uzor-desktop 1.2.2

//! Cross-process single-instance guard.
//!
//! Ensures only one process with the given mutex name is running at a time.
//! On Windows, uses a named Win32 mutex. On other platforms, currently a no-op.

/// RAII guard that holds the Win32 named mutex for the lifetime of the process.
pub struct SingleInstanceGuard {
    #[cfg(target_os = "windows")]
    handle: isize,
}

impl Drop for SingleInstanceGuard {
    fn drop(&mut self) {
        #[cfg(target_os = "windows")]
        {
            if self.handle != 0 {
                extern "system" {
                    fn CloseHandle(h_object: isize) -> i32;
                }
                unsafe {
                    CloseHandle(self.handle);
                }
            }
        }
    }
}

/// Acquire single-instance guard.
///
/// If another process already holds the mutex for `mutex_name`:
/// - if `--wait-pid <pid>` is present in `std::env::args()`, wait for that pid
///   to exit, then retry the lock once
/// - otherwise, exit the process with status 0 (graceful "already running")
pub fn single_instance(mutex_name: &str) -> SingleInstanceGuard {
    #[cfg(target_os = "windows")]
    {
        extern "system" {
            fn CreateMutexW(
                lp_mutex_attributes: *const std::ffi::c_void,
                b_initial_owner: i32,
                lp_name: *const u16,
            ) -> isize;
            fn GetLastError() -> u32;
            fn OpenProcess(dw_desired_access: u32, b_inherit_handle: i32, dw_process_id: u32)
                -> isize;
            fn WaitForSingleObject(h_handle: isize, dw_milliseconds: u32) -> u32;
            fn CloseHandle(h_object: isize) -> i32;
        }

        const ERROR_ALREADY_EXISTS: u32 = 183;
        const SYNCHRONIZE: u32 = 0x00100000;
        const INFINITE: u32 = 0xFFFFFFFF;

        let wait_pid: Option<u32> = {
            let args: Vec<String> = std::env::args().collect();
            args.windows(2)
                .find(|w| w[0] == "--wait-pid")
                .and_then(|w| w[1].parse::<u32>().ok())
        };

        let name_utf16: Vec<u16> = {
            let mut v: Vec<u16> = mutex_name.encode_utf16().collect();
            v.push(0);
            v
        };

        let try_acquire = || -> (isize, bool) {
            let handle = unsafe { CreateMutexW(std::ptr::null(), 1, name_utf16.as_ptr()) };
            let already_exists =
                handle != 0 && unsafe { GetLastError() } == ERROR_ALREADY_EXISTS;
            (handle, already_exists)
        };

        let (handle, already_exists) = try_acquire();

        if already_exists {
            if let Some(pid) = wait_pid {
                eprintln!(
                    "[single-instance] another instance running — waiting for pid {} to exit",
                    pid
                );
                let proc_handle =
                    unsafe { OpenProcess(SYNCHRONIZE, 0, pid) };
                if proc_handle != 0 {
                    unsafe {
                        WaitForSingleObject(proc_handle, INFINITE);
                        CloseHandle(proc_handle);
                    }
                }
                if handle != 0 {
                    unsafe { CloseHandle(handle); }
                }
                let (handle2, already_exists2) = try_acquire();
                if already_exists2 {
                    eprintln!("[single-instance] still running after wait — exiting.");
                    std::process::exit(0);
                }
                if handle2 == 0 {
                    eprintln!(
                        "[single-instance] WARNING: CreateMutexW failed (error {}), continuing without single-instance guard",
                        unsafe { GetLastError() }
                    );
                }
                return SingleInstanceGuard { handle: handle2 };
            } else {
                eprintln!("[single-instance] another instance is already running — exiting.");
                std::process::exit(0);
            }
        }

        if handle == 0 {
            eprintln!(
                "[single-instance] WARNING: CreateMutexW failed (error {}), continuing without single-instance guard",
                unsafe { GetLastError() }
            );
        }

        SingleInstanceGuard { handle }
    }

    #[cfg(not(target_os = "windows"))]
    {
        let _ = mutex_name;
        SingleInstanceGuard {}
    }
}