core: add "gf_ref_t" for common refcounting structures

Checks for compiler supported atomic operations comes from client_t.h.

An example usage of this change can be found in adding reference
counting to "struct auth_cache_entry" in http://review.gluster.org/11023

Basic usage looks like this:

   #include "refcount.h"

   struct my_struct {
       GF_REF_DECL;
       ... /* more members */
   }

   void my_destructor (void *data)
   {
       struct my_struct *my_ptr = (struct my_struct *) data;

       ... /* do some more cleanups */
       GF_FREE (my_ptr);
   }

   void init_ptr (struct parent *parent)
   {
       struct my_struct *my_ptr = malloc (sizeof (struct my_struct));

       GF_REF_INIT (my_ptr, my_destructor); /* refcount is set to 1 */

       ... /* my_ptr probably gets added to some parent structure */
       parent_add_ptr (parent, my_ptr);
   }

   void do_something (struct parent *parent)
   {
       struct my_struct *my_ptr = NULL;

       /* likely need to lock parent, depends on its access pattern */
       my_ptr = parent_remove_first_ptr (parent);
       /* unlock parent */

       ... /* do something */

       GF_REF_PUT (my_ptr); /* calls my_destructor on refcount = 0 */
   }

URL: http://thread.gmane.org/gmane.comp.file-systems.gluster.devel/11202
Change-Id: Idb98a5861a44c31676108ed8876db12c320912ef
BUG: 1235939
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/11022
Reviewed-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Tested-by: NetBSD Build System <jenkins@build.gluster.org>
(cherry picked from commit ea1d2b0045e2c2ad82a2162a58f9fc36f9d07b20)
Reviewed-on: http://review.gluster.org/11421
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Tested-by: Raghavendra G <rgowdapp@redhat.com>

3 files changed, 217 insertions, 2 deletions

diff --git a/libglusterfs/src/Makefile.am b/libglusterfs/src/Makefile.am
index fc0e3053a49..27d51dba7d6 100644
--- a/libglusterfs/src/Makefile.am
+++ b/libglusterfs/src/Makefile.am
@@ -22,7 +22,7 @@ libglusterfs_la_SOURCES = dict.c xlator.c logging.c \
 	$(CONTRIBDIR)/rbtree/rb.c rbthash.c store.c latency.c \
 	graph.c syncop.c graph-print.c trie.c run.c options.c fd-lk.c \
 	circ-buff.c event-history.c gidcache.c ctx.c client_t.c event-poll.c \
-	event-epoll.c syncop-utils.c cluster-syncop.c \
+	event-epoll.c syncop-utils.c cluster-syncop.c refcount.c \
 	$(CONTRIBDIR)/libgen/basename_r.c \
 	$(CONTRIBDIR)/libgen/dirname_r.c $(CONTRIBDIR)/stdlib/gf_mkostemp.c \
 	strfd.c parse-utils.c $(CONTRIBDIR)/mount/mntent.c \
@@ -40,7 +40,7 @@ noinst_HEADERS = common-utils.h defaults.h dict.h glusterfs.h hashfn.h timespec.
 	gf-dirent.h locking.h syscall.h iobuf.h globals.h statedump.h \
 	checksum.h daemon.h $(CONTRIBDIR)/rbtree/rb.h store.h\
 	rbthash.h iatt.h latency.h mem-types.h syncop.h cluster-syncop.h \
-	graph-utils.h trie.h \
+	graph-utils.h trie.h refcount.h \
 	run.h options.h lkowner.h fd-lk.h circ-buff.h event-history.h \
 	gidcache.h client_t.h glusterfs-acl.h glfs-message-id.h \
 	template-component-messages.h strfd.h syncop-utils.h parse-utils.h \
diff --git a/libglusterfs/src/refcount.c b/libglusterfs/src/refcount.c
new file mode 100644
index 00000000000..96edc10982a
--- /dev/null
+++ b/libglusterfs/src/refcount.c
@@ -0,0 +1,112 @@
+/*
+  Copyright (c) 2015 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+#include "common-utils.h"
+#include "refcount.h"
+
+#ifndef REFCOUNT_NEEDS_LOCK
+
+unsigned int
+_gf_ref_get (gf_ref_t *ref)
+{
+        unsigned int cnt = __sync_fetch_and_add (&ref->cnt, 1);
+
+        /* if cnt == 0, we're in a fatal position, the object will be free'd
+         *
+         * There is a race when two threads do a _gf_ref_get(). Only one of
+         * them may get a 0 returned. That is acceptible, because one
+         * _gf_ref_get() returning 0 should be handled as a fatal problem and
+         * when correct usage/locking is used, it should never happen.
+         */
+        GF_ASSERT (cnt != 0);
+
+        return cnt;
+}
+
+unsigned int
+_gf_ref_put (gf_ref_t *ref)
+{
+        unsigned int cnt = __sync_fetch_and_sub (&ref->cnt, 1);
+
+        /* if cnt == 1, the last user just did a _gf_ref_put()
+         *
+         * When cnt == 0, one _gf_ref_put() was done too much and there has
+         * been a thread using the refcounted structure when it was not
+         * supposed to.
+         */
+        GF_ASSERT (cnt != 0);
+
+        if (cnt == 1 && ref->release) {
+                ref->release (ref->data);
+                /* set return value to 0 to inform the caller correctly */
+                cnt = 0;
+        }
+
+        return cnt;
+}
+
+#else
+
+unsigned int
+_gf_ref_get (gf_ref_t *ref)
+{
+        unsigned int cnt = 0;
+
+        LOCK (&ref->lk);
+        {
+                /* never can be 0, should have been free'd */
+                if (ref->cnt > 0)
+                        cnt = ++ref->cnt;
+                else
+                        GF_ASSERT (ref->cnt > 0);
+        }
+        UNLOCK (&ref->lk);
+
+        return cnt;
+}
+
+unsigned int
+_gf_ref_put (gf_ref_t *ref)
+{
+        unsigned int cnt = 0;
+        int release = 0;
+
+        LOCK (&ref->lk);
+        {
+                if (ref->cnt != 0) {
+                        cnt = --ref->cnt;
+                        /* call release() only when cnt == 0 */
+                        release = (cnt == 0);
+                } else
+                        GF_ASSERT (ref->cnt != 0);
+        }
+        UNLOCK (&ref->lk);
+
+        if (release && ref->release)
+                ref->release (ref->data);
+
+        return cnt;
+}
+
+#endif /* REFCOUNT_NEEDS_LOCK */
+
+
+void
+_gf_ref_init (gf_ref_t *ref, gf_ref_release_t release, void *data)
+{
+        GF_ASSERT (ref);
+
+#ifdef REFCOUNT_NEEDS_LOCK
+        LOCK_INIT (&ref->lk);
+#endif
+        ref->cnt = 1;
+        ref->release = release;
+        ref->data = data;
+}
diff --git a/libglusterfs/src/refcount.h b/libglusterfs/src/refcount.h
new file mode 100644
index 00000000000..c8113a2d76b
--- /dev/null
+++ b/libglusterfs/src/refcount.h
@@ -0,0 +1,103 @@
+/*
+  Copyright (c) 2015 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+#ifndef _REFCOUNT_H
+#define _REFCOUNT_H
+
+/* check for compiler support for __sync_*_and_fetch()
+ *
+ * a more comprehensive feature test is shown at
+ * http://lists.iptel.org/pipermail/semsdev/2010-October/005075.html
+ * this is sufficient for RHEL5 i386 builds
+ */
+#if (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)) && !defined(__i386__)
+#undef REFCOUNT_NEEDS_LOCK
+#else
+#define REFCOUNT_NEEDS_LOCK
+#include "locking.h"
+#endif /* compiler support for __sync_*_and_fetch() */
+
+typedef void (*gf_ref_release_t)(void *data);
+
+struct _gf_ref_t {
+#ifdef REFCOUNT_NEEDS_LOCK
+        gf_lock_t          lk;      /* lock for atomically adjust cnt */
+#endif
+        unsigned int       cnt;     /* number of users, free on 0 */
+
+        gf_ref_release_t   release; /* cleanup when cnt == 0 */
+        void              *data;    /* parameter passed to release() */
+};
+typedef struct _gf_ref_t gf_ref_t;
+
+
+/* _gf_ref_get -- increase the refcount and return the number of references
+ *
+ * @return: greater then 0 when a reference was taken, 0 when not
+ */
+unsigned int
+_gf_ref_get (gf_ref_t *ref);
+
+/* _gf_ref_put -- decrease the refcount and return the number of references
+ *
+ * @return: greater then 0 when there are still references, 0 when cleanup
+ *          should be done
+ */
+unsigned int
+_gf_ref_put (gf_ref_t *ref);
+
+/* _gf_ref_init -- initalize an embedded refcount object
+ *
+ * @release: function to call when the refcount == 0
+ * @data: parameter to be passed to @release
+ */
+void
+_gf_ref_init (gf_ref_t *ref, gf_ref_release_t release, void *data);
+
+
+/*
+ * Strong suggestion to use the simplified GF_REF_* API.
+ */
+
+/* GF_REF_DECL -- declaration to put inside your structure
+ *
+ * Example:
+ *   struct my_struct {
+ *       GF_REF_DECL;
+ *
+ *       ... // additional members
+ *   };
+ */
+#define GF_REF_DECL         gf_ref_t _ref
+
+/* GF_REF_INIT -- initialize a GF_REF_DECL structure
+ *
+ * @p: allocated structure with GF_REF_DECL
+ * @d: destructor to call once refcounting reaches 0
+ *
+ * Sets the refcount to 1.
+ */
+#define GF_REF_INIT(p, d)   (_gf_ref_init (&p->_ref, d, p))
+
+/* GF_REF_GET -- increase the refcount of a GF_REF_DECL structure
+ *
+ * @return: greater then 0 when a reference was taken, 0 when not
+ */
+#define GF_REF_GET(p)       (_gf_ref_get (&p->_ref))
+
+/* GF_REF_PUT -- decrease the refcount of a GF_REF_DECL structure
+ *
+ * @return: greater then 0 when there are still references, 0 when cleanup
+ *          should be done
+ */
+#define GF_REF_PUT(p)       (_gf_ref_put (&p->_ref))
+
+
+#endif /* _REFCOUNT_H */