Sending an arbitrary Signal in Windows?

In Windows everything revolves around Win32 messages. I do not believe there is a command line tool to do this, but in C++ you could use FindWindow to send an arbitrary message to another Windows program. e.g.:

#define WM_MYMSG  ( WM_USER+0x100 )
HWND h = ::FindWindow(NULL,_T("Win32App"));
if (h) {
    ::PostMessage(h, WM_MYMSG, 0, 0);
}

This can also be done in C# using com interop.

Windows is not POSIX. It does not have signals. The only 'signals' that console programs get is if they call SetConsoleCtrlHandler, in which case it can be notified that the user has pressed Ctrl+C, Ctrl+Break, closed the console window, logged off, or shut the system down.

Everything else is done with IPC, typically with window messages or RPC. Check Sun's documentation to see if there's a way to do what you're asking on the Windows JRE.

If what you want is to explicitly/programmatically kill another program/process of any kind, within the SysInternals' pstools there is a small tool named "pskill" that behaves just like Unixen "kill" would do.

If you want something else, keep reading (though I may be wrong on some of the specifics below - it's been eons since I last developed a Windows program in C using only the WinAPI and Charles Petzold's excellent books "Programming for Windows" as a guide).

On Windows you don't properly have "signals", what functions WinMain and WinProc receive from the Operating System are simple messages. For instance, when you click on the "X" button of a window, Windows sends that windows' handler the message WM_CLOSE. When the window's deleted but program's still running, it sends WM_DESTROY. When it's about to get out of the main message processing loop, WinMain (not WinProc) receives WM_QUIT. Your program should respond to all these as expected - you can actually develop an "unclosable" application by not doing what it should upon receiving a WM_CLOSE.

When user selects the task from Windows Task Manager and clicks "End Task", the OS will send WM_CLOSE (and another one I don't remember). If you use "End Process", though, the process is killed directly, no messages sent ever (source: The Old New Thing)

I remember there was a way to get the HWND of another process' window, once you get that another process could send that window a message thru functions PostMessage and DispatchMessage.