Implement blocking file locking API for windows

lib/std/fs.zig

@@ -708,7 +708,12 @@ pub const Dir = struct {
         const access_mask = w.SYNCHRONIZE |
             (if (flags.read) @as(u32, w.GENERIC_READ) else 0) |
             (if (flags.write) @as(u32, w.GENERIC_WRITE) else 0);
-        return self.openFileWindows(sub_path_w, access_mask, w.FILE_OPEN);
+        const share_access = if (flags.lock)
+            w.FILE_SHARE_DELETE |
+                (if (flags.write) @as(os.windows.ULONG, 0) else w.FILE_SHARE_READ)
+        else
+            null;
+        return self.openFileWindows(sub_path_w, access_mask, share_access, w.FILE_OPEN);
     }
 
     /// Creates, opens, or overwrites a file with write access.
@@ -753,7 +758,7 @@ pub const Dir = struct {
             @as(u32, w.FILE_OVERWRITE_IF)
         else
             @as(u32, w.FILE_OPEN_IF);
-        return self.openFileWindows(sub_path_w, access_mask, creation);
+        return self.openFileWindows(sub_path_w, access_mask, null, creation);
     }
 
     /// Deprecated; call `openFile` directly.
@@ -775,8 +780,11 @@ pub const Dir = struct {
         self: Dir,
         sub_path_w: [*:0]const u16,
         access_mask: os.windows.ACCESS_MASK,
+        share_access_opt: ?os.windows.ULONG,
         creation: os.windows.ULONG,
     ) File.OpenError!File {
+        var delay: usize = 1;
+        while (true) {
             const w = os.windows;
 
             if (sub_path_w[0] == '.' and sub_path_w[1] == 0) {
@@ -808,6 +816,7 @@ pub const Dir = struct {
                 .SecurityQualityOfService = null,
             };
             var io: w.IO_STATUS_BLOCK = undefined;
+            const share_access = share_access_opt orelse w.FILE_SHARE_WRITE | w.FILE_SHARE_READ | w.FILE_SHARE_DELETE;
             const rc = w.ntdll.NtCreateFile(
                 &result.handle,
                 access_mask,
@@ -815,7 +824,7 @@ pub const Dir = struct {
                 &io,
                 null,
                 w.FILE_ATTRIBUTE_NORMAL,
-            w.FILE_SHARE_WRITE | w.FILE_SHARE_READ | w.FILE_SHARE_DELETE,
+                share_access,
                 creation,
                 w.FILE_NON_DIRECTORY_FILE | w.FILE_SYNCHRONOUS_IO_NONALERT,
                 null,
@@ -828,7 +837,17 @@ pub const Dir = struct {
                 .OBJECT_PATH_NOT_FOUND => return error.FileNotFound,
                 .NO_MEDIA_IN_DEVICE => return error.NoDevice,
                 .INVALID_PARAMETER => unreachable,
-            .SHARING_VIOLATION => return error.SharingViolation,
+                .SHARING_VIOLATION => {
+                    // TODO: check if async or blocking
+                    //return error.SharingViolation
+                    // Sleep so we don't consume a ton of CPU waiting to get lock on file
+                    std.time.sleep(delay);
+                    // Increase sleep time as long as it is less than 5 seconds
+                    if (delay < 5 * std.time.ns_per_s) {
+                        delay *= 2;
+                    }
+                    continue;
+                },
                 .ACCESS_DENIED => return error.AccessDenied,
                 .PIPE_BUSY => return error.PipeBusy,
                 .OBJECT_PATH_SYNTAX_BAD => unreachable,
@@ -836,6 +855,7 @@ pub const Dir = struct {
                 else => return w.unexpectedStatus(rc),
             }
         }
+    }
 
     pub fn makeDir(self: Dir, sub_path: []const u8) !void {
         try os.mkdirat(self.fd, sub_path, default_new_dir_mode);

lib/std/os.zig

@@ -1141,8 +1141,8 @@ pub fn freeNullDelimitedEnvMap(allocator: *mem.Allocator, envp_buf: []?[*:0]u8)
 }
 
 /// Attempts to get lock the file, blocking if the file is locked.
-pub fn fcntlFlockBlocking(fd: fd_t, flock_p: *flock) OpenError!void {
-    const rc = system.fcntlFlock(fd, F_SETLKW, flock_p);
+pub fn fcntlFlockBlocking(fd: fd_t, flock_p: *const flock) OpenError!void {
+    const rc = system.fcntl(fd, F_SETLKW, flock_p);
     if (rc < 0) {
         std.debug.panic("fcntl error: {}\n", .{rc});
     }

lib/std/os/bits/linux/i386.zig

@@ -8,6 +8,7 @@ const iovec = linux.iovec;
 const iovec_const = linux.iovec_const;
 const uid_t = linux.uid_t;
 const gid_t = linux.gid_t;
+const pid_t = linux.pid_t;
 const stack_t = linux.stack_t;
 const sigset_t = linux.sigset_t;
 

lib/std/os/linux.zig

@@ -219,7 +219,7 @@ pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, of
     }
 }
 
-pub fn fcntlFlock(fd: fd_t, cmd: i32, flock_p: *flock) usize {
+pub fn fcntl(fd: fd_t, cmd: i32, flock_p: *const c_void) usize {
     return syscall3(SYS_fcntl, @bitCast(usize, @as(isize, fd)), @bitCast(usize, @as(isize, cmd)), @ptrToInt(flock_p));
 }