Configurable storage engine for Netdata agents: step 3 (#12892)

* storage engine: add host context API

Add a new API to allow storage engines to manage host contexts.
* Replace single global context with per-engine global context
* Context is full managed by storage engines: a storage engine
  can use no context, a global engine context, per host contexts,
  or a mix of these.
* Currently, only dbengine uses contexts.
  Following the current logic, legacy hosts use their own context,
  while non-legacy hosts share the global context.

* storage engine: use empty function instead of null for context ops

* rrdhost: don't check return value for void call

* rrdhost: create context with host

* storage engine: move rrddim ops to rrddim_mem.{c,h}

* storage engine: don't use NULL for end-of-list marker

* storage engine: fallback to default engine

1 files changed, 147 insertions, 47 deletions

diff --git a/database/storage_engine.c b/database/storage_engine.c
index 36f01de166..0bfb19cb66 100644
--- a/database/storage_engine.c
+++ b/database/storage_engine.c
@@ -5,68 +5,144 @@
 #ifdef ENABLE_DBENGINE
 #include "engine/rrdengineapi.h"
 #endif
-
-#define im_collect_ops { \
-    .init = rrddim_collect_init,\
-    .store_metric = rrddim_collect_store_metric,\
-    .finalize = rrddim_collect_finalize\
-}
-
-#define im_query_ops { \
-    .init = rrddim_query_init, \
-    .next_metric = rrddim_query_next_metric, \
-    .is_finished = rrddim_query_is_finished, \
-    .finalize = rrddim_query_finalize, \
-    .latest_time = rrddim_query_latest_time, \
-    .oldest_time = rrddim_query_oldest_time \
-}
+#include "libnetdata/libnetdata.h"
 
 static STORAGE_ENGINE engines[] = {
     {
         .id = RRD_MEMORY_MODE_NONE,
         .name = RRD_MEMORY_MODE_NONE_NAME,
         .api = {
-            .collect_ops = im_collect_ops,
-            .query_ops = im_query_ops
-        }
+            .engine_ops = {
+                .create = rrddim_storage_engine_instance_new,
+                .exit = rrddim_storage_engine_instance_exit,
+                .destroy = rrddim_storage_engine_instance_destroy
+            },
+            .collect_ops = {
+                .init = rrddim_collect_init,
+                .store_metric = rrddim_collect_store_metric,
+                .finalize = rrddim_collect_finalize
+            },
+            .query_ops = {
+                .init = rrddim_query_init,
+                .next_metric = rrddim_query_next_metric,
+                .is_finished = rrddim_query_is_finished,
+                .finalize = rrddim_query_finalize,
+                .latest_time = rrddim_query_latest_time,
+                .oldest_time = rrddim_query_oldest_time
+            }
+        },
+        .context = NULL
     },
     {
         .id = RRD_MEMORY_MODE_RAM,
         .name = RRD_MEMORY_MODE_RAM_NAME,
         .api = {
-            .collect_ops = im_collect_ops,
-            .query_ops = im_query_ops
-        }
+            .engine_ops = {
+                .create = rrddim_storage_engine_instance_new,
+                .exit = rrddim_storage_engine_instance_exit,
+                .destroy = rrddim_storage_engine_instance_destroy
+            },
+            .collect_ops = {
+                .init = rrddim_collect_init,
+                .store_metric = rrddim_collect_store_metric,
+                .finalize = rrddim_collect_finalize
+            },
+            .query_ops = {
+                .init = rrddim_query_init,
+                .next_metric = rrddim_query_next_metric,
+                .is_finished = rrddim_query_is_finished,
+                .finalize = rrddim_query_finalize,
+                .latest_time = rrddim_query_latest_time,
+                .oldest_time = rrddim_query_oldest_time
+            }
+        },
+        .context = NULL
     },
     {
         .id = RRD_MEMORY_MODE_MAP,
         .name = RRD_MEMORY_MODE_MAP_NAME,
         .api = {
-            .collect_ops = im_collect_ops,
-            .query_ops = im_query_ops
-        }
+            .engine_ops = {
+                .create = rrddim_storage_engine_instance_new,
+                .exit = rrddim_storage_engine_instance_exit,
+                .destroy = rrddim_storage_engine_instance_destroy
+            },
+            .collect_ops = {
+                .init = rrddim_collect_init,
+                .store_metric = rrddim_collect_store_metric,
+                .finalize = rrddim_collect_finalize
+            },
+            .query_ops = {
+                .init = rrddim_query_init,
+                .next_metric = rrddim_query_next_metric,
+                .is_finished = rrddim_query_is_finished,
+                .finalize = rrddim_query_finalize,
+                .latest_time = rrddim_query_latest_time,
+                .oldest_time = rrddim_query_oldest_time
+            }
+        },
+        .context = NULL
     },
     {
         .id = RRD_MEMORY_MODE_SAVE,
         .name = RRD_MEMORY_MODE_SAVE_NAME,
         .api = {
-            .collect_ops = im_collect_ops,
-            .query_ops = im_query_ops
-        }
+            .engine_ops = {
+                .create = rrddim_storage_engine_instance_new,
+                .exit = rrddim_storage_engine_instance_exit,
+                .destroy = rrddim_storage_engine_instance_destroy
+            },
+            .collect_ops = {
+                .init = rrddim_collect_init,
+                .store_metric = rrddim_collect_store_metric,
+                .finalize = rrddim_collect_finalize
+            },
+            .query_ops = {
+                .init = rrddim_query_init,
+                .next_metric = rrddim_query_next_metric,
+                .is_finished = rrddim_query_is_finished,
+                .finalize = rrddim_query_finalize,
+                .latest_time = rrddim_query_latest_time,
+                .oldest_time = rrddim_query_oldest_time
+            }
+        },
+        .context = NULL
     },
     {
         .id = RRD_MEMORY_MODE_ALLOC,
         .name = RRD_MEMORY_MODE_ALLOC_NAME,
         .api = {
-            .collect_ops = im_collect_ops,
-            .query_ops = im_query_ops
-        }
+            .engine_ops = {
+                .create = rrddim_storage_engine_instance_new,
+                .exit = rrddim_storage_engine_instance_exit,
+                .destroy = rrddim_storage_engine_instance_destroy
+            },
+            .collect_ops = {
+                .init = rrddim_collect_init,
+                .store_metric = rrddim_collect_store_metric,
+                .finalize = rrddim_collect_finalize
+            },
+            .query_ops = {
+                .init = rrddim_query_init,
+                .next_metric = rrddim_query_next_metric,
+                .is_finished = rrddim_query_is_finished,
+                .finalize = rrddim_query_finalize,
+                .latest_time = rrddim_query_latest_time,
+                .oldest_time = rrddim_query_oldest_time
+            }
+        },
+        .context = NULL
     },
 #ifdef ENABLE_DBENGINE
     {
         .id = RRD_MEMORY_MODE_DBENGINE,
         .name = RRD_MEMORY_MODE_DBENGINE_NAME,
         .api = {
+            .engine_ops = {
+                .create = rrdeng_init,
+                .exit = rrdeng_prepare_exit,
+                .destroy = rrdeng_exit
+            },
             .collect_ops = {
                 .init = rrdeng_store_metric_init,
                 .store_metric = rrdeng_store_metric_next,
@@ -80,28 +156,34 @@ static STORAGE_ENGINE engines[] = {
                 .latest_time = rrdeng_metric_latest_time,
                 .oldest_time = rrdeng_metric_oldest_time
             }
-        }
-    },
+        },
+        .context = NULL
+    }
 #endif
-    { .id = RRD_MEMORY_MODE_NONE, .name = NULL }
 };
 
+const size_t engine_count = sizeof(engines) / sizeof(engines[0]);
+
 STORAGE_ENGINE* storage_engine_find(const char* name)
 {
-    for (STORAGE_ENGINE* it = engines; it->name; it++) {
-        if (strcmp(it->name, name) == 0)
-            return it;
-    }
-    return NULL;
+    for (size_t i = 0; i != engine_count; i++)
+        if (strcmp(engines[i].name, name) == 0)
+            return &engines[i];
+
+    error("No storage engine found for memory mode %s.", name);
+    return storage_engine_get(default_rrd_memory_mode);
 }
 
 STORAGE_ENGINE* storage_engine_get(RRD_MEMORY_MODE mmode)
 {
-    for (STORAGE_ENGINE* it = engines; it->name; it++) {
-        if (it->id == mmode)
-            return it;
-    }
-    return NULL;
+    for (size_t i = 0; i != engine_count; i++)
+        if (engines[i].id == mmode)
+            return &engines[i];
+    STORAGE_ENGINE* eng = mmode == default_rrd_memory_mode
+        ? &engines[0] // default engine not available, use NONE
+        : storage_engine_get(default_rrd_memory_mode);
+    error("No storage engine for memory mode %u, will use %s (%u) instead.", mmode, eng->name, eng->id);
+    return eng;
 }
 
 STORAGE_ENGINE* storage_engine_foreach_init()
@@ -112,9 +194,27 @@ STORAGE_ENGINE* storage_engine_foreach_init()
 
 STORAGE_ENGINE* storage_engine_foreach_next(STORAGE_ENGINE* it)
 {
-    if (!it || !it->name)
-        return NULL;
-
     it++;
-    return it->name ? it : NULL;
+    return (it >= &engines[engine_count]) ? NULL : it;
+}
+
+STORAGE_ENGINE_INSTANCE* storage_engine_new(STORAGE_ENGINE* eng, RRDHOST *host)
+{
+    STORAGE_ENGINE_INSTANCE* instance = host->rrdeng_ctx;
+    if (!instance && eng) {
+        instance = eng->api.engine_ops.create(eng, host);
+        if (instance) {
+            instance->engine = eng;
+        }
+    }
+    return instance;
+}
+
+void storage_engine_delete(STORAGE_ENGINE_INSTANCE* instance) {
+    if (instance) {
+        STORAGE_ENGINE* eng = instance->engine;
+        if (eng) {
+            eng->api.engine_ops.destroy(instance);
+        }
+    }
 }