downgradeLock
Assumes the file is already locked in exclusive mode. Atomically modifies the lock to be in shared mode, without releasing it.
TODO: integrate with async I/O
Function parameters
Parameters
Type definitions in this namespace
Types
- Permissions
- Cross-platform representation of permissions on a file.
- Reader
- Memoizes key information about a file handle such as:
Functions in this namespace
Functions
- close
- Upon success, the stream is in an uninitialized state.
- sync
- Blocks until all pending file contents and metadata modifications
- isTty
- Test whether the file refers to a terminal.
- getOrEnableAnsiEscapeSupport
- Returns whether or not ANSI escape codes will be treated as such,
- supportsAnsiEscapeCodes
- Test whether ANSI escape codes will be treated as such without
- setEndPos
- Shrinks or expands the file.
- seekBy
- Repositions read/write file offset relative to the current offset.
- seekFromEnd
- Repositions read/write file offset relative to the end.
- seekTo
- Repositions read/write file offset relative to the beginning.
- getPos
- TODO: integrate with async I/O
- getEndPos
- TODO: integrate with async I/O
- mode
- TODO: integrate with async I/O
- stat
- Returns `Stat` containing basic information about the `File`.
- chmod
- Changes the mode of the file.
- chown
- Changes the owner and group of the file.
- setPermissions
- Sets permissions according to the provided `Permissions` struct.
- updateTimes
- The underlying file system may have a different granularity than nanoseconds,
- readToEndAlloc
- Deprecated in favor of `Reader`.
- readToEndAllocOptions
- Deprecated in favor of `Reader`.
- readAll
- Deprecated in favor of `Reader`.
- pread
- On Windows, this function currently does alter the file pointer.
- preadAll
- Deprecated in favor of `Reader`.
- readv
- See https://github.com/ziglang/zig/issues/7699
- readvAll
- Deprecated in favor of `Reader`.
- preadv
- See https://github.com/ziglang/zig/issues/7699
- preadvAll
- Deprecated in favor of `Reader`.
- writeAll
- Deprecated in favor of `Writer`.
- pwrite
- On Windows, this function currently does alter the file pointer.
- pwriteAll
- Deprecated in favor of `Writer`.
- writev
- See https://github.com/ziglang/zig/issues/7699
- writevAll
- Deprecated in favor of `Writer`.
- pwritev
- See https://github.com/ziglang/zig/issues/7699
- pwritevAll
- Deprecated in favor of `Writer`.
- copyRange
- Deprecated in favor of `Writer`.
- copyRangeAll
- Deprecated in favor of `Writer`.
- deprecatedReader
- Deprecated in favor of `Reader`.
- deprecatedWriter
- Deprecated in favor of `Writer`.
- reader
- Defaults to positional reading; falls back to streaming.
- readerStreaming
- Positional is more threadsafe, since the global seek position is not
- writer
- Defaults to positional reading; falls back to streaming.
- writerStreaming
- Positional is more threadsafe, since the global seek position is not
- lock
- Blocks when an incompatible lock is held by another process.
- unlock
- Assumes the file is locked.
- tryLock
- Attempts to obtain a lock, returning `true` if the lock is
- downgradeLock
- Assumes the file is already locked in exclusive mode.
Error sets in this namespace
Error Sets
= posix.fd_t
Values
Source
Implementation
pub fn downgradeLock(file: File) LockError!void {
if (is_windows) {
// On Windows it works like a semaphore + exclusivity flag. To implement this
// function, we first obtain another lock in shared mode. This changes the
// exclusivity flag, but increments the semaphore to 2. So we follow up with
// an NtUnlockFile which decrements the semaphore but does not modify the
// exclusivity flag.
var io_status_block: windows.IO_STATUS_BLOCK = undefined;
windows.LockFile(
file.handle,
null,
null,
null,
&io_status_block,
&range_off,
&range_len,
null,
windows.TRUE, // non-blocking=true
windows.FALSE, // exclusive=false
) catch |err| switch (err) {
error.WouldBlock => unreachable, // File was not locked in exclusive mode.
else => |e| return e,
};
return windows.UnlockFile(
file.handle,
&io_status_block,
&range_off,
&range_len,
null,
) catch |err| switch (err) {
error.RangeNotLocked => unreachable, // File was not locked.
error.Unexpected => unreachable, // Resource deallocation must succeed.
};
} else {
return posix.flock(file.handle, posix.LOCK.SH | posix.LOCK.NB) catch |err| switch (err) {
error.WouldBlock => unreachable, // File was not locked in exclusive mode.
else => |e| return e,
};
}
}