xargs: kill children when interrupted by Ctrl-C

A user was running the following command in a clone of the
busybox-w32 repo from a busybox-w32 shell using Git for Windows:

   git rev-list --all | xargs git grep main.c

Using Ctrl-C to interrupt the command resulted in the familiar
problem that two processes ended up competing for user input:
in this case the busybox-w32 shell and the Git for Windows pager,
less.

Make the problem go away (in this particular case) by killing all
the children of xargs when it's interrupted.  This is probably a
sensible thing to do for other circumstances too.

Adds 64-100 bytes.

(GitHub issue #306)

1 files changed, 42 insertions, 3 deletions

diff --git a/findutils/xargs.c b/findutils/xargs.c
index d6cdec22e..1023f80a3 100644
--- a/findutils/xargs.c
+++ b/findutils/xargs.c
@@ -121,9 +121,12 @@ struct globals {
 #if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
         int running_procs;
         int max_procs;
-#if ENABLE_PLATFORM_MINGW32
+# if ENABLE_PLATFORM_MINGW32
         HANDLE *procs;
+# endif
 #endif
+#if ENABLE_PLATFORM_MINGW32
+        pid_t pid;
 #endif
         smalluint xargs_exitcode;
 #if ENABLE_FEATURE_XARGS_SUPPORT_QUOTES
@@ -189,6 +192,35 @@ enum {
         IF_FEATURE_XARGS_SUPPORT_ARGS_FILE(   "a:")
 
 
+#if ENABLE_PLATFORM_MINGW32
+static BOOL WINAPI ctrl_handler(DWORD dwCtrlType)
+{
+        if (dwCtrlType == CTRL_C_EVENT || dwCtrlType == CTRL_BREAK_EVENT) {
+# if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
+                if (G.max_procs == 1)
+# endif
+                {
+                        if (G.pid > 0)
+                                kill(-G.pid, SIGTERM);
+                }
+# if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
+                else {
+                        int i;
+
+                        for (i = 0; i < G.running_procs; ++i) {
+                                pid_t pid = GetProcessId(G.procs[i]);
+                                if (pid > 0)
+                                        kill(-pid, SIGTERM);
+                        }
+                }
+# endif
+                exit(128 + SIGINT);
+                return TRUE;
+        }
+        return FALSE;
+}
+#endif
+
 #if ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL && ENABLE_PLATFORM_MINGW32
 static int wait_for_slot(int *idx)
 {
@@ -255,10 +287,11 @@ static int xargs_exec(void)
 #if !ENABLE_FEATURE_XARGS_SUPPORT_PARALLEL
         status = spawn_and_wait(G.args);
 #else
+#if ENABLE_PLATFORM_MINGW32
         if (G.max_procs == 1) {
-                status = spawn_and_wait(G.args);
+                G.pid = spawn(G.args);
+                status = G.pid < 0 ? -1 : wait4pid(G.pid);
         } else {
-#if ENABLE_PLATFORM_MINGW32
                 int idx;
                 status = !G.running_procs && !G.max_procs ? 0 : wait_for_slot(&idx);
                 if (G.max_procs) {
@@ -275,6 +308,9 @@ static int xargs_exec(void)
                         }
                 }
 #else
+        if (G.max_procs == 1) {
+                status = spawn_and_wait(G.args);
+        } else {
                 pid_t pid;
                 int wstat;
  again:
@@ -723,6 +759,9 @@ int xargs_main(int argc UNUSED_PARAM, char **argv)
 
         INIT_G();
 
+#if ENABLE_PLATFORM_MINGW32
+        SetConsoleCtrlHandler(ctrl_handler, TRUE);
+#endif
         opt = getopt32long(argv, OPTION_STR,
                 "no-run-if-empty\0" No_argument "r",
                 &max_args, &max_chars, &G.eof_str, &G.eof_str