[glib] Partially revert "Merge waitpid() from g_spawn_sync into gmain()"

[Ryan Lortie <ryanl src gnome org>]

commit eb860fd898a6a2bd86c11d245294cd0e8cd4304b
Author: Ryan Lortie <desrt desrt ca>
Date:   Tue Apr 23 13:26:48 2013 -0400

    Partially revert "Merge waitpid() from g_spawn_sync into gmain()"
    
    This partially reverts commit ce0022933c255313e010b27f977f4ae02aad1e7e.
    
    It used to be safe to use g_spawn_sync() from processes that had their
    own SIGCHLD handler because it simply called wait().  When it was
    changed to depend on the GLib child watching infrastructure this meant
    that GLib had to own the SIGCHLD handler.
    
    This caused hangs in at least Pidgin.
    
    The patch contained two other improvements to the child watch code which
    we want to keep, so only revert the changes to gspawn itself.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=698081

 glib/gspawn.c |   80 +++++++++++++++++++++++++++------------------------------
 1 files changed, 38 insertions(+), 42 deletions(-)
---
diff --git a/glib/gspawn.c b/glib/gspawn.c
index 381ed5c..01cedf6 100644
--- a/glib/gspawn.c
+++ b/glib/gspawn.c
@@ -47,7 +47,6 @@
 
 #include "genviron.h"
 #include "gmem.h"
-#include "gmain.h"
 #include "gshell.h"
 #include "gstring.h"
 #include "gstrfuncs.h"
@@ -207,21 +206,6 @@ read_data (GString *str,
     }
 }
 
-typedef struct {
-  GMainLoop *loop;
-  gint *status_p;
-} SyncWaitpidData;
-
-static void
-on_sync_waitpid (GPid     pid,
-                 gint     status,
-                 gpointer user_data)
-{
-  SyncWaitpidData *data = user_data;
-  *(data->status_p) = status;
-  g_main_loop_quit (data->loop);
-}
-
 /**
  * g_spawn_sync:
  * @working_directory: (allow-none): child's current working directory, or %NULL to inherit parent's
@@ -277,7 +261,6 @@ g_spawn_sync (const gchar          *working_directory,
   GString *errstr = NULL;
   gboolean failed;
   gint status;
-  SyncWaitpidData waitpid_data;
   
   g_return_val_if_fail (argv != NULL, FALSE);
   g_return_val_if_fail (!(flags & G_SPAWN_DO_NOT_REAP_CHILD), FALSE);
@@ -410,32 +393,45 @@ g_spawn_sync (const gchar          *working_directory,
     close_and_invalidate (&outpipe);
   if (errpipe >= 0)
     close_and_invalidate (&errpipe);
-
-  /* Now create a temporary main context and loop, with just one
-   * waitpid source.  We used to invoke waitpid() directly here, but
-   * this way we unify with the worker thread in gmain.c.
+  
+  /* Wait for child to exit, even if we have
+   * an error pending.
    */
-  {
-    GMainContext *context;
-    GMainLoop *loop;
-    GSource *source;
-
-    context = g_main_context_new ();
-    loop = g_main_loop_new (context, TRUE);
+ again:
+      
+  ret = waitpid (pid, &status, 0);
 
-    waitpid_data.loop = loop;
-    waitpid_data.status_p = &status;
-    
-    source = g_child_watch_source_new (pid);
-    g_source_set_callback (source, (GSourceFunc)on_sync_waitpid, &waitpid_data, NULL);
-    g_source_attach (source, context);
-    g_source_unref (source);
-    
-    g_main_loop_run (loop);
+  if (ret < 0)
+    {
+      if (errno == EINTR)
+        goto again;
+      else if (errno == ECHILD)
+        {
+          if (exit_status)
+            {
+              g_warning ("In call to g_spawn_sync(), exit status of a child process was requested but ECHILD 
was received by waitpid(). Most likely the process is ignoring SIGCHLD, or some other thread is invoking 
waitpid() with a nonpositive first argument; either behavior can break applications that use g_spawn_sync 
either directly or indirectly.");
+            }
+          else
+            {
+              /* We don't need the exit status. */
+            }
+        }
+      else
+        {
+          if (!failed) /* avoid error pileups */
+            {
+              int errsv = errno;
 
-    g_main_context_unref (context);
-    g_main_loop_unref (loop);
-  }
+              failed = TRUE;
+                  
+              g_set_error (error,
+                           G_SPAWN_ERROR,
+                           G_SPAWN_ERROR_READ,
+                           _("Unexpected error in waitpid() (%s)"),
+                           g_strerror (errsv));
+            }
+        }
+    }
   
   if (failed)
     {