page: new library for reference counted buffers

2 files changed, 162 insertions, 0 deletions

diff --git a/src/page.c b/src/page.c
new file mode 100644
index 000000000..a4f52ae4a
--- /dev/null
+++ b/src/page.c
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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
+ * (at your option) 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "page.h"
+
+#include <glib.h>
+
+#include <assert.h>
+#include <string.h>
+
+/**
+ * Allocates a new #page object, without filling the data element.
+ */
+static struct page *
+page_new(size_t size)
+{
+	struct page *page = g_malloc(sizeof(*page) + size -
+				     sizeof(page->data));
+
+	assert(size > 0);
+
+	page->ref = 1;
+	page->size = size;
+	return page;
+}
+
+struct page *
+page_new_copy(const void *data, size_t size)
+{
+	struct page *page = page_new(size);
+
+	assert(data != NULL);
+
+	memcpy(page->data, data, size);
+	return page;
+}
+
+void
+page_ref(struct page *page)
+{
+	g_atomic_int_inc(&page->ref);
+}
+
+static void
+page_free(struct page *page)
+{
+	assert(page->ref == 0);
+
+	g_free(page);
+}
+
+bool
+page_unref(struct page *page)
+{
+	bool unused = g_atomic_int_dec_and_test(&page->ref);
+
+	if (unused)
+		page_free(page);
+
+	return unused;
+}
diff --git a/src/page.h b/src/page.h
new file mode 100644
index 000000000..6bee4996f
--- /dev/null
+++ b/src/page.h
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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
+ * (at your option) 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * This is a library which manages reference counted buffers.
+ */
+
+#ifndef MPD_PAGE_H
+#define MPD_PAGE_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+/**
+ * A dynamically allocated buffer which keeps track of its reference
+ * count.  This is useful for passing buffers around, when several
+ * instances hold references to one buffer.
+ */
+struct page {
+	/**
+	 * The number of references to this buffer.  This library uses
+	 * atomic functions to access it, i.e. no locks are required.
+	 * As soon as this attribute reaches zero, the buffer is
+	 * freed.
+	 */
+	int ref;
+
+	/**
+	 * The size of this buffer in bytes.
+	 */
+	size_t size;
+
+	/**
+	 * Dynamic array containing the buffer data.
+	 */
+	unsigned char data[sizeof(long)];
+};
+
+/**
+ * Creates a new #page object, and copies data from the specified
+ * buffer.  It is initialized with a reference count of 1.
+ *
+ * @param data the source buffer
+ * @param size the size of the source buffer
+ * @return the new #page object
+ */
+struct page *
+page_new_copy(const void *data, size_t size);
+
+/**
+ * Increases the reference counter.
+ *
+ * @param page the #page object
+ */
+void
+page_ref(struct page *page);
+
+/**
+ * Decreases the reference counter.  If it reaches zero, the #page is
+ * freed.
+ *
+ * @param page the #page object
+ * @return true if the #page has been freed
+ */
+bool
+page_unref(struct page *page);
+
+#endif