Update comments on Windows job objects

Author: ChrisDenton

src/bootstrap/bootstrap.py

@@ -1184,6 +1184,8 @@ def bootstrap(args):
     args = [build.bootstrap_binary()]
     args.extend(sys.argv[1:])
     env = os.environ.copy()
+    # The Python process ID is used when creating a Windows job object
+    # (see src\bootstrap\src\utils\job.rs)
     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
     env["BOOTSTRAP_PYTHON"] = sys.executable
     run(args, env=env, verbose=build.verbose, is_bootstrap=True)

src/bootstrap/src/utils/job.rs

@@ -15,11 +15,12 @@ pub unsafe fn setup(build: &mut crate::Build) {
 ///
 /// Most of the time when you're running a build system (e.g., make) you expect
 /// Ctrl-C or abnormal termination to actually terminate the entire tree of
-/// process in play, not just the one at the top. This currently works "by
+/// processes in play. This currently works "by
 /// default" on Unix platforms because Ctrl-C actually sends a signal to the
-/// *process group* rather than the parent process, so everything will get torn
-/// down. On Windows, however, this does not happen and Ctrl-C just kills the
-/// parent process.
+/// *process group* so everything will get torn
+/// down. On Windows, however, Ctrl-C is only sent to processes in the same console.
+/// If a process is detached or attached to another console, it won't receive the
+/// signal.
 ///
 /// To achieve the same semantics on Windows we use Job Objects to ensure that
 /// all processes die at the same time. Job objects have a mode of operation