Add (and use) generic reference counter, to improve signal:noise ratio

in code defining reference-counted objects.

src/core/interface.c

@@ -16,7 +16,6 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
-#include <assert.h>
 #include <gpxe/interface.h>
 
 /** @file
@@ -25,30 +24,6 @@
  *
  */
 
-/**
- * Obtain reference to interface
- *
- * @v intf		Interface
- * @ret intf		Interface
- *
- * Increases the reference count on the interface.
- */
-static struct interface * intf_get ( struct interface *intf ) {
-	intf->refcnt ( intf, +1 );
-	return intf;
-}
-
-/**
- * Drop reference to interface
- *
- * @v intf		Interface
- *
- * Decreases the reference count on the interface.
- */
-static void intf_put ( struct interface *intf ) {
-	intf->refcnt ( intf, -1 );
-}
-
 /**
  * Plug an interface into a new destination interface
  *
@@ -63,19 +38,7 @@ static void intf_put ( struct interface *intf ) {
  * interface into a null interface.
  */
 void plug ( struct interface *intf, struct interface *dest ) {
-	intf_put ( intf->dest );
-	intf->dest = intf_get ( dest );
-}
-
-/**
- * Null update reference count
- *
- * @v intf		Interface
- * @v delta		Change to apply to reference count
- *
- * Use this as the refcnt() method for an interface that does not need
- * to support reference counting.
- */
-void null_refcnt ( struct interface *intf __unused, int delta __unused ) {
-	/* Do nothing */
+	ref_put ( intf->refcnt );
+	ref_get ( dest->refcnt );
+	intf->dest = dest;
 }

src/core/job.c

@@ -71,7 +71,7 @@ struct job_interface_operations null_job_ops = {
 struct job_interface null_job = {
 	.intf = {
 		.dest = &null_job.intf,
-		.refcnt = null_refcnt,
+		.refcnt = NULL,
 	},
 	.op = &null_job_ops,
 };

src/core/refcnt.c

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdlib.h>
+#include <gpxe/refcnt.h>
+
+/** @file
+ *
+ * Reference counting
+ *
+ */
+
+/**
+ * Increment reference count
+ *
+ * @v refcnt		Reference counter, or NULL
+ *
+ * If @c refcnt is NULL, no action is taken.
+ */
+void ref_get ( struct refcnt *refcnt ) {
+
+	if ( ! refcnt )
+		return;
+
+	refcnt->refcnt++;
+
+	DBGC ( refcnt, "REFCNT %p incremented to %d\n",
+	       refcnt, refcnt->refcnt );
+}
+
+/**
+ * Decrement reference count
+ *
+ * @v refcnt		Reference counter, or NULL
+ *
+ * If the reference count decreases below zero, the object's free()
+ * method will be called.
+ *
+ * If @c refcnt is NULL, no action is taken.
+ */
+void ref_put ( struct refcnt *refcnt ) {
+
+	if ( ! refcnt )
+		return;
+
+	refcnt->refcnt--;
+	DBGC ( refcnt, "REFCNT %p decremented to %d\n",
+	       refcnt, refcnt->refcnt );
+
+	if ( refcnt->refcnt >= 0 )
+		return;
+
+	if ( refcnt->free ) {
+		refcnt->free ( refcnt );
+	} else {
+		free ( refcnt );
+	}
+}

src/core/xfer.c

@@ -230,7 +230,7 @@ struct xfer_interface_operations null_xfer_ops = {
 struct xfer_interface null_xfer = {
 	.intf = {
 		.dest = &null_xfer.intf,
-		.refcnt = null_refcnt,
+		.refcnt = NULL,
 	},
 	.op = &null_xfer_ops,
 };

src/include/gpxe/interface.h

@@ -7,6 +7,8 @@
  *
  */
 
+#include <gpxe/refcnt.h>
+
 /** An object communication interface */
 struct interface {
 	/** Destination interface
@@ -18,19 +20,14 @@ struct interface {
 	 * unplugged, it should point to a null interface.
 	 */
 	struct interface *dest;
-	/** Update reference count
-	 *
-	 * @v intf		Interface
-	 * @v delta		Change to apply to reference count
+	/** Reference counter
 	 *
-	 * This method updates the reference count for the object
-	 * containing the interface.
+	 * If this interface is not part of a reference-counted
+	 * object, this field may be NULL.
 	 */
-	void ( * refcnt ) ( struct interface *intf, int delta );
+	struct refcnt *refcnt;
 };
 
 extern void plug ( struct interface *intf, struct interface *dest );
 
-extern void null_refcnt ( struct interface *intf, int delta );
-
 #endif /* _GPXE_INTERFACE_H */

src/include/gpxe/job.h

@@ -76,12 +76,11 @@ extern void ignore_progress ( struct job_interface *job,
  *
  * @v job		Job control interface
  * @v op		Job control interface operations
- * @v refcnt		Job control interface reference counting method
+ * @v refcnt		Containing object reference counter, or NULL
  */
 static inline void job_init ( struct job_interface *job,
-			       struct job_interface_operations *op,
-			       void ( * refcnt ) ( struct interface *intf,
-						   int delta ) ) {
+			      struct job_interface_operations *op,
+			      struct refcnt *refcnt ) {
 	job->intf.dest = &null_job.intf;
 	job->intf.refcnt = refcnt;
 	job->op = op;

src/include/gpxe/refcnt.h

@@ -0,0 +1,39 @@
+#ifndef _GPXE_REFCNT_H
+#define _GPXE_REFCNT_H
+
+/** @file
+ *
+ * Reference counting
+ *
+ */
+
+/**
+ * A reference counter
+ *
+ * This data structure is designed to be embedded within a
+ * reference-counted object.
+ */
+struct refcnt {
+	/** Current reference count
+	 *
+	 * When this count is decremented below zero, the free()
+	 * method will be called.
+	 */
+	int refcnt;
+	/** Free containing object
+	 *
+	 * This method is called when the reference count is
+	 * decremented below zero.
+	 *
+	 * If this method is left NULL, the standard library free()
+	 * function will be called.  The upshot of this is that you
+	 * may omit the free() method if the @c refcnt object is the
+	 * first element of your reference-counted struct.
+	 */
+	void ( * free ) ( struct refcnt *refcnt );
+};
+
+extern void ref_get ( struct refcnt *refcnt );
+extern void ref_put ( struct refcnt *refcnt );
+
+#endif /* _GPXE_REFCNT_H */

src/include/gpxe/xfer.h

@@ -114,12 +114,11 @@ extern int ignore_deliver_raw ( struct xfer_interface *xfer,
  *
  * @v xfer		Data transfer interface
  * @v op		Data transfer interface operations
- * @v refcnt		Data transfer interface reference counting method
+ * @v refcnt		Containing object reference counter, or NULL
  */
 static inline void xfer_init ( struct xfer_interface *xfer,
 			       struct xfer_interface_operations *op,
-			       void ( * refcnt ) ( struct interface *intf,
-						   int delta ) ) {
+			       struct refcnt *refcnt ) {
 	xfer->intf.dest = &null_xfer.intf;
 	xfer->intf.refcnt = refcnt;
 	xfer->op = op;