Do Windows apps support SIGINT for user-defined signal handlers?

Question

The specs say:

SIGINT is not supported for any Win32 application. When a CTRL+C interrupt occurs, Win32 operating systems generate a new thread to specifically handle that interrupt. This can cause a single-thread application, such as one in UNIX, to become multithreaded and cause unexpected behavior.

I think it means by default, the SIG_DFL handler for SIGINT will create a new thread, handle the signal then terminate the program. I'd like to know, does Windows support user-defined SIGINT handler, or will the handler ignored by the OS and the default SIG_DFL handler will run if a CTRL+C interrupt occurs?

For example, will the following code print Signaled!?

#include <signal.h>
#include <stdio.h>

volatile sig_atomic_t signaled = 0;
void signal_handler(int) { signaled = 1; }

int main() {
    signal(SIGINT, signal_handler);
    while (!signaled) {}
    printf("Signaled!\n");
}

Answer 1

Actually Win32 does fire SIGINT on Ctrl-C, with a couple of caveats:

• it is fired from another thread (created by the OS),
• it needs to be re-armed after each hit.

The second point introduces a race condition, and so it might be better to use the Win32 native SetConsoleCtrlHandler instead.

See also this note in the Windows signal documentation:

SIGINT is not supported for any Win32 application. When a CTRL+C interrupt occurs, Win32 operating systems generate a new thread to specifically handle that interrupt. This can cause a single-thread application, such as one in UNIX, to become multithreaded and cause unexpected behavior.