os: filesystem level locking api (#11191)

vlib/os/filelock/filelock_test.v

@@ -0,0 +1,27 @@
+import os
+import os.filelock
+
+fn test_flock() {
+	lockfile := 'test.lock'
+	mut l := filelock.new(lockfile)
+	assert !os.exists(lockfile)
+	l.acquire() or { panic(err) }
+	assert os.exists(lockfile)
+	// do stuff
+	l.release()
+	assert !os.exists(lockfile)
+}
+
+fn test_flock_try() {
+	lockfile := 'test-try.lock'
+	mut l := filelock.new(lockfile)
+	assert l.try_acquire()
+	l.release()
+	assert !os.exists(lockfile)
+	assert l.try_acquire()
+	assert os.exists(lockfile)
+	l.release()
+	assert l.try_acquire()
+	l.release()
+	assert !os.exists(lockfile)
+}

vlib/os/filelock/lib.v

@@ -0,0 +1,14 @@
+module filelock
+
+pub struct FileLock {
+	name string
+mut:
+	fd int
+}
+
+pub fn new(fileName string) FileLock {
+	return FileLock{
+		name: fileName
+		fd: -1
+	}
+}

vlib/os/filelock/lib_nix.c.v

@@ -0,0 +1,82 @@
+module filelock
+
+import time
+
+#include <sys/file.h>
+
+fn C.unlink(&char) int
+fn C.open(&char, int, int) int
+fn C.flock(int, int) int
+
+[unsafe]
+pub fn (mut l FileLock) unlink() {
+	if l.fd != -1 {
+		C.close(l.fd)
+		l.fd = -1
+	}
+	C.unlink(&char(l.name.str))
+}
+
+pub fn (mut l FileLock) acquire() ?bool {
+	if l.fd != -1 {
+		// lock already acquired by this instance
+		return false
+	}
+	fd := open_lockfile(l.name)
+	if fd == -1 {
+		return error('cannot create lock file $l.name')
+	}
+	if C.flock(fd, C.LOCK_EX) == -1 {
+		C.close(fd)
+		return error('cannot lock')
+	}
+	l.fd = fd
+	return true
+}
+
+pub fn (mut l FileLock) release() bool {
+	if l.fd != -1 {
+		unsafe {
+			l.unlink()
+		}
+		return true
+	}
+	return false
+}
+
+pub fn (mut l FileLock) wait_acquire(s int) ?bool {
+	fin := time.now().add(s)
+	for time.now() < fin {
+		if l.try_acquire() {
+			return true
+		}
+		C.usleep(1000)
+	}
+	return false
+}
+
+fn open_lockfile(f string) int {
+	mut fd := C.open(&char(f.str), C.O_CREAT, 0o644)
+	if fd == -1 {
+		// if stat is too old delete lockfile
+		fd = C.open(&char(f.str), C.O_RDONLY, 0)
+	}
+	return fd
+}
+
+pub fn (mut l FileLock) try_acquire() bool {
+	if l.fd != -1 {
+		return true
+	}
+	fd := open_lockfile('$l.name')
+	if fd != -1 {
+		err := C.flock(fd, C.LOCK_EX | C.LOCK_NB)
+		if err == -1 {
+			C.close(fd)
+			return false
+		}
+		l.fd = fd
+		return true
+	}
+	return false
+}

vlib/os/filelock/lib_windows.c.v

@@ -0,0 +1,75 @@
+module filelock
+
+import time
+
+fn C.DeleteFileW(&u16) bool
+fn C.CreateFileW(&u16, u32, u32, voidptr, u32, u32, voidptr) voidptr
+fn C.CloseHandle(voidptr) bool
+
+pub fn (mut l FileLock) unlink() {
+	if l.fd != -1 {
+		C.CloseHandle(l.fd)
+		l.fd = -1
+	}
+	t_wide := l.name.to_wide()
+	C.DeleteFileW(t_wide)
+}
+
+pub fn (mut l FileLock) acquire() ?bool {
+	if l.fd != -1 {
+		// lock already acquired by this instance
+		return false
+	}
+	fd := open(l.name)
+	if fd == -1 {
+		return error('cannot create lock file $l.name')
+	}
+	l.fd = fd
+	return true
+}
+
+pub fn (mut l FileLock) release() bool {
+	if l.fd != -1 {
+		C.CloseHandle(l.fd)
+		l.fd = -1
+		t_wide := l.name.to_wide()
+		C.DeleteFileW(t_wide)
+		return true
+	}
+	return false
+}
+
+pub fn (mut l FileLock) wait_acquire(s int) ?bool {
+	fin := time.now().add(s)
+	for time.now() < fin {
+		if l.try_acquire() {
+			return true
+		}
+		time.sleep(1 * time.millisecond)
+	}
+	return false
+}
+
+fn open(f string) voidptr {
+	f_wide := f.to_wide()
+	// locking it
+	fd := C.CreateFileW(f_wide, C.GENERIC_READ | C.GENERIC_WRITE, 0, 0, C.OPEN_ALWAYS,
+		C.FILE_ATTRIBUTE_NORMAL, 0)
+	if fd == C.INVALID_HANDLE_VALUE {
+		fd == -1
+	}
+	return fd
+}
+
+pub fn (mut l FileLock) try_acquire() bool {
+	if l.fd != -1 {
+		// lock already acquired by this instance
+		return false
+	}
+	fd := open(l.name)
+	if fd == -1 {
+		return false
+	}
+	l.fd = fd
+	return true
+}

vlib/os/os_c.v

@@ -139,7 +139,7 @@ pub fn read_file(path string) ?string {
 // truncate changes the size of the file located in `path` to `len`.
 // Note that changing symbolic links on Windows only works as admin.
 pub fn truncate(path string, len u64) ? {
-	fp := C.open(&char(path.str), o_wronly | o_trunc)
+	fp := C.open(&char(path.str), o_wronly | o_trunc, 0)
 	defer {
 		C.close(fp)
 	}
@@ -236,7 +236,7 @@ pub fn cp(src string, dst string) ? {
 			return error_with_code('failed to copy $src to $dst', int(result))
 		}
 	} $else {
-		fp_from := C.open(&char(src.str), C.O_RDONLY)
+		fp_from := C.open(&char(src.str), C.O_RDONLY, 0)
 		if fp_from < 0 { // Check if file opened
 			return error_with_code('cp: failed to open $src', int(fp_from))
 		}