iproto: report active connections number

Now there is new member in box.stat.net() called "CONNECTIONS"
which is a number of active iproto connections.

Closes #3905

@TarantoolBot document
Title: box.stat.net
Update the documentation for box.stat.net
to reflect the addition of the field
which reports iproto connections number.
(cherry picked from commit c96eca3)

src/box/iproto.cc

@@ -2060,6 +2060,12 @@ iproto_mem_used(void)
 	return slab_cache_used(&net_cord.slabc) + slab_cache_used(&net_slabc);
 }
 
+size_t
+iproto_connection_count(void)
+{
+	return mempool_count(&iproto_connection_pool);
+}
+
 void
 iproto_reset_stat(void)
 {

src/box/iproto.h

@@ -62,6 +62,12 @@ extern unsigned iproto_readahead;
 size_t
 iproto_mem_used(void);
 
+/**
+ * Return the number of active iproto connections.
+ */
+size_t
+iproto_connection_count(void);
+
 /**
  * Reset network statistics.
  */

src/box/lua/stat.c

@@ -140,6 +140,10 @@ static int
 lbox_stat_net_index(struct lua_State *L)
 {
 	luaL_checkstring(L, -1);
+	if (strcmp("CONNECTIONS", lua_tostring(L, -1)) == 0) {
+		lua_pushnumber(L, iproto_connection_count());
+		return 1;
+	}
 	return rmean_foreach(rmean_net, seek_stat_item, L);
 }
 
@@ -148,6 +152,11 @@ lbox_stat_net_call(struct lua_State *L)
 {
 	lua_newtable(L);
 	rmean_foreach(rmean_net, set_stat_item, L);
+
+	lua_pushstring(L, "CONNECTIONS");
+	lua_pushnumber(L, iproto_connection_count());
+	lua_settable(L, -3);
+
 	return 1;
 }
 

test/box/stat_net.result

@@ -34,6 +34,15 @@ LISTEN = require('uri').parse(box.cfg.listen)
 cn = remote.connect(LISTEN.host, LISTEN.service)
 ---
 ...
+cn1 = remote.connect(LISTEN.host, LISTEN.service)
+---
+...
+cn2 = remote.connect(LISTEN.host, LISTEN.service)
+---
+...
+cn3 = remote.connect(LISTEN.host, LISTEN.service)
+---
+...
 cn.space.tweedledum:select() --small request
 ---
 - []
@@ -46,8 +55,32 @@ box.stat.net.RECEIVED.total > 0
 ---
 - true
 ...
+box.stat.net.CONNECTIONS == 4
+---
+- true
+...
 -- box.stat.net.EVENTS.total > 0
 -- box.stat.net.LOCKS.total > 0
+WAIT_COND_TIMEOUT = 10
+---
+...
+cn1:close()
+---
+...
+cn2:close()
+---
+...
+test_run:wait_cond(function() return box.stat.net.CONNECTIONS == 2 end, WAIT_COND_TIMEOUT)
+---
+- true
+...
+cn3:close()
+---
+...
+test_run:wait_cond(function() return box.stat.net.CONNECTIONS == 1 end, WAIT_COND_TIMEOUT)
+---
+- true
+...
 -- reset
 box.stat.reset()
 ---
@@ -60,6 +93,10 @@ box.stat.net.RECEIVED.total
 ---
 - 0
 ...
+box.stat.net.CONNECTIONS
+---
+- 1
+...
 space:drop() -- tweedledum
 ---
 ...

test/box/stat_net.test.lua

@@ -13,18 +13,31 @@ remote = require 'net.box'
 
 LISTEN = require('uri').parse(box.cfg.listen)
 cn = remote.connect(LISTEN.host, LISTEN.service)
+cn1 = remote.connect(LISTEN.host, LISTEN.service)
+cn2 = remote.connect(LISTEN.host, LISTEN.service)
+cn3 = remote.connect(LISTEN.host, LISTEN.service)
 
 cn.space.tweedledum:select() --small request
 
 box.stat.net.SENT.total > 0
 box.stat.net.RECEIVED.total > 0
+box.stat.net.CONNECTIONS == 4
 -- box.stat.net.EVENTS.total > 0
 -- box.stat.net.LOCKS.total > 0
 
+WAIT_COND_TIMEOUT = 10
+
+cn1:close()
+cn2:close()
+test_run:wait_cond(function() return box.stat.net.CONNECTIONS == 2 end, WAIT_COND_TIMEOUT)
+cn3:close()
+test_run:wait_cond(function() return box.stat.net.CONNECTIONS == 1 end, WAIT_COND_TIMEOUT)
+
 -- reset
 box.stat.reset()
 box.stat.net.SENT.total
 box.stat.net.RECEIVED.total
+box.stat.net.CONNECTIONS
 
 space:drop() -- tweedledum
 cn:close()