Commit 71c5aab3e7
lib/std/fs/file.zig
@@ -36,22 +36,29 @@ pub const File = struct {
pub const OpenError = windows.CreateFileError || os.OpenError || os.FlockError;
+ pub const Lock = enum {
+ None, Shared, Exclusive
+ };
+
/// TODO https://github.com/ziglang/zig/issues/3802
pub const OpenFlags = struct {
read: bool = true,
write: bool = false,
- /// Open the file with exclusive access. If `write` is true, then the file is opened with an
- /// exclusive lock, meaning that no other processes can read or write to the file. Otherwise
- /// the file is opened with a shared lock, allowing the other processes to read from the
- /// file, but not to write to the file.
+ /// Open the file with a lock to prevent other processes from accessing it at the
+ /// same time. An exclusive lock will prevent other processes from acquiring a lock.
+ /// A shared lock will prevent other processes from acquiring a exclusive lock, but
+ /// doesn't prevent other process from getting their own shared locks.
///
/// Note that the lock is only advisory on Linux, except in very specific cirsumstances[1].
- /// This means that a process that does not respect the locking API can still read and write
+ /// This means that a process that does not respect the locking API can still get access
/// to the file, despite the lock.
///
+ /// Windows' file locks are mandatory, and any process attempting to access the file will
+ /// receive an error.
+ ///
/// [1]: https://www.kernel.org/doc/Documentation/filesystems/mandatory-locking.txt
- lock: bool = false,
+ lock: Lock = .None,
/// This prevents `O_NONBLOCK` from being passed even if `std.io.is_async`.
/// It allows the use of `noasync` when calling functions related to opening
@@ -72,14 +79,20 @@ pub const File = struct {
/// `error.FileAlreadyExists` to be returned.
exclusive: bool = false,
- /// Prevent other files from accessing this file while this process has it is open.
+ /// Open the file with a lock to prevent other processes from accessing it at the
+ /// same time. An exclusive lock will prevent other processes from acquiring a lock.
+ /// A shared lock will prevent other processes from acquiring a exclusive lock, but
+ /// doesn't prevent other process from getting their own shared locks.
///
/// Note that the lock is only advisory on Linux, except in very specific cirsumstances[1].
- /// This means that a process that does not respect the locking API can still read and write
+ /// This means that a process that does not respect the locking API can still get access
/// to the file, despite the lock.
///
+ /// Windows' file locks are mandatory, and any process attempting to access the file will
+ /// receive an error.
+ ///
/// [1]: https://www.kernel.org/doc/Documentation/filesystems/mandatory-locking.txt
- lock: bool = false,
+ lock: Lock = .None,
/// For POSIX systems this is the file system mode the file will
/// be created with.
lib/std/fs.zig
@@ -596,13 +596,12 @@ pub const Dir = struct {
}
// Use the O_ locking flags if the os supports them
- const has_flock_open_flags = @hasDecl(os, "O_EXLOCK") and @hasDecl(os, "O_SHLOCK");
- const lock_flag: u32 = lock_flag: {
- if (has_flock_open_flags and flags.lock) {
- break :lock_flag if (flags.write) @as(u32, os.O_EXLOCK) else @as(u32, os.O_SHLOCK);
- }
- break :lock_flag @as(u32, 0);
- };
+ const has_flock_open_flags = @hasDecl(os, "O_EXLOCK");
+ const lock_flag: u32 = if (has_flock_open_flags) switch (flags.lock) {
+ .None => @as(u32, 0),
+ .Shared => os.O_SHLOCK,
+ .Exclusive => os.O_EXLOCK,
+ } else 0;
const O_LARGEFILE = if (@hasDecl(os, "O_LARGEFILE")) os.O_LARGEFILE else 0;
const os_flags = lock_flag | O_LARGEFILE | os.O_CLOEXEC | if (flags.write and flags.read)
@@ -616,9 +615,13 @@ pub const Dir = struct {
else
try os.openatZ(self.fd, sub_path, os_flags, 0);
- if (!has_flock_open_flags and flags.lock) {
+ if (!has_flock_open_flags and flags.lock != .None) {
// TODO: integrate async I/O
- try os.flock(fd, if (flags.write) os.LOCK_EX else os.LOCK_SH);
+ try os.flock(fd, switch (flags.lock) {
+ .None => unreachable,
+ .Shared => os.LOCK_SH,
+ .Exclusive => os.LOCK_EX,
+ });
}
return File{
@@ -638,11 +641,13 @@ 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);
- 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;
+
+ const share_access = switch (flags.lock) {
+ .None => @as(?w.ULONG, null),
+ .Shared => w.FILE_SHARE_READ,
+ .Exclusive => @as(?w.ULONG, 0),
+ };
+
return @as(File, .{
.handle = try os.windows.OpenFileW(self.fd, sub_path_w, null, access_mask, share_access, w.FILE_OPEN),
.io_mode = .blocking,
@@ -672,7 +677,11 @@ pub const Dir = struct {
// Use the O_ locking flags if the os supports them
const has_flock_open_flags = @hasDecl(os, "O_EXLOCK");
- const lock_flag: u32 = if (has_flock_open_flags and flags.lock) os.O_EXLOCK else 0;
+ const lock_flag: u32 = if (has_flock_open_flags) switch (flags.lock) {
+ .None => @as(u32, 0),
+ .Shared => os.O_SHLOCK,
+ .Exclusive => os.O_EXLOCK,
+ } else 0;
const O_LARGEFILE = if (@hasDecl(os, "O_LARGEFILE")) os.O_LARGEFILE else 0;
const os_flags = lock_flag | O_LARGEFILE | os.O_CREAT | os.O_CLOEXEC |
@@ -684,9 +693,13 @@ pub const Dir = struct {
else
try os.openatZ(self.fd, sub_path_c, os_flags, flags.mode);
- if (!has_flock_open_flags and flags.lock) {
+ if (!has_flock_open_flags and flags.lock != .None) {
// TODO: integrate async I/O
- try os.flock(fd, os.LOCK_EX);
+ try os.flock(fd, switch (flags.lock) {
+ .None => unreachable,
+ .Shared => os.LOCK_SH,
+ .Exclusive => os.LOCK_EX,
+ });
}
return File{ .handle = fd, .io_mode = .blocking };
@@ -705,10 +718,12 @@ pub const Dir = struct {
else
@as(u32, w.FILE_OPEN_IF);
- const share_access = if (flags.lock)
- @as(os.windows.ULONG, w.FILE_SHARE_DELETE)
- else
- null;
+ const share_access = switch (flags.lock) {
+ .None => @as(?w.ULONG, null),
+ .Shared => w.FILE_SHARE_READ,
+ .Exclusive => @as(?w.ULONG, 0),
+ };
+
return @as(File, .{
.handle = try os.windows.OpenFileW(self.fd, sub_path_w, null, access_mask, share_access, creation),
.io_mode = .blocking,
@@ -1671,8 +1686,8 @@ test "open file with lock twice, make sure it wasn't open at the same time" {
const filename = "file_lock_test.txt";
var contexts = [_]FileLockTestContext{
- .{ .filename = filename, .create = true, .exclusive = true },
- .{ .filename = filename, .create = true, .exclusive = true },
+ .{ .filename = filename, .create = true, .lock = .Exclusive },
+ .{ .filename = filename, .create = true, .lock = .Exclusive },
};
try run_lock_file_test(&contexts);
@@ -1703,9 +1718,9 @@ test "create file, lock and read from multiple process at once" {
try std.fs.cwd().writeFile(filename, filedata);
var contexts = [_]FileLockTestContext{
- .{ .filename = filename, .create = false, .exclusive = false },
- .{ .filename = filename, .create = false, .exclusive = false },
- .{ .filename = filename, .create = false, .exclusive = true },
+ .{ .filename = filename, .create = false, .lock = .Shared },
+ .{ .filename = filename, .create = false, .lock = .Shared },
+ .{ .filename = filename, .create = false, .lock = .Exclusive },
};
try run_lock_file_test(&contexts);
@@ -1740,8 +1755,8 @@ const FileLockTestContext = struct {
// use file.createFile
create: bool,
- // get a read/write lock, instead of just a read lock
- exclusive: bool,
+ // the type of lock to use
+ lock: File.Lock,
// Output variables
err: ?(File.OpenError || std.os.ReadError) = null,
@@ -1756,12 +1771,12 @@ const FileLockTestContext = struct {
fn run(ctx: *@This()) void {
var file: File = undefined;
if (ctx.create) {
- file = cwd().createFile(ctx.filename, .{ .lock = true }) catch |err| {
+ file = cwd().createFile(ctx.filename, .{ .lock = ctx.lock }) catch |err| {
ctx.err = err;
return;
};
} else {
- file = cwd().openFile(ctx.filename, .{ .lock = true, .write = ctx.exclusive }) catch |err| {
+ file = cwd().openFile(ctx.filename, .{ .lock = ctx.lock }) catch |err| {
ctx.err = err;
return;
};