Re: External PCM plugin SDK

[Takashi Iwai <tiwai@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 1729 bytes --]

At Fri, 11 Feb 2005 14:28:34 +0100,
I wrote:
> 
> At Fri, 11 Feb 2005 13:15:19 +0100,
> Marcel Holtmann wrote:
> > 
> > Hi Takashi,
> > 
> > > > > ... and doesn't work as it is, unfortunately :-<
> > > > > 
> > > > > dlcose() is called after snd_pcm_close().
> > > > > We may need to build object caches in alsa-lib.
> > > > > This will improve the perfomance eventually, too.
> > > > 
> > > > questions is what will break if you change it. The only official plugin
> > > > is the Jack plugin, right? So be bad and change this stuff and then fix
> > > > the plugins.
> > > 
> > > The compatibility will be kept, I think.  Only the plugins with a
> > > keep-alive flag are excluded from dlclose, and the objects are reused
> > > at the next open.
> > 
> > but I think we still should implement something like init() and exit()
> > of the objects. Otherwise it would not be possible to handle this in a
> > correct way and we will get memory leaks and unclosed descriptors.
> 
> We can add the clean up of cached plugin objects (i.e. calling
> dlclose) in the existing snd_config_update_free_global().  This
> function is supposed to be used for clean up of config tree cache.
> 
> Each plugin with the keep-alive flag can have functions with
> __attribute__((constructor)) and __attribute__((destructor)) for the
> purpose above.

The below is a test patch to add the dlobj cache.

It adds a new mode flag to pcm open mode, SND_PCM_KEEP_ALIVE.
In xmms, change the call of snd_pcm_open() like:

	snd_pcm_open(...., SND_PCM_NONBLOCK | SND_PCM_KEEP_ALIVE);

and the dl object will remain alive until
snd_config_update_free_global() is called explicitly.

If the plugin needs always keep-alive, a bit more change is needed.


Takashi

[-- Attachment #2: Type: text/plain, Size: 5552 bytes --]

Index: alsa-lib/include/local.h
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/include/local.h,v
retrieving revision 1.37
diff -u -r1.37 local.h
--- alsa-lib/include/local.h	11 Feb 2005 16:20:31 -0000	1.37
+++ alsa-lib/include/local.h	11 Feb 2005 16:58:50 -0000
@@ -232,4 +232,9 @@
 #define snd_open_device(filename, fmode) open(filename, fmode);
 #endif
 
+/* dlobj cache */
+void *snd_dlobj_cache_lookup(const char *name);
+int snd_dlobj_cache_add(const char *name, void *dlobj, void *open_func);
+void snd_dlobj_cache_cleanup(void);
+
 #endif
Index: alsa-lib/include/pcm.h
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/include/pcm.h,v
retrieving revision 1.102
diff -u -r1.102 pcm.h
--- alsa-lib/include/pcm.h	7 Feb 2005 20:53:06 -0000	1.102
+++ alsa-lib/include/pcm.h	11 Feb 2005 17:12:50 -0000
@@ -295,6 +295,8 @@
 #define SND_PCM_NONBLOCK		0x0001
 /** Async notification (flag for open mode) \hideinitializer */
 #define SND_PCM_ASYNC			0x0002
+/** Keep the dl object alive after close */
+#define SND_PCM_KEEP_ALIVE		0x0004
 
 /** PCM handle */
 typedef struct _snd_pcm snd_pcm_t;
Index: alsa-lib/include/pcm_ioplug.h
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/include/pcm_ioplug.h,v
retrieving revision 1.3
diff -u -r1.3 pcm_ioplug.h
--- alsa-lib/include/pcm_ioplug.h	8 Feb 2005 20:48:56 -0000	1.3
+++ alsa-lib/include/pcm_ioplug.h	11 Feb 2005 17:14:59 -0000
@@ -37,10 +37,13 @@
 typedef struct snd_pcm_ioplug snd_pcm_ioplug_t;
 typedef struct snd_pcm_ioplug_callback snd_pcm_ioplug_callback_t;
 
+#define SND_PCM_IOPLUG_FLAG_LISTED	(1<<0)
+
 /* exported pcm data */
 struct snd_pcm_ioplug {
 	/* must be filled before calling snd_pcm_ioplug_create() */
 	const char *name;
+	unsigned int flags;	/* SND_PCM_IOPLUG_FLAG_XXX */
 	int poll_fd;
 	unsigned int poll_events;
 	unsigned int mmap_rw;		/* pseudo mmap */
Index: alsa-lib/src/conf.c
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/src/conf.c,v
retrieving revision 1.58
diff -u -r1.58 conf.c
--- alsa-lib/src/conf.c	9 Feb 2005 16:57:45 -0000	1.58
+++ alsa-lib/src/conf.c	11 Feb 2005 17:00:06 -0000
@@ -3105,6 +3105,10 @@
 		snd_config_update_free(snd_config_global_update);
 	snd_config_global_update = NULL;
 	pthread_mutex_unlock(&snd_config_update_mutex);
+
+	/* FIXME: better to place this in another place... */
+	snd_dlobj_cache_cleanup();
+
 	return 0;
 }
 
Index: alsa-lib/src/dlmisc.c
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/src/dlmisc.c,v
retrieving revision 1.8
diff -u -r1.8 dlmisc.c
--- alsa-lib/src/dlmisc.c	9 Dec 2002 10:58:48 -0000	1.8
+++ alsa-lib/src/dlmisc.c	11 Feb 2005 17:19:10 -0000
@@ -29,6 +29,7 @@
 
 #define _GNU_SOURCE
 #include <dlfcn.h>
+#include "list.h"
 #include "local.h"
 
 #ifndef DOC_HIDDEN
@@ -143,3 +144,70 @@
 		return NULL;
 	return dlsym(handle, name);
 }
+
+/*
+ * dlobj cache
+ *
+ * FIXME: add reference counter and proper locking
+ */
+
+struct dlobj_cache {
+	const char *name;
+	void *obj;
+	void *func;
+	struct list_head list;
+};
+
+static LIST_HEAD(pcm_dlobj_list);
+
+void *snd_dlobj_cache_lookup(const char *name)
+{
+	struct list_head *p;
+	struct dlobj_cache *c;
+
+	list_for_each(p, &pcm_dlobj_list) {
+		c = list_entry(p, struct dlobj_cache, list);
+		if (strcmp(c->name, name) == 0)
+			return c->func;
+	}
+	return NULL;
+}
+
+int snd_dlobj_cache_add(const char *name, void *dlobj, void *open_func)
+{
+	struct list_head *p;
+	struct dlobj_cache *c;
+
+	list_for_each(p, &pcm_dlobj_list) {
+		c = list_entry(p, struct dlobj_cache, list);
+		if (strcmp(c->name, name) == 0)
+			return 0; /* already exists */
+	}
+	c = malloc(sizeof(*c));
+	if (! c)
+		return -ENOMEM;
+	c->name = strdup(name);
+	if (! c->name) {
+		free(c);
+		return -ENOMEM;
+	}
+	c->obj = dlobj;
+	c->func = open_func;
+	list_add_tail(&c->list, &pcm_dlobj_list);
+	return 0;
+}
+
+void snd_dlobj_cache_cleanup(void)
+{
+	struct list_head *p;
+	struct dlobj_cache *c;
+
+	while (! list_empty(&pcm_dlobj_list)) {
+		p = pcm_dlobj_list.next;
+		c = list_entry(p, struct dlobj_cache, list);
+		list_del(p);
+		snd_dlclose(c->obj);
+		free(c->name);
+		free(c);
+	}
+}
Index: alsa-lib/src/pcm/pcm.c
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/src/pcm/pcm.c,v
retrieving revision 1.168
diff -u -r1.168 pcm.c
--- alsa-lib/src/pcm/pcm.c	21 Jan 2005 19:27:44 -0000	1.168
+++ alsa-lib/src/pcm/pcm.c	11 Feb 2005 17:20:36 -0000
@@ -2019,6 +2019,11 @@
 #ifndef PIC
 	snd_pcm_open_symbols();	/* this call is for static linking only */
 #endif
+	open_func = snd_dlobj_cache_lookup(open_name);
+	if (open_func) {
+		err = 0;
+		goto _err;
+	}
 	h = snd_dlopen(lib, RTLD_NOW);
 	if (h)
 		open_func = snd_dlsym(h, open_name, SND_DLSYM_VERSION(SND_PCM_DLSYM_VERSION));
@@ -2032,17 +2037,22 @@
 		err = -ENXIO;
 	}
        _err:
-	if (type_conf)
-		snd_config_delete(type_conf);
 	if (err >= 0) {
 		err = open_func(pcmp, name, pcm_root, pcm_conf, stream, mode);
 		if (err >= 0) {
+			if (h && (mode & SND_PCM_KEEP_ALIVE)) {
+				snd_dlobj_cache_add(open_name, h, open_func);
+				h = NULL;
+			}
 			(*pcmp)->dl_handle = h;
 			err = 0;
 		} else {
-			snd_dlclose(h);
+			if (h)
+				snd_dlclose(h);
 		}
 	}
+	if (type_conf)
+		snd_config_delete(type_conf);
 	if (buf)
 		free(buf);
 	if (buf1)