Fix mem leak in read_csv (#57084)

* Fix memory leak in read_csv

* whatsnew

* peakmem benchmark

Author: WillAyd

asv_bench/benchmarks/io/csv.py

@@ -408,6 +408,9 @@ def time_read_stringcsv(self, engine):
     def time_read_bytescsv(self, engine):
         read_csv(self.data(self.BytesIO_input), engine=engine)
 
+    def peakmem_read_csv(self, engine):
+        read_csv(self.data(self.BytesIO_input), engine=engine)
+
 
 class ReadCSVCategorical(BaseIO):
     fname = "__test__.csv"

doc/source/whatsnew/v2.2.1.rst

@@ -13,6 +13,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
+- Fixed memory leak in :func:`read_csv` (:issue:`57039`)
 - Fixed performance regression in :meth:`Series.combine_first` (:issue:`55845`)
 - Fixed regression in :func:`merge_ordered` raising ``TypeError`` for ``fill_method="ffill"`` and ``how="left"`` (:issue:`57010`)
 - Fixed regression in :meth:`DataFrameGroupBy.idxmin`, :meth:`DataFrameGroupBy.idxmax`, :meth:`SeriesGroupBy.idxmin`, :meth:`SeriesGroupBy.idxmax` ignoring the ``skipna`` argument (:issue:`57040`)

pandas/_libs/src/parser/tokenizer.c

@@ -109,6 +109,14 @@ void parser_set_default_options(parser_t *self) {
 
 parser_t *parser_new(void) { return (parser_t *)calloc(1, sizeof(parser_t)); }
 
+static void parser_clear_data_buffers(parser_t *self) {
+  free_if_not_null((void *)&self->stream);
+  free_if_not_null((void *)&self->words);
+  free_if_not_null((void *)&self->word_starts);
+  free_if_not_null((void *)&self->line_start);
+  free_if_not_null((void *)&self->line_fields);
+}
+
 static void parser_cleanup(parser_t *self) {
   // XXX where to put this
   free_if_not_null((void *)&self->error_msg);
@@ -119,6 +127,7 @@ static void parser_cleanup(parser_t *self) {
     self->skipset = NULL;
   }
 
+  parser_clear_data_buffers(self);
   if (self->cb_cleanup != NULL) {
     self->cb_cleanup(self->source);
     self->cb_cleanup = NULL;