fixes #4 Statistics support

This introduces new public APIs for obtaining statistics,
and adds some generic stats for dialers, listeners, pipes, and
sockets.  Also added are stats for inproc and pairv1 protocol.

The other protocols and transports will have stats added
incrementally as time goes on.

A simple test program, and man pages are provided for this.
Start by looking at nng_stat(5).

Statistics does have some impact, and they can be disabled by
using the advanced NNG_ENABLE_STATS (setting it to OFF, it's
ON by default) if you need to build a minimized configuration.

1 files changed, 108 insertions, 0 deletions

diff --git a/src/core/stats.h b/src/core/stats.h
new file mode 100644
index 00000000..8cfe14de
--- /dev/null
+++ b/src/core/stats.h
@@ -0,0 +1,108 @@
+//
+// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2018 Capitar IT Group BV <info@capitar.com>
+//
+// 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_STATS_H
+#define CORE_STATS_H
+
+#include "core/defs.h"
+
+// Statistics support.  This is inspired in part by the Solaris
+// kstats framework, but we've simplified and tuned it for our use.
+//
+// Collection of the stats will be done in two steps.  First we
+// will walk the list of stats, with the chain held, allocating
+// a user local copy of the stat and pointers.
+//
+// In phase 2, we run the update, and copy the values. We conditionally
+// acquire the lock on the stat first though.
+
+typedef struct nni_stat_item nni_stat_item;
+
+typedef void (*nni_stat_update)(nni_stat_item *, void *);
+typedef enum nng_stat_type_enum nni_stat_type;
+typedef enum nng_unit_enum      nni_stat_unit;
+
+// nni_stat_item is used by providers
+struct nni_stat_item {
+#ifdef NNG_ENABLE_STATS
+	nni_list_node   si_node;     // list node, framework use only
+	nni_stat_item * si_parent;   // link back to parent, framework use only
+	nni_list        si_children; // children, framework use only
+	const char *    si_name;     // name of statistic
+	const char *    si_desc;     // description of statistic (English)
+	nni_mtx *       si_lock;     // lock for accessing, can be NULL
+	void *          si_private;  // provider private pointer
+	nni_stat_type   si_type;     // type of stat, e.g. NNG_STAT_LEVEL
+	nni_stat_unit   si_unit;     // units, e.g. NNG_UNIT_MILLIS
+	nni_stat_update si_update;   // update function (can be NULL)
+	const char *    si_string;   // string value (NULL for numerics)
+	uint64_t        si_value;    // numeric value
+	nni_atomic_u64  si_atomic;   // atomic value
+#endif
+};
+
+void nni_stat_append(nni_stat_item *, nni_stat_item *);
+void nni_stat_remove(nni_stat_item *);
+
+void nni_stat_set_value(nni_stat_item *, uint64_t);
+void nni_stat_set_string(nni_stat_item *, const char *);
+void nni_stat_set_lock(nni_stat_item *, nni_mtx *);
+void nni_stat_set_update(nni_stat_item *, nni_stat_update, void *);
+
+#ifdef NNG_ENABLE_STATS
+void nni_stat_init(nni_stat_item *, const char *, const char *);
+void nni_stat_init_scope(nni_stat_item *, const char *, const char *);
+void nni_stat_init_string(
+    nni_stat_item *, const char *, const char *, const char *);
+void nni_stat_init_id(nni_stat_item *, const char *, const char *, uint64_t);
+void nni_stat_init_bool(nni_stat_item *, const char *, const char *, bool);
+void nni_stat_init_atomic(nni_stat_item *, const char *, const char *);
+void nni_stat_inc_atomic(nni_stat_item *, uint64_t);
+void nni_stat_dec_atomic(nni_stat_item *, uint64_t);
+void nni_stat_set_type(nni_stat_item *, int);
+void nni_stat_set_unit(nni_stat_item *, int);
+#else
+// We override initialization so that we can avoid compiling static strings
+// into the binary.  Presumably if stats are disabled, we are trying to save
+// space for constrained environments.  We do evaluate an unused arg to
+// prevent the compiler from bitching about unused values.
+#define nni_stat_init(a, b, c) ((void) (a))
+#define nni_stat_init_scope(a, b, c) ((void) (a))
+#define nni_stat_init_atomic(a, b, c) ((void) (a))
+#define nni_stat_init_id(a, b, c, d) ((void) (a))
+#define nni_stat_init_bool(a, b, c, d) ((void) (a))
+#define nni_stat_init_string(a, b, c, d) ((void) (a))
+#define nni_stat_set_unit(a, b) ((void) (a))
+#define nni_stat_set_type(a, b) ((void) (a))
+#define nni_stat_inc_atomic(stat, inc)
+#define nni_stat_dec_atomic(stat, inc)
+#endif
+
+#if 0
+#define nni_stat_append(a, b)
+#define nni_stat_remove(a)
+#define nni_stat_init(a, b, c)
+#define nni_stat_init_scope(a, b, c)
+#define nni_stat_init_string(a, b, c, d)
+#define nni_stat_init_id(a, b, c, d)
+#define nni_stat_init_bool(a, b, c, d)
+#define nni_stat_dec_atomic(a, b)
+#define nni_stat_set_value(a, b)
+#define nni_stat_set_string(a, b)
+#define nni_stat_set_lock(a, b)
+#define nni_stat_set_update(a, b, c)
+#define nni_stat_set_type(a, b)
+#define nni_stat_set_unit(a, b)
+#endif
+
+int  nni_stat_sys_init(void);
+void nni_stat_sys_fini(void);
+
+#endif // CORE_STATS_H