@@ -1046,7 +1049,7 @@ _odict_popkey_hash(PyObject *od, PyObject *key, PyObject *failobj,
            resolution. */
         int res = _odict_clear_node((PyODictObject *)od, node, key, hash);
         if (res < 0) {
-            return NULL;
+            goto done;
         }
         /* Now delete the value from the dict. */
         if (_PyDict_Pop_KnownHash((PyDictObject *)od, key, hash,
@@ -1063,6 +1066,8 @@ _odict_popkey_hash(PyObject *od, PyObject *key, PyObject *failobj,
             PyErr_SetObject(PyExc_KeyError, key);
         }
     }
+    Py_END_CRITICAL_SECTION();
+done:
 
     return value;
 }

Objects/setobject.c

@@ -33,6 +33,7 @@
 
 #include "Python.h"
 #include "pycore_ceval.h"               // _PyEval_GetBuiltin()
+#include "pycore_critical_section.h"    // Py_BEGIN_CRITICAL_SECTION, Py_END_CRITICAL_SECTION
 #include "pycore_dict.h"                // _PyDict_Contains_KnownHash()
 #include "pycore_modsupport.h"          // _PyArg_NoKwnames()
 #include "pycore_object.h"              // _PyObject_GC_UNTRACK()
@@ -903,11 +904,17 @@ set_update_internal(PySetObject *so, PyObject *other)
             if (set_table_resize(so, (so->used + dictsize)*2) != 0)
                 return -1;
         }
+        int err = 0;
+        Py_BEGIN_CRITICAL_SECTION(other);
         while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
-            if (set_add_entry(so, key, hash))
-                return -1;
+            if (set_add_entry(so, key, hash)) {
+                err = -1;
+                goto exit;
             }
-        return 0;
+        }
+exit:
+        Py_END_CRITICAL_SECTION();
+        return err;
     }
 
     it = PyObject_GetIter(other);
@@ -1621,20 +1628,14 @@ set_isub(PySetObject *so, PyObject *other)
 }
 
 static PyObject *
-set_symmetric_difference_update(PySetObject *so, PyObject *other)
+set_symmetric_difference_update_dict(PySetObject *so, PyObject *other)
 {
-    PySetObject *otherset;
     PyObject *key;
     Py_ssize_t pos = 0;
     Py_hash_t hash;
-    setentry *entry;
+    PyObject *value;
     int rv;
 
-    if ((PyObject *)so == other)
-        return set_clear(so, NULL);
-
-    if (PyDict_CheckExact(other)) {
-        PyObject *value;
     while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
         Py_INCREF(key);
         rv = set_discard_entry(so, key, hash);
@@ -1651,6 +1652,29 @@ set_symmetric_difference_update(PySetObject *so, PyObject *other)
         Py_DECREF(key);
     }
     Py_RETURN_NONE;
+}
+
+static PyObject *
+set_symmetric_difference_update(PySetObject *so, PyObject *other)
+{
+    PySetObject *otherset;
+    PyObject *key;
+    Py_ssize_t pos = 0;
+    Py_hash_t hash;
+    setentry *entry;
+    int rv;
+
+    if ((PyObject *)so == other)
+        return set_clear(so, NULL);
+
+    if (PyDict_CheckExact(other)) {
+        PyObject *res;
+
+        Py_BEGIN_CRITICAL_SECTION(other);
+        res = set_symmetric_difference_update_dict(so, other);
+        Py_END_CRITICAL_SECTION();
+
+        return res;
     }
 
     if (PyAnySet_Check(other)) {