normal	2018-01-06 06:14:19 +0900 (Sat, 06 Jan 2018)

  New Revision: 61632

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=61632

  Log:
    io.c: clear Strings we create for IO.copy_stream
    
    While we can't recycle strings after giving them rb_funcall*,
    we can reduce their malloc overhead by resizing them to zero.
    This only affects cases where either `src' or `dst' is a non-IO
    object and either `copy_length' is passed or there is
    pre-existing data in the read buffer.
    
    * io.c (copy_stream_fallback_body): clear when done with `copy_length'
      (copy_stream_body): clear when done with pre-existing read buffer

  Modified files:
    trunk/io.c
Index: io.c
===================================================================
--- io.c	(revision 61631)
+++ io.c	(revision 61632)
@@ -11163,8 +11163,10 @@ copy_stream_fallback_body(VALUE arg) https://github.com/ruby/ruby/blob/trunk/io.c#L11163
             l = buflen;
         }
         else {
-            if (rest == 0)
-                break;
+	    if (rest == 0) {
+		rb_str_resize(buf, 0);
+		break;
+	    }
             l = buflen < rest ? buflen : (long)rest;
         }
         if (stp->src_fd == -1) {
@@ -11305,6 +11307,7 @@ copy_stream_body(VALUE arg) https://github.com/ruby/ruby/blob/trunk/io.c#L11307
         }
         else /* others such as StringIO */
 	    rb_io_write(dst_io, str);
+        rb_str_resize(str, 0);
         stp->total += len;
         if (stp->copy_length != (off_t)-1)
             stp->copy_length -= len;

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