fixup! mingw: kill unterminated child processes on signals

This reverts the change where we tried to make sure that child processes
are killed upon exit of the git.exe process.

This change was misguided: it wanted to pretend that each process was
responsible to signal its child processes upon receiving a signal. But
it is the responsibility of the syscall `signal()` (or in the case of
Windows, either MSYS2's signal() or whoever wanted to terminate the
git.exe process) to take care of the child processes.

We just changed the MSYS2 runtime accordingly, in the hope that this
addresses the Ctrl+C problems (stale .git/index.lock files, runaway
git-remote-https when interrupting a clone, killed pager when hitting
Ctrl+C in `git log`, interrupting node.js processes that listen to
SIGINT, C# programs installing a ConsoleCtrlHandler, etc) once and for
all.

This commit is part of the fix, as pressing Ctrl+C while `git log` is
running would kill the pager otherwise (it is a child process of git.exe
after all).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

compat/mingw.c

@@ -1528,39 +1528,6 @@ struct pinfo_t {
 static struct pinfo_t *pinfo = NULL;
 CRITICAL_SECTION pinfo_cs;
 
-#ifndef SIGRTMAX
-#define SIGRTMAX 63
-#endif
-
-static void kill_child_processes_on_signal(void)
-{
-	DWORD status;
-
-	/*
-	 * Only continue if the process was terminated by a signal, as
-	 * indicated by the exit status (128 + sig_no).
-	 *
-	 * As we are running in an atexit() handler, the exit code has been
-	 * set at this stage by the ExitProcess() function already.
-	 */
-	if (!GetExitCodeProcess(GetCurrentProcess(), &status) ||
-	    status <= 128 || status > 128 + SIGRTMAX)
-		return;
-
-	EnterCriticalSection(&pinfo_cs);
-
-	while (pinfo) {
-		struct pinfo_t *info = pinfo;
-		pinfo = pinfo->next;
-		if (exit_process(info->proc, status))
-			/* the handle is still valid in case of error */
-			CloseHandle(info->proc);
-		free(info);
-	}
-
-	LeaveCriticalSection(&pinfo_cs);
-}
-
 static int is_msys2_sh(const char *cmd)
 {
 	if (cmd && !strcmp(cmd, "sh")) {
@@ -1593,7 +1560,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 			      const char *dir, const char *prepend_cmd,
 			      int fhin, int fhout, int fherr)
 {
-	static int atexit_handler_initialized, restrict_handle_inheritance = 1;
+	static int restrict_handle_inheritance = 1;
 	STARTUPINFOEXW si;
 	PROCESS_INFORMATION pi;
 	LPPROC_THREAD_ATTRIBUTE_LIST attr_list = NULL;
@@ -1609,17 +1576,6 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	const char *(*quote_arg)(const char *arg) =
 		is_msys2_sh(*argv) ? quote_arg_msys2 : quote_arg_msvc;
 
-	if (!atexit_handler_initialized) {
-		atexit_handler_initialized = 1;
-		/*
-		 * On Windows, there is no POSIX signaling. Instead, we inject
-		 * a thread calling ExitProcess(128 + sig_no); and that calls
-		 * the *atexit* handlers. Catch this condition and kill child
-		 * processes with the same signal.
-		 */
-		atexit(kill_child_processes_on_signal);
-	}
-
 	do_unset_environment_variables();
 
 	/* Determine whether or not we are associated to a console */