* win32/win32.c (setup_overlapped): seek to the file end only when

writing (mode:a), not reading (mode:a+, read).

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50637 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Mon May 25 11:27:14 2015  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* win32/win32.c (setup_overlapped): seek to the file end only when
+	  writing (mode:a), not reading (mode:a+, read).
+
 Mon May 25 00:27:37 2015  Benoit Daloze  <eregontp@gmail.com>
 
 	* numeric.c (Numeric#negative?): [DOC] Fix call-seq.

win32/win32.c

@@ -6469,12 +6469,16 @@ rb_w32_close(int fd)
 }
 
 static int
-setup_overlapped(OVERLAPPED *ol, int fd)
+setup_overlapped(OVERLAPPED *ol, int fd, int iswrite)
 {
     memset(ol, 0, sizeof(*ol));
     if (!(_osfile(fd) & (FDEV | FPIPE))) {
 	LONG high = 0;
-	DWORD method = _osfile(fd) & FAPPEND ? FILE_END : FILE_CURRENT;
+	/* On mode:a, it can write only FILE_END.
+	 * On mode:a+, though it can write only FILE_END,
+	 * it can read from everywhere.
+	 */
+	DWORD method = ((_osfile(fd) & FAPPEND) && iswrite) ? FILE_END : FILE_CURRENT;
 	DWORD low = SetFilePointer((HANDLE)_osfhnd(fd), 0, &high, method);
 #ifndef INVALID_SET_FILE_POINTER
 #define INVALID_SET_FILE_POINTER ((DWORD)-1)
@@ -6571,7 +6575,7 @@ rb_w32_read(int fd, void *buf, size_t size)
 
     /* if have cancel_io, use Overlapped I/O */
     if (cancel_io) {
-	if (setup_overlapped(&ol, fd)) {
+	if (setup_overlapped(&ol, fd, FALSE)) {
 	    rb_acrt_lowio_unlock_fh(fd);
 	    return -1;
 	}
@@ -6701,7 +6705,7 @@ rb_w32_write(int fd, const void *buf, size_t size)
 
     /* if have cancel_io, use Overlapped I/O */
     if (cancel_io) {
-	if (setup_overlapped(&ol, fd)) {
+	if (setup_overlapped(&ol, fd, TRUE)) {
 	    rb_acrt_lowio_unlock_fh(fd);
 	    return -1;
 	}