fixes #1408 Reference count as a first class type

This starts by using this for the nni_pipe, but we will use it
for the other primary objects as well.  This should simplify
the tear down and hopefully eliminate some races.

It does mean that pipe destruction goes through an additional
context switch, for now at least.  This shouldn't be on the hot
data path anyway.

src/core/CMakeLists.txt

@@ -57,6 +57,8 @@ nng_sources(
         protocol.h
         reap.c
         reap.h
+        refcnt.c
+        refcnt.h
         sockaddr.c
         socket.c
         socket.h

src/core/nng_impl.h

@@ -40,6 +40,7 @@
 #include "core/pollable.h"
 #include "core/protocol.h"
 #include "core/reap.h"
+#include "core/refcnt.h"
 #include "core/stats.h"
 #include "core/stream.h"
 #include "core/strs.h"

src/core/pipe.c

@@ -25,19 +25,31 @@ static nni_id_map pipes =
 static nni_mtx pipes_lk = NNI_MTX_INITIALIZER;
 
 static void pipe_destroy(void *);
+static void pipe_reap(void *);
 
 static nni_reap_list pipe_reap_list = {
 	.rl_offset = offsetof(nni_pipe, p_reap),
-	.rl_func   = pipe_destroy,
+	.rl_func   = pipe_reap,
 };
 
 static void
 pipe_destroy(void *arg)
 {
 	nni_pipe *p = arg;
-	if (p == NULL) {
-		return;
+
+	if (p->p_proto_data != NULL) {
+		p->p_proto_ops.pipe_fini(p->p_proto_data);
 	}
+	if (p->p_tran_data != NULL) {
+		p->p_tran_ops.p_fini(p->p_tran_data);
+	}
+	nni_free(p, p->p_size);
+}
+
+void
+pipe_reap(void *arg)
+{
+	nni_pipe *p = arg;
 
 	nni_pipe_run_cb(p, NNG_PIPE_EV_REM_POST);
 
@@ -47,32 +59,21 @@ pipe_destroy(void *arg)
 	if (p->p_id != 0) {
 		nni_id_remove(&pipes, p->p_id);
 	}
-	// This wait guarantees that all callers are done with us.
-	while (p->p_ref != 0) {
-		nni_cv_wait(&p->p_cv);
-	}
 	nni_mtx_unlock(&pipes_lk);
 
-	if (p->p_proto_data != NULL) {
-		p->p_proto_ops.pipe_stop(p->p_proto_data);
-	}
-	if ((p->p_tran_data != NULL) && (p->p_tran_ops.p_stop != NULL)) {
-		p->p_tran_ops.p_stop(p->p_tran_data);
-	}
-
 #ifdef NNG_ENABLE_STATS
 	nni_stat_unregister(&p->st_root);
 #endif
 	nni_pipe_remove(p);
 
 	if (p->p_proto_data != NULL) {
-		p->p_proto_ops.pipe_fini(p->p_proto_data);
+		p->p_proto_ops.pipe_stop(p->p_proto_data);
 	}
-	if (p->p_tran_data != NULL) {
-		p->p_tran_ops.p_fini(p->p_tran_data);
+	if ((p->p_tran_data != NULL) && (p->p_tran_ops.p_stop != NULL)) {
+		p->p_tran_ops.p_stop(p->p_tran_data);
 	}
-	nni_cv_fini(&p->p_cv);
-	nni_free(p, p->p_size);
+
+	nni_pipe_rele(p);
 }
 
 int
@@ -86,7 +87,7 @@ nni_pipe_find(nni_pipe **pp, uint32_t id)
 	// close the pipe.
 	nni_mtx_lock(&pipes_lk);
 	if ((p = nni_id_get(&pipes, id)) != NULL) {
-		p->p_ref++;
+		nni_refcnt_hold(&p->p_refcnt);
 		*pp = p;
 	}
 	nni_mtx_unlock(&pipes_lk);
@@ -96,12 +97,7 @@ nni_pipe_find(nni_pipe **pp, uint32_t id)
 void
 nni_pipe_rele(nni_pipe *p)
 {
-	nni_mtx_lock(&pipes_lk);
-	p->p_ref--;
-	if (p->p_ref == 0) {
-		nni_cv_wake(&p->p_cv);
-	}
-	nni_mtx_unlock(&pipes_lk);
+	nni_refcnt_rele(&p->p_refcnt);
 }
 
 // nni_pipe_id returns the 32-bit pipe id, which can be used in backtraces.
@@ -250,15 +246,14 @@ pipe_create(nni_pipe **pp, nni_sock *sock, nni_sp_tran *tran, void *tran_data)
 	p->p_proto_ops  = *pops;
 	p->p_sock       = sock;
 	p->p_cbs        = false;
-	p->p_ref        = 1;
+
+	nni_refcnt_init(&p->p_refcnt, 2, p, pipe_destroy);
 
 	nni_atomic_init_bool(&p->p_closed);
 	nni_atomic_flag_reset(&p->p_stop);
 	NNI_LIST_NODE_INIT(&p->p_sock_node);
 	NNI_LIST_NODE_INIT(&p->p_ep_node);
 
-	nni_cv_init(&p->p_cv, &pipes_lk);
-
 	nni_mtx_lock(&pipes_lk);
 	rv = nni_id_alloc32(&pipes, &p->p_id, p);
 	nni_mtx_unlock(&pipes_lk);

src/core/refcnt.c

@@ -0,0 +1,33 @@
+// Copyright 2024 Staysail Systems, Inc. <[email protected]>
+//
+// This software is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+#include <core/refcnt.h>
+
+void
+nni_refcnt_init(
+    nni_refcnt *rc, unsigned value, void *data, void (*fini)(void *))
+{
+	nni_atomic_init(&rc->rc_cnt);
+	nni_atomic_set(&rc->rc_cnt, value);
+	rc->rc_data = data;
+	rc->rc_fini = fini;
+}
+
+void
+nni_refcnt_hold(nni_refcnt *rc)
+{
+	nni_atomic_inc(&rc->rc_cnt);
+}
+
+void
+nni_refcnt_rele(nni_refcnt *rc)
+{
+	if (nni_atomic_dec_nv(&rc->rc_cnt) == 0) {
+		rc->rc_fini(rc->rc_data);
+	}
+}

src/core/refcnt.h

@@ -0,0 +1,28 @@
+// Copyright 2024 Staysail Systems, Inc. <[email protected]>
+//
+// This software is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+#ifndef CORE_REFCNT_H
+#define CORE_REFCNT_H
+
+#include <nng/nng.h>
+
+#include <core/nng_impl.h>
+#include <core/platform.h>
+
+typedef struct {
+	nni_atomic_int rc_cnt;
+	void (*rc_fini)(void *);
+	void *rc_data;
+} nni_refcnt;
+
+extern void nni_refcnt_init(
+    nni_refcnt *rc, unsigned value, void *v, void (*fini)(void *));
+extern void nni_refcnt_hold(nni_refcnt *rc);
+extern void nni_refcnt_rele(nni_refcnt *rc);
+
+#endif // CORE_REFCNT_H

src/core/sockimpl.h

@@ -105,9 +105,8 @@ struct nni_pipe {
 	nni_atomic_bool    p_closed;
 	nni_atomic_flag    p_stop;
 	bool               p_cbs;
-	int                p_ref;
-	nni_cv             p_cv;
 	nni_reap_node      p_reap;
+	nni_refcnt         p_refcnt;
 
 #ifdef NNG_ENABLE_STATS
 	nni_stat_item st_root;