From 264ec7279046c68e24c3997dc773a11773f5a748 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 16 Aug 2019 11:03:37 +0200
Subject: [PATCH] cache bytes converter used for locale conversions

On platforms other than Windows and MacOS, locale encoding (inclduing
path <-> string conversion) opened a converter for each separate
operation. That can be slow on some OSes, so cache converters used for
locale conversions.

Relevant to #2781
---
 racket/src/io/converter/main.rkt      |   9 ++
 racket/src/io/locale/cache.rkt        |  80 +++++++++++++++++
 racket/src/io/locale/collate.rkt      |  10 ++-
 racket/src/io/locale/recase.rkt       |   6 +-
 racket/src/io/locale/string.rkt       |  11 ++-
 racket/src/io/main.rkt                |   3 +
 racket/src/racket/include/schthread.h |   6 ++
 racket/src/racket/src/env.c           |   1 +
 racket/src/racket/src/schpriv.h       |   1 +
 racket/src/racket/src/string.c        | 118 ++++++++++++++++++++++----
 racket/src/rktio/rktio.def            |   1 +
 racket/src/rktio/rktio.h              |   3 +
 racket/src/rktio/rktio.inc            |   1 +
 racket/src/rktio/rktio.rktl           |   5 ++
 racket/src/rktio/rktio_convert.c      |   5 ++
 15 files changed, 235 insertions(+), 25 deletions(-)
 create mode 100644 racket/src/io/locale/cache.rkt

diff --git a/racket/src/io/converter/main.rkt b/racket/src/io/converter/main.rkt
index 0c82e6034e..6b8a61e35e 100644
--- a/racket/src/io/converter/main.rkt
+++ b/racket/src/io/converter/main.rkt
@@ -12,6 +12,9 @@
          bytes-convert
          bytes-convert-end)
 
+(module+ reset
+  (provide bytes-reset-converter))
+
 (struct bytes-converter ([c #:mutable]
                          [custodian-reference #:mutable]))
 
@@ -229,3 +232,9 @@
      (define err (and (= converted RKTIO_CONVERT_ERROR)
                       (rktio_get_last_error rktio)))
      (values in-consumed out-produced err)]))
+
+;; in atomic mode
+(define (bytes-reset-converter converter)
+  (define c  (bytes-converter-c converter))
+  (unless (utf-8-converter? c)
+    (rktio_convert_reset rktio c)))
diff --git a/racket/src/io/locale/cache.rkt b/racket/src/io/locale/cache.rkt
new file mode 100644
index 0000000000..e2c44f8584
--- /dev/null
+++ b/racket/src/io/locale/cache.rkt
@@ -0,0 +1,80 @@
+#lang racket/base
+(require "../host/thread.rkt"
+         "../host/place-local.rkt"
+         "../converter/main.rkt"
+         (submod "../converter/main.rkt" reset)
+         "ucs-4.rkt")
+
+(provide convert-cache-init!
+
+         bytes-open-converter/cached-to
+         bytes-open-converter/cached-to2
+         bytes-open-converter/cached-from
+         bytes-close-converter/cached-to
+         bytes-close-converter/cached-to2
+         bytes-close-converter/cached-from)
+
+(struct cache (enc to to2 from)
+  #:mutable
+  #:authentic)
+
+(define (new-cache) (cache #f #f #f #f))
+
+(define-place-local local-cache (new-cache))
+
+(define (convert-cache-init!)
+  (set! local-cache (new-cache)))
+
+(define (cache-clear! get update!)
+  (define c (get local-cache))
+  (update! local-cache #f)
+  (when c
+    (bytes-close-converter c)))
+
+(define (cache-lookup! enc get update!)
+  (atomically
+   (and (equal? enc (cache-enc local-cache))
+        (let ([c (get local-cache)])
+          (when c
+            (update! local-cache #f))
+          c))))
+
+(define (cache-save! c enc get update!)
+  (atomically
+   (unless (equal? enc (cache-enc local-cache))
+     (cache-clear! cache-to set-cache-to!)
+     (cache-clear! cache-to2 set-cache-to2!)
+     (cache-clear! cache-from set-cache-from!)
+     (set-cache-enc! local-cache enc))
+   (cond
+     [(get local-cache)
+      (bytes-close-converter c)]
+     [else
+      (bytes-reset-converter c) ; must be in atomic mode
+      (update! local-cache c)])))
+
+;; ----------------------------------------
+
+(define (bytes-open-converter/cached-to enc)
+  (or (cache-lookup! enc cache-to set-cache-to!)
+      (bytes-open-converter ucs-4-encoding enc)))
+
+(define (bytes-open-converter/cached-to2 enc)
+  (or (cache-lookup! enc cache-to2 set-cache-to2!)
+      (bytes-open-converter ucs-4-encoding enc)))
+
+(define (bytes-open-converter/cached-from enc)
+  (or (cache-lookup! enc cache-from set-cache-from!)
+      (bytes-open-converter enc "UTF-8")))
+
+(define (bytes-close-converter/cached-to c enc)
+  (or (cache-save! c enc cache-to set-cache-to!)
+      (bytes-close-converter c)))
+
+(define (bytes-close-converter/cached-to2 c enc)
+  (or (cache-save! c enc cache-to2 set-cache-to2!)
+      (bytes-close-converter c)))
+
+(define (bytes-close-converter/cached-from c enc)
+  (or (cache-save! c enc cache-from set-cache-from!)
+      (bytes-close-converter c)))
diff --git a/racket/src/io/locale/collate.rkt b/racket/src/io/locale/collate.rkt
index 85351c1c17..bc308a7a60 100644
--- a/racket/src/io/locale/collate.rkt
+++ b/racket/src/io/locale/collate.rkt
@@ -4,6 +4,7 @@
          "../host/rktio.rkt"
          "../string/utf-16-encode.rkt"
          "../converter/main.rkt"
+         "cache.rkt"
          "parameter.rkt"
          "string.rkt"
          "recase.rkt"
@@ -93,10 +94,11 @@
      (define c2 #f)
      (define in-bstr1 (string->bytes/ucs-4 s1 0 (string-length s1)))
      (define in-bstr2 (string->bytes/ucs-4 s2 0 (string-length s2)))
+     (define enc (locale-string-encoding))
      (dynamic-wind
       (lambda ()
-        (set! c1 (bytes-open-converter ucs-4-encoding (locale-string-encoding)))
-        (set! c2 (bytes-open-converter ucs-4-encoding (locale-string-encoding))))
+        (set! c1 (bytes-open-converter/cached-to enc))
+        (set! c2 (bytes-open-converter/cached-to2 enc)))
       (lambda ()
         (let loop ([pos1 0] [pos2 0] [end1 (bytes-length in-bstr1)] [end2 (bytes-length in-bstr2)])
           (define-values (bstr1 in-used1 status1)
@@ -154,5 +156,5 @@
                [else
                 (loop pos1 pos2 (+ pos1 len) (+ pos2 len))])])))
       (lambda ()
-        (bytes-close-converter c1)
-        (bytes-close-converter c2)))]))
+        (bytes-close-converter/cached-to c1 enc)
+        (bytes-close-converter/cached-to2 c2 enc)))]))
diff --git a/racket/src/io/locale/recase.rkt b/racket/src/io/locale/recase.rkt
index c247ebe1a9..03e0321b56 100644
--- a/racket/src/io/locale/recase.rkt
+++ b/racket/src/io/locale/recase.rkt
@@ -6,6 +6,7 @@
          "../string/utf-16-encode.rkt"
          "../string/utf-16-decode.rkt"
          "../converter/main.rkt"
+         "cache.rkt"
          "parameter.rkt"
          "string.rkt"
          "nul-char.rkt"
@@ -64,9 +65,10 @@
      ;; encoding-error bytes alone.
      (define c #f)
      (define in-bstr (string->bytes/ucs-4 s 0 (string-length s)))
+     (define enc (locale-string-encoding))
      (dynamic-wind
       (lambda ()
-        (set! c (bytes-open-converter ucs-4-encoding (locale-string-encoding))))
+        (set! c (bytes-open-converter/cached-to enc)))
       (lambda ()
         (let loop ([pos 0])
           (cond
@@ -94,7 +96,7 @@
                     (apply string-append ls err-s r)
                     (list* ls err-s r))])])))
       (lambda ()
-        (bytes-close-converter c)))]))
+        (bytes-close-converter/cached-to c enc)))]))
 
 ;; in atomic mode
 ;; Assumes that the locale is sync'ed
diff --git a/racket/src/io/locale/string.rkt b/racket/src/io/locale/string.rkt
index 8312a8f81f..188ddcbac7 100644
--- a/racket/src/io/locale/string.rkt
+++ b/racket/src/io/locale/string.rkt
@@ -3,6 +3,7 @@
          "../string/convert.rkt"
          "../string/utf-8-decode.rkt"
          "../converter/main.rkt"
+         "cache.rkt"
          "parameter.rkt"
          "ucs-4.rkt")
 
@@ -20,9 +21,10 @@
      (string->bytes/utf-8 str err-byte start end)]
     [else
      (define c #f)
+     (define enc (locale-string-encoding))
      (dynamic-wind
       (lambda ()
-        (set! c (bytes-open-converter ucs-4-encoding (locale-string-encoding))))
+        (set! c (bytes-open-converter/cached-to enc)))
       (lambda ()
         (define in-bstr (string->bytes/ucs-4 str start end))
         (let loop ([pos 0])
@@ -51,7 +53,7 @@
                     (apply bytes-append (cons bstr (cons err-bstr r)))
                     (cons bstr (cons err-bstr r)))])])))
       (lambda ()
-        (bytes-close-converter c)))]))
+        (bytes-close-converter/cached-to c enc)))]))
 
 (define/who (bytes->string/locale in-bstr [err-char #f] [start 0] [end (and (bytes? in-bstr)
                                                                             (bytes-length in-bstr))])
@@ -65,9 +67,10 @@
      (bytes->string/utf-8 in-bstr err-char start end)]
     [else
      (define c #f)
+     (define enc (locale-string-encoding))
      (dynamic-wind
       (lambda ()
-        (set! c (bytes-open-converter (locale-string-encoding) "UTF-8")))
+        (set! c (bytes-open-converter/cached-from enc)))
       (lambda ()
         (let loop ([pos 0])
           (define-values (bstr in-used status)
@@ -95,4 +98,4 @@
                     (bytes->string/utf-8 (apply bytes-append (cons bstr (cons err-bstr r))))
                     (cons bstr (cons err-bstr r)))])])))
       (lambda ()
-        (bytes-close-converter c)))]))
+        (bytes-close-converter/cached-from c enc)))]))
diff --git a/racket/src/io/main.rkt b/racket/src/io/main.rkt
index 50cf463ea7..9dbc73d0c6 100644
--- a/racket/src/io/main.rkt
+++ b/racket/src/io/main.rkt
@@ -30,6 +30,8 @@
                  place-init)
          (only-in "sandman/ltps.rkt"
                   shared-ltps-place-init!)
+         (only-in "locale/cache.rkt"
+                  convert-cache-init!)
          "port/place.rkt")
 
 (provide (all-from-out "port/main.rkt")
@@ -60,6 +62,7 @@
 
 (define (io-place-init! in-fd out-fd err-fd cust plumber)
   (rktio-place-init!)
+  (convert-cache-init!)
   (logger-init!)
   (shared-ltps-place-init!)
   (install-error-value->string-handler!)
diff --git a/racket/src/racket/include/schthread.h b/racket/src/racket/include/schthread.h
index 374cd412a9..fe8b2ec510 100644
--- a/racket/src/racket/include/schthread.h
+++ b/racket/src/racket/include/schthread.h
@@ -321,6 +321,9 @@ typedef struct Thread_Local_Variables {
   int num_minor_garbage_collections_;
   int locale_on_;
   void *current_locale_name_ptr_;
+  char *cached_locale_encoding_name_;
+  struct rktio_converter_t *cached_locale_to_converter_;
+  struct rktio_converter_t *cached_locale_from_converter_;
   int gensym_counter_;
   struct Scheme_Object *dummy_input_port_;
   struct Scheme_Object *dummy_output_port_;
@@ -706,6 +709,9 @@ XFORM_GC_VARIABLE_STACK_THROUGH_THREAD_LOCAL;
 #define num_minor_garbage_collections XOA (scheme_get_thread_local_variables()->num_minor_garbage_collections_)
 #define locale_on XOA (scheme_get_thread_local_variables()->locale_on_)
 #define current_locale_name_ptr XOA (scheme_get_thread_local_variables()->current_locale_name_ptr_)
+#define cached_locale_encoding_name XOA (scheme_get_thread_local_variables()->cached_locale_encoding_name_)
+#define cached_locale_to_converter XOA (scheme_get_thread_local_variables()->cached_locale_to_converter_)
+#define cached_locale_from_converter XOA (scheme_get_thread_local_variables()->cached_locale_from_converter_)
 #define gensym_counter XOA (scheme_get_thread_local_variables()->gensym_counter_)
 #define dummy_input_port XOA (scheme_get_thread_local_variables()->dummy_input_port_)
 #define dummy_output_port XOA (scheme_get_thread_local_variables()->dummy_output_port_)
diff --git a/racket/src/racket/src/env.c b/racket/src/racket/src/env.c
index 4e44c9b479..0898091f82 100644
--- a/racket/src/racket/src/env.c
+++ b/racket/src/racket/src/env.c
@@ -586,6 +586,7 @@ void scheme_place_instance_destroy(int force)
   GC_destruct_child_gc();
 #endif
   scheme_free_all_code();
+  scheme_clear_locale_cache();
   rktio_destroy(scheme_rktio);
 }
 
diff --git a/racket/src/racket/src/schpriv.h b/racket/src/racket/src/schpriv.h
index adb984089d..dc5f20cb5a 100644
--- a/racket/src/racket/src/schpriv.h
+++ b/racket/src/racket/src/schpriv.h
@@ -436,6 +436,7 @@ void scheme_register_network_evts();
 
 void scheme_free_dynamic_extensions(void);
 void scheme_free_all_code(void);
+void scheme_clear_locale_cache(void);
 
 XFORM_NONGCING int scheme_is_multithreaded(int now);
 
diff --git a/racket/src/racket/src/string.c b/racket/src/racket/src/string.c
index 7519783339..47b57f751d 100644
--- a/racket/src/racket/src/string.c
+++ b/racket/src/racket/src/string.c
@@ -166,6 +166,8 @@ static char *string_to_from_locale(int to_bytes,
 				   intptr_t *olen, int perm,
 				   int *no_cvt);
 
+static void cache_locale_or_close(int to_bytes, rktio_converter_t *cd, char *le);
+
 #define portable_isspace(x) (((x) < 128) && isspace(x))
 
 ROSYM static Scheme_Object *sys_symbol;
@@ -184,6 +186,10 @@ SHARED_OK static Scheme_Object *banner_str;
 
 THREAD_LOCAL_DECL(static Scheme_Object *fs_change_props);
 
+THREAD_LOCAL_DECL(static char *cached_locale_encoding_name);
+THREAD_LOCAL_DECL(struct rktio_converter_t *cached_locale_to_converter);
+THREAD_LOCAL_DECL(struct rktio_converter_t *cached_locale_from_converter);
+
 READ_ONLY static Scheme_Object *complete_symbol, *continues_symbol, *aborts_symbol, *error_symbol;
 
 READ_ONLY Scheme_Object *scheme_string_p_proc;
@@ -2571,6 +2577,18 @@ static Scheme_Object *system_language_country(int argc, Scheme_Object *argv[])
   return s;
 }
 
+static void do_convert_close(rktio_converter_t *cd, int cache_mode, const char *to_e, const char *from_e)
+/* If `cache_mode` is -1, then `to_e` needs to be freed (or cached).
+   If `cache_mode` is 1, then `from_e` needs to be freed (or cached). */
+{
+  if (cache_mode == -1)
+    cache_locale_or_close(1, cd, (char *)to_e);
+  else if (cache_mode == 1)
+    cache_locale_or_close(0, cd, (char *)from_e);
+  else if (!cache_mode)
+    rktio_converter_close(scheme_rktio, cd);
+}
+
 static char *do_convert(rktio_converter_t *cd,
 			/* if !cd and either from_e or to_e can be NULL, then
 			   reset_locale() must have been called */
@@ -2598,7 +2616,7 @@ static char *do_convert(rktio_converter_t *cd,
 			   1 for more avail */
 			int *status)
 {
-  int dip, dop, close_it = 0, mz_utf8 = 0;
+  int dip, dop, close_it = 0, cache_mode = 0, mz_utf8 = 0;
   intptr_t il, ol, r;
   GC_CAN_IGNORE char *ip, *op;
 
@@ -2611,6 +2629,12 @@ static char *do_convert(rktio_converter_t *cd,
   if (!cd) {
     if (rktio_convert_properties(scheme_rktio) & RKTIO_CONVERTER_SUPPORTED) {
       char *tmp_from_e = NULL, *tmp_to_e = NULL;
+
+      if (!to_e && !strcmp(from_e, MZ_UCS4_NAME))
+        cache_mode = -1;
+      else if (!from_e && !strcmp(to_e, MZ_UCS4_NAME))
+        cache_mode = 1;
+
       if (!from_e) {
 	tmp_from_e = rktio_locale_encoding(scheme_rktio);
         from_e = tmp_from_e;
@@ -2619,10 +2643,23 @@ static char *do_convert(rktio_converter_t *cd,
 	tmp_to_e = rktio_locale_encoding(scheme_rktio);
         to_e = tmp_to_e;
       }
-      cd = rktio_converter_open(scheme_rktio, to_e, from_e);
+
+      if ((cache_mode == -1)
+          && cached_locale_to_converter
+          && !strcmp(to_e, cached_locale_encoding_name)) {
+        cd = cached_locale_to_converter;
+        cached_locale_to_converter = NULL;
+      } else if ((cache_mode == 1)
+                 && cached_locale_from_converter
+                 && !strcmp(from_e, cached_locale_encoding_name)) {
+        cd = cached_locale_from_converter;
+        cached_locale_from_converter = NULL;
+      } else {
+        cd = rktio_converter_open(scheme_rktio, to_e, from_e);
+      }
       close_it = 1;
-      if (tmp_from_e) free(tmp_from_e);
-      if (tmp_to_e) free(tmp_to_e);
+      if (tmp_from_e && ((cache_mode != 1) || !cd)) free(tmp_from_e);
+      if (tmp_to_e && ((cache_mode != -1) || !cd)) free(tmp_to_e);
     } else if (to_from_utf8) {
       /* Assume UTF-8 */
       mz_utf8 = 1;
@@ -2737,7 +2774,7 @@ static char *do_convert(rktio_converter_t *cd,
 	} else {
 	  *status = 1;
 	  if (close_it)
-	    rktio_converter_close(scheme_rktio, cd);
+            do_convert_close(cd, cache_mode, to_e, from_e);
 	  while (extra--) {
 	    out[od + dop + extra] = 0;
 	  }
@@ -2748,7 +2785,7 @@ static char *do_convert(rktio_converter_t *cd,
 	if (icerr == RKTIO_ERROR_CONVERT_BAD_SEQUENCE)
 	  *status = -2;
 	if (close_it)
-	  rktio_converter_close(scheme_rktio, cd);
+          do_convert_close(cd, cache_mode, to_e, from_e);
 	while (extra--) {
 	  out[od + dop + extra] = 0;
 	}
@@ -2766,7 +2803,7 @@ static char *do_convert(rktio_converter_t *cd,
       } else {
 	*status = 0;
 	if (close_it)
-          rktio_converter_close(scheme_rktio, cd);
+          do_convert_close(cd, cache_mode, to_e, from_e);
 	while (extra--) {
 	  out[od + dop + extra] = 0;
 	}
@@ -2792,18 +2829,32 @@ static char *string_to_from_locale(int to_bytes,
   rktio_converter_t *cd;
 
   le = rktio_locale_encoding(scheme_rktio);
-  if (to_bytes)
-    cd = rktio_converter_open(scheme_rktio, le, MZ_UCS4_NAME);
-  else
-    cd = rktio_converter_open(scheme_rktio, MZ_UCS4_NAME, le);
-  free(le);
-  
+  if (cached_locale_encoding_name
+      && !strcmp(le, cached_locale_encoding_name)
+      && (to_bytes ? cached_locale_to_converter : cached_locale_from_converter)) {
+    if (to_bytes) {
+      cd = cached_locale_to_converter;
+      cached_locale_to_converter = NULL;
+    } else {
+      cd = cached_locale_from_converter;
+      cached_locale_from_converter = NULL;
+    }
+  } else {  
+    if (to_bytes)
+      cd = rktio_converter_open(scheme_rktio, le, MZ_UCS4_NAME);
+    else
+      cd = rktio_converter_open(scheme_rktio, MZ_UCS4_NAME, le);
+  }
+
   if (!cd) {
+    free(le);
     *no_cvt = 1;
     return NULL;
   }
   *no_cvt = 0;
 
+  status = 0;
+
   while (len) {
     /* We might have conversion errors... */
     c = do_convert(cd, NULL, NULL, 0,
@@ -2818,6 +2869,7 @@ static char *string_to_from_locale(int to_bytes,
 
     if ((perm < 0) && (used < len)) {
       rktio_converter_close(scheme_rktio, cd);
+      free(le);
       return NULL;
     }
 
@@ -2832,7 +2884,7 @@ static char *string_to_from_locale(int to_bytes,
 	*olen = (clen >> 2);
 	((mzchar *)c)[*olen] = 0;
       }
-      rktio_converter_close(scheme_rktio, cd);
+      cache_locale_or_close(to_bytes, cd, le);
       return c;
     }
 
@@ -2864,7 +2916,7 @@ static char *string_to_from_locale(int to_bytes,
     }
   }
 
-  rktio_converter_close(scheme_rktio, cd);
+  cache_locale_or_close(to_bytes, cd, le);
 
   if (to_bytes) {
     parts = append_all_byte_strings_backwards(parts);
@@ -2879,6 +2931,42 @@ static char *string_to_from_locale(int to_bytes,
   }
 }
 
+void cache_locale_or_close(int to_bytes, rktio_converter_t *cd, char *le)
+{
+  if (to_bytes ? cached_locale_to_converter : cached_locale_from_converter) {
+    rktio_converter_close(scheme_rktio, cd);
+    free(le);
+  } else {
+    if (!cached_locale_encoding_name || strcmp(le, cached_locale_encoding_name)) {
+      scheme_clear_locale_cache();
+      cached_locale_encoding_name = le;
+    } else
+      free(le);
+
+    rktio_convert_reset(scheme_rktio, cd);
+    if (to_bytes)
+      cached_locale_to_converter = cd;
+    else
+      cached_locale_from_converter = cd;
+  }
+}
+
+void scheme_clear_locale_cache(void)
+{
+  if (cached_locale_encoding_name) {
+    if (cached_locale_to_converter) {
+      rktio_converter_close(scheme_rktio, cached_locale_to_converter);
+      cached_locale_to_converter = NULL;
+    }
+    if (cached_locale_from_converter) {
+      rktio_converter_close(scheme_rktio, cached_locale_from_converter);
+      cached_locale_from_converter = NULL;
+    }
+    free(cached_locale_encoding_name);
+    cached_locale_encoding_name = NULL;
+  }
+}
+
 static char *locale_recase(int to_up,
 			   /* in must be null-terminated, iilen doesn't include it */
 			   char *in, int id, int iilen,
diff --git a/racket/src/rktio/rktio.def b/racket/src/rktio/rktio.def
index dd339ec4da..5c0e965399 100644
--- a/racket/src/rktio/rktio.def
+++ b/racket/src/rktio/rktio.def
@@ -176,6 +176,7 @@ rktio_converter_open
 rktio_converter_close
 rktio_convert
 rktio_convert_in
+rktio_convert_reset
 rktio_locale_recase
 rktio_recase_utf16
 rktio_locale_strcoll
diff --git a/racket/src/rktio/rktio.h b/racket/src/rktio/rktio.h
index 09003eca38..846f2e8c97 100644
--- a/racket/src/rktio/rktio.h
+++ b/racket/src/rktio/rktio.h
@@ -1119,6 +1119,9 @@ RKTIO_EXTERN rktio_convert_result_t *rktio_convert_in(rktio_t *rktio,
    doesn't return a NULL result; instead, `converted` in the result
    reports the error. */
 
+RKTIO_EXTERN void rktio_convert_reset(rktio_t *rktio, rktio_converter_t *cvt);
+/* Resets a converter to its initial state. */
+
 RKTIO_EXTERN_NOERR char *rktio_locale_recase(rktio_t *rktio,
                                              rktio_bool_t to_up,
                                              rktio_const_string_t in);
diff --git a/racket/src/rktio/rktio.inc b/racket/src/rktio/rktio.inc
index 91774411b4..12814a5918 100644
--- a/racket/src/rktio/rktio.inc
+++ b/racket/src/rktio/rktio.inc
@@ -176,6 +176,7 @@ Sforeign_symbol("rktio_converter_open", (void *)rktio_converter_open);
 Sforeign_symbol("rktio_converter_close", (void *)rktio_converter_close);
 Sforeign_symbol("rktio_convert", (void *)rktio_convert);
 Sforeign_symbol("rktio_convert_in", (void *)rktio_convert_in);
+Sforeign_symbol("rktio_convert_reset", (void *)rktio_convert_reset);
 Sforeign_symbol("rktio_locale_recase", (void *)rktio_locale_recase);
 Sforeign_symbol("rktio_recase_utf16", (void *)rktio_recase_utf16);
 Sforeign_symbol("rktio_locale_strcoll", (void *)rktio_locale_strcoll);
diff --git a/racket/src/rktio/rktio.rktl b/racket/src/rktio/rktio.rktl
index d4f36f87c9..a27178576a 100644
--- a/racket/src/rktio/rktio.rktl
+++ b/racket/src/rktio/rktio.rktl
@@ -1261,6 +1261,11 @@
   ((*ref char) out)
   (intptr_t out_start)
   (intptr_t out_end)))
+(define-function
+ ()
+ void
+ rktio_convert_reset
+ (((ref rktio_t) rktio) ((ref rktio_converter_t) cvt)))
 (define-function
  ()
  (ref char)
diff --git a/racket/src/rktio/rktio_convert.c b/racket/src/rktio/rktio_convert.c
index 6b7c37161f..0eb814ae7a 100644
--- a/racket/src/rktio/rktio_convert.c
+++ b/racket/src/rktio/rktio_convert.c
@@ -507,6 +507,11 @@ rktio_convert_result_t *rktio_convert_in(rktio_t *rktio,
   return r;
 }
 
+void rktio_convert_reset(rktio_t *rktio, rktio_converter_t *cvt)
+{
+  (void)iconv(cvt->cd, NULL, NULL, NULL, NULL);
+}
+
 /*============================================================*/
 /* Case conversion                                            */
 /*============================================================*/