Fix the handle locking in stdio

Fix the handle locking in stdio to use flockfile/funlockfile
internally when and where required.  Macros in <stdio.h> are updated
to automatically call the underlying functions when the process is
threaded to obtain the necessary locking.  A private mutex is added
to protect __sglue, the internal list of FILE handles, and another
to protect the one-time initialization.  Some routines in libc that
use getc() change to use getc_unlocked() as they're either protected
by their own lock or aren't thread-safe routines anyway.

Based on OpenBSD change by guenther@openbsd.org
http://www.mail-archive.com/source-changes@cvs.openbsd.org/msg01015.html

Bug: 3446659
Change-Id: Ie82116e358c541718d6709ec45ca6796be5a007b

1 files changed, 5 insertions, 1 deletions

diff --git a/libc/stdio/fwrite.c b/libc/stdio/fwrite.c
index 8a508dcdb..a97313ead 100644
--- a/libc/stdio/fwrite.c
+++ b/libc/stdio/fwrite.c
@@ -45,6 +45,7 @@ fwrite(const void *buf, size_t size, size_t count, FILE *fp)
 	size_t n;
 	struct __suio uio;
 	struct __siov iov;
+	int ret;
 
 	iov.iov_base = (void *)buf;
 	uio.uio_resid = iov.iov_len = n = count * size;
@@ -56,7 +57,10 @@ fwrite(const void *buf, size_t size, size_t count, FILE *fp)
 	 * skip the divide if this happens, since divides are
 	 * generally slow and since this occurs whenever size==0.
 	 */
-	if (__sfvwrite(fp, &uio) == 0)
+	FLOCKFILE(fp);
+	ret = __sfvwrite(fp, &uio);
+	FUNLOCKFILE(fp);
+	if (ret == 0)
 		return (count);
 	return ((n - uio.uio_resid) / size);
 }