GChildWatch source -- take two
- From: Jonathan Blandford <jrb redhat com>
- To: gtk-devel-list gnome org
- Subject: GChildWatch source -- take two
- Date: 17 Jul 2003 17:05:22 -0400
Here's another attempt at the GChildWatch source. I incorporated most
of the changes proposed, and hope it can now handle the single-threaded
case better. It now always writes down the pipe and doesn't count on
poll being interrupted by the signal.
Comments?
-Jonathan
Index: ChangeLog
===================================================================
RCS file: /cvs/gnome/glib/ChangeLog,v
retrieving revision 1.1351
diff -u -p -r1.1351 ChangeLog
--- ChangeLog 2 Jan 1997 22:24:13 -0000 1.1351
+++ ChangeLog 17 Jul 2003 20:49:52 -0000
@@ -1,3 +1,16 @@
+Fri Jul 4 00:40:35 2003 Jonathan Blandford <jrb gnome org>
+
+ * glib/gmain.c (g_child_watch_source_new): Source to handle
+ SIGCHLD messages. This way multiple libraries can monitor their
+ children's exit status without fighting over who installs the
+ signal handler.
+
+ * glib/gmain.c (g_child_watch_add_full): function to create a
+ GChildWatch source and attach it to a loop.
+
+ * glib/gmain.c (g_child_watch_add): simple function to create a
+ GChildWatch source and attach it to a GMainLoop.
+
2003-07-12 Matthias Clasen <maclas gmx de>
* glib/gprintf.c: Doc additions.
Index: glib/gmain.c
===================================================================
RCS file: /cvs/gnome/glib/glib/gmain.c,v
retrieving revision 1.96
diff -u -p -r1.96 gmain.c
--- glib/gmain.c 9 Jul 2003 23:31:20 -0000 1.96
+++ glib/gmain.c 17 Jul 2003 20:49:52 -0000
@@ -39,7 +39,9 @@
#include "glib.h"
#include "gthreadinit.h"
#include <sys/types.h>
+#include <sys/wait.h>
#include <time.h>
+#include <fcntl.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif /* HAVE_SYS_TIME_H */
@@ -65,6 +67,7 @@
/* Types */
typedef struct _GTimeoutSource GTimeoutSource;
+typedef struct _GChildWatchSource GChildWatchSource;
typedef struct _GPollRec GPollRec;
typedef struct _GSourceCallback GSourceCallback;
@@ -157,6 +160,15 @@ struct _GTimeoutSource
guint interval;
};
+struct _GChildWatchSource
+{
+ GSource source;
+ gint pid;
+ gint child_status;
+ gint count;
+ gboolean child_exited;
+};
+
struct _GPollRec
{
gint priority;
@@ -213,6 +225,12 @@ static gboolean g_timeout_check (GSou
static gboolean g_timeout_dispatch (GSource *source,
GSourceFunc callback,
gpointer user_data);
+static gboolean g_child_watch_prepare (GSource *source,
+ gint *timeout);
+static gboolean g_child_watch_check (GSource *source);
+static gboolean g_child_watch_dispatch (GSource *source,
+ GSourceFunc callback,
+ gpointer user_data);
static gboolean g_idle_prepare (GSource *source,
gint *timeout);
static gboolean g_idle_check (GSource *source);
@@ -221,8 +239,22 @@ static gboolean g_idle_dispatch (GSou
gpointer user_data);
G_LOCK_DEFINE_STATIC (main_loop);
+G_LOCK_DEFINE_STATIC (main_context_list);
+
static GMainContext *default_main_context;
static GSList *main_contexts_without_pipe = NULL;
+static GMainContext *main_context_about_to_poll = NULL;
+
+/* Child status monitoring code */
+enum {
+ CHILD_WATCH_UNINITIALIZED,
+ CHILD_WATCH_INITIALIZED_SINGLE,
+ CHILD_WATCH_INITIALIZED_THREADED
+};
+static gint child_watch_init_state = CHILD_WATCH_UNINITIALIZED;
+static volatile sig_atomic_t child_watch_count = 1;
+static gint child_watch_wake_up_pipe[2] = {0, 0};
+static GSList *main_context_list = NULL;
#if defined(G_PLATFORM_WIN32) && defined(__GNUC__)
__declspec(dllexport)
@@ -235,6 +267,14 @@ GSourceFuncs g_timeout_funcs =
NULL
};
+GSourceFuncs g_child_watch_funcs =
+{
+ g_child_watch_prepare,
+ g_child_watch_check,
+ g_child_watch_dispatch,
+ NULL
+};
+
#if defined(G_PLATFORM_WIN32) && defined(__GNUC__)
__declspec(dllexport)
#endif
@@ -561,6 +601,10 @@ g_main_context_unref_and_unlock (GMainCo
return;
}
+ G_LOCK (main_context_list);
+ main_context_list = g_slist_remove (main_context_list, context);
+ G_UNLOCK (main_context_list);
+
source = context->source_list;
while (source)
{
@@ -615,7 +659,6 @@ g_main_context_unref (GMainContext *cont
g_main_context_unref_and_unlock (context);
}
-#ifdef G_THREADS_ENABLED
static void
g_main_context_init_pipe (GMainContext *context)
{
@@ -640,8 +683,9 @@ g_main_context_init_pipe (GMainContext *
g_main_context_add_poll_unlocked (context, 0, &context->wake_up_rec);
}
-void
-_g_main_thread_init ()
+/* called when initializing threads and the child_watch source */
+static void
+add_pipes_to_main_contexts (void)
{
GSList *curr = main_contexts_without_pipe;
while (curr)
@@ -652,6 +696,14 @@ _g_main_thread_init ()
g_slist_free (main_contexts_without_pipe);
main_contexts_without_pipe = NULL;
}
+
+#ifdef G_THREADS_ENABLED
+
+void
+_g_main_thread_init ()
+{
+ add_pipes_to_main_contexts ();
+}
#endif /* G_THREADS_ENABLED */
/**
@@ -700,7 +752,11 @@ g_main_context_new ()
context);
#endif
- return context;
+ G_LOCK (main_context_list);
+ main_context_list = g_slist_append (main_context_list, context);
+ G_UNLOCK (main_context_list);
+
+ return context;
}
/**
@@ -1513,11 +1569,11 @@ g_main_context_find_source_by_user_data
* g_source_remove:
* @tag: the id of the source to remove.
*
- * Removes the source with the given id from the default main
- * context. The id of a #GSource is given by g_source_get_id(),
- * or will be returned by the functions g_source_attach(),
- * g_idle_add(), g_idle_add_full(), g_timeout_add(),
- * g_timeout_add_full(), g_io_add_watch, and g_io_add_watch_full().
+ * Removes the source with the given id from the default main context. The id of
+ * a #GSource is given by g_source_get_id(), or will be returned by the
+ * functions g_source_attach(), g_idle_add(), g_idle_add_full(),
+ * g_timeout_add(), g_timeout_add_full(), g_child_watch_add(),
+ * g_child_watch_add_full(), g_io_add_watch(), and g_io_add_watch_full().
*
* See also g_source_destroy().
*
@@ -2173,8 +2229,8 @@ g_main_context_check (GMainContext *cont
if (!context->poll_waiting)
{
#ifndef G_OS_WIN32
- gchar c;
- read (context->wake_up_pipe[0], &c, 1);
+ gchar a;
+ read (context->wake_up_pipe[0], &a, 1);
#endif
}
else
@@ -2328,6 +2384,16 @@ g_main_context_iterate (GMainContext *co
UNLOCK_CONTEXT (context);
+ /* main_context_about_to_poll is entirely for the SIGCHLD source. We normally
+ * count on SIGCHLD waking up the poll when it occurs during that time.
+ * However, if the SIGCHLD occurs between prepare and poll, we can miss it and
+ * block indefinitely, waiting for the child to exit. To avoid this, we store
+ * the context in main_context_about_to_poll in the expectation that the
+ * signal handler can deal with it. We expect that no code in prepare or
+ * query tries to send data to the wake up pipe, and that we can safely write
+ * a byte down it. */
+
+ main_context_about_to_poll = context;
some_ready = g_main_context_prepare (context, &max_priority);
while ((nfds = g_main_context_query (context, max_priority, &timeout, fds,
@@ -2344,7 +2410,8 @@ g_main_context_iterate (GMainContext *co
timeout = 0;
g_main_context_poll (context, timeout, max_priority, fds, nfds);
-
+ main_context_about_to_poll = NULL;
+
g_main_context_check (context, max_priority, fds, nfds);
if (dispatch)
@@ -3211,6 +3278,299 @@ g_timeout_add (guint32 interval,
interval, function, data, NULL);
}
+/* Child watch functions */
+
+static void
+check_for_child_exited (GSource *source)
+{
+ GChildWatchSource *child_watch_source;
+ volatile gint count;
+
+ /* protect against another SIGCHLD in the middle of this call */
+ count = child_watch_count;
+
+ child_watch_source = (GChildWatchSource *) source;
+
+ if (child_watch_source->count < count)
+ {
+ gint child_status;
+
+ if (waitpid (child_watch_source->pid, &child_status, WNOHANG) > 0)
+ {
+ child_watch_source->child_status = child_status;
+ child_watch_source->child_exited = TRUE;
+ }
+
+ child_watch_source->count = count;
+ }
+}
+
+static gboolean
+g_child_watch_prepare (GSource *source,
+ gint *timeout)
+{
+ GChildWatchSource *child_watch_source;
+ *timeout = -1;
+
+ child_watch_source = (GChildWatchSource *) source;
+
+ check_for_child_exited (source);
+ return child_watch_source->child_exited;
+}
+
+
+static gboolean
+g_child_watch_check (GSource *source)
+{
+ GChildWatchSource *child_watch_source;
+
+ child_watch_source = (GChildWatchSource *) source;
+
+ return child_watch_source->child_exited;
+}
+
+static gboolean
+g_child_watch_dispatch (GSource *source,
+ GSourceFunc callback,
+ gpointer user_data)
+{
+ GChildWatchSource *child_watch_source;
+ GChildWatchFunc child_watch_callback = (GChildWatchFunc) callback;
+
+ child_watch_source = (GChildWatchSource *) source;
+
+ if (!callback)
+ {
+ g_warning ("Child watch source dispatched without callback\n"
+ "You must call g_source_set_callback().");
+ return FALSE;
+ }
+
+ (child_watch_callback) (child_watch_source->pid, child_watch_source->child_status, user_data);
+
+ /* We never keep a child watch source around as the child is gone */
+ return FALSE;
+}
+
+static void
+g_child_watch_signal_handler (int signum)
+{
+ child_watch_count ++;
+ /* guard against us modifying errno during the write */
+ int old_errno = errno;
+
+ if (child_watch_init_state == CHILD_WATCH_INITIALIZED_THREADED)
+ {
+ write (child_watch_wake_up_pipe[1], "B", 1);
+ }
+ else
+ {
+ if (main_context_about_to_poll)
+ {
+ g_main_context_wakeup_unlocked (main_context_about_to_poll);
+ }
+ }
+ errno = old_errno;
+}
+
+static void
+g_child_watch_set_up_signal_handler (void)
+{
+ sigset_t newset;
+
+ signal (SIGCHLD, g_child_watch_signal_handler);
+
+ sigemptyset (&newset);
+ sigaddset (&newset, SIGCHLD);
+ sigprocmask (SIG_UNBLOCK, &newset, NULL);
+}
+
+static void
+g_child_watch_source_init_single (void)
+{
+ g_assert (! g_thread_supported());
+ g_assert (child_watch_init_state == CHILD_WATCH_UNINITIALIZED);
+
+ add_pipes_to_main_contexts ();
+
+ child_watch_init_state = CHILD_WATCH_INITIALIZED_SINGLE;
+
+ g_child_watch_set_up_signal_handler ();
+}
+
+/* Separate thread that sits around waiting for messages from the signal
+ * handler.
+ */
+static gpointer
+child_watch_helper_thread (gpointer data)
+{
+ while (1)
+ {
+ gchar b[20];
+ GSList *list;
+
+ read (child_watch_wake_up_pipe[0], b, 20);
+
+ /* We were woken up. Wake up all other contexts in all other threads */
+ G_LOCK (main_context_list);
+ for (list = main_context_list; list; list = list->next)
+ {
+ GMainContext *context;
+
+ context = list->data;
+ g_main_context_wakeup (context);
+ }
+ G_UNLOCK (main_context_list);
+ }
+ return NULL;
+}
+
+#ifdef G_THREADS_ENABLED
+
+static void
+g_child_watch_source_init_multi_threaded (void)
+{
+ GError *error = NULL;
+
+ g_assert (g_thread_supported());
+
+ if (pipe (child_watch_wake_up_pipe) < 0)
+ g_error ("Cannot create wake up pipe: %s\n", g_strerror (errno));
+ fcntl (child_watch_wake_up_pipe[1], F_SETFL, O_NONBLOCK | fcntl (child_watch_wake_up_pipe[1], F_GETFL));
+
+ /* We create a helper thread that polls on the wakeup pipe indefinitely */
+ /* FIXME: Think this through for races */
+ if (g_thread_create_full (child_watch_helper_thread, NULL, 0, FALSE, FALSE, G_THREAD_PRIORITY_NORMAL, &error) == NULL)
+ g_error ("Cannot create a thread to monitor child exit status: %s\n", error->message);
+ child_watch_init_state = CHILD_WATCH_INITIALIZED_THREADED;
+
+ g_child_watch_set_up_signal_handler ();
+}
+
+static void
+g_child_watch_source_init_promote_single_to_threaded (void)
+{
+ g_child_watch_source_init_multi_threaded ();
+}
+
+#endif
+
+static void
+g_child_watch_source_init (void)
+{
+#ifdef G_THREADS_ENABLED
+ if (g_thread_supported())
+ {
+ if (child_watch_init_state == CHILD_WATCH_UNINITIALIZED)
+ g_child_watch_source_init_multi_threaded ();
+ else if (child_watch_init_state == CHILD_WATCH_INITIALIZED_SINGLE)
+ g_child_watch_source_init_promote_single_to_threaded ();
+ }
+ else
+ {
+#endif
+ if (child_watch_init_state == CHILD_WATCH_UNINITIALIZED)
+ g_child_watch_source_init_single ();
+#ifdef G_THREADS_ENABLED
+ }
+#endif
+}
+
+/**
+ * g_child_watch_source_new:
+ * @pid: process id of a child process to watch
+ *
+ * Creates a new child_watch source. This source is used to monitor a child
+ * process. It will be triggered once when a SIGCHLD occurs, and the process
+ * specified by pid has exited. Any application using this source should not
+ * modify the SIGCHILD signal handler. Instead, they should use a child watch
+ * source to keep track of the exit status of any children that they care about.
+ * Additionally, as glib installs a SIGCHLD signal handler, system calls can be
+ * interrupted and should probably be checked for EINTR.
+ *
+ * The source will not initially be associated with any #GMainContext and must
+ * be added to one with g_source_attach() before it will be executed. Unlike
+ * other sources, any callback associated with it will only be called at most
+ * once and no return value is expected.
+ *
+ * Return value: the newly-created child watch source
+ **/
+GSource *
+g_child_watch_source_new (gint pid)
+{
+ GSource *source = g_source_new (&g_child_watch_funcs, sizeof (GChildWatchSource));
+ GChildWatchSource *child_watch_source = (GChildWatchSource *)source;
+
+ g_child_watch_source_init ();
+
+ child_watch_source->pid = pid;
+ /* We want to run on the first pass no matter what, to catch the case where
+ * the child has exited before the signal handler has been installed. */
+ child_watch_source->count = child_watch_count - 1;
+
+ return source;
+}
+
+/**
+ * g_child_watch_add_full:
+ * @priority: the priority of the idle source. Typically this will be in the
+ * range between #G_PRIORITY_DEFAULT_IDLE and #G_PRIORITY_HIGH_IDLE.
+ * @pid: process id of a child process to watch
+ * @function: function to call
+ * @data: data to pass to @function
+ * @notify: function to call when the idle is removed, or %NULL
+ *
+ * Sets a function to be called when the child indicated by pid exits, at a
+ * default priority, #G_PRIORITY_DEFAULT. See g_child_watch_source_new() for
+ * additional comments regarding this source.
+ *
+ * Return value: the id of event source.
+ **/
+guint
+g_child_watch_add_full (gint priority,
+ gint pid,
+ GChildWatchFunc function,
+ gpointer data,
+ GDestroyNotify notify)
+{
+ GSource *source;
+ guint id;
+
+ g_return_val_if_fail (function != NULL, 0);
+
+ source = g_child_watch_source_new (pid);
+
+ if (priority != G_PRIORITY_DEFAULT)
+ g_source_set_priority (source, priority);
+
+ g_source_set_callback (source, (GSourceFunc) function, data, notify);
+ id = g_source_attach (source, NULL);
+ g_source_unref (source);
+
+ return id;
+}
+
+/**
+ * g_child_watch_add:
+ * @pid: process id of a child process to watch
+ * @function: function to call
+ * @data: data to pass to @function
+ *
+ * Sets a function to be called when the child indicated by pid exits, at a
+ * default priority, #G_PRIORITY_DEFAULT. See g_child_watch_source_new() for
+ * additional comments regarding this source.
+ *
+ * Return value: the id of event source.
+ **/
+guint
+g_child_watch_add (gint pid,
+ GChildWatchFunc function,
+ gpointer data)
+{
+ return g_child_watch_add_full (G_PRIORITY_DEFAULT, pid, function, data, NULL);
+}
+
+
/* Idle functions */
static gboolean
Index: glib/gmain.h
===================================================================
RCS file: /cvs/gnome/glib/glib/gmain.h,v
retrieving revision 1.16
diff -u -p -r1.16 gmain.h
--- glib/gmain.h 5 Jun 2003 22:18:27 -0000 1.16
+++ glib/gmain.h 17 Jul 2003 20:49:52 -0000
@@ -32,6 +32,9 @@ typedef struct _GSourceCallbackFuncs GSo
typedef struct _GSourceFuncs GSourceFuncs;
typedef gboolean (*GSourceFunc) (gpointer data);
+typedef void (*GChildWatchFunc) (gint pid,
+ gint status,
+ gpointer data);
struct _GSource
{
@@ -243,8 +246,9 @@ void g_source_get_current_time (GSou
/* Specific source types
*/
-GSource *g_idle_source_new (void);
-GSource *g_timeout_source_new (guint interval);
+GSource *g_idle_source_new (void);
+GSource *g_child_watch_source_new (gint pid);
+GSource *g_timeout_source_new (guint interval);
/* Miscellaneous functions
*/
@@ -278,25 +282,34 @@ gboolean g_source_remove_by_user_data
gboolean g_source_remove_by_funcs_user_data (GSourceFuncs *funcs,
gpointer user_data);
-/* Idles and timeouts */
-guint g_timeout_add_full (gint priority,
- guint interval,
- GSourceFunc function,
- gpointer data,
- GDestroyNotify notify);
-guint g_timeout_add (guint interval,
- GSourceFunc function,
- gpointer data);
-guint g_idle_add (GSourceFunc function,
- gpointer data);
-guint g_idle_add_full (gint priority,
- GSourceFunc function,
- gpointer data,
- GDestroyNotify notify);
-gboolean g_idle_remove_by_data (gpointer data);
+/* Idles, child watchers and timeouts */
+guint g_timeout_add_full (gint priority,
+ guint interval,
+ GSourceFunc function,
+ gpointer data,
+ GDestroyNotify notify);
+guint g_timeout_add (guint interval,
+ GSourceFunc function,
+ gpointer data);
+guint g_child_watch_add_full (gint priority,
+ gint pid,
+ GChildWatchFunc function,
+ gpointer data,
+ GDestroyNotify notify);
+guint g_child_watch_add (gint pid,
+ GChildWatchFunc function,
+ gpointer data);
+guint g_idle_add (GSourceFunc function,
+ gpointer data);
+guint g_idle_add_full (gint priority,
+ GSourceFunc function,
+ gpointer data,
+ GDestroyNotify notify);
+gboolean g_idle_remove_by_data (gpointer data);
/* Hook for GClosure / GSource integration. Don't touch */
GLIB_VAR GSourceFuncs g_timeout_funcs;
+GLIB_VAR GSourceFuncs g_child_watch_funcs;
GLIB_VAR GSourceFuncs g_idle_funcs;
G_END_DECLS
Index: tests/Makefile.am
===================================================================
RCS file: /cvs/gnome/glib/tests/Makefile.am,v
retrieving revision 1.56
diff -u -p -r1.56 Makefile.am
--- tests/Makefile.am 27 May 2003 22:12:40 -0000 1.56
+++ tests/Makefile.am 17 Jul 2003 20:49:52 -0000
@@ -64,6 +64,7 @@ endif
test_programs = \
array-test \
$(CXX_TEST) \
+ child-test \
date-test \
dirname-test \
gio-test \
@@ -109,6 +110,7 @@ thread_ldadd = $(libgthread) $(G_THREAD_
module_ldadd = $(libgmodule) $(G_MODULE_LIBS) $(progs_ldadd)
array_test_LDADD = $(progs_ldadd)
+child_test_LDADD = $(thread_ldadd)
date_test_LDADD = $(progs_ldadd)
dirname_test_LDADD = $(progs_ldadd)
gio_test_LDADD = $(progs_ldadd)
Index: tests/child-test.c
===================================================================
RCS file: tests/child-test.c
diff -N tests/child-test.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ tests/child-test.c 17 Jul 2003 20:49:52 -0000
@@ -0,0 +1,69 @@
+#include <sys/types.h>
+#include <unistd.h>
+#include "glib.h"
+#include <stdlib.h>
+
+GMainLoop *main_loop;
+
+gint
+get_a_child (void)
+{
+ gint pid;
+
+ pid = fork ();
+ if (pid < 0)
+ exit (1);
+
+ if (pid > 0)
+ return pid;
+
+ sleep (1);
+ _exit (0);
+}
+
+gint
+child_watch_callback (gint pid, gint status, gpointer data)
+{
+ g_print ("child %d exited, status %d\n", pid, status);
+}
+
+static gpointer
+test_thread (gpointer data)
+{
+ GMainLoop *new_main_loop;
+ GSource *source;
+ gint pid;
+
+ new_main_loop = g_main_loop_new (NULL, FALSE);
+
+ pid = get_a_child ();
+ source = g_child_watch_source_new (pid);
+ g_source_set_callback (source, (GSourceFunc) child_watch_callback, NULL, NULL);
+ g_source_attach (source, g_main_loop_get_context (new_main_loop));
+ g_source_unref (source);
+
+ g_print ("whee! created pid: %d\n", pid);
+ g_main_loop_run (new_main_loop);
+
+}
+
+int
+main (int argc, char *argv[])
+{
+ g_thread_init (NULL);
+ main_loop = g_main_loop_new (NULL, FALSE);
+
+
+ system ("/bin/true");
+#if 0
+ pid = get_a_child ();
+ g_child_watch_add (pid, child_watch_callback, NULL);
+#endif
+ g_thread_create (test_thread, NULL, FALSE, NULL);
+
+ g_thread_create (test_thread, NULL, FALSE, NULL);
+
+ g_main_loop_run (main_loop);
+
+ return 0;
+}
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