git-compat-util: add fallbacks for unlocked stdio

POSIX.1-2001 specifies some functions for optimizing the
locking out of tight getc() loops. Not all systems are
POSIX, though, and even not all POSIX systems are required
to implement these functions. We can check for the
feature-test macro to see if they are available, and if not,
provide a noop implementation.

There's no Makefile knob here, because we should just detect
this automatically. If there are very bizarre systems, we
may need to add one, but it's not clear yet in which
direction:

1. If a system defines _POSIX_THREAD_SAFE_FUNCTIONS but
these functions are missing or broken, we would want a
knob to manually turn them off.

2. If a system has these functions but does not define
_POSIX_THREAD_SAFE_FUNCTIONS, we would want a knob to
manually turn them on.

We can add such a knob when we find a real-world system that
matches this.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-compat-util.h b/git-compat-util.h
index bc8fc8cf854e96badfdf4d96673d33b799207ff3..685a0a4063edd2a6700533df7faa2a910df60bb3 100644 (file)
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -883,4 +883,10 @@ struct tm *git_gmtime_r(const time_t *, struct tm *);
 # define SHELL_PATH "/bin/sh"
 #endif
 
+#ifndef _POSIX_THREAD_SAFE_FUNCTIONS
+#define flockfile(fh)
+#define funlockfile(fh)
+#define getc_unlocked(fh) getc(fh)
+#endif
+
 #endif