Avoid heap allocation

python · vstinner · May 31, 2025 · May 10, 2025 · May 10, 2025 · May 10, 2025
commit 01c45a95ba4422961afe597e7f0fd87e206530ff
diff --git a/Modules/_json.c b/Modules/_json.c
@@ -360,13 +360,6 @@ _build_rval_index_tuple(PyObject *rval, Py_ssize_t idx) {
    return tpl;
 }

-static inline int
-_PyUnicodeWriter_IsEmpty(PyUnicodeWriter *writer_pub)
-{
-    _PyUnicodeWriter *writer = (_PyUnicodeWriter*)writer_pub;
-    return (writer->pos == 0);
-}
-
 static PyObject *
 scanstring_unicode(PyObject *pystr, Py_ssize_t end, int strict, Py_ssize_t *next_end_ptr)
 {
@@ -385,10 +378,7 @@ scanstring_unicode(PyObject *pystr, Py_ssize_t end, int strict, Py_ssize_t *next
    const void *buf;
    int kind;

-    PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
-    if (writer == NULL) {
-        goto bail;
-    }
+    PyUnicodeWriter *writer = NULL;

    len = PyUnicode_GET_LENGTH(pystr);
    buf = PyUnicode_DATA(pystr);
@@ -419,19 +409,23 @@ scanstring_unicode(PyObject *pystr, Py_ssize_t end, int strict, Py_ssize_t *next

        if (c == '"') {
            // Fast path for simple case.
-            if (_PyUnicodeWriter_IsEmpty(writer)) {
+            if (writer == NULL) {
                PyObject *ret = PyUnicode_Substring(pystr, end, next);
                if (ret == NULL) {
                    goto bail;
                }
-                PyUnicodeWriter_Discard(writer);
                *next_end_ptr = next + 1;;
                return ret;
            }
        }
        else if (c != '\\') {
            raise_errmsg("Unterminated string starting at", pystr, begin);
            goto bail;
+        } else if (writer == NULL) {
+            writer = PyUnicodeWriter_Create(0);
+            if (writer == NULL) {
+                goto bail;
+            }
        }

        /* Pick up this chunk if it's not zero length */