MAJOR: stream-interface: dynamically allocate the applet context

From now on, a call to stream_int_register_handler() causes a call
to si_alloc_appctx() and returns an initialized appctx for the
current stream interface. If one was previously allocated, it is
released. If the stream interface was attached to a connection, it
is released as well.

The appctx are allocated from the same pools as the connections, because
they're substantially smaller in size, and we can't have both a connection
and an appctx on an interface at any moment.

In case of memory shortage, the call may return NULL, which is already
handled by all consumers of stream_int_register_handler().

The field appctx was removed from the stream interface since we only
rely on the endpoint now. On 32-bit, the stream_interface size went down
from 108 to 44 bytes. On 64-bit, it went down from 144 to 64 bytes. This
represents a memory saving of 160 bytes per session.

It seems that a later improvement could be to move the call to
stream_int_register_handler() to session.c for most cases.

include/proto/stream_interface.h

@@ -45,6 +45,47 @@ extern struct data_cb si_conn_cb;
 struct appctx *stream_int_register_handler(struct stream_interface *si, struct si_applet *app);
 void stream_int_unregister_handler(struct stream_interface *si);
 
+/* Initializes all required fields for a new appctx. Note that it does the
+ * minimum acceptable initialization for an appctx. This means only the
+ * 3 integer states st0, st1, st2 are zeroed.
+ */
+static inline void appctx_init(struct appctx *appctx)
+{
+	appctx->st0 = appctx->st1 = appctx->st2 = 0;
+}
+
+/* sets <appctx>'s applet to point to <applet> */
+static inline void appctx_set_applet(struct appctx *appctx, struct si_applet *applet)
+{
+	appctx->applet = applet;
+}
+
+/* Tries to allocate a new appctx and initialize its main fields. The
+ * appctx is returned on success, NULL on failure. The appctx must be
+ * released using pool_free2(connection) or appctx_free(), since it's
+ * allocated from the connection pool.
+ */
+static inline struct appctx *appctx_new()
+{
+	struct appctx *appctx;
+
+	appctx = pool_alloc2(pool2_connection);
+	if (likely(appctx != NULL)) {
+		appctx->obj_type = OBJ_TYPE_APPCTX;
+		appctx->applet = NULL;
+		appctx_init(appctx);
+	}
+	return appctx;
+}
+
+/* Releases an appctx previously allocated by appctx_new(). Note that
+ * we share the connection pool.
+ */
+static inline void appctx_free(struct appctx *appctx)
+{
+	pool_free2(pool2_connection, appctx);
+}
+
 /* initializes a stream interface in the SI_ST_INI state. It's detached from
  * any endpoint and is only attached to an owner (generally a task).
  */
@@ -68,16 +109,27 @@ static inline void si_set_state(struct stream_interface *si, int state)
 	si->state = si->prev_state = state;
 }
 
-/* release the endpoint if it's a connection, then nullify it */
+/* Release the endpoint if it's a connection or an applet, then nullify it.
+ * Note: released connections are closed then freed.
+ */
 static inline void si_release_endpoint(struct stream_interface *si)
 {
 	struct connection *conn;
+	struct appctx *appctx;
 
-	conn = objt_conn(si->end);
-	if (conn)
-		pool_free2(pool2_connection, conn);
+	if (!si->end)
+		return;
+
+	if ((conn = objt_conn(si->end))) {
+		conn_force_close(conn);
+		conn_free(conn);
+	}
+	else if ((appctx = objt_appctx(si->end))) {
+		if (appctx->applet->release)
+			appctx->applet->release(si);
+		appctx_free(appctx); /* we share the connection pool */
+	}
 	si->end = NULL;
-	si->appctx.applet = NULL;
 }
 
 static inline void si_detach(struct stream_interface *si)
@@ -97,13 +149,15 @@ static inline void si_attach_conn(struct stream_interface *si, struct connection
 	conn_attach(conn, si, &si_conn_cb);
 }
 
-static inline void si_attach_applet(struct stream_interface *si, struct si_applet *applet)
+/* Attach appctx <appctx> to the stream interface <si>. The stream interface
+ * is configured to work with an applet context. It is left to the caller to
+ * call appctx_set_applet() to assign an applet to this context.
+ */
+static inline void si_attach_appctx(struct stream_interface *si, struct appctx *appctx)
 {
-	si_release_endpoint(si);
 	si->ops = &si_embedded_ops;
-	si->appctx.applet = applet;
-	si->appctx.obj_type = OBJ_TYPE_APPCTX;
-	si->end = &si->appctx.obj_type;
+	appctx->obj_type = OBJ_TYPE_APPCTX;
+	si->end = &appctx->obj_type;
 }
 
 /* returns a pointer to the appctx being run in the SI or NULL if none */
@@ -156,12 +210,16 @@ static inline struct connection *si_alloc_conn(struct stream_interface *si)
 {
 	struct connection *conn;
 
-	/* we return the connection whether it's a real connection or NULL
-	 * in case another entity (an applet) is registered instead.
+	/* If we find a connection, we return it, otherwise it's an applet
+	 * and we start by releasing it.
 	 */
+	if (si->end) {
 		conn = objt_conn(si->end);
-	if (si->end)
+		if (conn)
 			return conn;
+		/* it was an applet then */
+		si_release_endpoint(si);
+	}
 
 	conn = conn_new();
 	if (conn)
@@ -170,6 +228,23 @@ static inline struct connection *si_alloc_conn(struct stream_interface *si)
 	return conn;
 }
 
+/* Release the interface's existing endpoint (connection or appctx) and
+ * allocate then initialize a new appctx which is assigned to the interface
+ * and returned. NULL may be returned upon memory shortage. It is left to the
+ * caller to call appctx_set_applet() to assign an applet to this context.
+ */
+static inline struct appctx *si_alloc_appctx(struct stream_interface *si)
+{
+	struct appctx *appctx;
+
+	si_release_endpoint(si);
+	appctx = appctx_new();
+	if (appctx)
+		si_attach_appctx(si, appctx);
+
+	return appctx;
+}
+
 /* Sends a shutr to the connection using the data layer */
 static inline void si_shutr(struct stream_interface *si)
 {

include/types/stream_interface.h

@@ -162,13 +162,11 @@ struct stream_interface {
 	struct channel *ib, *ob; /* input and output buffers */
 	void *owner;            /* generally a (struct task*) */
 	enum obj_type *end;     /* points to the end point (connection or appctx) */
-
 	struct si_ops *ops;     /* general operations at the stream interface layer */
 
 	/* struct members below are the "remote" part, as seen from the buffer side */
 	unsigned int err_type;  /* first error detected, one of SI_ET_* */
 	int conn_retries;	/* number of connect retries left */
-	struct appctx appctx;   /* context of the running applet if any */
 };
 
 /* An applet designed to run in a stream interface */

src/stream_interface.c

@@ -352,9 +352,15 @@ static void stream_int_chk_snd(struct stream_interface *si)
  */
 struct appctx *stream_int_register_handler(struct stream_interface *si, struct si_applet *app)
 {
+	struct appctx *appctx;
+
 	DPRINTF(stderr, "registering handler %p for si %p (was %p)\n", app, si, si->owner);
 
-	si_attach_applet(si, app);
+	appctx = si_alloc_appctx(si);
+	if (!si)
+		return NULL;
+
+	appctx_set_applet(appctx, app);
 	si->flags |= SI_FL_WAIT_DATA;
 	return si_appctx(si);
 }