File locks now work on Windows (#480)

* File locks now work on Windows

Uses LockFileEx() and UnlockFileEx(). Fixes HDFFV-10191 (partial).

* Committing clang-format changes

* Committing clang-format changes

* Fixes commenting in h5repack

* Reworks H5Fis_accessible()

H5Fis_accessible() created a new file handle and attempted to read
through it, which will fail when a file has been opened with an
exclusive lock on operating systems that have mandatory locks.

This change uses the same scheme we use in H5Fopen() to check if
the file is already open and only tries to read the file signature
if the file has not already been opened.

Also adds a test for this behavior.

* Committing clang-format changes

* Trivial change to force github to run actions

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

1 files changed, 27 insertions, 24 deletions

diff --git a/src/H5system.c b/src/H5system.c
index 1d94816..745476d 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -618,40 +618,43 @@ c99_vsnprintf(char *str, size_t size, const char *format, va_list ap)
  *-------------------------------------------------------------------------
  */
 int
-Wflock(int H5_ATTR_UNUSED fd, int H5_ATTR_UNUSED operation)
+Wflock(int fd, int operation)
 {
 
-/* This is a no-op while we implement a Win32 VFD */
-#if 0
-int
-Wflock(int fd, int operation) {
-
-    HANDLE          hFile;
-    DWORD           dwFlags = LOCKFILE_FAIL_IMMEDIATELY;
-    DWORD           dwReserved = 0;
-                    /* MAXDWORD for entire file */
-    DWORD           nNumberOfBytesToLockLow = MAXDWORD;
-    DWORD           nNumberOfBytesToLockHigh = MAXDWORD;
-                    /* Must initialize OVERLAPPED struct */
-    OVERLAPPED      overlapped = {0};
+    HANDLE hFile;
+    DWORD  dwFlags    = LOCKFILE_FAIL_IMMEDIATELY;
+    DWORD  dwReserved = 0;
+    /* MAXDWORD locks the entire file */
+    DWORD nNumberOfBytesToLockLow  = MAXDWORD;
+    DWORD nNumberOfBytesToLockHigh = MAXDWORD;
+    /* Must initialize OVERLAPPED struct */
+    OVERLAPPED overlapped = {0};
 
     /* Get Windows HANDLE */
-    hFile = _get_osfhandle(fd);
+    if (INVALID_HANDLE_VALUE == (hFile = (HANDLE)_get_osfhandle(fd)))
+        return -1;
 
     /* Convert to Windows flags */
-    if(operation & LOCK_EX)
+    if (operation & LOCK_EX)
         dwFlags |= LOCKFILE_EXCLUSIVE_LOCK;
 
     /* Lock or unlock */
-    if(operation & LOCK_UN)
-        if(0 == UnlockFileEx(hFile, dwReserved, nNumberOfBytesToLockLow,
-                            nNumberOfBytesToLockHigh, &overlapped))
-            return -1;
-    else
-        if(0 == LockFileEx(hFile, dwFlags, dwReserved, nNumberOfBytesToLockLow,
-                            nNumberOfBytesToLockHigh, &overlapped))
+    if (operation & LOCK_UN) {
+        if (0 ==
+            UnlockFileEx(hFile, dwReserved, nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh, &overlapped)) {
+            /* Attempting to unlock an already unlocked file will fail and this can happen
+             * in H5Fstart_swmr_write(). For now, just ignore the "error" (error code: 0x9e / 158).
+             */
+            if (GetLastError() != 158)
+                return -1;
+        }
+    }
+    else {
+        if (0 == LockFileEx(hFile, dwFlags, dwReserved, nNumberOfBytesToLockLow, nNumberOfBytesToLockHigh,
+                            &overlapped))
             return -1;
-#endif /* 0 */
+    }
+
     return 0;
 } /* end Wflock() */