Use file locking on the save file to prevent corruption from running Crawl twice.

This fixes Mantis 2061.

I did not reuse the existing lk_open() because it's non-portable, waits for the
lock to become available and works using FILE* not a descriptor (bad for random
access).

1 files changed, 32 insertions, 0 deletions

diff --git a/crawl-ref/source/syscalls.cc b/crawl-ref/source/syscalls.cc
new file mode 100644
index 0000000000..c223b7db98
--- /dev/null
+++ b/crawl-ref/source/syscalls.cc
@@ -0,0 +1,32 @@
+/*
+ *  File:       syscalls.cc
+ *  Summary:    Wrappers for sys/libc calls, mostly for charset purposes.
+ *  Written by: Adam Borowski
+ */
+
+#include "AppHdr.h"
+#include "syscalls.h"
+
+#ifdef TARGET_OS_WINDOWS
+
+// FIXME!  This file doesn't yet use rename() (but we'll redefine it anyway once
+// charset handling comes).
+#undef rename
+
+#include <io.h>
+#endif
+
+bool lock_file(int fd)
+{
+#ifdef TARGET_OS_WINDOWS
+    return !!LockFile((HANDLE)_get_osfhandle(fd), 0, 0, -1, -1);
+#else
+    struct flock fl;
+    fl.l_type = F_WRLCK;
+    fl.l_whence = SEEK_SET;
+    fl.l_start = 0;
+    fl.l_len = 0;
+
+    return !fcntl(fd, F_SETLK, &fl);
+#endif
+}