mingw: work around irregular failures of unlink on windows

If a file is opened by another process (e.g. indexing of an IDE) for
reading it is not allowed to be deleted. So in case unlink fails retry
after waiting for some time. This extends the workaround from 6ac6f87.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -3,6 +3,8 @@
 #include <conio.h>
 #include "../strbuf.h"
 
+static const int delay[] = { 0, 1, 10, 20, 40 };
+
 int err_win_to_posix(DWORD winerr)
 {
 	int error = ENOSYS;
@@ -116,12 +118,38 @@ int err_win_to_posix(DWORD winerr)
 	return error;
 }
 
+static inline int is_file_in_use_error(DWORD errcode)
+{
+	switch (errcode) {
+	case ERROR_SHARING_VIOLATION:
+	case ERROR_ACCESS_DENIED:
+		return 1;
+	}
+
+	return 0;
+}
+
 #undef unlink
 int mingw_unlink(const char *pathname)
 {
+	int ret, tries = 0;
+
 	/* read-only files cannot be removed */
 	chmod(pathname, 0666);
-	return unlink(pathname);
+	while ((ret = unlink(pathname)) == -1 && tries < ARRAY_SIZE(delay)) {
+		if (!is_file_in_use_error(GetLastError()))
+			break;
+		/*
+		 * We assume that some other process had the source or
+		 * destination file open at the wrong moment and retry.
+		 * In order to give the other process a higher chance to
+		 * complete its operation, we give up our time slice now.
+		 * If we have to retry again, we do sleep a bit.
+		 */
+		Sleep(delay[tries]);
+		tries++;
+	}
+	return ret;
 }
 
 #undef open
@@ -1257,7 +1285,6 @@ int mingw_rename(const char *pold, const char *pnew)
 {
 	DWORD attrs, gle;
 	int tries = 0;
-	static const int delay[] = { 0, 1, 10, 20, 40 };
 
 	/*
 	 * Try native rename() first to get errno right.