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, 23 insertions, 13 deletions

diff --git a/mysys/my_write.c b/mysys/my_write.c
index 52127545888..5b916d6cb65 100644
--- a/mysys/my_write.c
+++ b/mysys/my_write.c
@@ -22,7 +22,7 @@
 
 size_t my_write(int Filedes, const uchar *Buffer, size_t Count, myf MyFlags)
 {
-  size_t writenbytes, written;
+  size_t writtenbytes, written;
   uint errors;
   DBUG_ENTER("my_write");
   DBUG_PRINT("my",("fd: %d  Buffer: 0x%lx  Count: %lu  MyFlags: %d",
@@ -35,17 +35,27 @@ size_t my_write(int Filedes, const uchar *Buffer, size_t Count, myf MyFlags)
   
   for (;;)
   {
-    if ((writenbytes= write(Filedes, Buffer, Count)) == Count)
+#ifdef _WIN32
+    if(Filedes < 0)
+    {
+      errno = EINVAL;
+      return -1;
+    }
+    writtenbytes= my_win_write(Filedes, Buffer, Count);
+#else
+    writtenbytes= write(Filedes, Buffer, Count);
+#endif
+    if (writtenbytes == Count)
       break;
-    if (writenbytes != (size_t) -1)
+    if (writtenbytes != (size_t) -1)
     {						/* Safeguard */
-      written+=writenbytes;
-      Buffer+=writenbytes;
-      Count-=writenbytes;
+      written+= writtenbytes;
+      Buffer+= writtenbytes;
+      Count-= writtenbytes;
     }
-    my_errno=errno;
+    my_errno= errno;
     DBUG_PRINT("error",("Write only %ld bytes, error: %d",
-			(long) writenbytes, my_errno));
+			(long) writtenbytes, my_errno));
 #ifndef NO_BACKGROUND
 #ifdef THREAD
     if (my_thread_var->abort)
@@ -59,19 +69,19 @@ size_t my_write(int Filedes, const uchar *Buffer, size_t Count, myf MyFlags)
       continue;
     }
 
-    if ((writenbytes == 0 || writenbytes == (size_t) -1))
+    if ((writtenbytes == 0 || writtenbytes == (size_t) -1))
     {
       if (my_errno == EINTR)
       {
         DBUG_PRINT("debug", ("my_write() was interrupted and returned %ld",
-                             (long) writenbytes));
+                             (long) writtenbytes));
         continue;                               /* Interrupted */
       }
 
-      if (!writenbytes && !errors++)		/* Retry once */
+      if (!writtenbytes && !errors++)		/* Retry once */
       {
         /* We may come here if the file quota is exeeded */
-        errno=EFBIG;				/* Assume this is the error */
+        errno= EFBIG;				/* Assume this is the error */
         continue;
       }
     }
@@ -92,5 +102,5 @@ size_t my_write(int Filedes, const uchar *Buffer, size_t Count, myf MyFlags)
   }
   if (MyFlags & (MY_NABP | MY_FNABP))
     DBUG_RETURN(0);			/* Want only errors */
-  DBUG_RETURN(writenbytes+written);
+  DBUG_RETURN(writtenbytes+written);
 } /* my_write */