save&undo libev's SICHLD handler when installed; install it when first child...

save&undo libev's SICHLD handler when installed; install it when first child is created or when install_sigchld() is called

gevent/core.ppyx

@@ -244,7 +244,7 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
             if _default_loop_destroyed:
                 default = False
             if default:
-                self._ptr = libev.ev_default_loop(c_flags)
+                self._ptr = libev.gevent_ev_default_loop(c_flags)
                 if not self._ptr:
                     raise SystemError("ev_default_loop(%s) failed" % (c_flags, ))
                 libev.ev_prepare_start(self._ptr, &self._signal_checker)
@@ -421,6 +421,9 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
     def child(self, int pid, bint trace=0, ref=True):
         return child(self, pid, trace, ref)
 
+    def install_sigchld(self):
+        libev.gevent_install_sigchld_handler()
+
 #endif
 
     def stat(self, bytes path, float interval=0.0, ref=True, priority=None):
@@ -851,6 +854,7 @@ cdef public class child(watcher) [object PyGeventChildObject, type PyGeventChild
     def __init__(self, loop loop, int pid, bint trace=0, ref=True):
         if not loop.default:
             raise TypeError('child watchers are only available on the default loop')
+        libev.gevent_install_sigchld_handler()
         libev.ev_child_init(&self._watcher, <void *>gevent_callback_child, pid, trace)
         self.loop = loop
         if ref:

gevent/libev.h

@@ -2,4 +2,43 @@
 #include "ev.c"
 #else
 #include "ev.h"
+
+#if EV_CHILD_ENABLE
+#include <signal.h>
+#endif
+
+#endif
+
+#if EV_CHILD_ENABLE
+
+static struct sigaction libev_sigchld;
+static int sigchld_state = 0;
+
+static struct ev_loop* gevent_ev_default_loop(unsigned int flags)
+{
+    if (sigchld_state)
+        return ev_default_loop(flags);
+    struct ev_loop* result;
+    struct sigaction tmp;
+    sigaction(SIGCHLD, NULL, &tmp);
+    result = ev_default_loop(flags);
+    // XXX what if SIGCHLD received there?
+    sigaction(SIGCHLD, &tmp, &libev_sigchld);
+    sigchld_state = 1;
+    return result;
+}
+
+
+static void gevent_install_sigchld_handler(void) {
+    if (sigchld_state == 1) {
+        sigaction(SIGCHLD, &libev_sigchld, NULL);
+        sigchld_state = 2;
+    }
+}
+
+#else
+
+#define gevent_ev_default_loop ev_default_loop
+static void gevent_install_sigchld_handler(void) { }
+
 #endif

gevent/libev.pxd

@@ -185,3 +185,6 @@ cdef extern from "libev.h":
     void ev_unref(ev_loop*)
     void ev_break(ev_loop*, int)
     unsigned int ev_pending_count(ev_loop*)
+
+    ev_loop* gevent_ev_default_loop(unsigned int flags)
+    void gevent_install_sigchld_handler()

gevent/subprocess.py

@@ -598,6 +598,8 @@ class Popen(object):
             if executable is None:
                 executable = args[0]
 
+            self._loop.install_sigchld()
+
             # For transferring possible exec failure from child to parent
             # The first char specifies the exception type: 0 means
             # OSError, 1 means some other error.