Backport Fix for Bug#24509 - 2048 file descriptor limit on windows needs increasing.

The patch replaces the use of the POSIX I/O interfaces in mysys on Windows with 
the Win32 API calls (CreateFile, WriteFile, etc). The Windows HANDLE for the open
 file is stored in the my_file_info struct, along with a flag for append mode 
(because the Windows API does not support opening files in append mode in all cases)
The default max open files has been increased to 16384 and can be increased further
by setting --max-open-files=<value> during the server start.

Noteworthy benefit of this patch is that it removes limits from the table_cache size - 
allowing for more simultaneus users

1 files changed, 7 insertions, 10 deletions

diff --git a/mysys/my_seek.c b/mysys/my_seek.c
index d186d56869a..24941517487 100644
--- a/mysys/my_seek.c
+++ b/mysys/my_seek.c
@@ -56,16 +56,11 @@ my_off_t my_seek(File fd, my_off_t pos, int whence, myf MyFlags)
       Make sure we are using a valid file descriptor!
   */
   DBUG_ASSERT(fd != -1);
-#if defined(THREAD) && !defined(HAVE_PREAD)
-  if (MyFlags & MY_THREADSAFE)
-  {
-    pthread_mutex_lock(&my_file_info[fd].mutex);
-    newpos= lseek(fd, pos, whence);
-    pthread_mutex_unlock(&my_file_info[fd].mutex);
-  }
-  else
+#ifdef _WIN32
+  newpos= my_win_lseek(fd, pos, whence);
+#else
+  newpos= lseek(fd, pos, whence);
 #endif
-    newpos= lseek(fd, pos, whence);
   if (newpos == (os_off_t) -1)
   {
     my_errno= errno;
@@ -91,7 +86,9 @@ my_off_t my_tell(File fd, myf MyFlags)
   DBUG_ENTER("my_tell");
   DBUG_PRINT("my",("fd: %d  MyFlags: %d",fd, MyFlags));
   DBUG_ASSERT(fd >= 0);
-#ifdef HAVE_TELL
+#ifdef _WIN32
+  pos= my_seek(fd, 0, MY_SEEK_CUR,0);
+#elif defined(HAVE_TELL)
   pos=tell(fd);
 #else
   pos=lseek(fd, 0L, MY_SEEK_CUR);