Detect forks

Some really stupid applications (Hey, vim, that means you!)
love to fork after initializing gtk/libcanberra. This is really
bad style. We however have to deal with this cleanly, so we try
to detect the forks making sure all our calls fail cleanly
after the fork.

6 files changed, 104 insertions, 4 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 1fb5168..e40ec1f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -52,7 +52,8 @@ libcanberra_la_SOURCES = \
 	sound-theme-spec.c sound-theme-spec.h \
 	llist.h \
 	macro.h macro.c \
-	malloc.c malloc.h
+	malloc.c malloc.h \
+	fork-detect.c fork-detect.h
 libcanberra_la_CFLAGS = \
 	$(AM_CFLAGS) \
 	$(VORBIS_CFLAGS)
diff --git a/src/canberra-gtk.c b/src/canberra-gtk.c
index 70b8d7e..cb36a0f 100644
--- a/src/canberra-gtk.c
+++ b/src/canberra-gtk.c
@@ -31,6 +31,7 @@
 #include "common.h"
 #include "malloc.h"
 #include "proplist.h"
+#include "fork-detect.h"
 
 /**
  * SECTION:canberra-gtk
@@ -93,7 +94,8 @@ ca_context *ca_gtk_context_get(void) {
     if ((c = g_static_private_get(&context_private)))
         return c;
 
-    ca_assert_se(ca_context_create(&c) == CA_SUCCESS);
+    if (ca_context_create(&c) != CA_SUCCESS)
+        return NULL;
 
     if ((name = g_get_application_name()))
         ca_context_change_props(c, CA_PROP_APPLICATION_NAME, name, NULL);
@@ -154,6 +156,7 @@ int ca_gtk_proplist_set_for_widget(ca_proplist *p, GtkWidget *widget) {
 
     ca_return_val_if_fail(p, CA_ERROR_INVALID);
     ca_return_val_if_fail(widget, CA_ERROR_INVALID);
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
 
     if (!(w = get_toplevel(widget)))
         return CA_ERROR_INVALID;
@@ -224,6 +227,7 @@ int ca_gtk_proplist_set_for_event(ca_proplist *p, GdkEvent *e) {
 
     ca_return_val_if_fail(p, CA_ERROR_INVALID);
     ca_return_val_if_fail(e, CA_ERROR_INVALID);
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
 
     if ((gw = e->any.window)) {
         gdk_window_get_user_data(gw, (gpointer*) &w);
@@ -297,6 +301,7 @@ int ca_gtk_play_for_widget(GtkWidget *w, uint32_t id, ...) {
     ca_proplist *p;
 
     ca_return_val_if_fail(w, CA_ERROR_INVALID);
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
 
     if ((ret = ca_proplist_create(&p)) < 0)
         return ret;
@@ -346,6 +351,7 @@ int ca_gtk_play_for_event(GdkEvent *e, uint32_t id, ...) {
     ca_proplist *p;
 
     ca_return_val_if_fail(e, CA_ERROR_INVALID);
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
 
     if ((ret = ca_proplist_create(&p)) < 0)
         return ret;
diff --git a/src/canberra.h b/src/canberra.h
index ff09146..9664ef2 100644
--- a/src/canberra.h
+++ b/src/canberra.h
@@ -414,7 +414,8 @@ enum {
     CA_ERROR_IO = -14,
     CA_ERROR_INTERNAL = -15,
     CA_ERROR_DISABLED = -16,
-    _CA_ERROR_MAX = -17
+    CA_ERROR_FORKED = -17,
+    _CA_ERROR_MAX = -18
 };
 
 /**
diff --git a/src/common.c b/src/common.c
index e1445f4..ac8b982 100644
--- a/src/common.c
+++ b/src/common.c
@@ -30,6 +30,7 @@
 #include "driver.h"
 #include "proplist.h"
 #include "macro.h"
+#include "fork-detect.h"
 
 /**
  * SECTION:canberra
@@ -127,6 +128,7 @@ int ca_context_create(ca_context **_c) {
     int ret;
     const char *d;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(_c, CA_ERROR_INVALID);
 
     if (!(c = ca_new0(ca_context, 1)))
@@ -171,6 +173,7 @@ int ca_context_create(ca_context **_c) {
 int ca_context_destroy(ca_context *c) {
     int ret = CA_SUCCESS;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
 
     /* There's no locking necessary here, because the application is
@@ -209,6 +212,7 @@ int ca_context_set_driver(ca_context *c, const char *driver) {
     char *n;
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_mutex_lock(c->mutex);
     ca_return_val_if_fail_unlock(!c->opened, CA_ERROR_STATE, c->mutex);
@@ -250,6 +254,7 @@ int ca_context_change_device(ca_context *c, const char *device) {
     char *n;
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_mutex_lock(c->mutex);
 
@@ -277,6 +282,7 @@ fail:
 static int context_open_unlocked(ca_context *c) {
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
 
     if (c->opened)
@@ -302,6 +308,7 @@ static int context_open_unlocked(ca_context *c) {
 int ca_context_open(ca_context *c) {
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_mutex_lock(c->mutex);
     ca_return_val_if_fail_unlock(!c->opened, CA_ERROR_STATE, c->mutex);
@@ -336,6 +343,7 @@ int ca_context_change_props(ca_context *c, ...)  {
     int ret;
     ca_proplist *p = NULL;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
 
     va_start(ap, c);
@@ -368,6 +376,7 @@ int ca_context_change_props_full(ca_context *c, ca_proplist *p) {
     int ret;
     ca_proplist *merged;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_return_val_if_fail(p, CA_ERROR_INVALID);
 
@@ -438,6 +447,7 @@ int ca_context_play(ca_context *c, uint32_t id, ...) {
     va_list ap;
     ca_proplist *p = NULL;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
 
     va_start(ap, id);
@@ -478,6 +488,7 @@ int ca_context_play_full(ca_context *c, uint32_t id, ca_proplist *p, ca_finish_c
     const char *t;
     ca_bool_t enabled = TRUE;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_return_val_if_fail(p, CA_ERROR_INVALID);
     ca_return_val_if_fail(!userdata || cb, CA_ERROR_INVALID);
@@ -532,6 +543,7 @@ finish:
 int ca_context_cancel(ca_context *c, uint32_t id)  {
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_mutex_lock(c->mutex);
     ca_return_val_if_fail_unlock(c->opened, CA_ERROR_STATE, c->mutex);
@@ -566,6 +578,7 @@ int ca_context_cache(ca_context *c, ...) {
     va_list ap;
     ca_proplist *p = NULL;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
 
     va_start(ap, c);
@@ -599,6 +612,7 @@ int ca_context_cache(ca_context *c, ...) {
 int ca_context_cache_full(ca_context *c, ca_proplist *p) {
     int ret;
 
+    ca_return_val_if_fail(!ca_detect_fork(), CA_ERROR_FORKED);
     ca_return_val_if_fail(c, CA_ERROR_INVALID);
     ca_return_val_if_fail(p, CA_ERROR_INVALID);
 
@@ -648,7 +662,8 @@ const char *ca_strerror(int code) {
         [-CA_ERROR_ACCESS] = "Access forbidden",
         [-CA_ERROR_IO] = "IO error",
         [-CA_ERROR_INTERNAL] = "Internal error",
-        [-CA_ERROR_DISABLED] = "Sound disabled"
+        [-CA_ERROR_DISABLED] = "Sound disabled",
+        [-CA_ERROR_FORKED] = "Process forked"
     };
 
     ca_return_val_if_fail(code <= 0, NULL);
diff --git a/src/fork-detect.c b/src/fork-detect.c
new file mode 100644
index 0000000..622037c
--- /dev/null
+++ b/src/fork-detect.c
@@ -0,0 +1,51 @@
+/***
+  This file is part of libcanberra.
+
+  Copyright 2009 Lennart Poettering
+
+  libcanberra is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation, either version 2.1 of the
+  License, or (at your option) any later version.
+
+  libcanberra is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with libcanberra. If not, see
+  <http://www.gnu.org/licenses/>.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <unistd.h>
+#include <sys/types.h>
+
+#include "fork-detect.h"
+
+int ca_detect_fork(void) {
+    static volatile pid_t pid = (pid_t) -1;
+    pid_t v;
+
+    /* Some really stupid applications (Hey, vim, that means you!)
+     * love to fork after initializing gtk/libcanberra. This is really
+     * bad style. We however have to deal with this cleanly, so we try
+     * to detect the forks making sure all our calls fail cleanly
+     * after the fork. */
+
+    /* Ideally we'd use atomic operations here, but we don't have them
+     * and this is not exactly crucial, so we don't care */
+
+    v = pid;
+
+    if (v == getpid() || v == (pid_t) -1) {
+        pid = getpid();
+        return 0;
+    }
+
+    return 1;
+}
diff --git a/src/fork-detect.h b/src/fork-detect.h
new file mode 100644
index 0000000..9050ef8
--- /dev/null
+++ b/src/fork-detect.h
@@ -0,0 +1,26 @@
+#ifndef foocanberraforkdetecth
+#define foocanberraforkdetecth
+
+/***
+  This file is part of libcanberra.
+
+  Copyright 2009 Lennart Poettering
+
+  libcanberra is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation, either version 2.1 of the
+  License, or (at your option) any later version.
+
+  libcanberra is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with libcanberra. If not, see
+  <http://www.gnu.org/licenses/>.
+***/
+
+int ca_detect_fork(void);
+
+#endif