1 files changed, 13 insertions, 3 deletions

diff --git a/lib/libc/stdio/fwrite.c b/lib/libc/stdio/fwrite.c
index dbc2e978d7d0..7efb0ac4e277 100644
--- a/lib/libc/stdio/fwrite.c
+++ b/lib/libc/stdio/fwrite.c
@@ -41,6 +41,10 @@ static char sccsid[] = "@(#)fwrite.c	8.1 (Berkeley) 6/4/93";
 #include <stdio.h>
 #include "local.h"
 #include "fvwrite.h"
+#ifdef _THREAD_SAFE
+#include <pthread.h>
+#include "pthread_private.h"
+#endif
 
 /*
  * Write `count' objects (each size `size') from memory to the given file.
@@ -61,12 +65,18 @@ fwrite(buf, size, count, fp)
 	uio.uio_iov = &iov;
 	uio.uio_iovcnt = 1;
 
+#ifdef _THREAD_SAFE
+	_thread_flockfile(fp,__FILE__,__LINE__);
+#endif
 	/*
 	 * The usual case is success (__sfvwrite returns 0);
 	 * skip the divide if this happens, since divides are
 	 * generally slow and since this occurs whenever size==0.
 	 */
-	if (__sfvwrite(fp, &uio) == 0)
-		return (count);
-	return ((n - uio.uio_resid) / size);
+	if (__sfvwrite(fp, &uio) != 0)
+	    count = (n - uio.uio_resid) / size;
+#ifdef _THREAD_SAFE
+	_thread_funlockfile(fp);
+#endif
+	return (count);
 }