Do not force internal collectors to call rrdset_next. (#13926)

* Remove calls to rrdset_next().

* Rm checks plugin

* Update documentantion

* Call rrdset_next from within rrdset_done

This wraps up the removal of rrdset_next from internal collectors, which
removes a lot of unecessary code and the need for if/else clauses in
every place.

The pluginsd parser is the only component that calls rrdset_next*()
functions because it's not strictly speaking a collector but more of a
collector manager/proxy.

With the current changes it's possible to simplify the API we expose
from RRD significantly, but this will be follow-up work in the future.

* Remove stale reference to checks.plugin

* Fix RRD unit test

rrdset_next is not meant to be called from these tests.

* Fix db engine unit test.

* Schedule rrdset_next when we have completed at least one collection.

* Mark chart creation clauses as unlikely.

* Add missing brace to fix FreeBSD plugin.

56 files changed, 227 insertions, 1629 deletions

diff --git a/collectors/COLLECTORS.md b/collectors/COLLECTORS.md
index 5c41b704fd..7f66076ff0 100644
--- a/collectors/COLLECTORS.md
+++ b/collectors/COLLECTORS.md
@@ -514,6 +514,5 @@ default. To use a third-party collector, visit their GitHub/documentation page a
 
 ## Etc
 
-- [checks.plugin](checks.plugin/README.md): A debugging collector, disabled by default.
 - [charts.d example](charts.d.plugin/example/README.md): An example `charts.d` collector.
 - [python.d example](python.d.plugin/example/README.md): An example `python.d` collector.
diff --git a/collectors/Makefile.am b/collectors/Makefile.am
index a0a972e8f3..9f8bf52807 100644
--- a/collectors/Makefile.am
+++ b/collectors/Makefile.am
@@ -7,7 +7,6 @@ SUBDIRS = \
     apps.plugin \
     cgroups.plugin \
     charts.d.plugin \
-    checks.plugin \
     cups.plugin \
     diskspace.plugin \
     timex.plugin \
diff --git a/collectors/REFERENCE.md b/collectors/REFERENCE.md
index 949858f600..939b189ee7 100644
--- a/collectors/REFERENCE.md
+++ b/collectors/REFERENCE.md
@@ -148,11 +148,6 @@ collect_data() {
         // attach a metric to it
         rd = rrddim_add(st, "id", "name", multiplier, divider, algorithm);
     }
-    else {
-        // this chart is already created
-        // let Netdata know we start a new iteration on it
-        rrdset_next(st);
-    }
 
     // give the collected value(s) to the chart
     rrddim_set_by_pointer(st, rd, collected_value);
diff --git a/collectors/cgroups.plugin/sys_fs_cgroup.c b/collectors/cgroups.plugin/sys_fs_cgroup.c
index 3bee46dcf4..8f7548286c 100644
--- a/collectors/cgroups.plugin/sys_fs_cgroup.c
+++ b/collectors/cgroups.plugin/sys_fs_cgroup.c
@@ -1447,7 +1447,6 @@ static inline void cgroup2_read_pressure(struct pressure *res) {
             return;
         }
 
-    
         res->some.share_time.value10 = strtod(procfile_lineword(ff, 0, 2), NULL);
         res->some.share_time.value60 = strtod(procfile_lineword(ff, 0, 4), NULL);
         res->some.share_time.value300 = strtod(procfile_lineword(ff, 0, 6), NULL);
@@ -2847,57 +2846,45 @@ void update_systemd_services_charts(
 
     // create the charts
 
-    if(likely(do_cpu)) {
-        if(unlikely(!st_cpu)) {
-            char title[CHART_TITLE_MAX + 1];
-            snprintfz(title, CHART_TITLE_MAX, "Systemd Services CPU utilization (100%% = 1 core)");
-
-            st_cpu = rrdset_create_localhost(
-                    "services"
-                    , "cpu"
-                    , NULL
-                    , "cpu"
-                    , "services.cpu"
-                    , title
-                    , "percentage"
-                    , PLUGIN_CGROUPS_NAME
-                    , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
-                    , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD
-                    , update_every
-                    , RRDSET_TYPE_STACKED
-            );
-
-        }
-        else
-            rrdset_next(st_cpu);
+    if (unlikely(do_cpu && !st_cpu)) {
+        char title[CHART_TITLE_MAX + 1];
+        snprintfz(title, CHART_TITLE_MAX, "Systemd Services CPU utilization (100%% = 1 core)");
+
+        st_cpu = rrdset_create_localhost(
+                "services"
+                , "cpu"
+                , NULL
+                , "cpu"
+                , "services.cpu"
+                , title
+                , "percentage"
+                , PLUGIN_CGROUPS_NAME
+                , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
+                , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD
+                , update_every
+                , RRDSET_TYPE_STACKED
+        );
     }
 
-    if(likely(do_mem_usage)) {
-        if(unlikely(!st_mem_usage)) {
-
-            st_mem_usage = rrdset_create_localhost(
-                    "services"
-                    , "mem_usage"
-                    , NULL
-                    , "mem"
-                    , "services.mem_usage"
-                    , "Systemd Services Used Memory"
-                    , "MiB"
-                    , PLUGIN_CGROUPS_NAME
-                    , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
-                    , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 10
-                    , update_every
-                    , RRDSET_TYPE_STACKED
-            );
-
-        }
-        else
-            rrdset_next(st_mem_usage);
+    if (unlikely(do_mem_usage && !st_mem_usage)) {
+        st_mem_usage = rrdset_create_localhost(
+                "services"
+                , "mem_usage"
+                , NULL
+                , "mem"
+                , "services.mem_usage"
+                , "Systemd Services Used Memory"
+                , "MiB"
+                , PLUGIN_CGROUPS_NAME
+                , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
+                , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 10
+                , update_every
+                , RRDSET_TYPE_STACKED
+        );
     }
 
     if(likely(do_mem_detailed)) {
         if(unlikely(!st_mem_detailed_rss)) {
-
             st_mem_detailed_rss = rrdset_create_localhost(
                     "services"
                     , "mem_rss"
@@ -2912,13 +2899,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_mem_detailed_rss);
 
         if(unlikely(!st_mem_detailed_mapped)) {
-
             st_mem_detailed_mapped = rrdset_create_localhost(
                     "services"
                     , "mem_mapped"
@@ -2933,13 +2916,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_mem_detailed_mapped);
 
         if(unlikely(!st_mem_detailed_cache)) {
-
             st_mem_detailed_cache = rrdset_create_localhost(
                     "services"
                     , "mem_cache"
@@ -2954,13 +2933,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_mem_detailed_cache);
 
         if(unlikely(!st_mem_detailed_writeback)) {
-
             st_mem_detailed_writeback = rrdset_create_localhost(
                     "services"
                     , "mem_writeback"
@@ -2977,11 +2952,8 @@ void update_systemd_services_charts(
             );
 
         }
-        else
-            rrdset_next(st_mem_detailed_writeback);
 
         if(unlikely(!st_mem_detailed_pgfault)) {
-
             st_mem_detailed_pgfault = rrdset_create_localhost(
                     "services"
                     , "mem_pgfault"
@@ -2997,11 +2969,8 @@ void update_systemd_services_charts(
                     , RRDSET_TYPE_STACKED
             );
         }
-        else
-            rrdset_next(st_mem_detailed_pgfault);
 
         if(unlikely(!st_mem_detailed_pgmajfault)) {
-
             st_mem_detailed_pgmajfault = rrdset_create_localhost(
                     "services"
                     , "mem_pgmajfault"
@@ -3016,13 +2985,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_mem_detailed_pgmajfault);
 
         if(unlikely(!st_mem_detailed_pgpgin)) {
-
             st_mem_detailed_pgpgin = rrdset_create_localhost(
                     "services"
                     , "mem_pgpgin"
@@ -3039,11 +3004,8 @@ void update_systemd_services_charts(
             );
 
         }
-        else
-            rrdset_next(st_mem_detailed_pgpgin);
 
         if(unlikely(!st_mem_detailed_pgpgout)) {
-
             st_mem_detailed_pgpgout = rrdset_create_localhost(
                     "services"
                     , "mem_pgpgout"
@@ -3058,61 +3020,45 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_mem_detailed_pgpgout);
     }
 
-    if(likely(do_mem_failcnt)) {
-        if(unlikely(!st_mem_failcnt)) {
-
-            st_mem_failcnt = rrdset_create_localhost(
-                    "services"
-                    , "mem_failcnt"
-                    , NULL
-                    , "mem"
-                    , "services.mem_failcnt"
-                    , "Systemd Services Memory Limit Failures"
-                    , "failures"
-                    , PLUGIN_CGROUPS_NAME
-                    , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
-                    , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 110
-                    , update_every
-                    , RRDSET_TYPE_STACKED
-            );
-
-        }
-        else
-            rrdset_next(st_mem_failcnt);
+    if(unlikely(do_mem_failcnt && !st_mem_failcnt)) {
+        st_mem_failcnt = rrdset_create_localhost(
+                "services"
+                , "mem_failcnt"
+                , NULL
+                , "mem"
+                , "services.mem_failcnt"
+                , "Systemd Services Memory Limit Failures"
+                , "failures"
+                , PLUGIN_CGROUPS_NAME
+                , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
+                , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 110
+                , update_every
+                , RRDSET_TYPE_STACKED
+        );
     }
 
-    if(likely(do_swap_usage)) {
-        if(unlikely(!st_swap_usage)) {
-
-            st_swap_usage = rrdset_create_localhost(
-                    "services"
-                    , "swap_usage"
-                    , NULL
-                    , "swap"
-                    , "services.swap_usage"
-                    , "Systemd Services Swap Memory Used"
-                    , "MiB"
-                    , PLUGIN_CGROUPS_NAME
-                    , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
-                    , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 100
-                    , update_every
-                    , RRDSET_TYPE_STACKED
-            );
-
-        }
-        else
-            rrdset_next(st_swap_usage);
+    if (do_swap_usage && !st_swap_usage) {
+        st_swap_usage = rrdset_create_localhost(
+                "services"
+                , "swap_usage"
+                , NULL
+                , "swap"
+                , "services.swap_usage"
+                , "Systemd Services Swap Memory Used"
+                , "MiB"
+                , PLUGIN_CGROUPS_NAME
+                , PLUGIN_CGROUPS_MODULE_SYSTEMD_NAME
+                , NETDATA_CHART_PRIO_CGROUPS_SYSTEMD + 100
+                , update_every
+                , RRDSET_TYPE_STACKED
+        );
     }
 
     if(likely(do_io)) {
         if(unlikely(!st_io_read)) {
-
             st_io_read = rrdset_create_localhost(
                     "services"
                     , "io_read"
@@ -3127,13 +3073,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_io_read);
 
         if(unlikely(!st_io_write)) {
-
             st_io_write = rrdset_create_localhost(
                     "services"
                     , "io_write"
@@ -3148,15 +3090,11 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_io_write);
     }
 
     if(likely(do_io_ops)) {
         if(unlikely(!st_io_serviced_read)) {
-
             st_io_serviced_read = rrdset_create_localhost(
                     "services"
                     , "io_ops_read"
@@ -3171,13 +3109,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_io_serviced_read);
 
         if(unlikely(!st_io_serviced_write)) {
-
             st_io_serviced_write = rrdset_create_localhost(
                     "services"
                     , "io_ops_write"
@@ -3192,10 +3126,7 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_io_serviced_write);
     }
 
     if(likely(do_throttle_io)) {
@@ -3217,11 +3148,8 @@ void update_systemd_services_charts(
             );
 
         }
-        else
-            rrdset_next(st_throttle_io_read);
 
         if(unlikely(!st_throttle_io_write)) {
-
             st_throttle_io_write = rrdset_create_localhost(
                     "services"
                     , "throttle_io_write"
@@ -3236,15 +3164,11 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_throttle_io_write);
     }
 
     if(likely(do_throttle_ops)) {
         if(unlikely(!st_throttle_ops_read)) {
-
             st_throttle_ops_read = rrdset_create_localhost(
                     "services"
                     , "throttle_io_ops_read"
@@ -3259,13 +3183,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_throttle_ops_read);
 
         if(unlikely(!st_throttle_ops_write)) {
-
             st_throttle_ops_write = rrdset_create_localhost(
                     "services"
                     , "throttle_io_ops_write"
@@ -3280,15 +3200,11 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_throttle_ops_write);
     }
 
     if(likely(do_queued_ops)) {
         if(unlikely(!st_queued_ops_read)) {
-
             st_queued_ops_read = rrdset_create_localhost(
                     "services"
                     , "queued_io_ops_read"
@@ -3303,10 +3219,7 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_queued_ops_read);
 
         if(unlikely(!st_queued_ops_write)) {
 
@@ -3324,15 +3237,11 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_queued_ops_write);
     }
 
     if(likely(do_merged_ops)) {
         if(unlikely(!st_merged_ops_read)) {
-
             st_merged_ops_read = rrdset_create_localhost(
                     "services"
                     , "merged_io_ops_read"
@@ -3347,13 +3256,9 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_merged_ops_read);
 
         if(unlikely(!st_merged_ops_write)) {
-
             st_merged_ops_write = rrdset_create_localhost(
                     "services"
                     , "merged_io_ops_write"
@@ -3368,10 +3273,7 @@ void update_systemd_services_charts(
                     , update_every
                     , RRDSET_TYPE_STACKED
             );
-
         }
-        else
-            rrdset_next(st_merged_ops_write);
     }
 
     // update the values
@@ -3828,8 +3730,6 @@ void update_cgroup_charts(int update_every) {
                     rrddim_add(cg->st_cpu, "system", NULL, 100, 1000000, RRD_ALGORITHM_INCREMENTAL);
                 }
             }
-            else
-                rrdset_next(cg->st_cpu);
 
             rrddim_set(cg->st_cpu, "user", cg->cpuacct_stat.user);
             rrddim_set(cg->st_cpu, "system", cg->cpuacct_stat.system);
@@ -3896,8 +3796,6 @@ void update_cgroup_charts(int update_every) {
                                 rrddim_add(cg->st_cpu_limit, "used", NULL, 1, 1000000, RRD_ALGORITHM_ABSOLUTE);
                             cg->prev_cpu_usage = (NETDATA_DOUBLE)(cg->cpuacct_stat.user + cg->cpuacct_stat.system) * 100;
                         }
-                        else
-                            rrdset_next(cg->st_cpu_limit);
 
                         NETDATA_DOUBLE cpu_usage = 0;
                         cpu_usage = (NETDATA_DOUBLE)(cg->cpuacct_stat.user + cg->cpuacct_stat.system) * 100;
@@ -3945,7 +3843,6 @@ void update_cgroup_charts(int update_every) {
                 rrdset_update_rrdlabels(cg->st_cpu_nr_throttled, cg->chart_labels);
                 rrddim_add(cg->st_cpu_nr_throttled, "throttled", NULL, 1, 1, RRD_ALGORITHM_ABSOLUTE);
             } else {
-                rrdset_next(cg->st_cpu_nr_throttled);
                 rrddim_set(cg->st_cpu_nr_throttled, "throttled", cg->cpuacct_cpu_throttling.nr_throttled_perc);
                 rrdset_done(cg->st_cpu_nr_throttled);
             }
@@ -3971,7 +3868,6 @@ void update_cgroup_charts(int update_every) {
                 rrdset_update_rrdlabels(cg->st_cpu_throttled_time, cg->chart_labels);
                 rrddim_add(cg->st_cpu_throttled_time, "duration", NULL, 1, 1000000, RRD_ALGORITHM_INCREMENTAL);
             } else {
-                rrdset_next(cg->st_cpu_throttled_time);
                 rrddim_set(cg->st_cpu_throttled_time, "duration", cg->cpuacct_cpu_throttling.throttled_time);
                 rrdset_done(cg->st_cpu_throttled_time);
             }
@@ -3999,7 +3895,6 @@ void update_cgroup_charts(int update_every) {
                 rrdset_update_rrdlabels(cg->st_cpu_shares, cg->chart_labels);
                 rrddim_add(cg->st_cpu_shares, "shares", NULL, 1, 1, RRD_ALGORITH